Souissi, H.; Gromovyi, M.; Septembre, I.; Develay, V.; Brimont, C.; Doyennette, L.; Cambril, E.; Bouchoule, S.; Alloing, B.; Frayssinet, E.; Zuniga-Perez, J.; Ackemann, T.; Malpuech, G.; Solnyshkov, D. D.; Guillet, T. Mode-locked waveguide polariton laser; OPTICA 11, 962 (2024),
https://doi.org/10.1364/OPTICA.524753

So far, exciton-polariton (polariton) lasers were mostly single-mode lasers based on microcavities. Despite the large repulsive polariton-polariton interaction, a pulsed mode-locked polariton laser was never, to our knowledge, reported. Here, we use a 60-µm-long GaN-based waveguide surrounded by distributed Bragg reflectors forming a multi-mode horizontal cavity. We demonstrate experimentally and theoretically a polariton mode-locked micro-laser operating in the blue-UV, at room temperature, with a 300 GHz repetition rate and 100-fs-long pulses. The mode-locking is demonstrated by the compensation (linearization) of the mode dispersion by the self-phase modulation induced by the polariton-polariton interaction. It is also supported by the observation in experiment and theory of the typical envelope frequency profile of a bright soliton.

Zhang, Zhaoyang; Liang, Shun; Septembre, Ismael; Yu, Jiawei; Huang, Yongping; Liu, Maochang; Zhang, Yanpeng; Xiao, Min; Malpuech, Guillaume; Solnyshkov, Dmitry Non-Hermitian Delocalization in a Two-Dimensional Photonic Quasicrystal, Phys. Rev. Lett. 132, 263801 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.263801

Theoretical and experimental studies suggest that both Hermitian and non-Hermitian quasicrystals show localization due to the fractal spectrum and to the transition to diffusive bands via exceptional points, respectively. Here, we present an experimental study of a dodecagonal photonic quasicrystal based on electromagnetically induced transparency in a Rb vapor cell. First, we observe the suppression of the wave packet expansion in the Hermitian case. We then discover a new regime, where increasing the non-Hermiticity leads to delocalization, demonstrating that the behavior in non-Hermitian quasicrystals is richer than previously thought.

Sannikov, Denis A.; Baranikov, Anton V.; Putintsev, Anton D.; Misko, Mikhail; Zasedatelev, Anton V.; Scherf, Ullrich; Lagoudakis, Pavlos G. Room temperature, cascadable, all-optical polariton universal gates Nature Communications 15, 5362 (2024) http://dx.doi.org/10.1038/s41467-024-49690-3

Today, almost all information processing is performed using electronic logic circuits operating at several gigahertz frequency. All-optical logic holds the promise to allow for up to three orders of magnitude higher speed. Whereas essential all-optical transistor functionalities were demonstrated across a range of platforms, utilising them to implement a complete Boolean logic gate set and in particular negation, i.e. switching off an optical signal with another, weaker, optical signal, poses a major challenge. Here, we realize a cascadable NOT gate by introducing the concept of non-ground-state polariton amplification in organic semiconductor microcavities under non-resonant optical excitation. We unravel the importance of vibron-mediated stimulated scattering in room temperature operation of the inverter. Moreover, we extend the concept to a multi-input universal NOR logic gate, where in the presence of any of the input signals non-ground-state amplification supersedes spontaneous ground-state condensation, resulting in a NOR gate with ~1 ps switching time. The realisation of an ultrafast universal logic gate constitutes an essential step for more complex optical circuitry that could boost information processing applications.

Septembre, I.; Foudjo, I.; Develay, V.; Guillet, T.; Bouchoule, S.; Zuniga-Perez, J.; Solnyshkov, D. D.; Malpuech, G. Soliton formation in an exciton-polariton condensate at a bound state in the continuum Phys. Rev. B 109, 205302 (2024) https://doi.org/10.1103/PhysRevB.109.205302

Bound states in the continuum (BICs) are of special interest in photonics due to their theoretically infinite radiative lifetime. In this work, we take a specific example (a structure composed of GaN and a TiO 2 photonic crystal slab), showcasing how the interactions affect BICs. The photonic BIC hosted by the photonic crystal slab couples with the excitons of GaN to form a polaritonic BIC with a negative mass. This allows condensation to be reached with a low threshold in a structure suitable for electrical injection, paving the way for room -temperature polariton microdevices. We study in detail how the repulsive interaction between exciton-polaritons affects the condensate distribution in reciprocal space and, consequently, the condensate’s overlap with the BIC resonance and, therefore, the condensate lifetime. We study an intrinsic contribution related to the formation of a bright soliton and the extrinsic contribution related to the interaction with an excitonic reservoir induced by spatially focused nonresonant pumping. We then study the peculiar dynamics of the condensation process in a BIC state for interacting particles using Boltzmann equations and hybrid Boltzmann-Gross-Pitaevskii equations. We find optimal conditions allowing one to benefit from the long lifetime of the BIC for polariton condensation in a real structure.

Sawicki, Krzysztof; Dovzhenko, Dmitriy; Wang, Yuan; Cookson, Tamsin; Sigurosson, Helgi; Lagoudakis, Pavlos G. Occupancy-driven Zeeman suppression and inversion in trapped polariton condensates Phys. Rev. B 109, 125307 (2024) https://doi.org/10.1103/PhysRevB.109.125307

We study the magnetophotoluminescence of an optically trapped exciton-polariton condensate in a planar semiconductor microcavity with multiple In 0 . 08 Ga 0 . 92 As quantum wells. Extremely high condensate coherence time and continuous control over the polariton confinement are among the advantages provided by optical trapping. This allows us to resolve magnetically induced ~mu eV fine-energy shifts in the condensate and identify unusual dynamical regions in its parameter space. We observe polariton Zeeman splitting and, in small traps with tight confinement, demonstrate its full parametric screening when the condensate density exceeds a critical value, reminiscent of the spin-Meissner effect. For larger optical traps, we observe a complete inversion in the Zeeman splitting as a function of power, underlining the importance of condensate confinement and interactions with its background reservoir excitons.

Oliwa, Przemyslaw; Bardyszewski, Witold; Szczytko, Jacek Quantum mechanical-like approach with non-Hermitian effective Hamiltonians in spin-orbit coupled optical cavities Phys. Rev. Research 6, 013324 (2024) https://doi.org/10.1103/PhysRevResearch.6.013324

We present a comprehensive analytical model of resonant states in birefringent microcavities with permeable mirrors. We derive an effective, non-Hermitian photonic Hamiltonian describing cavity mode dispersion and modal lifetimes by applying the Green’s function technique based on the Mittag-Leffler expansion with respect to the resonant states and the 𝒌·𝒑 perturbation theory known from semiconductor physics. Using this formalism we obtained results which can be interpreted as effective cavity mode spin-orbit coupling. We use this method to derive the two-mode Hamiltonian to describe the properties of light in the cavity, which significantly reduces the computational effort and properly captures the polarization of the eigenmodes. This is done by introducing the necessary corrections to the Hamiltonian matrix and modifying the basis modes resulting from the coupling with other optical modes present in the system. This simplified Hamiltonian allows us to determine the positions of exceptional points in momentum space. These points are connected by Fermi arcs and appear due to non-Hermiticity and 𝒫𝒯 symmetry.

Gnusov, I.; Harrison, S.; Alyatkin, S.; Sitnik, K.; Sigurdsson, H.; Lagoudakis, P. G. Simultaneous creation of multiple vortex-antivortex pairs in momentum space in photonic lattices
Phys. Rev. B 109, 104503 (2024) http://dx.doi.org/10.1103/PhysRevB.109.104503

Recently, we realized the formation of a single quantized vortex in nonresonantly optically stirred exciton-polariton condensates [I. Gnusov et al., Sci. Adv. 9, eadd1299 (2023)]. In this work, we demonstrate that the number of emerging vortices depends on the characteristic size of the rotating potential induced by the nonresonant laser excitation. For smaller sizes, we observe only a single vortex with a topological charge of ±1 defined by the stirring direction. For larger trap sizes, clusters of up to four corotating vortices are observed, also following the stirring direction. We find that the interplay of stirring speed and confining potential size dictates the number of vortices in a cluster. This is confirmed by observed energy distribution of condensed polaritons as a function of rotation frequency. Our findings offer an insight into the behavior of stirred condensates, complementing previous works on optically trapped polariton condensates in static traps.

D. D. Solnyshkov, I. Septembre, K. Ndiaye, and G. Malpuech Analog of Foucault precession in two-dimensional quantum harmonic oscillators with Berry curvature Phys. Rev. B 108, 144306 https://doi.org/10.1103/PhysRevB.108.144306

The geometric phase plays a key role both in the rotation of the Foucault pendulum and in the anomalous Hall effect (AHE), where an accelerated wave packet shows a transverse motion induced by the Berry curvature. Here, we show that the motion of quantum particles described by a spin-orbit-coupling Hamiltonian showing nonzero Berry curvature and placed in a two-dimensional harmonic-oscillator potential in real space exhibits Foucault precession. The plane of the oscillations rotates with time. The rotating pendulum configuration enhances the spatial deviation with respect to the AHE case, simplifying its observation and allowing high-precision measurements of the Berry curvature. We show how the nonadiabaticity and anharmonicity determine the maximal rotation angle and find the optimal conditions for the observations.

Septembre, I.; Solnyshkov, D. D.; Malpuech, G. Angle-dependent Andreev reflection at an interface with a polaritonic superfluid PHYSICAL REVIEW B 108, 115309 (2023) http://dx.doi.org/10.1103/PhysRevB.108.1153

We study analytically an analog of the Andreev reflection at a normal-superfluid interface. The polariton gapped superfluid region is achieved by quasiresonant optical pumping. The interacting polaritons are described with the driven-dissipative Gross-Pitaevskii equation. We find analytical formulas for the angles and amplitudes of the reflected and transmitted particles. There are limit angles and energies, above which Andreev reflection and transmission cannot be observed anymore and where the Andreev wave becomes a surface mode, exponentially localized on the interface. These properties are confirmed by solving numerically the Gross-Pitaevskii equation in simulations reproducing realistic experimental conditions.

Aristov, Denis; Baryshev, Stepan; Topfer, Julian D.; Sigurdsson, Helgi; Lagoudakis, Pavlos G.
Directional planar antennae in polariton condensates APPLIED PHYSICS LETTERS 123, 121101 (2023) https://doi.org/10.1063/5.0159665

We report on the realization of all-optical planar microlensing for exciton–polariton condensates in semiconductor microcavities. We utilize spatial light modulators to structure a nonresonant pumping beam into a plano–concave lens-shape focused onto the microcavity plane. When pumped above condensation threshold, the system effectively becomes a directional polariton antenna, generating an intense focused beam of coherent polaritons away from the pump region. The effects of pump intensity, which regulates the interplay between gain and blueshift of polaritons, as well as the geometry of the lens-shaped pump are studied, and a strategy to optimize the focusing of the condensate is proposed. Our work underpins the feasibility to guide nonlinear light in microcavities using nonresonant excitation schemes, offering perspectives on optically reprogramable on-chip polariton circuitry.