Exploratory Photonics

“Moore's Law” has successfully directed the industry to cram ever-more transistors onto chips over the past 50 years, but processor clock speeds have not kept up with this growth and have been stagnant since roughly 2005. A solution to this problem might be found in exploring alternative computing approaches that use photons rather than electrons. However, because of the inherently weak light-matter interaction, these devices used to be bulky and inefficient in terms of energy, which has impeded the development of optical computers. By utilizing quantum optical phenomena in the strong light-matter interaction regime, we are investigating how novel photonic approaches can be used to overcome such limitations. The ultimate goal is to have photons interact so strongly that collective, strongly correlated phenomena can be observed. As this is a multi-disciplinary endeavour at the cross-over between fundamental science and applications, we are collaborating with many partners within projects funded by the European Horizon framework as well as the Swiss National Science Foundation.

Our Approach

Our approach to boost the interaction between photons is to make use of exciton-polariton quasiparticles, which are part-light and part-matter. They are formed when the coherent coupling between photons and active material dominates over the photonic and electronic losses, i.e., in the so-called strong light-matter interaction regime. This requires suitable optoelectronic materials with high oscillator strength and narrow homogeneous and inhomogeneous linewidths as well as photonic microcavities close to the size limit of the optical wavelength to confine the light strongly. As the polaritons obey Bosonic quantum statistics they can eventually behave like a quantum fluid, exhibiting superfluid properties and high nonlinearities.

All-Optical Logic

As the energy of a single photon is in the sub-attojoule regime, optical single-photon switches require about 100 times less switching energy than state-of-the-art CMOS transistors whereas the switching time could be on the order of picoseconds or less. Because the areal density of such photonic devices would be naturally much lower than for modern electronic transistors, it would be rather comparatively simple logic that could first benefit from ultimate speed and energy. We explore the foundations towards such devices and circuits by harnessing seeded polariton condensates and investigating materials and structures suitable to achieve polariton blockade.

Towards Analogue Quantum Simulation in Lattices

Another potential application of strongly interacting photons are analogue quantum simulations. Richard Feynman was among the first to envision that well-controlled and measurable systems could be used to efficiently mimic and explore the physics of the otherwise inaccessible and intractable systems. In particular, phenomena like strongly correlated and topological phases that are key to both fundamental and exotic material features such as superconductivity and the spin Hall effect are notoriously difficult to tackle experimentally and theoretically. We are building on our demonstration of non-equilibrium Bose-Einstein condensates of exciton-polaritons with an amorphous polymer at room temperature to create photonic potential landscapes for polariton condensates by harnessing novel nanostructured, tunable cavity arrays. On this platform, meaningful Hamiltonians can be realized and manipulated, and the quantum mechanical wavefunctions are “calculated” by literally taking a photo.

Novel Materials for Strong Light-Matter Interaction

Novel materials with outstanding opto-electronic properties such as high oscillator strength, low dephasing and small inhomogeneous broadening are key for strong light-matter interaction. Therefore, we are exploring colloidal nanoparticles that can be relatively easily synthesized and assembled. We were able to demonstrate that fully inorganic lead halide perovskites nanocrystals have exceptionally strong light-matter interaction and even support collective optical emission, so-called superfluorescence. These features make them excellent candidates for enabling scalable systems of strongly interacting polaritons.

Collaborative projects

• SNSF (Grant No. 10003004) “CHIP-QD” (05/2025 – 04/2029) Cavity-Enhanced Many-Body Interactions in Deterministically Positioned Perovskite Quantum Dots
• SNSF (Grant No. 192308) “Q-Light” (01/2021 – 04/2025) Engineered Quantum Light Sources with Nanocrystal Assemblies
• EU H2020-FETOPEN (Grant No. 964770) “TOPOLIGHT” (09/2021 – 05/2025) Soft Matter Platform for Optical Devices via Engineering of Non-Linear Topological States of Light
• EU H2020-MSCA-ITN (Grant No. 956270) “PERSEPHONe“ (03/2020 – 08/2025) PERovskite SEmiconductors for PHOtoNics
• EU H2020-MSCA-ITN (Grant No. 956071) “AppQInfo“ (03/2020 – 02/2025) Applications and Hardware for Photonic Quantum Information Processing
• EU H2020-FETOPEN (Grant No. 899141) “PoLLoC” (10/2020 – 09/2023) An all-optical photonic approach will boost computational energy efficiency
• ERA-NET QuantERA (SNSF Grant No. 175389) “RouTe” (04/2018 – 06/2022) Towards Room Temperature Quantum Technologies