Exciton-polariton Condensates Research Articles

Controllable switching based on vortex–antivortex pairs in exciton–polariton condensates

Abstract Vortex–antivortex pairs hold significant prospect for applications in high-capacity optical communications, multiparticle manipulations, and data processing systems. In this work, based on vortex–antivortex pairs, we explore a straightforward method to produce a 1–4 optical switch in a polariton condensate with a C-shaped potential. The switch, seeded by a degenerate state containing two vortex–antivortex pairs, can selectively target four objective states: two orthogonal states with a single vortex–antivortex pair and two concentric vortices with opposite circulations. All these topological states are stable states with the application of a single incoherent pump, while the switch is activated by an additional coherent control pulse.

Plasmon–Exciton–Polariton Condensation in Organic Semiconductor‐Covered Plasmonic Lattices

AbstractExciton–polariton condensates featuring collective coherence and large nonlinearities are promising for advancing coherent light sources and functional devices. Nevertheless, their reliance on planar cavities with large lateral device footprints and mode volumes hinders device integration. Plasmon–exciton–polaritons (PEPs), arising from the strong coupling between excitons and plasmons, provide an intriguing platform to explore emergent polariton condensation at the nanoscale due to their ultrasmall mode volumes in metal nanoparticles. However, the substantial radiative and Ohmic losses in metals hamper PEPs condensation, particularly in the short wavelength range (<600 nm). Here, a method is proposed to address metal losses by integrating organic semiconductor neat films onto plasmonic lattices. The use of organic semiconductors with large transition dipole moment and low non‐radiation loss enables efficient coupling between massive excitons and lattice plasmons, leading to high‐density PEPs. This ensures a macroscopic number of polaritons populating the low‐lying band edge at relatively low fluences to obtain bosonic stimulation, resulting in PEP condensation. By tailoring the band structures of plasmonic lattices, the condensation of PEPs are further manipulated into different energy states. These findings offer valuable insights for the design of PEP systems and all‐optical polaritonic devices.

Condensation of Exciton-Polaritons in a Bound State in the Continuum: Effects of the Excitation Spot Size and Polariton Transport.

We report the formation of polariton condensates from strongly coupled molecules to bound states in the continuum with quadrupolar character in a metasurface of silicon nanoparticles. Our experiments demonstrate a strong dependence of the condensation threshold on the excitation spot size. The condensation threshold decreases as the excitation spot size increases, achieving thresholds below 3 μm cm-2 for spot sizes of around 1 mm2 and condensate lifetimes exceeding 20 ps. The strong dependence of the condensation threshold on the spot size is caused by the long propagation length of the polaritons. We reproduce this dependence in simulations by including a term for the ballistic transport of exciton-polaritons in the rate equations describing the condensation. These results illustrate the critical role that polariton transport plays in condensation and highlight the relevance of considering the size of the excitation in condensation experiments.

Dual-Wavelength Exciton-Polariton Condensation via Relaxation of Multiple Vibrational Quanta in Organic Microcavities

Dual-Wavelength Exciton-Polariton Condensation via Relaxation of Multiple Vibrational Quanta in Organic Microcavities

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.

Predesigned perovskite crystal waveguides for room-temperature exciton-polariton condensation and edge lasing.

Perovskite crystals-with their exceptional nonlinear optical properties, lasing and waveguiding capabilities-offer a promising platform for integrated photonic circuitry within the strong-coupling regime at room temperature. Here we demonstrate a versatile template-assisted method to efficiently fabricate large-scale waveguiding perovskite crystals of arbitrarily predefined geometry such as microwires, couplers and splitters. We non-resonantly stimulate a condensate of waveguided exciton-polaritons resulting in bright polariton lasing from the transverse interfaces and corners of our perovskite microstructures. Large blueshifts with excitation power and high mutual coherence between the different edge and corner lasing signals are detected in the far-field photoluminescence, implying that a spatially extended condensates of coherent polaritons has formed. The condensate polaritons are found to propagate over long distances in the wires from the excitation spot and can couple to neighbouring wires through large air gaps, making our platform promising for integrated polaritonic circuitry and on-chip optical devices with strong nonlinearities.

Acceleration-induced spectral beats in strongly driven harmonic oscillators

The harmonic modulation of coherent systems gives rise to a wealth of physical phenomena, e.g., the AC-Stark effect and Mollow triplets, with important implications for coherent control and frequency conversion. Here, we demonstrate a novel regime of temporal coherence in oscillators harmonically driven at extreme energy modulation amplitudes relative to the modulation quantum. The studies were carried out by modulating a confined exciton-polariton Bose-Einstein condensate (BEC) by an acoustic wave. Features of the new regime are the appearance, in the spectral domain, of a comb of resonances termed acceleration beats with energy spacing tunable by the modulation amplitude and, in the time domain, of temporal correlations at time scales much shorter than the acoustic period, which also depend on the modulation amplitude. These features are quantitatively accounted for by a theoretical framework, which associates the beats with accelerated energy-change rates during the harmonic cycle. These observations are underpinned by the high sensitivity of the BEC energy to the acoustic driving, which simultaneously preserves the BEC’s temporal coherence. The acceleration beats are a general feature associated with accelerated energy changes: analogous features are thus also expected to appear under highly accelerated motion e.g., in connection with Cherenkov and Hawking radiation.

Ultrafast dynamics of exciton-polariton fluids at non-zero momenta

In this study, we have explored the ultrafast formation and decay dynamics of exciton-polariton fluids at non-zero momenta, non-resonantly excited by a small-spot femtosecond pump pulse in a ZnO microcavity. Using the femtosecond angle-resolved spectroscopic imaging technique, multidimensional dynamics in both the energy and momentum degrees of freedom have been obtained. Two distinct regions with different decay rate in the energy dimension and various decay-channels in the momentum dimension can be well-resolved. Theoretical simulations based on the generalized Gross–Pitaevskii equation can reach a qualitative agreement with the experimental observations, demonstrating the significance of the initial potential barrier induced by the pump pulse during the decay process. The finding of our study can provide additional insights into the fundamental understanding of exciton-polariton condensates, enabling further advancements for controlling the fluids and practical applications.

Temporal mode switching during polariton condensation

Multimode behavior plays a key role in a wide range of nonlinear optical phenomena. Multiple exciton-polariton modes can attain macroscopic population as observed in time-integrated measurements. Recent theory work has shown that, rather than being simultaneously in many modes, the population may temporally switch between the modes. However, the origin and the dynamics of multimode condensation has not been experimentally addressed. Here, we study the dynamics of exciton-polariton condensation into multiple modes of Gaussian defect microcavities filled with ladder type polymer gain material methyl-substituted ladder-type poly(p-phenylene) MeLPPP. We deploy a second-order cumulant model to simulate the dynamics of the system and find picosecond-timescale switching between condensate modes. By interferometric measurements we reveal the experimental signatures of such mode competition behaviour.

Topological unwinding in an exciton-polariton condensate array

The phase distribution in a Bose-Einstein condensate can realize various topological states classified by distinct winding numbers. While states with different winding numbers are topologically protected in the linear Schrödinger equation, when nonlinearities are introduced, violations of the topological protection can occur, leading to unwinding. Exciton-polariton condensates constitute a nonlinear open-dissipative system that is well suited to studying such physics. Here we show that a one-dimensional array of exciton-polariton condensates displays a spontaneous phase unwinding from a π- to zero-state. We clarify that this collective mode transition is caused by the combined effect of nonlinearity and topological defects in the condensates. While the mode-switching phenomenon observed in our previous experiment was interpreted as the single-particle mode competition, we offer an alternative explanation in terms the collective phase unwinding and find its evidence by reanalyzing the experimental data. Our results open a route towards active control of the mode switching by manipulating the topological defects in prospective quantum polaritonic devices.

Narrow-linewidth exciton-polariton laser

Exciton-polariton lasers are a promising source of coherent light for low-energy applications due to their low-threshold operation. However, a detailed experimental study of their spectral purity, which directly affects their coherence properties, is still missing. Here, we present a high-resolution spectroscopic investigation of the energy and linewidth of an exciton-polariton laser in the single-mode regime, which derives its coherent emission from an optically pumped and confined exciton-polariton condensate. We report an ultra-narrow linewidth of 56 MHz or 0.24 µeV, corresponding to a coherence time of 5.7 ns. The narrow linewidth is consistently achieved by using an exciton-polariton condensate with a high photonic content confined in an optically induced trap. Contrary to previous studies, we show that the excitonic reservoir created by the pump and responsible for creating the trap does not strongly affect the emission linewidth as long as the condensate is trapped and the pump power is well above the condensation (lasing) threshold. The long coherence time of the exciton-polariton system uncovered here opens up opportunities for manipulating its macroscopic quantum state, which is essential for applications in classical and quantum computing.

Realization of photonic time crystals via spin bifurcations of exciton-polariton condensates.

We have theoretically realized a photonic time crystal in a homogeneous spinor exciton-polariton condensate subject to a cavity strain induced energy splitting between the x- and y-polarized polaritons with distinct loss rates. Numerical modeling based on the time-dependent open dissipative Gross-Pitaevskii equation results in the phase transition from linearly-polarized spinor condensate at low pump powers into a circularly-polarized one and then a photonic time crystal at higher pump powers. This phenomenon occurs only under the condition that the lower-energy x-polarized condensate has a higher loss rate than the y-polaried condensate, which can exist intrinsically in the semiconductor microcavities.

Stochastic circular persistent currents of exciton polaritons

We monitor the orbital degree of freedom of exciton-polariton condensates confined within an optical trap and unveil the stochastic switching of persistent annular polariton currents under pulse-periodic excitation. Within an elliptical trap, the low-lying in energy polariton current states manifest as a two-petaled density distribution with a swirling phase. In the stochastic regime, the density distribution, averaged over multiple excitation pulses, becomes homogenized in the azimuthal direction. Meanwhile, the weighted phase, extracted from interference experiments, exhibits two compensatory jumps when varied around the center of the trap. Introducing a supplemental control optical pulse to break the reciprocity of the system enables the transition from a stochastic to a deterministic regime, allowing for controlled polariton circulation direction.

Solid-state continuous time crystal in a polariton condensate with a built-in mechanical clock.

Time crystals (TCs) are many-body systems that display spontaneous breaking of time translation symmetry. We demonstrate a TC by using driven-dissipative condensates of microcavity exciton-polaritons, spontaneously formed from an incoherent particle bath. The TC phases are controlled by the power of a continuous-wave nonresonant optical drive exciting the condensate and the interaction with cavity phonons. Those phases are, for increasing power, Larmor-like precession of the condensate pseudo-spins-a signature of continuous TC; locking of the frequency of precession to self-sustained coherent phonons-stabilized TC; and doubling of TC's period by phonons-a discrete TC with continuous excitation. These results establish microcavity polaritons as a platform for the investigation of time-broken symmetry in nonhermitian systems.

Beyond mean-field corrections to the blueshift of a driven-dissipative exciton-polariton condensate

Beyond mean-field corrections to the blueshift of a driven-dissipative exciton-polariton condensate

Soliton formation in an exciton-polariton condensate at a bound state in the continuum

Soliton formation in an exciton-polariton condensate at a bound state in the continuum

Topological excitation of exciton-polariton half-vortices and skyrmions in a magnetic field with TE-TM splitting

We explore the topological generation of skyrmions and half-vortices in a uniform spinor exciton-polariton condensate featuring TE-TM splitting and exposed to an external magnetic field. The manipulation of pump intensity and magnetic field enables precise control over the spin texture and integrated winding number. Specifically, under an excitation condition where the power applied to the vortex state surpasses that on the non-vortex state by an amount dictated by the magnetic field, skyrmions emerge. These skyrmions exhibit a distinctive spin texture characterized by a circular polarization inversion extending from the center to the periphery. Conversely, reversing the excitation condition, where the power on the vortex state is diminished with the reversal of the magnetic field direction, leads to the creation of half-vortices across the entire condensate, devoid of any circular polarization inversion. In additional to the skyrmions and half-vortices, half-skyrmions can be also generated in the same configuration without magnetic field.

Modulational instability mechanisms in exciton-polariton condensates

Modulational instability mechanisms in exciton-polariton condensates

Optical spin hall effect in exciton-polariton condensates in lead halide perovskite microcavities.

An exciton-polariton condensate is a hybrid light-matter state in the quantum fluid phase. The photonic component endows it with characters of spin, as represented by circular polarization. Spin-polarization can form stochastically for quasi-equilibrium exciton-polariton condensates at parallel momentum vector k|| ∼ 0 from bifurcation or deterministically for propagating condensates at k|| > 0 from the optical spin-Hall effect (OSHE). Here, we report deterministic spin-polarization in exciton-polariton condensates at k|| ∼ 0 in microcavities containing methylammonium lead bromide perovskite (CH3NH3PbBr3) single crystals under non-resonant and linearly polarized excitation. We observe two energetically split condensates with opposite circular polarizations and attribute this observation to the presence of strong birefringence, which introduces a large OSHE at k|| ∼ 0 and pins the condensates in a particular spin state. Such spin-polarized exciton-polariton condensates may serve not only as circularly polarized laser sources but also as effective alternatives to ultracold atom Bose-Einstein condensates in quantum simulators of many-body spin-orbit coupling processes.

Exciton polariton condensation from bound states in the continuum at room temperature

Exciton–polaritons (polaritons) resulting from the strong exciton–photon interaction stimulates the development of novel low-threshold coherent light sources to circumvent the ever-increasing energy demands of optical communications1–3. Polaritons from bound states in the continuum (BICs) are promising for Bose–Einstein condensation owing to their theoretically infinite quality factors, which provide prolonged lifetimes and benefit the polariton accumulations4–7. However, BIC polariton condensation remains limited to cryogenic temperatures ascribed to the small exciton binding energies of conventional material platforms. Herein, we demonstrated room-temperature BIC polariton condensation in perovskite photonic crystal lattices. BIC polariton condensation was demonstrated at the vicinity of the saddle point of polariton dispersion that generates directional vortex beam emission with long-range coherence. We also explore the peculiar switching effect among the miniaturized BIC polariton modes through effective polariton−polariton scattering. Our work paves the way for the practical implementation of BIC polariton condensates for integrated photonic and topological circuits.