Access profile

The doctoral programme in Photonics is designed for students with outstanding academic records at the international level who wish to complete a doctoral project in a field related to photonics.

With respect to entrance qualifications, it should be noted that photonics is a very broad discipline and that the ICFO is made up of a number of research groups that work in the various branches of the photonic sciences. Accordingly, the doctoral programme in Photonics is open to applicants with a wide range of qualifications, including degrees in physics; electronic, electrical, materials and telecommunications engineering; mathematics, chemistry, biology, bioengineering and biophysics.

As for language skills, the ICFO is a research institute with a strongly international character and English is the language used for everyday communication. Students admitted to the doctoral programme in Photonics must therefore have a high level of written and spoken English.

As for career goals, the doctoral programme in Photonics admits both students who wish to pursue academic careers and those aiming to become future leaders in knowledge and technology transfer or R&D in the business environment.

When it comes to personal characteristics, we are looking for students with high potential, motivation and the drive to carry out a project of excellence at the highest international level.

Output profile

Doctoral candidates who complete a doctoral degree will have acquired the following competencies, which are needed to carry out quality research (Royal Decree 99/2011, of 28 January, which regulates official doctoral studies):

a) A systematic understanding of the field of study and a mastery of the research skills and methods related to the field.
b) An ability to conceive, design or create, put into practice and adopt a substantial process of research or creation.
c) An ability to contribute to pushing back the frontiers of knowledge through original research.
d) A capacity for critical analysis and an ability to assess and summarise new and complex ideas.
e) An ability to communicate with the academic and scientific community and with society in general as regards their fields of knowledge in the manner and languages that are typical of the international scientific community to which they belong.
f) An ability to foster scientific, technological, social, artistic and cultural progress in academic and professional contexts within a knowledge-based society.

The award of a doctoral degree must equip the graduate for work in a variety of settings, especially those requiring creativity and innovation. Doctoral graduates must have at least acquired the personal skills needed to:

a) Develop in contexts in which there is little specific information.
b) Find the key questions that must be answered to solve a complex problem.
c) Design, create, develop and undertake original, innovative projects in their field.
d) Work as part of a team and independently in an international or multidisciplinary context.
e) Integrate knowledge, deal with complexity and make judgements with limited information.
f) Offer criticism on and intellectually defend solutions.

Finally, with respect to competencies, doctoral students must:
a) have acquired advanced knowledge at the frontier of their discipline and demonstrated, in the context of internationally recognised scientific research, a deep, detailed and well-grounded understanding of theoretical and practical issues and scientific methodology in one or more research fields;
b) have made an original and significant contribution to scientific research in their field of expertise that has been recognised as such by the international scientific community;
c) have demonstrated that they are capable of designing a research project that serves as a framework for carrying out a critical analysis and assessment of imprecise situations, in which they are able to apply their contributions, expertise and working method to synthesise new and complex ideas that yield a deeper knowledge of the research context in which they work;
d) have developed sufficient autonomy to set up, manage and lead innovative research teams and projects and scientific collaborations (both national and international) within their subject area, in multidisciplinary contexts and, where appropriate, with a substantial element of knowledge transfer;
e) have demonstrated that they are able to carry out their research activity in a socially responsible manner and with scientific integrity;
f) have demonstrated, within their specific scientific context, that they are able to make cultural, social or technological advances and promote innovation in all areas within a knowledge-based society;
g) have demonstrated that they are able to participate in scientific discussions at the international level in their field of expertise and disseminate the results of their research activity to audiences of all kinds.

Number of places

30

Duration of studies and dedication regime

Duration
The maximum period of study for full-time doctoral studies is three years, counted from the date of admission to the programme to the date of submission of the doctoral thesis. The academic committee of the doctoral programme may authorise a doctoral candidate to pursue doctoral studies on a part-time basis. In this case, the maximum period of study is five years, counting from the date of admission to the programme to the date of submission of the doctoral thesis. For calculating these periods, the date of admission is considered to be the date of the first enrolment for tutorials, and the date of submission the moment in which the Doctoral School officially deposits the doctoral thesis.

For full-time doctoral candidates, the minimum period of study is two years, counted from the date of an applicant's admission to the programme until the date on which the doctoral thesis is deposited; for part-time doctoral candidates it is four years. When there are justified grounds for doing so, and the thesis supervisor and academic tutor have given their authorisation, doctoral candidates may request that the academic committee of their doctoral programme exempt them from the minimum period of study requirement.

The calculation of periods of study will not include periods of absence due to illness, pregnancy or any other reason provided for in the regulations in force. Students who find themselves in any of these circumstances must notify the academic committee of the doctoral programme, which, where appropriate, must inform the Doctoral School. Doctoral candidates may also temporarily withdraw from the programme for up to one year, and this period may be extended for an additional year. Doctoral candidates who wish to interrupt their studies must submit a justified request to the academic committee of the doctoral programme, which will decide whether or not to approve the request. Each programme will establish conditions for readmission to doctoral studies.

Extension
If full-time doctoral candidates have not applied to deposit their thesis by the end of the three-year period of study, the academic committee of the programme may authorise an extension of up to one year. In exceptional circumstances, a further one-year extension may be granted, subject to the conditions established by the corresponding doctoral programme. In the case of part-time doctoral candidates, an extension of two years may be authorised. In both cases, in exceptional circumstances a further one-year extension may be granted by the Doctoral School's Standing Committee, upon the submission of a reasoned application by the academic committee of the doctoral programme.

Dismissal from the doctoral programme
A doctoral candidate may be dismissed from a doctoral programme for the following reasons:

• The doctoral candidate submitting a justified application to withdraw from the programme.
• The maximum period of study and of extensions thereof ending.
• The doctoral candidate not having enrolled every academic year (unless he or she has been authorised to temporarily withdraw).
• The doctoral candidate failing two consecutive assessments.
• The doctoral candidate having disciplinary proceedings filed against him or her that rule that he or she must be dismissed from the UPC.

Dismissal from the programme implies that doctoral candidates cannot continue studying at the UPC and the closing of their academic record. This notwithstanding, they may apply to the academic committee of the programme for readmission and the committee must reevaluate them in accordance with the criteria established in the regulations.

Organization

• Sewell, Robert

• Acin Dalmaschio, Antonio
• Artigas Garcia, David
• Garcia-Parajo, Maria
• Konstantatos, Gerasimos
• Sewell, Robert
• Van Hulst, Niek
• Winkler, Pamina

• Institute of Photonic Sciences (PROMOTORA)

Natalia García Tusquellas
The Institute of Photonic Sciences (ICFO)
Av. Carl Friedrich Gauss, 3
08860 Castelldefels

Tel: (+34) 93 554 22 10
E-mail: academicaffairs@icfo.eu

Agreements with other institutions

The ICFO has collaboration agreements in effect with a significant number of companies, including Leica Microsystems, Corning, Nikon-Izasa Grupo Sorigué, Accelerate Diagnostics, S.L., Fyla All-Fiber Ultrafast Lasers and GRAPHENEA. The Institute also participates in networks of excellence (Euro-BioImaging, Laserlab Europe, Corbel, etc.) and coordinates various Graphene Flagship and Quantum Flagship projects under the EU's Horizon 2020 Programme.

Access profile

The doctoral programme in Photonics is designed for students with outstanding academic records at the international level who wish to complete a doctoral project in a field related to photonics.

With respect to entrance qualifications, it should be noted that photonics is a very broad discipline and that the ICFO is made up of a number of research groups that work in the various branches of the photonic sciences. Accordingly, the doctoral programme in Photonics is open to applicants with a wide range of qualifications, including degrees in physics; electronic, electrical, materials and telecommunications engineering; mathematics, chemistry, biology, bioengineering and biophysics.

As for language skills, the ICFO is a research institute with a strongly international character and English is the language used for everyday communication. Students admitted to the doctoral programme in Photonics must therefore have a high level of written and spoken English.

As for career goals, the doctoral programme in Photonics admits both students who wish to pursue academic careers and those aiming to become future leaders in knowledge and technology transfer or R&D in the business environment.

When it comes to personal characteristics, we are looking for students with high potential, motivation and the drive to carry out a project of excellence at the highest international level.

Access requirements

Applicants must hold a Spanish bachelor’s degree or equivalent and a Spanish master’s degree or equivalent, provided they have completed a minimum of 300 ECTS credits on the two degrees (Royal Decree 43/2015, of 2 February)

In addition, the following may apply:

• Holders of an official degree awarded by a university in Spain or any other country in the European Higher Education Area, pursuant to the provisions of Article 16 of Royal Decree 1393/2007, of 29 October, which establishes official university course regulations, who have completed a minimum of 300 ECTS credits on official university degrees, of which at least 60 must be at the master's degree level.
• Holders of an official Spanish bachelor’s degree comprising at least 300 credits, as provided for by EU regulations. Holder of degrees of this kind must complete bridging courses unless the curriculum of the bachelor’s degree in question included research training credits equivalent in value to those which would be earned on a master's degree.
• Holders of an official university qualification who, having passed the entrance examination for specialised medical training, have completed at least two years of a training course leading to an official degree in a health-sciences specialisation.
• Holders of a degree issued under a foreign education system. In these cases, homologation is not required, but the UPC must verify that the degree certifies a level of training equivalent to an official Spanish master's degree and qualifies the holder for admission to doctoral studies in the country where it was issued. Admission on this basis does not imply homologation of the foreign degree or its recognition for any purpose other than admission to doctoral studies.
• Holders of a Spanish doctoral qualification issued under previous university regulations.

Note 1: Doctoral studies entrance regulations for holders of an undergraduate degree awarded before the introduction of the EHEA (CG 47/02 2014)

Note 2: Governing Council Decision 64/2014, which approves the procedure and criteria for assessing the fulfilment of academic admission requirements for doctoral studies by holders of non-homologated foreign degrees (CG 25/03 2014)

Admission criteria and merits assessment

Applications for admission to the doctoral programme in Photonics must be submitted through the website http://jobs.icfo.eu/, to which interested students are directed. Detailed information on specific vacancies available for doctoral students at any given time in each of the ICFO's research groups is published on this web page.

Finally, measures are taken to ensure that the principles of transparency, efficiency and international compatibility set out in the European Charter for Researchers and the European Code of Conduct for the Recruitment of Researchers are followed throughout the admission process for the doctoral programme in Photonics. The process will also be free of any discrimination based on gender or nationality.

Training complements

Students who hold one of the following UPC master’s degrees, which are linked to the doctoral programme, will not be required to complete bridging courses: Erasmus Mundus master's degree in Photonics; master's degree in Photonics Engineering, Nanophotonics and Biophotonics; master's degree in Engineering Physics; and master's degree in Quantum Science and Technology.

Neither will students who have completed a master's degree in photonics or physics from another university be required to complete bridging courses.

In the case of students who have completed a master's degree in another field – such as a master's degree in biomedical sciences or a multidisciplinary master's degree in experimental sciences – the applicant’s academic record and the project they propose to work on will be assessed, and the academic committee will determine on a case-by-case basis whether specific bridging courses must be completed. If the academic committee so determines, these students will be required to take one of the following subjects as a bridging course:

• Introduction to Photonics. Optics and Lasers (5 ECTS credits), from the master’s degree in Photonics
• Applied Photonics (5 ECTS credits), from the master's degree in Enabling Technologies for the Food and Bioprocessing Industry.

Enrolment period for new doctoral students

Enrolment is open year round, subject to the calendar established by the Doctoral School.

More information at the registration section for new doctoral students

Enrolment period

In September.

More information at the general registration section

Procedure for the preparation and defense of the research plan

Doctoral candidates must submit a research plan, which will be included in their doctoral student activity report, before the end of the first year. The plan may be improved over the course of the doctoral degree. It must be endorsed by the tutor and the supervisor, and it must include the method that is to be followed and the aims of the research.

At least one of these annual assessments will include a public presentation and defence of the research plan and work done before a committee composed of three doctoral degree holders, which will be conducted in the manner determined by each academic committee. The examination committee awards a Pass or Fail mark. A Pass mark is a prerequisite for continuing on the doctoral programme. Doctoral candidates awarded a Fail mark must submit a new research plan for assessment by the academic committee of the doctoral programme within six months.

The committee assesses the research plan every year, in addition to all of the other activities in the doctoral student activity report. Doctoral candidates who are awarded two consecutive Fail marks for the research plan will be obliged to definitely withdraw from the programme.

If they change the subject of their thesis, they must submit a new research plan.

Formation activities

The doctoral programme in Photonics does not specify any minimum requirements with respect to number of papers published, conferences attended, or other activities. However, the academic committee for the programme will seek to ensure that each thesis meets the highest international standards before it is accepted for oral defence.

The training activities that make up the programme (including details of their duration and whether they are compulsory or optional) are listed below.

Mobility, 3 months (optional)
Preparation and initial defence of research plan, 50 hours (compulsory)
Training in information skills, 1.5 hours (optional)
Research Methodology, 12 hours (optional)
Innovation and Creativity, 8 hours (optional)
Language and Communication Skills, 18 hours (optional)
Scientific seminars, 25 hours/year (optional)
ICONS seminars, 40 hours/year (optional)
Coffee sessions with prominent researchers, 2 hours/year (optional)
Programme-specific workshops, 1 day/year (optional)
Publications, 50 hours (compulsory)
PhD lectures, 65 hours/year (optional)
Outreach activities, 18 hours (optional)
Training in technical skills, 5 hours for each technique (optional)
Effective Oral Presentations, 10 hours (optional)
ICFO-ESADE: From Science to Business, 24 hours (optional)
Introduction to Patent Engineering and Management, 7.5 hours (optional)
Language courses, 40 hours (Spanish, Catalan and English; optional)
Research Integrity, 3 hours (compulsory)
Career Development, 10 hours (optional)
Resilience and Well-Being, 6 hours (optional)
Essential Transferable Skills for Early Career Researchers, 12 hours (optional).

Procedure for assignment of tutor and thesis director

The academic committee of the doctoral programme assigns a thesis supervisor to each doctoral candidate when they are admitted or enrol for the first time, taking account of the thesis supervision commitment referred to in the admission decision.

The thesis supervisor will ensure that training activities carried out by the doctoral candidate are coherent and suitable, and that the topic of the candidate’s doctoral thesis will have an impact and make a novel contribution to knowledge in the relevant field. The thesis supervisor will also guide the doctoral candidate in planning the thesis and, if necessary, tailoring it to any other projects or activities undertaken. The thesis supervisor will generally be a UPC professor or researcher who holds a doctoral degree and has documented research experience. This includes PhD-holding staff at associated schools (as determined by the Governing Council) and UPC-affiliated research institutes (in accordance with corresponding collaboration and affiliation agreements). When thesis supervisors are UPC staff members, they also act as the doctoral candidate’s tutor.

PhD holders who do not meet these criteria (as a result of their contractual relationship or the nature of the institution to which they are attached) must be approved by the UPC Doctoral School's Standing Committee in order to participate in a doctoral programme as researchers with documented research experience.

The academic committee of the doctoral programme may approve the appointment of a PhD-holding expert who is not a UPC staff member as a candidate’s thesis supervisor. In such cases, the prior authorisation of the UPC Doctoral School's Standing Committee is required. A UPC staff member who holds a doctoral degree and has documented research experience must also be proposed to act as a co-supervisor, or as the doctoral candidate’s tutor if one has not been assigned.

A thesis supervisor may step down from this role if there are justified reasons (recognised as valid by the committee) for doing so. If this occurs, the academic committee of the doctoral programme will assign the doctoral candidate a new thesis supervisor.

Provided there are justified reasons for doing so, and after hearing any relevant input from the doctoral candidate, the academic committee of the doctoral programme may assign a new thesis supervisor at any time during the period of doctoral study.

If there are academic reasons for doing so (an interdisciplinary topic, joint or international programmes, etc.) and the academic committee of the programme gives its approval, an additional thesis supervisor may be assigned. Supervisors and co-supervisors have the same responsibilities and academic recognition.

The maximum number of supervisors of a doctoral thesis is two: a supervisor and a co-supervisor.

For theses carried out under a cotutelle agreement or as part of an Industrial Doctorate, if necessary and if the agreement foresees it this maximum number of supervisors may not apply. This notwithstanding, the maximum number of supervisors belonging to the UPC is two.

More information at the PhD theses section

Permanence

The academic committee of the programme may authorise an extension of up to one year for full-time doctoral candidates who have not applied to deposit their thesis by the end of the three-year period of study, in the terms outlined in the Academic Regulations for Doctoral Studies of the Universitat Politècnica de Catalunya. In the case of part-time candidates, an extension of two years may be authorised. In both cases, in exceptional circumstances a further one-year extension may be granted by the Doctoral School's Standing Committee, upon the submission of a reasoned application by the academic committee of the doctoral programme.

A doctoral candidate may be dismissed from a doctoral programme for the following reasons:

• The doctoral candidate submitting a justified application to withdraw from the programme.
• The maximum period of study and of extensions thereof ending.
• The doctoral candidate not having enrolled every academic year (unless he or she has been authorised to temporarily withdraw).
• The doctoral candidate failing two consecutive assessments.
• The doctoral candidate having disciplinary proceedings filed against him or her that rule that he or she must be dismissed from the UPC.

Dismissal from the programme implies that doctoral candidates cannot continue studying at the UPC and the closing of their academic record. This notwithstanding, they may apply to the academic committee of the programme for readmission and the committee must reevaluate them in accordance with the criteria established in the regulations.

International Mention

The doctoral degree certificate may include International Doctorate mention. In this case, the doctoral candidate must meet the following requirements:

a) During the period of study leading to the award of the doctoral degree, the doctoral candidate must have spent at least three months at a respected higher education institution or research centre outside Spain to complete courses or do research work. The stays and activities carried out must be endorsed by the thesis supervisor and authorised by the academic committee of the programme. The candidate must provide a certifying document issued by the person responsible for the research group of the body or bodies where the stay or activity was completed. This information will be added to the doctoral student’s activity report.
b) Part of the thesis (at least the summary and conclusions) must be written and presented in one of the languages commonly used for science communication in the relevant field of knowledge, which must not be an official language of Spain. This rule does not apply to stays and reports in Spanish or to experts from Spanish-speaking countries.
c) At least two PhD-holding experts belonging to a higher education institution or research centre outside Spain must have issued officially certified reports on the thesis.
d) The thesis examination committee must have included at least one PhD-holding expert from a higher education or research institution outside Spain who was not responsible for the candidate’s stay abroad (point a) above).
e) The thesis defence must have taken place on UPC premises or, in the case of joint programmes, at the location specified in the collaboration agreement.

List of authorized thesis for defense

• HELLER, LUKAS: Exploring quantum memory schemes in cold
  
  Author: HELLER, LUKAS
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Deposit date: 08/09/2023
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: DE RIEDMATTEN, HUGUES
  Committee:
       PRESIDENT: TARRUELL PELLEGRIN, LETICIA
       SECRETARI: LAURAT, JULIEN
       VOCAL: SANGOUARD, NICOLAS
  Thesis abstract: Quantum memories are devices that are able to store photonic quantum states and entanglement. Future quantum networks, which could enhance cybersecurity through quantum key distribution, improve the precision in atomic clock networks, and connect quantum devices over long distances, rely on them. This thesis reports on experiments towards improved quantum memories for quantum repeaters used in long-distance quantum communication.The quantum memory is based on a cloud of laser-cooled Rubidium-87. Thanks to collective interference effects, this system enhances the light-matter interaction compared to that of a single atom. This is exploited to either create long-lived quantum correlations between light and atomic excitations through probabilistic light scattering (DLCZ protocol) or to efficiently absorb an incoming single photon (Raman protocol). In both cases, the excitation is retrieved after a programmable delay as a single photon. An optical cavity around the atoms further enhances the light-matter coupling. In a first experiment, the DLCZ protocol is combined with a photon echo protocol, allowing for the sequential creation of excitations in N distinguishable temporal modes. This is known as temporal multiplexing. Multiplexing improves the rate at which entanglement is created in a network link by a factor N. Here, the cavity is essential to suppress noise originating from the probabilistic scattering of light in the DLCZ protocol. Ten temporal modes are stored while maintaining strong quantum correlations between the scattered photon and the atomic excitation. In a second experiment, a quasi-deterministic single photon is stored in the cloud following the Raman protocol. The photon originates from an ensemble of laser-cooled Rydberg atoms. Strong dipole-dipole interactions prevent the excitation of more than one atom to the Rydberg level, leading to the creation of a single collective Rydberg excitation which is later retrieved as a single photon. A deterministic source, opposed to a probabilistic source, improves the entanglement creation rate as it generates single photons at higher rates. The single photon is stored and faithfully retrieved from the memory while maintaining its single-photon nature. The cavity is not being used in this experiment. In a third experiment, the retrieval efficiency of a stored excitation is increased by cavity-enhancing the read-out process. Highly-efficient memories are important because the entanglement distribution scales strongly with memory efficiency. The intra-cavity efficiency could be improved by a factor 2-3, depending on the protocol, even for a non-optimal cavity setup. Finally, ongoing work towards efficient entanglement between an atomic excitation and a telecom photon is presented, involving a cavity-enhanced DLCZ memory, an atomic dipole trap and quantum frequency conversion (QFC) to the telecom C-band. As the memory operates in the optical domain, where photonic transmission losses are large, QFC will be needed to communicate over large distances. This setup will be used in the future for a hybrid experiment connecting the cold atomic memory to a solid state memory. These investigations target intrinsic limitations of early, proof-of-principle quantum links. They can therefore help to build practical links in the future.
  

Last update: 04/10/2023 04:45:29.

List of lodged theses

• MALAIWONG, NAWAPHAT: Molecular and Cellular Aspects of Proprioceptive Control in C. elegans
  
  Author: MALAIWONG, NAWAPHAT
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Deposit date: 22/09/2023
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: KRIEG, MICHAEL
  Committee:
       PRESIDENT: LOZA ALVAREZ, PABLO
       SECRETARI: RAFFA, VITTORIA
       VOCAL: CERON MADRIGAL, JULIAN
  Thesis abstract: Locomotion behavior is the output of the integrated clues by the nervous system along with proprioceptive regulation, which encompasses responses such as avoiding, feeding, and reproduction. Mechanosensation, the ability to sense mechanical force, relies on mechanically-gated ion channels that convert force into neuronal signals through conformational changes. Unraveling the mechanisms underlying these mechanosensitive channels poses a significant challenge for neurobiologists and cell biologists. My PhD work employed multidisciplinary approaches in biology, physics, mathematics, and engineering to investigate the regulation of proprioception in the model organism C. elegans in the molecular and cellular scales.In my research, I focused on understanding the role of the interneuron DVA during movement and its ability to draft signals from body curvatures. Using genetically modified strains and calcium imaging techniques, I demonstrated that DVA responds to compressive forces through its axon, leading to an influx of calcium ions through the TRP-4 channel. Additionally, I discovered that bending of the worm stretches the DVA axon and activates the potassium ion channel TWK-16. Both channels detect mechanical forces and modulate DVA signal, such interplay encodes calcium signals along the body curves, facilitating the reception and fine-tuning of muscle contractions in different body segments. Moreover, I discovered the critical role of beta-spectrin in maintaining the structural integrity and proprioceptive function in response to force. To delve deeper into the subject, additional research was conducted to examine the role of beta-spectrin in the ageing process and its impact on proprioception and protein expression in C. elegans. Apart from the proprioceptive regulation through neuronal signal, my study revealed that the DVA-specific neuropeptide, NLP-12, is responsible to modulate locomotion behavior. Using transgenic animals, imaging techniques, and protein modification approaches, the results showed that NLP-12 is required to promote the DVA-mediated motor output. Interestingly, first evidences suggest that NLP-12 release is controlled by mechanical force. However, the exact mechanism on such effect will be further characterized.During my PhD research, I developed a novel technique called Fluorescent Landmark Interference (FLInt) for integrating transgenes into the C. elegans genome using CRISPR/Cas9. FLInt is a simple, rapid, and flexible method for establishing transgenic C. elegans strains based on the precise excision of fluorescent genes at a specific locus as markers of integration. FLInt has gained widespread popularity and is now employed as a routine method in C. elegans research laboratories around the world.The novelty of my PhD study lies in its pursuit of both fundamental knowledge and practical applications: (1) to understand the broader concept of mechanosensation and gain valuable insights into how organisms perceive and respond to mechanical stimuli and (2) to offer an accessible and efficient tool for C. elegans research community and enhance future studies using C. elegans model.
  
• URREGO GONZALEZ, DANIEL FERNANDO: Demonstration of new experimental schemes for imaging and sensing: from quantum to classical and back
  
  Author: URREGO GONZALEZ, DANIEL FERNANDO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Deposit date: 29/09/2023
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: PEREZ TORRES, JUAN
  Committee:
       PRESIDENT: CAPMANY FRANCOY, JOSÉ
       SECRETARI: ARTIGAS GARCIA, DAVID
       VOCAL: FELIX PEREIRA, SILVANIA
  Thesis abstract: This Ph.D. thesis presents research in imaging and optical sensing, exploring novel concepts, and diverse applications. The experimental schemes put forward here are based on simulating specific aspects of quantum concepts using classical Optics. The last scheme takes the opposite direction. Employing quantum techniques, it develops the quantum version of a Differential Interference Contrast (DIC) microscope. The thesis is divided into several chapters, each addressing distinct aspects of an experimental scheme and its potential applications.item The first scheme introduces a proof-of-concept demonstration of an optical gate that uses light beam with orbital angular momentum. Inspired by the quantum fingerprinting protocol, this gate enables the efficient comparison of data strings and waveforms without the need for signal disclosure. The gate is tested comparing string of bits, strings of quarts and different waveforms.The second scheme presents a protocol to assess the presence of a particular spatial shape (or waveform) in a database, by evaluating the degree of similarity between the unknown spatial shape with all the elements contained in the database. The protocol is tested by comparing the shape of a trimmed disk in a database. The protocol is extended to the temporal domain, where theshapes are encoded in the amplitude of the electric fields.The third scheme is a novel approach to do Optical Coherence Tomography (OCT) with a fully non-mechanical scan. By leveraging the principles of spectral domain OCT and integrating a spatial light modulator (SLM) into the setup, non-mechanical steering of the illumination optical beam is achieved. This innovation eliminates the necessity of transverse scans using mechanical platformspotentially boosting the enhancement of the size, weight, and power (SWaP) of future commercial products.The last scheme is a quantum version of the Differential Interference Contrast (DIC) microscope, harnessing the remarkable Hong-Ou-Mandel (HOM) effect to retrieve phase gradients induced by varying optical thickness. In this case, the knowledge of quantum optics is applied to a microscope technique.The work presented in this thesis contributes to the idea of using protocols from the quantum world that could be mimicked in classical applications.
  

Last update: 04/10/2023 04:30:30.

List of defended theses by year

• AFRIDI, ADEEL: Reconfigurable metasurfaces based on thermo-optical and optomechanical controls
  
  Author: AFRIDI, ADEEL
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 28/04/2023
  Thesis director: QUIDANT, ROMAIN
  

  Committee:
       PRESIDENT: VAN HULST, NIEK
       SECRETARI: TAGLIABUE, GIULIA
       VOCAL: GENEVET, PATRICE
  Thesis abstract: Optical metasurfaces established themselves as potential platform for planar and integrated optics. Progress in the material sciences and fabrication process paves the way towards ultra-thin metasurface based devices, also known as meta-devices. Meta-devices include holograms, flat lenses, wave-plates, polarizers and deflectors. Amongst these meta-devices, great effort focuses toward the development of high performance, aberrations-free, and multi-functional metalenses. High refractive index and lossless dielectric materials have enabled metalenses with near-unity transmission and high numerical aperture. However, the static nature of metalenses limits their use for the applications where continuous and on demand tunability of lens operation is required such as imaging and adaptive vision. In this thesis, I developed two different techniques to achieve reconfigurability in metasurfaces which I used to create reconfigurable metalens devices. devices based on two types of reconfigurability techniques. First technique achieves focal length tunability of a dielectric metalens by utilizing the electro-thermo-optical effect to change the refractive index of the surrounding media. The electro-thermo-optically controlled metalens exhibits linear and continuous focal length tunability, high efficiency and low power consumption with switching time of the order of 100 ms. The second varifocal metalens device takes advantage of the optomechanial effect to introduce change in the geometry of the metalens itself. Carved onto a free-standing ultra-thin silicon membrane, the metalens exhibits continuous and linear focal length tunability with fast response time as short as a few µs.
  

• AGARWAL, HITESH: Graphene based optical interconnects and IR photodetectors
  
  Author: AGARWAL, HITESH
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 23/01/2023
  Thesis director: KOPPENS, FRANK
  

  Committee:
       PRESIDENT: PRUNERI, VALERIO
       SECRETARI: MUELLER, THOMAS
       VOCAL: STAMPFER, CHRISTOPH
  Thesis abstract: Despite the extensive research in the semiconductor industry, Moore¿s law is finally slowing down due to increased complexity. Hence, intense efforts are being carried out to explore hybrid solutions by adding additional functionalities to the existing silicon plat- form to keep up with the growing demand. It is colloquially called as ¿Beyond Moore¿ phase. This thesis is a humble attempt to propose graphene, a single atomic sheet of carbon, as an excellent candidate for the ¿Beyond Moore¿ phase optoelectronic applications. In particular, we demonstrate graphene-based optical interconnects: photodetectors and modulators for data communication applications and broadband infrared sensors for hyperspectral space astronomy. Graphene has the highest room temperature mobility known to us, is complementary metal-oxide semiconductor (CMOS) compatible, and has rich electronic and optoelectronic properties. In the first part of this thesis, we used graphene as an active element with a passive silicon waveguide platform to demonstrate electro-absorption modulators and photodetectors. We developed a novel dielectric combination by integrating 2D material with 3D oxides, which enabled us to build a high-quality clean interface with graphene and high-¿ properties. This helped us to overcome fundamental limitations and demonstrate a high modulation efficiency (~ 2.2 dB/V) and high speed (39 GHz) in the same device, surpassing other CMOS-based modulators. In the case of the photodetector, we demonstrated a photo thermoelectric effect (PTE) based detector with high responsivity (55 mA/W) and a set up limited bandwidth of 40 GHz. In the second part of the thesis, we address the perpetual issue of limited light absorption in graphene by demonstrating the first 3D photoconductor based on decoupled bilayer graphene layers with 2D-like properties. Due to the asymmetric environment experienced by our decoupled bilayer graphene layers, they perceive a strong internal crystal field, which results in an intrinsic bandgap opening. We exploited this bandgap to observe a giant photoconductive photoresponse in a broad wavelength range from 2 to 150 µm. This is the first reported alternative to slow and expensive thermal detectors for broadband operation and could be instrumental for hyperspectral imaging and infrared astronomy, bringing us one step closer to unveiling the secrets of the universe. Finally, we reported a strong photoresponse in the out-of-equilibrium criticality state in graphene superlattices at high bias. We found that the criticality state shifts with a change in temperature or light, resulting in a photoresponse, impersonating transition-edge behaviour, which can be potentially interesting for THz single-photon detection in future.
  

• ANDREOLI, FRANCESCO: Multiple light scattering in atomic media: from metasurfaces to the ultimate refractive index
  
  Author: ANDREOLI, FRANCESCO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 23/03/2023
  Thesis director: CHANG, DARRICK
  

  Committee:
       PRESIDENT: TARRUELL PELLEGRIN, LETICIA
       SECRETARI: MILLER, OWEN DENNIS
       VOCAL: KAISER, ROBIN PIERRE LÉON
  Thesis abstract: Our ability to confine, guide, and bend light has led to astonishing technological achievements, playing a fundamental role in diverse fields like microscopy, photochemistry, telecommunications or material design. The key property of materials that allows to control light is the refractive index. Notably, regardless of very different microscopic structures, all natural materials exhibit a modest, near-unity index of refraction, n ~ 1. This universality suggests the existence of some simple, ubiquitous origin, whose complete characterization from microscopic considerations, surprisingly, is still missing. Moreover, one can wonder which principles might allow to synthesize a material with an ultra-high index, to boost the performance of photonic devices. In this thesis, we address these questions from an atomic-physics standpoint, exploring if the macroscopic optical properties can be related to simple, electrodynamical processes occurring between well-separated atoms, which only interact via light scattering. Standard theories neglect that light can be scattered multiple times, and lead to unphysical predictions when strong interference occurs between the coherent atomic emission, such as in dense atomic ensembles or ordered lattices. We here develop new techniques to address the physics of multiple light scattering, with the ultimate goal of understanding the fundamental limits to the refractive index, as well as proposing unexpected photonic applications. Our results are divided in three parts. First, we investigate an ensemble of ideal atoms with increasing atomic density, starting from the dilute gas limit, up to dense regimes where a non-perturbative treatment of multiple scattering and near-field interactions is required. In this situation, we find that these effects limit the index to a maximum value of n ~ 1.7, in contrast with standard theories. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interactions combined with random atomic positions result in an inhomogeneous broadening of the atomic resonance frequencies. This basic mechanism ensures that regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the index attainable. Afterwards, we show that a radically different behavior is expected for an ideal, atomic crystal. As long as the inter-atomic interactions are only mediated by multiple scattering, each 2D array of the crystal exhibits a lossless, single-mode response, which builds up a very large and purely real refractive index. To address the limits to this picture, we extend our theoretical analysis to much higher densities, where the electronic orbitals on neighboring nuclei begin to overlap. We develop a minimal model to include the onset of this regime into our non-perturbative analysis of multiple light scattering, arguing that the emergence of quantum magnetism, density-density correlations and tunneling dynamics of the electrons effectively suppresses the single-mode response, decreasing the index back to unity. Nonetheless, right before the onset of chemistry, our theory predicts that an ultra-high-index (n ~ 30) and low-loss material could in principle be allowed by the laws of nature.Finally, inspired by the impressive optical response of atomic arrays, we propose their use as a more complex optical device, namely a thin lens. The building blocks of this "atomic metalens" are composed of three consecutive 2D arrays, whose distance and lattice constants are suitably chosen to guarantee a high transmission of light, as well as an arbitrary phase shift. To characterize its efficiency and prove its robustness against losses, we perform large-scale numerical simulations, on a number of atoms between one and two orders of magnitude larger than comparable works.
  

• CAMPHAUSEN, ROBIN: Quantum-enhanced imaging with SPAD array cameras
  
  Author: CAMPHAUSEN, ROBIN
  Thesis link: http://hdl.handle.net/10803/688566
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 12/04/2023
  Thesis director: PRUNERI, VALERIO
  

  Committee:
       PRESIDENT: ACÍN DAL MASCHIO, ANTONIO
       SECRETARI: LAPKIEWICZ, RADEK
       VOCAL: JULIA DIAZ, BRUNO
  Thesis abstract: Entangled photon pairs can enhance optical imaging capabilities. Phase imaging allows detecting fine detail of transparent samples without potentially invasive fluorescent labelling, and here entanglement enables a higher signal-to-noise ratio (SNR) than possible with only classical light. Spatial correlations from spontaneous parametric down conversion (SPDC) photon pair sources can also be used to increase spatial resolution and robustness to noise and aberrations in imperfect optical systems. Quantum imaging therefore represents a powerful approach to push imaging science beyond its current limits.Until recently, the principal barrier to implementing useful quantum imaging schemes based on entangled photons has been technological, as scalable image sensors capable of multi-photon imaging were unavailable. However, this situation has changed with the development of single photon avalanche diode (SPAD) array cameras, as well as efficient high brightness entangled photon pair sources based on SPDC. These advances have led to the required components now approaching relative technological maturity, opening the window towards engineering useful and scalable systems that exploit entanglement in order to improve optical imaging.In this thesis, we show the development of a quantum imaging platform able to perform practical and fast spatially resolved multi-photon coincidence imaging with high SNR. Special focus is placed on wide-field entanglement-enhanced phase imaging capability, in order to extend experimental sensitivity beyond limits imposed by classical light. The main components of our platform are: sources of hyper-entangled photon pairs, a large field-of-view optical imaging system with phase measurement capabilities, and coincidence imaging using SPAD array cameras. More specifically, the thesis describes:¿The first realization of a wide-field entanglement-enhanced phase imager. Wide-field here refers to the ability to acquire images across the entire field-of-view simultaneously (i.e. without need for pixel-to-pixel scanning, sometimes also called full-field). Quantum-enabled super-sensitivity in phase imaging beyond the capability of equivalent classical measurement is demonstrated by careful experimental noise and resource analysis methods. Our system¿s capabilities were tested through several sample measurements corresponding to use cases with real-world relevance, including nanometre-scale feature step heights in transparent material, biomedical protein microarrays, as well as birefringent phase samples.¿The development of general experimental and numerical tools to calculate photon pair coincidence images and videos from SPAD array cameras, with photon-counting and time-tagging readout modalities, as well as the retrieval of phase images resulting from multi-photon entanglement interference, by adapting techniques from interferometry and holography. We performed also a detailed study and optimization of the influence of different experimental parameters resulting image quality factors.¿The evolution and optimization of our system towards real-time quantum imaging capability. Acquisition speed is a key element of usefulness, and in this thesis we integrate, first, a visible-wavelength entangled photon source, and second, a novel time-tagging SPAD array camera. The resulting entanglement-enabled imager presents an improvement by at least four orders of magnitude in measurement speed compared to previous state-of-the-art demonstrations, resulting in the ability to record ~Hz frame rate entangled photon pair coincidence videos. We show that this system, besides phase imaging, has additional applications in the form of real-time entangled state fidelity monitoring, and real-time point spread function characterization of optical systems, which has important applicability to adaptive optical imaging.
  

• CHISHOLM, CRAIG STERLING: Raman Dressed Bose-Einstein Condensates with Tunable Interactions: Topological Gauge Theories and Supersolids
  
  Author: CHISHOLM, CRAIG STERLING
  Thesis link: http://hdl.handle.net/10803/688921
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 19/06/2023
  Thesis director: TARRUELL PELLEGRIN, LETICIA
  

  Committee:
       PRESIDENT: MITCHELL, MORGAN
       SECRETARI: OBERTHALER, MARKUS
       VOCAL: STRINGARI, SANDRO
  Thesis abstract: The exquisite control available in atomic ultracold quantum gases experiments makes them an ideal candidate for quantum simulation of diverse topics ranging from high energy physics and analogue quantum gravity to strongly correlated condensed matter systems and exotic states of matter. This thesis describes the use of Raman coupling to engineer novel chiral interactions and a double well dispersion relation in potassium Bose-Einstein condensates and exploits them to realise a topological gauge theory and an exotic state of matter known as a supersolid, respectively.A common feature of many topics of interest for quantum simulation is the ability to describe them from the perspective of a gauge theory. Raman coupling has been used to produce artificial gauge fields for more than a decade but usually the gauge fields lack the symmetry constraints necessary to constitute a gauge theory. A well known gauge theory which is used to describe fractional quantum Hall states is the Chern-Simons theory. The Chern-Simons theory is a topological gauge theory so does not have gauge field dynamics in the absence of matter. We have used optical dressing to create chiral interactions in a Bose-Einstein condensate of potassium atoms and encode the dynamics of a one-dimensional reduction of the Chern-Simons theory known as the chiral BF theory into the dynamics of the matter. We have observed chiral solitons and a density-dependent electric field. Our experimental results represent the first successful quantum simulation of a topological gauge theory in the continuum.Supersolids were predicted theoretically more than fifty years ago and have been realised in Bose-Einstein condensates in recent years. In a second series of experiments, we have taken advantage of the unique interaction properties of potassium to engineer a supersolid in a Raman coupled Bose-Einstein condensate with greater stability and contrast than what can be achieved with other alkali atoms. Using matterwave optics techniques, we have been able to image the characteristic density modulations of a supersolid in a Raman coupled Bose-Einstein condensate for the first time. We explore a previously inaccessible parameter regime and demonstrate that the fringe spacing depends on the optical intensity, in contrast to a shallow optical lattice where the fringe spacing is given by the lattice wavevector.Our method of engineering chiral interactions broadens the field of quantum simulation of gauge theories to include topological gauge theories in the continuum and is a step towards simulating the Chern-Simons theory in two dimensions. Our application of matterwave optics to the supersolid phase in a Raman coupled Bose-Einstein condensate introduces a new tool for probing low energy Goldstone modes and phase coherence properties.
  

• DAS, IPSITA: Investigation of the Interaction Driven Quantum Phases in Magic-Angle Twisted Bilayer Graphene
  
  Author: DAS, IPSITA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 24/05/2023
  Thesis director: EFETOV, DIMITRI
  

  Committee:
       PRESIDENT: PAPADAKI, GEORGIA
       SECRETARI: ENSSLIN, KLAUS WILHELM EBERHANRD
       VOCAL: ALLAN, MILAN PETER
  Thesis abstract: The discovery of two dimensional materials opened a unique pathway to study the electronic properties of quantum materials which are otherwise absent in bulk systems. Soon after the discovery of graphene (2004), a plethora of 2D materials were found with various diverse properties such as, metals, insulators, semiconductors, superconductors, magnets etc. These materials can be assembled by using the van der Waals (vdW) force, which greatly extends the possibilities of studying new phenomena. Initially vdW heterostructures have been made by vertically stacking different layers. However, twist angle plays an interesting tuning knob to engineer the electronic properties of the 2D heterostructures. Following long standing theoretical predictions, people have observed exotic quantum phenomena in twisted bilayer graphene in 2018.In this thesis, we have studied the electronic properties of magic angle twisted bilayer graphene (MATBG), which consists of two graphene layers rotated by an angle ¿ = 1.1°. It has been experimentally shown that MATBG possesses flat electronic bands in the low energy scale, which hosts multiple correlated phenomena such as correlated insulators, superconductivity, magnetism etc.We studied different phases of MATBG in the presence of a magnetic field to reveal the zero-field ground state of the system. In the presence of a small magnetic field (B < 3 T), the Hall conductance of MATBG shows quantisation with the Chern numbers C = ±1, ±2, ±3 and ±4 which nucleate from different integer fillings of the moiré bands, ¿ = ±3, ±2, ±1 and 0 respectively. These phases can be interpreted as spin and valley polarized many body Chern insulators. The exact sequence and correspondence of the Chern numbers and filling factors suggest that these states are directly driven by electronic interaction, which specifically break the time-reversal symmetry in the system. We have also studied the evolution of the phase space of MATBG in high magnetic field and explored the Hofstadter spectrum. Due to the large moiré unit cell area, MATBG reaches one full flux quantum (F0) per moiré unit cell close to 30 T. We studied a detailed magneto-transport behaviour of MATBG upto B = 31 T. At F0, reentrant correlated insulators are observed at ¿ = +2, +3. Interaction driven Fermi surface reconstruction is also observed at other fillings of the band which are identified by the emergence of a new set of Landau levels (LLs).We further studied the higher energy dispersive bands in the presence of a magnetic field. The analysis of the LL crossings in the Rashba-like dispersive bands enables a parameter free comparison to a newly derived magic series of level crossings in a magnetic field and provides constraints on the parameters of the Bistritzer-MacDonald Hamiltonian. For the first time, this allows us to experimentally verify the band structure of MATBG.In the next section of this thesis, we have studied the effect of Coulomb screening on the ground state of the quantum phases such as correlated insulator and superconductor. The coexistence of these two states prompts intriguing questions about their relationships. We have directly tuned the electronic correlations by changing the separation between the graphene and a metallic screening layer. Correlated insulators are suppressed when the separations are smaller than the typical Wannier orbital size ( ~ 15 nm) and also in devices with twist angles slightly away from magic angle (¿ = 1.1° ± 0.05°). Upon extinction of the insulating orders, the vacated phase space is taken over by the superconductors. Finally, we study the temperature depe0ndence of the resistance and unveil a strange metal phase upto a very low temperature T = 40 mK.We thus have experimentally demonstrated the effect of several external parameters (magnetic field, screening, temperature etc.) on the ground state of MATBG and how they alter the microscopic mechanism of different correlated phenomena in the
  

• DI GIULIO, VALERIO: Nanophotonics with charged particles
  
  Author: DI GIULIO, VALERIO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 12/04/2023
  Thesis director: GARCÍA DE ABAJO, JAVIER
  

  Committee:
       PRESIDENT: KOCIAK, MATHIEU
       SECRETARI: ROPERS, CLAUS
       VOCAL: MANJACAVAS AREVALO, ALEJANDRO
  Thesis abstract: Among the fundamental constituents of matter, charged particles such electrons and positrons are leading protagonists in physical phenomena associated with small (~ meV) and high (~ MeV) energy scales. For example, conductive electrons in condensed-matter systems can collectively respond to the action of an external electromagnetic field and sustain plasmon excitations that dominate their visible optical behavior. The presence of material boundaries produces a dramatic modulation of such modes, allowing us to mold their interaction with light for the exploration of fundamental phenomena and the design of practical applications, which are central themes in the field of nanophotonics.Electrons traveling in free space, such as those in electron microscopes, constitute ideal probes for imaging materials with nanometric resolution. In an effort to push energy resolution down to the meV regime and simultaneously perform time-resolved measurements with fs precision, laser and electron pulses in transmission electron microscopes can now be synchronized to meet at the specimen in the so-called photon-induced near-field electron microscopy (PINEM). Here, efficient electron coupling to intense laser-driven evanescent fields results in a strong energy reshaping of the electron wave function. Over the last decade, PINEM has been used to tailor the wave function of free electrons, thus emphasizing the role of these microscopy probes as information carriers. This Thesis lies in this general and broad context as an effort to explore new scenarios in the interaction between free electrons and optical excitations. In particular, Chapter 2 addresses the theoretical investigation of quantum-mechanical aspects associated with PINEM interaction by means of a quantum-optics description of the optical field. Building up on those results, in Chapter 3 we show that improved control over electron pulse shaping, compression, and statistics can be gained by replacing coherent laser excitation by interaction with quantum light, such as phase- and amplitude-squeezed optical fields.Chapter 4 explores the role played by fluctuations of the electromagnetic vacuum in the coupled dynamics of a free-electron beam and a macroscopic object, producing elastic diffraction and decoherence. In particular, we show that diffraction can dominate over decoherence, therefore suggesting a nondestructive approach to microscopy based on the specific choice of parameters that minimize the inelastic interaction with the specimen.As a radically different aspect of electron-light interaction, Chapter 5 is devoted to the study of the interference produced in the cathodoluminescence emission by the synchronized interaction of free electrons and dimmed laser pulses scattered by the specimen. Here, we argue that such effect may enable measurements combining the spectral and temporal selectivity of the light with the atomic resolution of electron beams to resolve the phase associated with optical modes in the sample.In Chapter 6, we consider that elastic diffraction, similar to that studied in Chapter 4, is also experienced by conduction electrons in a two-dimensional material, therefore altering the properties of the latter by simply adding a neighboring neutral structure.Going to higher energy scales, Chapter 7 explores the potential of confined optical modes to assist electron-positron pair production arising from the scattering of gamma rays by surface polaritons propagating along a material interface.In summary, throughout this Thesis we exploit the coupling between evanescent light, harnessed in the vicinity of material boundaries, and charged free particles in order to access new effects only found at the point where nanophotonics, quantum optics and high-energy physics meet through strong light-matter interaction.
  

• DURANTI, STEFANO: Towards efficient quantum repeater nodes based on solid-state quantum memories
  
  Author: DURANTI, STEFANO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 24/03/2023
  Thesis director: DE RIEDMATTEN, HUGUES
  

  Committee:
       PRESIDENT: CHANG, DARRICK
       SECRETARI: KRÖLL, RICHARD STEFAN
       VOCAL: ETESSE, JEAN FRANÇOIS YVES
  Thesis abstract: Quantum repeaters are the foundation of future long-distance quantum networks. In most architectures, their functional core is constituted by quantum memories, which are devices that can store and re-emit photonic quantum information on-demand. The goal of this thesis is to progress towards efficient quantum repeater nodes enabling quantum correlations between telecom photons and matter qubits. To these ends, we performed three main experiments.In our first work, we built a solid-state entanglement photon source with embedded storage capabilities. This emissive quantum memory was implemented in a Pr3+:Y2SiO5 crystal, by means of the atomic frequency comb (AFC) protocol. Thanks to the AFC, we were able to adapt the Duan-Lukin-Cirac-Zoller (DLCZ) protocol, initially conceived for cold atoms, to a solid-state ensemble. This experiment proved that we can produce light-matter entanglement between a heralding photon, at 606 nm, and a spin-wave excitation delocalized inside the ensemble. The matter excitation could be read on-demand at a later time with a read pulse, and mapped as a second photon, at 606 nm as well, emitted by the memory. Quantum correlations between the two photons were measured, enabling the violation of a Bell inequality, thus demonstrating the presence of entanglement. The read-out efficiency of this experiment was low, 1.6%, but solutions were identified to increase this value.In the second experiment, we laid the groundwork for the quantum frequency conversion (QFC) of these photons to the telecom band. The long duration of these photons, up to 1 µs, makes their conversion with high signal-to-noise ratio (SNR) challenging. The conversion from the visible 606 nm wavelength to the telecom regime (1552 nm) was achieved by difference-frequency generation (DFG) in a PPLN waveguide using a strong pump field at 994 nm. A proof of principle with weak coherent pulses showed that we can convert µs-long photons with the low heralding efficiency of the previous experiment with a SNR around 2.6. This sets the stage for interfacing an AFC-DLCZ memory, working at 606 nm, with the telecom network and with material systems working at a different wave length.Finally, in the last experiment, we implemented an AFC impedance-matched cavity (IMC) storage experiment. It has been demonstrated theoretically and experimentally that the IMC enhances the storage and read-out efficiency of the AFC protocol. We harnessed this cavity to store weak coherent Gaussian pulses with up to 62% efficiency. Moreover, we stored weak coherent time-bin qubits in the same system, achieving 52% efficiency and, with an additional analysis carried out by means of an unbalanced Mach-Zehnder AFC-based interferometer, assessing a measured fidelity of 95% for the retrieved qubit, leading to a quantum memory fidelity compatible with 100%, within uncertainty. We additionally studied the influence of slow-light effects in our crystal, confirming that they lead to a reduction of cavity bandwidth by two orders of magnitude. Moreover, the AFC storage time was extended up to 50 µs, to certify that the efficiency enhancement holds for different combs.The achievements of this thesis represent the state of the art for the AFC efficiency and for qubit storage in solid-state systems, and pave the way towards efficient quantum memories. In addition, we reported the first demonstration of a solid-state photon pair source of entangled photons with embedded solid-state multimode memory. The results accomplished by this last AFC-DLCZ experiment in terms of heralding efficiency make it possible to interface it with our quantum frequency conversion experiment. Indeed, the QFC experiment, combined with the AFC-DLCZ one, enables to establish a quantum node and to interface it with different kind of nodes via conversion to the telecom band.
  

• KOBAYASHI FRISK, LISA: Application and development of diffuse optical methods for the non-invasive bedside assessment of cerebral hemodynamics in the stroke unit
  
  Author: KOBAYASHI FRISK, LISA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 14/07/2023
  Thesis director: DURDURAN, TURGUT
  

  Committee:
       PRESIDENT: VAN HULST, NIEK
       SECRETARI: BAKER, WESLEY BOEHS
       VOCAL: URRA NUIN, XABIER
  Thesis abstract: The brain is an organ with a large energy budget compared to its volume and weight and constantly requires oxygen-rich blood to meet its metabolic needs. Given this fact, a tool that enables the continuous non-invasive monitoring of cerebral hemodynamics would be an important addition to a clinician's toolbox. In this thesis, I focus on stroke, a disease in which cerebral blood flow is impaired in different regions of the brain. Hybrid diffuse optical techniques are capable of the non-invasive measurement of regional cerebral hemodynamics. The main objectives of this PhD thesis were to demonstrate the potential utility of diffuse optical techniques in stroke patients as well as to advance the technology to become more portable and less expensive with the capability of measuring hemodynamics with a greater precision and accuracy. In the first part of the thesis, I report on data from a randomized controlled trial which monitored the cerebral hemodynamics in one hundred-and-six stroke patients during first mobilization using two optical techniques: time-resolved near-infrared spectroscopy (TRS) and diffuse correlation spectroscopy (DCS). The aim of the clinical trial was to determine whether cerebral hemodynamics measured during mobilization could be used as biomarkers for individualizing mobilization therapies.In the first set of results, the cerebral hemodynamic response to mobilization and posture change was characterized. In the second set of results, cerebral autoregulation was assessed during first mobilization and was found to be associated with neurological deterioration. These results suggest that patients with impaired cerebral autoregulation during mobilization should perhaps avoid further mobilization in the early hours post-stroke. In the third set of results, the safety and efficacy of standard and intensive mobilization therapy was compared. No differences were found, and cerebral autoregulation status was not associated with neither safety nor efficacy outcome variables.The clinical portion of the thesis is an example of the potential application and demonstrates the value of non-invasive measurements of cerebral hemodynamics at the bed-side. However, a major disadvantage of current diffuse optical technologies is the difficulty in acquiring data with a high signal to noise ratio (SNR) in areas with higher probability of absorption, e.g. in regions covered by hair. In the context of stroke patients, this limits measurements to anterior hemodynamics irrespective of the location of the stroke. The second part of the thesis consists of the development of another diffuse optical technique (speckle contrast optical spectroscopy/tomography (SCOS/SCOT)) that may be able to overcome this limitation. As a first step, a simulation model was developed to model the generation and acquisition of the speckle contrast signal. This model allowed for the study of the properties of the speckle contrast signal both in terms of detection and measured tissue parameters. In addition, the simulation model allows for the definition of certain measurement goals to achieve a predetermined acquisition accuracy and precision. Then, a prototype device was built that is not only cheaper and more portable than more standard diffuse optical technologies, but also has a high SNR. The device was characterized, and the measurement goals for accuracy were established. Finally, I developed an analysis method for extracting blood flow data from SCOS signals. This method allows for the simplification of system designs and/or protocols and can also increase data acquisition frequencies. This thesis covers a range of topics from clinical research to simulation models and system design. However, the overall contribution of this work is to demonstrate the clinical utility of these techniques as well as to propel the technology further to achieve a more complete picture of cerebral health.
  

• KRAMARENKO, MARIIA: FLUORESCENCE QUANTUM YIELD AND THE OPEN CIRCUIT VOLTAGE IN PEROVSKITE SOLAR
  
  Author: KRAMARENKO, MARIIA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 24/03/2023
  Thesis director: MARTORELL PENA, JORDI
  

  Committee:
       PRESIDENT: LIRA CANTÚ, MÓNICA
       SECRETARI: GARCÍA DE ARQUER, FRANCISCO PELAYO
       VOCAL: ALARCON LLADO, ESTHER
  Thesis abstract: To mitigate the energy and climate crisis we are already facing and address the increasing energy consumption, it is essential to foster energy transition strategies. The energy transition success largely depends on being able to transform the global energy sector from fossil fuel-based to neutral or zero carbon dioxide emission sources. A decades-long study of photovoltaics has produced several generations of solar energy conversion technologies that do not emit greenhouse gases or air pollution when they operate. However, considering the sun is our planet's most abundant energy source, when compared to fossil fuels, the use of photovoltaics is still very limited. In such a transition from fossil fuels to photovoltaics, it is essential to enhance affordability combined with high efficiency. In recent years, perovskite solar cells have emerged as the most prominent thin-film PV technology to provide high efficiency simultaneously at a low cost. In this thesis, we study perovskite-based solar cells and optical routes to maximise their power conversion efficiency. The theoretical limit for converting sunlight into electricity by the photovoltaic effect was first established by William Shockley and Hans-Joachim Queisser in 1961 based on the principle of detailed balance. According to their work, a solar cell can reach a limiting efficiency if all loss mechanisms are eliminated and the fluorescence quantum yield is equal to unity. The conversion efficiency for all PV technologies is still considerably lower than the Shockley ¿ Queisser efficiency limit, but perovskite-based ones have demonstrated outstanding optoelectronic properties and high fluorescence quantum yields, which may help get their maximum PV efficiency closer to such limit. In this thesis, we provide several optical routes to optimise the photovoltaic parameters of perovskite solar cells, placing a special emphasis on the open circuit voltage by studying its relation to the absorption and emission of photons by the perovskite layer.This thesis is organised into five chapters. Chapter 1 serves as an introduction, which includes a discussion of the current world energy demand and available photovoltaic technologies, focusing more on the ones based on perovskite materials. The Shockley ¿ Queisser efficiency limit and power loss mechanism are also described in this chapter. In Chapter 2, we analyse the relationship between open circuit voltage and fluorescence quantum yield in perovskite-based solar cells, both theoretically and experimentally, and discuss the observed deviation from the predicted behaviour. Chapter 3 describes the new fabrication method of high-quality perovskites with low band gaps and big grain size is described. The two-step compact PbI2-templated growth method facilitated the achievement of solar cells with high fluorescence quantum yield and open circuit voltage. In Chapter 4, we developed a model and optimisation algorithm to find the optimum photonic structures to optically enhance the photovoltaic parameters for different band gap perovskite solar cells. Theoretical results from this chapter suggest that a simple dielectric multilayer placed on top of the substrate of the solar cell can simultaneously improve the open circuit voltage and short circuit current, resulting in a relative gain of power conversion efficiency larger than 4%. Finally, in Chapter 5, the concept theoretically studied in the previous chapter is experimentally implemented. The dielectric multilayer is fabricated and placed on top of a perovskite solar cell, resulting in an enhanced open-circuit voltage and power conversion efficiency.
  

• LIGA, SHANTI MARIA: Environmentally-friendly perovskite nanocrystals based on titanium and tin
  
  Author: LIGA, SHANTI MARIA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 22/03/2023
  Thesis director: KONSTANTATOS, GERASIMOS
  

  Committee:
       PRESIDENT: LIGUORI, NICOLETTA
       SECRETARI: MALAVASI, LORENZO
       VOCAL: FIGUEROLA SILVESTRE, ALBERT
  Thesis abstract: The availability of energy is a fundamental ingredient for the development of society. However, the intense consumption of fossil fuels as an energy resource since the second industrial revolution has caused a massive increase in the concentration of CO2 and other greenhouse gases in the atmosphere, which is nowadays known to be the first cause of climate catastrophe. For this reason, it has become a priority to replace fossil fuels with more sustainable sources, which are renewable and produce low greenhouse gas emissions. Photovoltaics is one of the suitable technologies to carry out this fast transition because it is already well-developed and is based on the use of the infinite energy source, the Sun. However, increasing the efficiency of solar light conversion into electricity and reducing the cost of photovoltaic devices is fundamental to achieve the goals set by policy makers. Consequently, the development of novel optoelectronic materials, based on abundant and environmentally friendly elements, is one of the fundamental scientific advances needed to boost the shift towards a low-carbon society.Perovskites, whose solar cells reached this year a certified record efficiency of 25.7%, are the first solution-processed materials to outperform multicrystalline and thin-film silicon and therefore one of the most interesting new materials for photovoltaic applications. In spite of their astonishing performances in solar cells, the most promising perovskites contain lead, which is toxic for human beings and potentially a threat to the environment. Hence, over the last decade, there has been intensive research on strategies to replace lead in the perovskite structure with nontoxic elements. Among all the novel perovskites studied, titanium-based vacancy-ordered double perovskites demonstrated one of the most promising performances when applied in solar cells.This thesis focuses on the development of new solution syntheses for the preparation of novel lead-free vacancy-ordered double perovskite nanocrystals based on titanium and tin in the oxidation state +4, which are nontoxic and abundant elements. All the synthesized perovskite nanocrystals were characterized structurally, chemically and optically. Moreover, the experimentally observed optical properties and the stabilities of these materials were further confirmed by ab initio density functional theory calculations.We initially developed a colloidal synthesis to prepare mixed bromide-iodide Cs2TiBr6-xIx perovskites. All these materials are intrinsically stable with bandgaps in the visible region; suitable for solar cell applications. However, they showed very high instability in air, which prevented their application in devices and that motivated us to search for strategies to stabilize them.Encouraged by the higher reported stabilities of Sn+4 perovskites with the same vacancy-ordered double perovskite structure, we synthesized pure tin halide perovskite NCs and novel mixed titanium/tin iodide and bromide perovskite NCs. The experiments confirmed that tin perovskites are stable in air and that the mixtures with the highest amount of tin in the structure are stable in air for longer than pure titanium perovskites. Finally, for the case of Cs2TiBr6, we developed a room temperature method to reach comparable stabilities in air through a surface treatment with tin compounds.In summary, we have developed a low-temperature solution method for the preparation of novel environmentally-friendly perovskites based on tin and titanium and studied their properties for the first time, both computationally and experimentally. Finally, we have found a way to increase the stability in air of titanium-based perovskites through the addition of tin in the structure. Overall, this thesis provides an insight into novellead-free perovskites based on titanium and tin and it represents a milestone for the understanding and development of this new class of materials.
  

• MATEOS ESTÉVEZ, NICOLÁS: Advanced single molecule fluorescent tools to reveal spatiotemporal multi-molecular interactions in living cells
  
  Author: MATEOS ESTÉVEZ, NICOLÁS
  Thesis link: ICFO, Mediterranean Technology Park, Avinguda Carl Friedrich Gauss, 3, 08860 Castelldefels, Barcelona
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 28/04/2023
  Thesis director: GARCÍA PARAJO, MARÍA | TORREÑO PIÑA, JUAN ANDRÉS
  

  Committee:
       PRESIDENT: LOZA ALVAREZ, PABLO
       SECRETARI: PADILLA PARRA, SERGIO
       VOCAL: DOS SANTOS DUARTE VIEIRA HENRIQUES, RICARDO JOSÉ
  Thesis abstract: The spatiotemporal organisation and compartmentalisation of molecules in living cells is crucial to regulate cell function. Dysregulation in how molecules dynamically explore their environment and interact with other molecules can lead to disease and death. Therefore, understanding the nature of these dynamic interactions is pivotal in cell biology studies. Fluorescence light microscopy is the preferred approach to perform the necessary biophysical studies and it has led to major findings in the field. Nevertheless, spatial and temporal studies are typically conducted separately due to technical limitations. Moreover, quantitative imaging and novel analysis toolboxes are required to address new questions in the field. The aim of this thesis is three-fold: (1) develop and implement novel algorithms to analyse super-resolution microscopy data to study the spatial organisation of a variety of proteins at the plasma membrane of cells; (2) develop a novel methodology to study the spatiotemporal organisation of receptors at the plasma membrane of cells based on high-density single particle tracking; and (3) apply our novel methodology in a multi-colour scheme to study the compartmentalisation of DC-SIGN and its multi-component interactions with CD44 and Galectin 9 during viral engagement.In Chapter 1, we overview how cells are compartmentalised from the intra-cellular organisation to how the cell membrane is compartmentalised by multiple organisers acting most probably in synergy. Also, in Chapter 1, we review the main fluorescence microscopy techniques used in the field of cell biology to study the spatiotemporal organisation of molecules in cells. In Chapter 2, we present the analyses that we have performed to super-resolution microscopy techniques such as stimulated emission depletion (STED) and stochastic optical reconstruction microscopy (STORM). We have used these techniques to elucidate the spatial organisation of proteins at the plasma membrane such as Siglec-1, integrins or PRL-3. We have implemented state-of-the-art algorithms into our analysis workflow to resolve the biological inquiries of our research. In Chapter 3, we change gears and present our novel methodology to analyse high-density single particle tracking, which consists on generating high-density maps (HiDenMaps). In this chapter, we specify the technical requirements to obtain a faithful representation on how molecules explore space. In Chapter 4, we study CD44 which is a transmembrane protein extremely interesting because it can interact with the underlying cortical actin and the extracellular milieu. Moreover, it is thought to act as a key actor in the spatiotemporal compartmentalisation of the plasma membrane for third receptors that do not interact directly with actin. In this Chapter, we have used HiDenMaps to elucidate the hierarchical organisation of CD44 at the plasma membrane of living cells. In Chapter 5, we present a palette of analysis tools to further quantify the patterns revealed by HiDenMaps and resolve the temporal dynamics of these patterns. Moreover, our work reveals a multi-scale organisation of CD44 ranging from fast single molecules dynamics with a mesoscale dynamic compartmentalisation. In Chapter 6, we present a functional study on viral capture by DC-SIGN in immature dendritic cells. We extended our HiDenMap methodology to a multi-colour scheme to study the multi-component interactions of DC-SIGN with CD44 and Galectin 9 during viral engagement. Importantly, we demonstrate the existence of DC-SIGN/CD44/Galectin 9 tripartite pre-docking platform that enhances the successful engagement of HIV-1 and SARS-CoV-2 virus-like particles in immature dendritic cells. Finally, in Chapter 7 we summarise the main results of this thesis and highlight future directions of our research.
  

• MAZZINGHI, CHIARA: Cavity-enhanced non-destructive measurements of atomic magnetism
  
  Author: MAZZINGHI, CHIARA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 26/07/2023
  Thesis director: MITCHELL, MORGAN
  

  Committee:
       PRESIDENT: TARRUELL PELLEGRIN, LETICIA
       SECRETARI: DUMKE, RAINER HELMUT
       VOCAL: HOSTEN, ONUR
  Thesis abstract: In this work we propose and demonstrate cavity-enhanced polarization rotation to detect magnetic effects in transparent media with greater sensitivity at equal optical disturbance to the atomic medium. We use the Jones calculus to compute theeffective polarization rotation effect in a cavity containing a magnetic medium. We include the losses due to enclosure window or other sources. The results show that to measure polarization rotation collecting the transmitted light has advantages in terms of linearity and simplicity with respect to collecting the reflected light. We show also the description of a "commensurate lattice'', to position the atoms at the anti-nodes of the probing light: this increases the atom-light coupling and therefore the cavity enhancement. The trapping light is also used to stabilize the cavity.Then we describe the experimental realization of the cavity and we demonstrate the theory described by measuring the Faraday rotation in a Rb-87 atomic ensemble in the single-pass and cavity enhanced geometries. We observe theenhancement given by the cavity in good agreement with the theoretical predictions. We also demonstrate shot-noise-limited operation of the enhanced rotation scheme in a small angle regime.We conclude with the expected squeezing effect given by the cavity in a cold and ultra-cold ensembles. The cavity tested gives a measurement squeezing 5 dB larger with respect to the SP case.
  

• ORTIZ DE ORRUÑO CUESTA, UNAI: Optical Holographic Microscopy for Bio- and Nanoparticle Characterization
  
  Author: ORTIZ DE ORRUÑO CUESTA, UNAI
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 21/04/2023
  Thesis director: VAN HULST, NIEK
  

  Committee:
       PRESIDENT: PRUNERI, VALERIO
       SECRETARI: LECHUGA GÓMEZ, LAURA M.
       VOCAL: ALVAREZ PUEBLA, RAMON ANGEL
  Thesis abstract: Nowadays, being able to precisely characterize nanoparticles is of key relevance in a wide range of scenarios. For instance, chemical and pharmaceutical industries often rely in particle-sizing for quality control. In a clinical context, in contrast, sensitive bioparticle characterization platforms can lead to the diagnosis of early-stage illnesses. However, the needs between each scenario vary, due to the differences in samples¿ composition and the particle-property of interest. Hence, several nanoparticle characterization techniques have emerged, each one based on a different physical principle and best suited for particular usage scopes.In this thesis, I improve the optical nanoparticle sizing techniques by using holography. I present different optical systems that image nanoparticles and record their scattering signal into holograms. I show how to reconstruct the scattered light¿s wavefront using holographic processing tools and how to extract the particle size information from it. I prove the capabilities of the holographic imaging systems that I introduce by providing their technical characterization and by measuring relevant samples.First, I introduce an imaging system with an extended the dynamic range compared to conventional darkfield microscopes. I demonstrate the nanoparticle sizing capabilities of such holographic platform using calibration samples. Moreover, I provide a proof-of-concept in the form of the characterization of a clinical sample, composed by extracellular vesicles, to demonstrate the feasibility of the platform for the development of point-of-care systems.Afterwards, I show how nanoparticle tracking analysis (NTA), that is to size particles from their diffusion, can be improved by using holography. The use of holography not only increases the NTA¿s precision, thanks to its ability to capture better the particles¿ diffusion, but also provides the refractive index information of the sample. The latter is of especial interest when measuring samples of unknown compositions, such as clinical extractions. I present experimental evidence of the improvements in the NTA¿s sizing precision and the simultaneous retrieval of the refractive index. Additionally, I measure the radial shift of the nanoparticles induced by the formation of protein-coronas, which I believe that proves the platform¿s relevance for studying the particles¿ behaviour in biological fluids.Finally, I present a system that confines particles in the volume-of-view of a holographic imaging system for further improving the NTA¿s sizing precision. Such platform¿s design was motivated by the promising results obtained using holographic NTA and its potential usage on fundamental research of protein-corona formation. The idea behind the system is to obtain longer particle-diffusion trajectories for pushing the holographic NTA sensitivity down to what is necessary to detect the absorption of a single protein onto a nanoparticle. I demonstrate the capabilities of such platform by showing a thorough technical evaluation based on experimental evidence.I foresee that the presented holographic platforms will find many applications of both fundamental and applied nature. In particular, considering the ability of such platforms to analyse polydisperse samples, I expect to contribute to advances in the fundamental research of extracellular vesicles.
  

• RAKONJAC, JELENA VELIBOR: Light-matter entanglement between telecom photons and solid-state quantum memories
  
  Author: RAKONJAC, JELENA VELIBOR
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 26/06/2023
  Thesis director: DE RIEDMATTEN, HUGUES
  

  Committee:
       PRESIDENT: MITCHELL, MORGAN
       SECRETARI: LEDINGHAM, PATRICK
       VOCAL: HUNGER, DAVID
  Thesis abstract: Future networks for quantum communication will require a new form of technology in order to operate over long distances. The no-cloning theorem precludes the use of amplification, so quantum repeater schemes have been proposed to achieve long-distance quantum communication through the distribution of entanglement. A key device for this setup is a quantum memory, which is required in order to store entanglement and synchronise its distribution.Among the many physical systems than can be used as a quantum memory, rare-earth ion-doped crystals stand out due to their long coherence times and potential for multiplexing and integration. This thesis reports the use of one such system, Pr3+:Y2SiO5, as a quantum memory using the atomic frequency comb (AFC) protocol. Building on previous work, we improved the performance of the memory to be able to demonstrate light-matter entanglement with a telecommunications wavelength photon and the quantum memory, for both a bulk memory and an integrated version.To measure light-matter entanglement, we use photon pairs generated through cavity-enhanced spontaneous parametric down conversion, where one photon (the signal) is stored in the memory and the other (the idler) is at a telecommunications wavelength. These photon pairs exhibit energy-time entanglement, which we analyse in the time basis using fibre- and AFC-based Mach-Zehnder interferometers. In the first experiment, we demonstrate light-matter entanglement where the bulk quantum memory is used with on-demand retrieval via storage in a spin-wave. We measure interference fringes with average visibilities of 89(2)% for AFC storage, and 70(3)% for spin-wave storage, sufficient to demonstrate entanglement. This is the first such demonstration using an on-demand multimode solid-state memory and telecom photon. We show that entanglement is maintained for up to 47.7 µs of storage. These results were made possible through improvements in the AFC efficiency and the noise filtering. Furthermore, we perform on-demand storage and retrieval of up to 30 temporal modes.We take the next step towards implementing our system in a real world scenario by measuring entanglement over a distance. To do so, we send the idler photons through both optical fibre spools and deployed fibre in the metropolitan area of Barcelona, Spain, while the photon detection still occurs in the same lab. The resulting visibilities (80% or higher) demonstrate that the photonic qubit does not decohere during transmission through the optical fibre. We then decouple the photon creation and detection by measuring non-classical correlations between signal photons detected in the lab, and idler photons detected 16 km away (44 km in fibre) in a different location.The final experiment uses a fibre-integrated memory for light-matter entanglement. We use a Pr3+:Y2SiO5 crystal containing a Type I laser-written waveguide, interfaced directly with optical fibre. The fibre-integration allows for improved transmission and AFC efficiency compared to a free-space coupled waveguide memory. To analyse the performance of the memory, we demonstrate non-classical correlations for storage times up to 28 µs. We perform qubit tomography in the time basis for storage times of 3 and 10 µs, measuring two-qubit fidelities of 86(2)% and 86(4)%, respectively, demonstrating storage of entanglement.These experiments demonstrate the potential of our system for use as part of a quantum repeater, with many opportunities for further improvement to the storage time, efficiency, and multiplexing capability.
  

• SEVERINO, STEFANO: Attosecond soft X-ray absorption revealing the ultrafast non-adiabatic dynamics of furan
  
  Author: SEVERINO, STEFANO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 13/03/2023
  Thesis director: BIEGERT, JENS
  

  Committee:
       PRESIDENT: LIGUORI, NICOLETTA
       SECRETARI: CERULLO, GIULIO
       VOCAL: PALACIOS CAÑAS, ALICIA
  Thesis abstract: One of the fundamental goals of the physical chemistry community has always been to be able to follow the details of the evolution of chemical reactions in real-time. Besides the extreme temporal resolution (sub-femtoseconds) required, a blurred picture of the dynamics often arises from the difficulties of spectroscopically disentangling the interplay between the electronic and nuclear degrees of freedom in complex compounds. This depends on the observable used for the experiments, which defines the direct and indirect information that can be retrieved. For example, electron diffraction or X-ray scattering methods directly track the structural changes of a species during a reaction. X-rays Absorption Fine Structure (XAFS) spectroscopy, instead, follows the dynamics from the electron perspective by probing transitions from a core orbital to an empty valence orbital. Especially when applied to the soft X-ray wavelength region, the core-hole transitions minimize the spectral congestion and provides inherent element, charge and state sensitivity. At the same time, the observable is strongly dependent on the geometrical changes and, hence, provides information regarding the nuclear dynamics.With the emergence of attosecond science, the remarkable properties of XAFS spectroscopy were combined with unprecedented temporal resolution matching the natural timescales of electronic motion in matter. This equipped the scientific community with a tool capable of disentangling the details of the intricate dynamics that arise from the interaction between light and matter, and initiated a revolution in the field of ultrafast spectroscopy. Among the many chemical dynamics that can be investigated, Attosecond XAFS (AttoXAFS) spectroscopy is very appealing for the study of non-adiabatic processes of polyatomic systems involving degeneracy points of the potential energy surfaces, i.e., conical intersections (CIs), in which electronic and vibrational coherence play a crucial role. In these phenomena, the ability to disentangle the nuclear and electronic degrees of freedom is fundamental for a correct interpretation of the process.In this thesis, AttoXAFS in the soft X-rays is applied to the study of the complex non-adiabatic dynamics of a prototypical heterocyclic molecule, furan. Analysis of the experimental data, with the support of high-level simulations, provides a clear interpretation of the ultrafast coupled electron and nuclear dynamics. The temporal resolution and sensitivity to both electronic occupancies and structural changes allow following the dynamics step by step, revealing information about the nuclear and electronic configuration of the molecule with an unprecedented level of detail. The resulting picture shows how the passage through subsequent CIs defines the flow of the electronic population through transient dark states and the complete relaxation to the ground state, as well as the interplay between electronic and vibrational coherence dynamics.In chapter 1 of this thesis, I will provide the framework for these results. This consists, on the one hand, of the recent development of attosecond science and its achievements in the study of light-matter interaction and, on the other, the coupled nuclear and electronic dynamics that characterize the photoinduced chemical reaction of polyatomic systems. In chapter 2 I will present the experimental setup developed in Prof. Dr. Jens Biegert¿s lab with which the results of this thesis were obtained. In chapter 3, I will discuss the importance of high photon energy pulses for materials science, focusing on XAFS and its capabilities, and show its exemplary applications on various solid state and gas phase samples achieved during my PhD. The core of this thesis is presented in chapter 4, where I will describe the experimental data on furan and the main results of the combined theoretical and experimental investigation. Finally, I will conclude with a summary and an outlook.
  

• TAGHIPOUR, NIMA: SOLUTION-PROCESSED QUANTUM DOT INFRARED LASERS
  
  Author: TAGHIPOUR, NIMA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 21/03/2023
  Thesis director: KONSTANTATOS, GERASIMOS
  

  Committee:
       PRESIDENT: EBRAHIM-ZADEH, MAJID
       SECRETARI: NORRIS, DAVID JAMES
       VOCAL: BROVELLI, SERGIO
  Thesis abstract: Colloidal semiconductors quantum dots (CQDs) have emerged as a promising solutionprocessed gain material that can be engineered via low-cost and scalable chemical techniques. Owing to quantum confinement, their emission wavelengths and optical properties can be tuned from the visible to the infrared. Despite these possible advantages, the realization of lasing action in CQDs is complicated and fundamentally stems from the non-unity degeneracy of the band-edge state. This results in high optical gain thresholds, demanding multiexcitons for achieving lasing action. This, in turn, leads to a very short optical gain lifetime which is caused by Auger recombination.Following the first demonstration of lasing action in CQDs, this field has thus far experienced remarkable development with materials offering emission in the visible showing limited application potential. However, the possibility of lasing in the infraredregion would open a new realm of applications for this material platform in optical telecommunications, photonic integrated circuits, and LIDAR applications. To unleash those applications, the demonstration of solution-processed infrared lasers in the eye-safe window between 1.5-1.6 µm operating robustly at room temperature is a prerequisite.Midgap trap states in CQDs limit the performance of optoelectronics devices. In particular, PbS CQDs suffer from a very fast trap-assisted Auger process leading to high lasing thresholds. To suppress this type of Auger process, in this work, we use a binary nanocomposite of PbS CQDs and ZnO nanocrsystals (NCs) where the former serves as the infrared gain medium and the latter as a remote passivant for midgap traps in PbS CQDs. This binary heterostructure drastically suppresses the Auger process and lowers the lasing thresholds.Low threshold infrared CQD-laser has been thought to be not possible because of 8-fold degeneracy of the band-edge state in the infrared-emitting Pb-chalcogenide CQDs. In this Thesis, we demonstrate that using core-alloyed shell heterostructuredCQD comprising PbS as core and PbSSe as shell allows suppressing Auger process. Furthermore, by applying doping to specially engineered CQDs, we demonstrate a substantial reduction in lasing threshold down to sub-single exciton level per-dot thanks to the blocking of the ground state absorption. Employing these CQDs has drastically improved the net modal coefficient of the medium and brought it on par with a gain coefficient of epitaxially grown III-V infrared semiconductors.The realization of CQD infrared laser-diodes will have a profound impact in many disciplines. Here, by engineering the electric field distribution in our devices, we show stimulated emission in a record ultra-thin gain media which is beyond the slabwaveguide theoretical limit by introducing scatterers implemented by ZnO NCs. We employ this thin gain media as the active layer in a full-stack light emitting diode (LED) device. Also, to overcome the existing challenge underpinned by the optical losses of the metal contacts that have prevented the realization of stimulated emission in a LED, we use an engineered transparent conductive oxide and graphene as anode and cathodeof the LED, respectively. Finally, our proposed LED structure leads us to realize a dual function device showing strong infrared spontaneous- and stimulated-emission underelectrical- and optical-pumping, respectively.In summary, we have demonstrated that CQDs can emerge as a robust technology for the realization of infrared lasers. Our proposed CQD systems lead us to achieve high performance laser devices under optical excitation and using CQD heterostructures asan active medium in the proposed LED structure paves the way towards the future development of infrared CQD-laser diodes.
  

• VILLEGAS JUAREZ, ARTURO: Optical parameter sensing: sensitivity limits and the advantages of using spatial modes of l ight
  
  Author: VILLEGAS JUAREZ, ARTURO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 26/04/2023
  Thesis director: PEREZ TORRES, JUAN
  

  Committee:
       PRESIDENT: LOZA ALVAREZ, PABLO
       SECRETARI: BRASSELET, ETIENNE GARY
       VOCAL: KOOLEN, ARMAND EUGENE ALBERT
  Thesis abstract: Resolution enhancement in modern optical metrology techniques has been possible due to significant technological improvements. The accurate and precise control of wavelength, bandwidth, and power of light sources; homogeneity, high-quality composition materials and surface smoothness of optical elements; and highly stable nanopositioners and optomechanical components, allow more sensitive imaging and sensing, in certain scenarios even beyond the standard diffraction limit. This has motivated a more detailed study of the fundamental resolution limitations of an optical system. The chosen approach to address this problem is to consider optical imaging as a parameter estimation problem. With this in mind, the theory of quantum estimation and statistical inference provides the tools to determine the estimation precision limits. Starting by considering the state of light as a quantum state that carries information of interest; the Cr\'amer-Rao lower bound provides a fundamental limit for the achievable precision. This lower bound is directly associated to optical resolution in practical terms.In this thesis, we present an overview of the useful tools of quantum estimation theory that can be applied to optical metrology. We focus on the Cr\'amer-Rao lower bound, and provide methods to calculate it. Since the bound depends on specific characteristics of the system, we explore three specific possibilities. First we present with an example the validity regimes for different bounds; explicitly %to calculate the parameters of entangled photon pairs in in the frame of a quantum Lidar System. Second, we show the dependency of the lower bound on the photonic model selection, showing a discrepancy between %N copies of a single photon and a multimode coherent state with average photon number N.two particular models. Third, we study the effects of lossy environments in the informational content of the quantum state. Additionally, we present the conditions that a measuring strategy must satisfy to allow attainability of the fundamental limit. %If the measurement strategy is not feasible or it is not possible to implement, one can evaluate the resolution improvement of the available technique by comparing to the standard and fundamental limits. For specific scenarios of interest, measurement methods based on the use of spatial modes of light allow to asymptotically attain the resolution limit. This has drawn attention to the information carried by specific modes, and has motivated the design of measurement strategies based on probing or sensing using spatial modes. In this thesis we include an overview of spatial modes of light, their generation and detection, and their use for optical sensing. We present a method for optical beam localization in the transverse plane using spatial mode information. Moreover, we propose a technique to retrieve the full modal decomposition of an arbitrary beam; which combined with the adequate set of modes allows to estimate certain parameters of an optical state with the maximum precision possible.Finally, motivated by the informational content of an optical beam that is not easily accessible, we explore the use of artificial intelligence to extract information about spatial features of an object from its diffraction pattern; without the need of solving the inverse problem nor using a physical model of scattering.
  

• WANG, YONGJIE: Eco-Friendly Solar Cells with Cation-Engineered AgBiS2 Nanocrystals
  
  Author: WANG, YONGJIE
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN PHOTONICS
  Department: Institute of Photonic Sciences (ICFO)
  Mode: Normal
  Reading date: 23/02/2023
  Thesis director: KONSTANTATOS, GERASIMOS
  

  Committee:
       PRESIDENT: VAYNZOF, YANA
       SECRETARI: SAUCEDO SILVA, EDGARDO
       VOCAL: HOYE, ROBERT LIANQI ZHAO
  Thesis abstract: Climate change and global energy demand urge the development of renewable energy sources for worldwide power supply. Photovoltaic devices that convert solar energy directly into electricity are the most promising, if not the only, technique to meet the requirements. Solution-processed solar cells are especially attractive due to their lightweight, low cost, and large-area mass manufacturing features. Among solution-processed materials, nanocrystals are one of the most promising, thanks to their material-property tunabilities, such as size, morphology, composition, electronic and optical properties, just to name a few. In the last decade, nanocrystal solar cells are mainly based on lead chalcogenide nanocrystals, although they face problems related to the toxicity of the element lead. Silver-bismuth sulfide nanocrystals are excellent substitutes for lead chalcogenides, thanks to their adequate bandgaps and extraordinarily high absorption coefficients. However, the energy conversion efficiency has lagged behind their toxic counterparts, mainly due to limited charge-carrier diffusion length and uncontrolled cation-disorder.In this thesis, we pinpoint the detrimental effects of cation inhomogeneity in ternary silver bismuth sulfide nanocrystals and further homogenize the cation-disorder by a facile post-annealing process, leading to absorption coefficients higher than any other commonly used solar materials over a wide range of 400 - 1000 nm. The cation-disorder configuration transition was further confirmed by the combination of ab initio density functional theory calculation and experimental material characterizations. Further optical modelling suggested a 30nm absorber layer possesses the potential for high Jsc up to 30 mA/cm2 and efficiency up to 26%. In addition to optical absorption enhancements, we also found elongated diffusion length up annealing, pointing to an anticipated high performance with ultrathin absorber. Ultrathin solar cells were thus fabricated with specially designed architecture and we achieved a record efficiency up to 9.17%, independently certified as 8.85% by Newport. The ultrathin solar cells also showed excellent stability under ambient conditions.In order to comply with mass manufacturing processes, we developed a solution-phase ligand-exchange procedure based on aqueous nanocrystal inks that enable single-step deposition of the active layer, reducing drastically the number of processing steps. Solar cell devices were built with the nanocrystal inks based on single-step deposition process and they showed a promising efficiency up to 7.3%, much higher than previous ink device record. In sum, we have achieved record-high performance, exceptionally stable AgBiS2 nanocrystal solar cells with both solid-state and solution-phase ligand-exchange procedures. This work sets a landmark for the development of environmentally friendly, low-temperature, solution-processed inorganic solar cells and opens a new field of engineering the atomic configuration of semiconductors as a means to achieve extraordinary optoelectronic properties.
  

Last update: 04/10/2023 05:01:11.

Research groups

• FOTONICA-Photonics Research Group

Teachers

• Acin Dalmaschio, Antonio
• Artigas Garcia, David
• Bachtold, Adrian
• Biegert, Jens
• Chang, Darrick
• de Riedmatten, Hugues
• Durduran, Turgut
• Ebrahim-Zadeh, Majid
• Efetov, Dmitri K.
• Garcia de Abajo, Javier
• García de Arquer, Francisco Pelayo
• Garcia-Parajo, Maria
• Konstantatos, Gerasimos
• Koppens, Frank
• Krieg, Michael
• Lewenstein, Maciej
• Loza Alvarez, Pablo
• Martorell Pena, Jordi
• Mitchell, Morgan
• Papadakis, Georgia
• Perez Torres, Juan
• Pruneri, Valerio
• Sewell, Robert
• Tarruell, Leticia
• Torner Sabata, Lluis
• Van Hulst, Niek
• Wall, Simon
• Wieser, Stefan