International Workshop on Polaritons in Emerging Materials

Last week I had the pleasure of attending an IBS PCS International Workshop on Polaritons in Emerging Materials held in Daejeon, Korea. Smaller workshops such a this one (~40 participants) with a more relaxed schedule (40 minutes per speaker and generous coffee/lunch breaks) are great for getting a more in-depth and candid picture of an unfamiliar research field!

One of the hot topics was polaritons in transition metal dichalcogenides - a rapidly-maturing family of two-dimensional graphene-inspired materials. Prof. Myung-Ki Kim from Korea University talked about plasmon resonances in multi-layer TMDs, Prof. Deep Jariwala from the University of Pennsylvania presented experiments with cavity-free polaritonic structures. The high refractive index of 2D materials such as molybdenum disulphide means that they can already exhibit strong light-matter coupling without requiring embedding in a microcavity. Thanks to the different localization of the photonic and electronic degrees of freedom one can form ultra-thin multilayer structures either as thin sheets of the 2D material (with the thickness controlling the electronic band structure), or as lattices formed by multiple non-interacting single sheets. Prof. Su-Hyun Gong (Korea University) presented waveguides based on multilayer tungsten disulphide can achieve tight (nanoscale) light confinement with lower losses compared to conventional plasonic materials such as gold. Expect to see many more works in this area as high-quality and large-area samples of these exotic materials start to become commercially available.

Another active area was optically-driven rotation and localization of exciton-polariton condensates. Dr. Michael Fraser (RIKEN) presented experiments in which a condensate is stirred via incoherent pumping with two slightly-detuned Laguerre-Gaussian layer beams, leading to an asymmetric reservoir density that undergoes a rotation, producing condensates with vortices. Theoretical analyses of vortex generation and turbulence in stirred exciton-polaritons were presented by Dr. Alexey Yulin (ITMO) and Dr. Helgi Sigurðsson (Warsaw), and Dr. Sergei Koniakhin (IBS PCS). Prof. Alberto Amo (Lille) showed that the dynamics of resonantly-driven condensates in lossy lattices can be remarkably counterintuitive - the strongest localization occurs between the pumped sites, not at them!

While not the main theme of the workshop, topological photonics was represented in talks by Profs. Sven Höfling, Sebastian Klembt (both from Würzburg University), Dr. Xingran Xu (NTU), who focused on lasing and non-Hermitian topological phenomena, and Dr. Alexander Cerjan (Sandia National Labs), who showed how real-space topological markers can be used to quantify the robustness of nonlinear topological edge states.

Prof. Fabrice Laussey (Wolverhampton) gave a captivating talk on quantum light and the importance of taking detector bandwidth into account when modelling quantum light sources. Since quantum light is so weak, signals measured using a finite bandwidth filter will inevitably be dominated by the tails of the much stronger pump beam unless homodyne detection is used. Look for quantum correlations in the spectral minima, not the dips! In related talks, Prof. Andrey Moskalenko (KAIST) analyzed entanglement between cavities generated by coherent optical driving, and Prof. Hyang-Tag Lim (KIST) covered experimental generation of multi-mode N00N states.

Most of the talks should become available to watch on the PCS Youtube account at some point.