Quantum nonlinear optics with 2D materials

Lead Research Organisation: UNIVERSITY OF EXETER
Department Name: Physics and Astronomy

Abstract

When two beams from light torches cross, they do not clash like sabres from "Star Wars", but simply continue each its own way. This follows from the fact that free photons do not interact. However, when placed in an appropriate medium, photons can effectively feel the presence of each other, making the response of the optical system dependent on the number of photons. In this case, we say it has an optical nonlinearity provided by the medium. Typically the larger the volume, the stronger the nonlinearity, and the goal is to achieve prominent nonlinearity at the smallest possible scale. Together with the "sabre-effect", nonlinearity can ultimately provide the efficient manipulation of quantum states for photons. Thus with high level of nonlinearity single photon states can be prepared and used in quantum information processing. This would result in ultrafast quantum computing and communication platforms, serving as the basis for quantum applications that include secure communication networks, increased computational power and sensing at a level impossible to reach without quantum technologies.

When light is confined in an optical cavity (for instance, set by two mirrors), its interaction with the medium is greatly enhanced. If the average number of roundtrips made by photons becomes large, they can hybridize with excitations in the medium, leading to half-light half-matter quasiparticles - polaritons. The hybridization makes confined light and the resulting polaritons able to interact. This ability stays behind the progress in numerous applications of classical nonlinear optics, including optical solitons for fast broadband communication. However, the task of finding an optimal system, where large nonlinearity for polaritons is achieved in the limit of few quanta, remains an open question.

In the project, I will discover ways to increase optical nonlinearity at the minuscule scale. This will become possible by studying strong light-matter coupling in two-dimensional (2D) materials, where monolayer thickness can be smaller than a nanometer. Considering combinations of a few layers, I will show that the nonlinear response for polaritons can be elevated to the level where single photon processes become observable. The research will thus enable these easy-to-produce miniature systems for quantum optical processing to function as a platform for affordable quantum technologies.

Planned Impact

The planned outcome of the "2D-for-quantum" project corresponds to establishing two-dimensional (2D) materials strongly coupled to light as a versatile platform for observing quantum effects. This urge is motivated by the following arguments: 1) relative simplicity of the planned 2D material sample fabrication; 2) fast operation for optical devices; 3) operation at relatively high temperatures, where strong coupling is routinely observed even at room temperature; 4) potential for producing cost-efficient quantum devices based on semiconductor monolayers and heterostructures.

The main beneficiaries from the project are thus:
1) experimentalists working on 2D material-based devices, who will get access to the quantum operation mode;
2) emergent start-ups in quantum communication that will receive a new platform for single photon generation;
3) companies in computing and healthcare, the combination of lowered cost for quantum-enabled devices and fast operation times will boost application in optical information processing and sensing;
4) general public and students who will benefit from technological developments, as well as the educational side of the project.

The proposal lays the plan for the theoretical investigation and qualitative transformation of 2D material optics at strong coupling, required to harness its nonlinear properties and reach the quantum operation regime. However, while being a theoretical proposal, it specifically targets optimal sample configurations, putting an emphasis on realization in experiments. This will directly impact the field of optical nonlinear and quantum components, setting the path towards commercialization.

The development of the 2D material polaritonics will further impact the landscape of start-ups and companies working on the single photon based solutions. For instance, emergent businesses in quantum communication, with the example of Nu Quantum (Cambridge, UK), will benefit from proposals for novel ways to generate single photons using 2D materials. Other companies that expressed interest include KETS Quantum Security in Bristol and Nordic Quantum Computing Group in Oslo, opening further prospects for future prototyping of quantum devices.

Finally, two-level impact of society is expected. First, in the short term this will correspond to outreach activities and engagement in public discussions on the use of cases of quantum technologies. I will make sure that benefits from the 2D materials platform and quantum optical solutions are thoroughly communicated. Second, future impact shall become visible at the commercialization stage, where cost-efficient optical components will bring quantum technologies closer to an end-user, and benefit areas of medicine, chemistry, and sensing.

Publications

10 25 50
 
Description The aim of the project is to push our understanding of 2D polaritonics, and develop theories that can describe the nonlinear response. For this, we have developed tools that successfully described experiments on nonlinear effects in transition metal dichalcogenides and quantum wells (see Collaborations with Sheffield) and made them available as an open source project (see Software and Technical Products). The key finding are: 1) nonlinear phase space filling plays a critical role for nonlinear response in 2D materials; 2) trion-trion interaction can lead to attraction, and this changes the way how we understand spectral signatures in charged systems; 3) nonlinear phase space filling in the presence of Rydberg interactions can greatly enhance the nonlinear response - we have now developed a full theory that can describe this strongly correlated regime and proposed devices. With this, the goals for work packages one and two are fully met.
Exploitation Route Concentrating on microscopic modelling that avoids major simplifications yet does not involve heavy numerical calculations, we opened the route to scalable design of nonlinear polaritonic devices with 2D materials. This results can be used by experimentalists in the community for prototyping nonlinear optical devices, and in the future contributing to industrial applications of 2D materials.

From the research perspective, we are on the track to use the developed theories for quantum polaritonics, and apply them for developing blueprints of polaritonic neuromorphic devices in the New Horizons project.
Sectors Digital/Communication/Information Technologies (including Software)

Electronics

Other

 
Description First, to date the project has generated an academic impact in the form of world-first quantum nonlinear phase shift induced by a single polariton [Nature Photonics 16, 566 (2022)]. This has proven that quantum polaritonics can be seen as an emergent platform for quantum technologies, including sensing and computing. Second, our theoretical findings and developed models have guided experimental efforts in the field of 2D polaritonics, helping to shape the future directions for nonlinear optics based on transition metal dichalcogenides (large research area with >100 groups working worldwide). This has been extended to describe novel magnetic monolayers, homobilayers and Moire heterobilayers. Third, the organised 2-week scientific meeting has helped to shape the future directions in 2D polaritonics, specifically addressing the question: can we spin-out the academic activities into start-ups providing 2D material-based optical components? While more time shall pass to see the field maturing, in the future this shall provide a long-term impact going beyond the academic excellence.
Sector Digital/Communication/Information Technologies (including Software),Electronics,Other
 
Description Participating in UK Parliamentary session on quantum technologies
Geographic Reach National 
Policy Influence Type Contribution to a national consultation/review
 
Description 2D polaritons for optoelectronic devices and networks
Amount £202,249 (GBP)
Funding ID EP/X017222/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2023 
End 09/2025
 
Description Constructing novel non-classical states of electromagnetic field for far-field sensing, RADAR and LIDAR applications
Amount € 334,200 (EUR)
Funding ID NATO.SPS.MYP.G5860 
Organisation North Atlantic Treaty Organization (NATO) 
Sector Public
Country Belgium
Start 08/2021 
End 08/2024
 
Description Standard Grant call by EPSRC (consortium)
Amount £1,079,471 (GBP)
Funding ID EP/Y021339/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2024 
End 02/2027
 
Title Data for Nonlinear Rydberg exciton-polaritons in Cu2O microcavities 
Description Experimental data for the Light: Science & Applications article "Nonlinear Rydberg exciton-polaritons in Cu2O microcavities" 
Type Of Material Database/Collection of data 
Year Produced 2024 
Provided To Others? Yes  
Impact We have helped preparing and analysing the experimental dataset for nonlinear properties of polaritons in Cu2O. 
URL https://orda.shef.ac.uk/articles/dataset/Data_for_Nonlinear_Rydberg_exciton-polaritons_in_Cu2O_micro...
 
Title Data for Nonlinear Rydberg exciton-polaritons in Cu2O microcavities 
Description Experimental data for the Light: Science & Applications article "Nonlinear Rydberg exciton-polaritons in Cu2O microcavities" 
Type Of Material Database/Collection of data 
Year Produced 2024 
Provided To Others? Yes  
Impact We have compiled a dataset for nonlinear properties of polaritons in Cu2O and corresponding theoretical model for nonlinearity (n2 coefficient). 
URL https://orda.shef.ac.uk/articles/dataset/Data_for_Nonlinear_Rydberg_exciton-polaritons_in_Cu2O_micro...
 
Title Dataset for Few-photon all-optical phase rotation in a quantum-well micropillar cavity 
Description Dataset for Few-photon all-optical phase rotation in a quantum-well micropillar cavity 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
Impact This dataset allows to analyze quantum effects in polaritonic pillars, opening the route to quantum polaritonics. 
URL https://figshare.shef.ac.uk/articles/dataset/Dataset_for_Few-photon_all-optical_phase_rotation_in_a_...
 
Title Microscopic theory of nonlinear phase space filling 
Description We have develop a versatile tool (model) which allows studying phase space filling effects in various polaritonic systems. 
Type Of Material Data analysis technique 
Year Produced 2022 
Provided To Others? Yes  
Impact The model allows explaining nonlinear behaviour in various 2D polaritonic systems. Unlike previous theoretical explanations developed on case-by-case basis, our full microscopic model can be used by experimentalists and theorists in the field, working in a broad range of parameter regimes. 
URL https://arxiv.org/abs/2212.07968
 
Description Partnership with Krizhanovskii group at the University of Sheffield 
Organisation University of Sheffield
Country United Kingdom 
Sector Academic/University 
PI Contribution To date, the contributions from Exeter has provided theoretical explanations of nontrivial quantum and nonlinear effects in polaritonic systems. We started to develop a collaboration with the group of Prof. D. N. Krizhanovskii in 2019, with the first project being the theoretical explanation of nonlinear saturation of trion polaritons in monolayers. Seeing tremendous promise in this area (part of the WP1 of the project), we have described theoretically quantum effects in TMD polaritonic system (published in Phys. Rev. Lett. prior to NIA start due to COVID-related delay, see portfolio). The collaboration with the group of Prof. A. Tartakovskii has started in 2021 as a part of NIA project, and has lead to completed experimental and theoretical studies of dipolaritons in TMD bilayers. We have successfully described the experimental findings in homobilayers, and new .
Collaborator Contribution In the first year of NIA the close collaboration with experimental teams in Sheffield has allowed to reach two crucial milestones. First is an observation of the single polariton phase shift, with far reaching implications for polaritonic quantum information processing. Second milestone is observation of TMD dipolaritons with enhanced nonlinear response, which we have modelled with a distinct theoretical model. In the second year of the project we have continued collaboration on the nonlinear polaritonic effects, explaining the Rydberg blockade-induced nonlinearity (theory + experiment). The paper is in the preparation stage and shall be submitted soon. We have also conducted several collaborative visits, in particular staying in Sheffield for discussions with groups of Prof. Krizhanovskii and Tartakovskii.
Impact Current collaboration has led to 3 published papers, including Nature Photonics. Other our papers are regularly presented to experimental colleagues in order to implement them in practice.
Start Year 2021
 
Title Code for Nonlinear Rydberg exciton-polaritons in Cu2O microcavities 
Description code for the Light: Science & Applications article "Nonlinear Rydberg exciton-polaritons in Cu2O microcavities" 
Type Of Technology Software 
Year Produced 2024 
Impact Nonlinear optics requires robust methods for benchmarking the strength of nonlinearity. We have developed a package that can convert interaction constants and specific nonlinear saturation processes into a standard nonlinear refractivity (known as n2 coefficient). 
URL https://orda.shef.ac.uk/articles/software/Code_for_Nonlinear_Rydberg_exciton-polaritons_in_Cu2O_micr...
 
Title Trion.jl: Julia-based toolbox for calculating properties of trions and excitons in 2D materials 
Description We have developed an efficient tool for describing excitons and trions in 2D materials (transition metal dichalcogenides), which decomposes their states in large scale Gaussian basis. The package is live, and we are adding bilayer systems together with available monolayer examples. The documentation will be expanded, and we are working on the whitepaper to highlight the package. 
Type Of Technology Physical Model/Kit 
Year Produced 2023 
Open Source License? Yes  
Impact The allows accessing properties of trions and excitons that before required ab initial calculations, or are too simplified. It provides community with the toolbox for studying 2D materials, avoiding supercomputing runs and thus reducing the gap for entering the field. 
 
Description Conference on Research and Innovations in Science and Technology of Materials 2023 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I have presented our advances and project's work during the CRISTMAS conference in Paris. This has led to follow up discussions with researchers from Trinity College Dublin (invitation to contribute research to the new quantum tech journal) and arranged visit to the University of Bath for the general colloquium.
Year(s) Of Engagement Activity 2023
 
Description Exeter Scholars: leading an outreach event for school students from disadvantaged backgrounds 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Around 40 students visited Exeter to listen an introductory lecture on quantum mechanics, followed with an interactive session. Students have played with tools for creating superpositions and entangled photons. This sparked their interest in quantum technologies, and feedback largely exceeded expectations. The potential impact is largely increased engagement in QT, and more scientists coming from disadvantaged backgrounds in the future.
Year(s) Of Engagement Activity 2023
 
Description Invited participation in a panel discussion 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact As a part of FermiPolar workshop I was invited to participate in the panel. Specifically, we discussed the differences and similarities between trion polaritons and exciton polarons. This has set an important step of consolidating communities working in optics/condensed matter and cold atomic gases.
Year(s) Of Engagement Activity 2022
URL https://www.ifimac.uam.es/conferences-events/workshops/fermi-polarons-from-ultracold-gases-to-2d-sem...
 
Description Invited talk at EPIC 2023 in Singapore (top year's conference in polaritonics) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I have presented our results on the project to the core audience in polaritonics that included major groups active in the field. The dissemination led to 1 paper we are finishing with Germany/Singapore consortium, invitation to Poland (Warsaw) and Germany (Oldenburg) for discussing polaritonic computing, and joint project with another German group (Wuerzburg) on bilayers.
Year(s) Of Engagement Activity 2023
 
Description Organisation of NORDITA scientific programme 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I am an initiator and co-organiser of the Nordita programme "Light-matter interaction in nonlinear 2D materials". This 2-week programme will collect leaders in the field, hosting invited talks and round-table discussions, aiming to brainstorm future directions in the field.
Year(s) Of Engagement Activity 2022
URL https://indico.fysik.su.se/event/7627/
 
Description Polaritonic community meeting in Natal, Brazil 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Being invited to the conference on polaritonics, I have engaged with Brazilian physics community, visiting IIP Natal and promoted connections between our academic systems. I have presented our recently developed toolbox for nonlinear phase space filling effects, and collected feedback for features that can be included in future iterations.
Year(s) Of Engagement Activity 2022
 
Description Presenting and panel participation in Paignton Quantum Forum 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Industry/Business
Results and Impact I have been by SETSquared and Photonic Cluster to discuss the impact of quantum photonic solutions, and the state-of-the-art in the field.
Year(s) Of Engagement Activity 2022
 
Description QuDOS group webpage 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact I have created a webpage for the group, where regular updates are followed by the audience from 24 countries. This has largely increased visibility of the group and its members, and improved recruitment process attracting highly qualified applicants.
Year(s) Of Engagement Activity 2021
URL https://kyriienko.github.io/
 
Description Research coverage in LinkedIn 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact As a part of presenting the research, I regularly prepare posts (usually LinkedIn) about our works. With the audience of several thousand viewers, this has drove attention to polaritonic systems and influenced community, motivating development of trion-based polaritonics. This activity continues throughout the project.
Year(s) Of Engagement Activity 2021,2022
URL https://www.linkedin.com/in/oleksandr-kyriienko/