Injection of Orbital Angular Momentum and Storage of Quantized Vortices in Polariton Superfluids

Antiferromagnetic Ising model in a triangular vortex lattice of quantum fluids of light

Vortices are topologically distinctive objects appearing as phase twists in coherent fields of optical beams and Bose-Einstein condensates. Structured networks and artificial lattices of coupled vortices could offer a powerful platform to study and simulate interaction mechanisms between constituents of condensed matter systems, such as antiferromagnetic interactions, by replacement of spin angular momentum with orbital angular momentum. Here, we realize such a platform using a macroscopic quantum fluid of light based on exciton-polariton condensates. We imprint all-optical hexagonal lattice that results into a triangular vortex lattice, with each cell having a vortex of charge l = ±1. We reveal that pairs of coupled condensates spontaneously arrange their orbital angular momentum antiparallel, implying a form of artificial orbital "antiferromagnetism." We discover that correlation exists between the emergent vortex patterns in triangular condensate lattices and the low-energy solutions of the corresponding antiferromagnetic Ising system. Our study offers a path toward spontaneously ordered vortex arrays with nearly arbitrary configurations and controlled couplings.

Optically Driven Rotation of Exciton-Polariton Condensates

The rotational response of quantum condensed fluids is strikingly distinct from rotating classical fluids, especially notable for the excitation and ordering of quantized vortex ensembles. Although widely studied in conservative systems, the dynamics of rotating open-dissipative superfluids such as exciton-polariton condensates remains largely unexplored, as it requires high-frequency rotation while avoiding resonantly driving the condensate. We create a rotating polariton condensate at gigahertz frequencies by off-resonantly pumping with a rotating optical stirrer composed of the time-dependent interference of two frequency-offset, structured laser modes. Acquisition of angular momentum exceeding the critical 1ℏ/particle is directly measured, accompanied by the deterministic nucleation and capture of quantized vortices with a handedness controlled by the pump rotation direction. The demonstration of controlled optical rotation of a spontaneously formed polariton condensate enables new opportunities for the study of open dissipative superfluidity, ordering of non-Hermitian quantized vortex matter, and topological states in a highly nonlinear, photonic platform.

Quantum vortex formation in the "rotating bucket" experiment with polariton condensates

The appearance of quantized vortices in the classical "rotating bucket" experiments of liquid helium and ultracold dilute gases provides the means for fundamental and comparative studies of different superfluids. Here, we realize the rotating bucket experiment for optically trapped quantum fluid of light based on exciton-polariton Bose-Einstein condensate in semiconductor microcavity. We use the beating note of two frequency-stabilized single-mode lasers to generate an asymmetric time-periodic rotating, nonresonant excitation profile that both injects and stirs the condensate through its interaction with a background exciton reservoir. The pump-induced external rotation of the condensate results in the appearance of a corotating quantized vortex. We investigate the rotation frequency dependence and reveal the range of stirring frequencies (from 1 to 4 GHz) that favors quantized vortex formation. We describe the phenomenology using the generalized Gross-Pitaevskii equation. Our results enable the study of polariton superfluidity on a par with other superfluids, as well as deterministic, all-optical control over structured nonlinear light.

Controllable vortex lasing arrays in a geometrically frustrated exciton-polariton lattice at room temperature

Quantized vortices appearing in topological excitations of quantum phase transition play a pivotal role in strongly correlated physics involving the underlying confluence of superfluids, Bose-Einstein condensates and superconductors. Exciton polaritons as bosonic quasiparticles have enabled studies of non-equilibrium quantum gases and superfluidity. Exciton-polariton condensates in artificial lattices intuitively emulate energy-band structures and quantum many-body effects of condensed matter, underpinning constructing vortex lattices and controlling quantum fluidic circuits. Here, we harness exciton-polariton quantum fluids of light in a frustrated kagome lattice based on robust metal-halide perovskite microcavities, to demonstrate vortex lasing arrays and modulate their configurations at room temperature. Tomographic energy-momentum spectra unambiguously reveal massless Dirac bands and quenched kinetic-energy flat bands coexisting in kagome lattices, where polariton condensates exhibit prototypical honeycomb and kagome spatial patterns. Spatial coherence investigations illustrate two types of phase textures of polariton condensates carrying ordered quantized-vortex arrays and π-phase shifts, which could be selected when needed using lasing emission energy. Our findings offer a promising platform on which it is possible to study quantum-fluid correlations in complex polaritonic lattices and highlight feasible applications of structured light.

Room-temperature polariton lasing in GaN microrods with large Rabi splitting

Room-temperature polariton lasing is achieved in GaN microrods grown by metal-organic vapor phase epitaxy. We demonstrate a large Rabi splitting (Ω = 2g₀) up to 162 meV, exceeding the results from both the state-of-the-art nitride-based planar microcavities and previously reported GaN microrods. An ultra-low threshold of 1.8 kW/cm² is observed by power-dependent photoluminescence spectra, with the linewidth down to 1.31 meV and the blue shift up to 17.8 meV. This large Rabi splitting distinguishes our coherent light emission from a conventional photon lasing, which strongly supports the preparation of coherent light sources in integrated optical circuits and the study of exciting phenomena in macroscopic quantum states.

Thermalization of Light's Orbital Angular Momentum in Nonlinear Multimode Waveguide Systems

We show that the orbital angular momentum (OAM) of a light field can be thermalized in a nonlinear cylindrical multimode optical waveguide. We find that upon thermal equilibrium, the maximization of the optical entropy leads to a generalized Rayleigh-Jeans distribution that governs the power modal occupancies with respect to the discrete OAM charge numbers. This distribution is characterized by a temperature that is by nature different from that associated with the longitudinal electromagnetic momentum flow of the optical field. Counterintuitively and in contrast to previous results, we demonstrate that even under positive temperatures, the ground state of the fiber is not always the most populated in terms of power. Instead, because of OAM, the thermalization processes may favor higher-order modes. A new equation of state is derived along with an extended Euler equation resulting from the extensivity of the entropy itself. By monitoring the nonlinear interaction between two multimode optical wave fronts with opposite spins, we show that the exchange of angular momentum is dictated by the difference in OAM temperatures, in full accord with the second law of thermodynamics. The theoretical analysis presented here is corroborated by numerical simulations that take into account the complex nonlinear dynamics of hundreds of modes. Our results may pave the way toward high-power optical sources with controllable orbital angular momenta, and at a more fundamental level, they may open up opportunities in drawing parallels with other complex multimode nonlinear systems like rotating atomic clouds.

Half-skyrmions with higher topological quantum numbers in homogeneous exciton-polariton condensates

We investigate the topological excitations of half-quantum vortices (HQVs) with higher topological quantum numbers in a homogeneous spinor exciton-polariton condensate pumped by a laser beam and an additional coherent light carrying orbital angular momentum. The spin texture and integrated topological charge can be controlled through the pump. Among these textures, the polaritonic half-skyrmions (or polaritonic merons) can be created with a suitable excitation condition. Moreover, when the pump polarization is in favor of the vortex component of the HQV, there is an inversion of circular polarization (spin flipping) from the center of the HQV towards the edge. The radial flipping position can be manipulated by the pump polarization or power. Finally, we demonstrate that the HQVs can stably exist from the linear stability analysis.

Direct Transfer of Light's Orbital Angular Momentum onto a Nonresonantly Excited Polariton Superfluid

Recently, exciton polaritons in a semiconductor microcavity were found to condense into a coherent ground state much like a Bose-Einstein condensate and a superfluid. They have become a unique testbed for generating and manipulating quantum vortices in a driven-dissipative superfluid. Here, we generate an exciton-polariton condensate with a nonresonant Laguerre-Gaussian optical beam and verify the direct transfer of light's orbital angular momentum to an exciton-polariton quantum fluid. Quantized vortices are found in spite of the large energy relaxation involved in nonresonant pumping. We identified phase singularity, density distribution, and energy eigenstates for the vortex states. Our observations confirm that nonresonant optical Laguerre-Gaussian beam can be used to manipulate chirality, topological charge, and stability of the nonequilibrium quantum fluid. These vortices are quite robust, only sensitive to the orbital angular momentum of light and not other parameters such as energy, intensity, size, or shape of the pump beam. Therefore, optical information can be transferred between the photon and exciton-polariton with ease and the technique is potentially useful to form the controllable network of multiple topological charges even in the presence of spectral randomness in a solid state system.

Optically Controlled Orbital Angular Momentum Generation in a Polaritonic Quantum Fluid

Applications of the orbital angular momentum (OAM) of light range from the next generation of optical communication systems to optical imaging and optical manipulation of particles. Here we propose a micron-sized semiconductor source that emits light with predefined OAM pairs. This source is based on a polaritonic quantum fluid. We show how in this system modulational instabilities can be controlled and harnessed for the spontaneous formation of OAM pairs not present in the pump laser source. Once created, the OAM states exhibit exotic flow patterns in the quantum fluid, characterized by generation-annihilation pairs. These can only occur in open systems, not in equilibrium condensates, in contrast to well-established vortex-antivortex pairs.