Quantum nonlinear optics with 2D materials

Lead Research Organisation: University of Exeter
Department Name: Physics and Astronomy


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.


10 25 50
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 Partnership with Sheffield University 
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 expect more progress in the coming years.
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.
Impact Current collaboration has led to 3 papers submitted (1 under review in Nature Photonics), and 1 paper being submitted to one of Nature journal in the coming week. 2 more theoretical papers will be submitted with next quarter with experimental colleagues.
Start Year 2021
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 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 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.
Year(s) Of Engagement Activity 2021