Timothy C. H. Liew

Artificial gauge fields allow uncharged particles such as photons to mimic the behaviour of charged particles subjected to magnetic fields, providing a powerful platform to alter the effective dynamics and exploring topological physics. Topological exciton-polariton lasers have attracted considerable interest, but often require strong magnetic fields to realise propagating topological edge states. Here we experimentally realise the topological Hall effect in a micron-scale micropillar chain by using an artificial gauge field, exploiting the circular polarisation of polaritons as an artificial dimension. Careful rotational alignment of elliptical micropillars induces strictly polarisation-dependent edge-state propagation, demonstrating non-reciprocal transport of the polariton pseudospins. Our results demonstrate that the dimensionality limitation of topological interface states as well as requirements for strong external magnetic fields in coupled topological laser arrays can be overcome. Our results open new ways towards the implementation of topological polariton lattices and related optically active devices with additional artificial dimension.

The non Hermitian skin effect, where bulk states accumulate at system boundaries, challenges the conventional bulk boundary correspondence. Here we propose a scheme to realize hybrid skin topological states in exciton polariton honeycomb lattices by introducing sublattice dependent gain and loss. This non Hermiticity couples with the intrinsic topological edge modes, leading to relocalization of edge states. We show two distinct regimes: hybrid skin Chern states with switchable localization controlled by TE TM splitting , and hybrid skin antichiral states which preserves the spin polarized property. Our results bridge polariton spin physics and non-Hermitian topology, opening routes toward controllable non reciprocal and spin polarized transport.

Rydberg exciton polaritons are promising for quantum optoelectronic devices exploiting their strong optical nonlinearities. Conventional polaritonic devices consist of optical microcavities made by vertically stacking distributed Bragg reflectors (DBR) and/or metallic mirrors and excitonic active regions, which may restrain their applicability in photonic integrated technologies. Here, we demonstrate the first on-chip photonic crystal (PhC) Rydberg polaritons based on monolayer WS₂, which survive up to 80 K. These Rydberg polaritons exhibit a nonlinearity 8.0 ± 2.3 times larger than that of the ground polaritonic states due mostly to their extended exciton radii and, additionally, due to a stronger spatially localized electric field distribution compared to the dual-DBR geometry. Furthermore, the coexistence of 2s and 1s polaritonic states enables us to experimentally quantify their cross-interaction constant (14.4 ± 6.8 μeV μm²). The first realization of on-chip Rydberg polaritons represents a solid step towards polaritonic-based integrated circuits.

Characterising optical quantum states is essential for the development of quantum technologies. While traditional approaches to perform full quantum state tomography are often experimentally demanding, neuromorphic architectures may provide an effective alternative. In this work, we demonstrate how a quantum nonlinear driven-dissipative mode is sufficient to act as a quantum reservoir. By analyzing the occupations at different frequencies in the emission spectrum, a linear regression suffices in many cases to recognize the relevant parameters of incident squeezed states. Beyond highlighting the general potential of this approach under continuous driving, we illustrate its effectiveness in an explicit nontrivial example where the source is a degenerate optical parametric oscillator (OPO), coupled to a nonlinear polariton microcavity.

Exciton-polariton bound states in the continuum (BICs) are hybrid quasiparticles formed under strong coupling between optical BICs and excitons. However, as BICs have vanishing line width, it is impossible to excite them directly with external optical sources. Consequently, their infinite lifetime cannot be efficiently utilized for coherently driven polaritonic applications. In this Letter, we show that the nonlinear nature of exciton-polaritons enables an efficient coherent excitation of the BIC via optical parametric oscillation (OPO). Thanks to the enhanced lifetime of the BIC, the requirement for the pump and the idler to be in resonance with a polariton mode is lifted. This allows the OPO process to take place over a large range of pump wavevectors and energy, thereby efficiently populating the polariton BICs.

Moiré superlattices exhibit fascinating moiré flat bands when two layers of van der Waals materials are twisted at specific magic angles, providing unparalleled opportunities to explore unconventional correlated quantum phenomena. Exciton polaritons, hybrid quasiparticles of excitons and photons, have emerged as promising synthetic platforms for exploring moiré physics beyond conventional systems. However, the realization of moiré exciton-polariton flat bands and their condensation remains challenging. Here, we experimentally demonstrate a moiré exciton-polariton flat band with condensation in a perovskite moiré superlattice at room temperature. By engineering a 21.79° magic-angle moiré superlattice potential with enhanced interlayer coupling, we experimentally observe a polaritonic moiré flat band near the corresponding monolayer’s Dirac points position in the perovskite microcavity. Under a nonresonant pulsed excitation, polaritons with proper detuning condense into the moiré flat band at room temperature. Our work provides a unique platform for investigating exotic moiré phenomena and unlocks promising avenues toward advanced polaritonic devices.

Long-life interlayer excitons (IXs) in transition metal dichalcogenide (TMD) heterostructure are promising for realizing excitonic condensates at high temperatures. Critical to this objective is to separate the IX ground state (the lowest energy of IX state) emission from other states emissions. Filtering the IX ground state is also essential in uncovering the dynamics of correlated excitonic states, such as the excitonic Mott insulator. Here, we show that the IX ground state in WSe2/MoS2 heterobilayer can be separated from other states by its spatial profile. The emissions from different moire IX modes are identified by their different energies and spatial distributions, which fits well with the rate-diffusion model for cascading emission. Our results show spatial filtering of the ground state mode and enrich the toolbox to realize correlated states at elevated temperatures.