arXiv subjects

A. Fainstein

Publications and source records attributed to A. Fainstein.

At least 19 recordsLinked to original sources

arXiv2026

Synchronization in coherently and dissipatively coupled spinor polariton time crystals

The spinor degree of freedom associated to exciton-polariton condensates can spontaneously self-oscillate breaking time translation symmetry, thus showing a continuous time-crystal (CTC) behavior. An open question in such driven-dissipative and non-linear quantum open systems is what happens when CTCs are brought together to interact. Here we experimentally study polariton condensates in coupled traps, evidencing mutual induction and synchronization of the pseudospin temporal GHz dynamics in the CTC phase. The individual and relative orientation of the (limit cycle) precessing pseudospins can be tuned by the optical excitation power, displaying both ferro and anti-ferro dynamical configurations. We theoretically show that the exciton reservoir, and both the coherent and long-range dissipative inter-trap coupling, play important roles in the CTC dynamics. The investigation of time-broken symmetry is thus extended here to more complex non-hermitian systems opening the path to study self-sustained collective dynamics in lattices of non-linear quantum condensates.

cond-mat.other↗

arXiv2026

Coherent Control of a Polariton Continuous Time Crystal

Spontaneous breaking of time-translation symmetry and the emergence of self-sustained oscillations in quantum driven-dissipative systems is the hallmark of continuous time crystals (CTCs). An outstanding challenge is to achieve precise, coherent control of such dynamical phases, whose complex nonlinear dynamics makes them inherently difficult to manipulate. Here, we experimentally demonstrate coherent control of a solid-state CTC realized in a non-resonantly excited spin-polarized exciton-polariton condensate in a Ga(Al)As microcavity. We exploit two complementary control channels: an additional weak control laser and the optomechanical interaction with confined GHz phonons. By tuning the control laser energy and power, we stabilize distinct dynamical regimes, including frequency pushing, injection locking with continuous tuning of the limit-cycle frequency, and full suppression of the autonomous dynamics via phase locking. Under appropriate detuning conditions, the control excitation generates coherent mechanical self-oscillation through the polariton--phonon deformation-potential interaction, evidenced by spectral sidebands. The resulting dynamical back-action provides a phonon-mediated locking channel that fixes the frequency of the CTC. Together, the two channels dramatically enhance the temporal coherence of the GHz limit-cycle dynamics, as established through linewidth narrowing and time-resolved first-order correlation measurements $\gone(\tau)$. Our work establishes a way to harness the unique aspects of CTCs for practical applications in the GHz-range.

physics.optics↗

arXiv2025

Polariton cascade phonon laser

Phonon lasers, as their photon counterparts, rely on the physics of stimulated emission. Arguably, because light does not require a material substrate to propagate, while sound does, the impact of the two technologies has however been highly contrasting, with "sasers" (for sound amplification by stimulated emission of radiation) mostly remaining as an academic curiosity. This might be changing due to the possibility to use coherent sound generation for on-chip processing of information at ultra-high frequencies, and in the quantum realm, in integrated photonic and optomechanical devices. Inspired by the concept of unipolar lasers based on the quantum engineering of states in semiconductor heterostructures, we propose and implement a quantum cascade phonon laser (QCPL). A condensate of exciton-photon quasiparticles (polaritons) is optically induced in a microstructured semiconductor device to jump down a ladder of engineered levels. This down-cascade is accompanied by the efficient stimulated emission of phonons of $\sim 20$, $\sim 60$, and $\sim 100$~GHz, which are designed to strongly interact with the polaritons on the same chip. The proposed concept opens the path for the design of integrated high-frequency optomechanical devices, as for example for non-reciprocal photon transport and multi-wavelength Brillouin lasers.

physics.optics↗

arXiv2025

Shapiro resonances in ac-self-modulated exciton-polariton Josephson junctions

We experimentally investigate the dynamics of exciton polariton Josephson junctions when the coupling between condensates is periodically modulated through self-induced mechanical oscillations. The condensates energy detuning, the analog of the bias voltage in superconducting junctions, displays a plateau behavior akin to the Shapiro steps. At each step massive tunneling of particles occurs featuring Shapiro-like spikes. These characteristic changes are observed when the condensates Josephson frequency $\omega_\textrm{J}$ is an integer multiple of the modulation frequency $\omega_\mathrm{M}$.

cond-mat.other↗

arXiv2024

Solid-state continuous time crystal with a built-in clock

Time crystals (TCs) are many-body systems displaying spontaneous breaking of time translation symmetry. Here, we demonstrate a TC using driven-dissipative condensates of microcavity exciton-polaritons, spontaneously formed from an incoherent particle bath. In contrast to other realizations, the TC phases can be controlled by the power of continuous-wave non-resonant optical drive exciting the condensate and optomechanical interactions with phonons. Those phases are for increasing power: (i) Larmor precession of pseudo-spins - a signature of continuous TC, (ii) locking of the frequency of precession to self-sustained coherent phonons - stabilized TC, (iii) doubling of TC frequency by phonons - a discrete TC with continuous excitation. These results establish microcavity polaritons as a platform for the investigation of time-broken symmetry in non-hermitian systems.

cond-mat.other↗

arXiv2023

Theory of Optomechanical Locking in Driven-Dissipative Coupled Polariton Condensates

The ubiquitous phenomenon of synchronization is inherently characteristic of dynamical dissipative non-linear systems. In particular, synchronization has been theoretically and experimentally demonstrated for exciton-polariton condensates with time-independent coupling. Unlike that case, we theoretically investigate the effects of a fixed mechanical harmonic driving, i.e., a coherent phonon population, that induces time modulation in the coupling of two coupled condensates. Our model applies both to electrically generated modulation, through coherent bulk acoustic waves, and to self-induced optomechanical vibrations. We consider linear as well as quadratic phonon-displacement-induced modulations of the polariton coupling. Peculiar asynchronously locked phases are found and analyzed in the context of synchronization and Josephson-type oscillations phenomena that appear in the non-driven case. Notably, Arnold tongues corresponding to the asynchronously locked phases emerge at condensate detunings that correspond to integer numbers of the mechanical frequency and also to rational fractions of it. Unlocked quasiperiodic and chaotic regimes can also be reached. In particular, the phonon-induced fractional locking frequencies arrange in a Farey sequence that produces a devil's staircase of the steady-state dressed detuning between the condensates. Importantly, both polariton-polariton and reservoir-polariton interactions facilitate the realization of coherent phonon-induced asynchronously locked phases. The relation to recent experiments on optomechanically driven condensates in arrays of polariton traps is discussed.

physics.optics↗

arXiv2022

Giant optomechanical coupling and dephasing protection with cavity exciton-polaritons

Electronic resonances can significantly enhance the photon-phonon coupling in cavity optomechanics, but are normally avoided due to absorption losses and dephasing by inhomogeneous broadening. We experimentally demonstrate that exciton-polaritons in semiconductor microcavities enable GHz optomechanics with single-particle resonant couplings reaching record values in the 10s of MHz range. Moreover, this resonant enhancement is protected from inhomogeneous broadening by the Rabi gap. Single-polariton non-linearities and the optomechanical strong-coupling regime become accessible in this platform.

cond-mat.mes-hall↗

arXiv2022

Microcavity phonoritons -- a coherent optical-to-microwave interface

Optomechanical systems provide a pathway for the bidirectional optical-to-microwave interconversion in (quantum) networks. We demonstrate the implementation of this functionality and non-adiabatic optomechanical control in a single, $\mu$m-sized potential trap for phonons and exciton-polariton condensates in a structured semiconductor microcavity. The exciton-enhanced optomechanical coupling leads to self-oscillations (phonon lasing) -- thus proving reversible photon-to-phonon conversion. We show that these oscillations are a signature of the optomechanical strong coupling signalizing the emergence of elusive phonon-exciton-photon quasiparticles -- the phonoritons. We then demonstrate full control of the phonoriton spectrum as well as coherent microwave-to-photon interconversion using electrically generated GHz-vibrations and a resonant optical laser beam. These findings establish the zero-dimensional polariton condensates as a scalable coherent interface between microwave and optical domains with enhanced microwave-to-mechanical and mechanical-to-optical coupling rates.

physics.optics↗

arXiv2021

Optomechanical parametric oscillation of a quantum light-fluid lattice

Two-photon coherent states are one of the main building pillars of non-linear and quantum optics. It is the basis for the generation of minimum-uncertainty quantum states and entangled photon pairs, applications not obtainable from standard coherent states or one-photon lasers. Here we describe a fully-resonant optomechanical parametric amplifier involving a polariton condensate in a trap lattice quadratically coupled to mechanical modes. The quadratic coupling derives from non-resonant virtual transitions to extended discrete excited states induced by the optomechanical coupling. Non-resonant continuous wave (cw) laser excitation leads to striking experimental consequences, including the emergence of optomechanically induced inter-site parametric oscillations and inter-site tunneling of polaritons at discrete inter-trap detunings corresponding to sums of energies of the two involved mechanical oscillations (20 and 60 GHz confined vibrations). We show that the coherent mechanical oscillations correspond to parametric resonances with threshold condition different to that of standard linear optomechanical self-oscillation. The associated Arnold tongues display a complex scenario of states within the instability region. The observed new phenomena can have applications for the generation of entangled phonon pairs, squeezed mechanical states relevant in sensing and quantum computation, and for the bidirectional frequency conversion of signals in a technologically relevant range.

cond-mat.mes-hall↗

arXiv2021

Asynchronous Locking in Metamaterials of Fluids of Light and Sound

Phonons, the quanta of vibrations, are very important for the equilibrium and dynamical properties of matter. GHz coherent phonons can also interact with and act as interconnects in a wide range of quantum systems. Harnessing and tailoring their coupling to opto-electronic excitations thus becomes highly relevant for engineered materials for quantum technologies. With this perspective we introduce polaromechanical metamaterials, two-dimensional arrays of $\mu$m-size zero-dimensional traps confining light-matter polariton fluids and GHz phonons. A strong exciton-mediated polariton-phonon interaction determines the inter-site polariton coupling with remarkable consequences for the dynamics. When locally perturbed by optical excitation, polaritons respond by locking the energy detuning between neighbor sites at integer multiples of the phonon energy, evidencing synchronization involving the polariton and phonon fields. These results open the path for the coherent control of quantum light fluids with hypersound in a scalable platform.

physics.optics↗

arXiv2020

Cavity Optomechanics with a Laser Engineered Optical Trap

Laser engineered exciton-polariton networks could lead to dynamically configurable integrated optical circuitry and quantum devices. Combining cavity optomechanics with electrodynamics in laser configurable hybrid designs constitutes a platform for the vibrational control, conversion, and transport of signals. With this aim we investigate 3D optical traps laser-induced in quantum-well embedded semiconductor planar microcavities. We show that the laser generated and controlled discrete states of the traps dramatically modify the interaction between photons and phonons confined in the resonators, accessing through coupling of photoelastic origin $g_\mathrm{0}/2\pi\sim 1.7$ MHz an optomechanical cooperativity $C>1$ for mW excitation. The quenching of Stokes processes and double-resonant enhancement of anti-Stokes ones involving pairs of discrete optical states in the side-band resolved regime, allows the optomechanical cooling of 180 GHz bulk acoustic waves, starting from room temperature down to $\sim120$ K. These results pave the way for dynamical tailoring of optomechanical actuation in the extremely-high-frequency range (30-300 GHz) for future network and quantum technologies.

physics.optics↗

arXiv2020

Cavity Optomechanics with Polariton Bose-Einstein Condensates

We report the experimental study of a hybrid quantum solid state system comprising two-level artificial atoms coupled to cavity confined optical and vibrational modes. In this system combining cavity quantum electrodynamics and cavity optomechanics, excitons in quantum wells play the role of the two-level atoms and are strongly coupled to the optical field leading to mixed polariton states. The planar optical microcavities are laterally microstructured, so that polaritons can be confined in wires, 3D traps, and arrays of traps, providing an additional tuning degree of freedom for the polariton energies. Upon increasing the non-resonant laser excitation power, a Bose-Einstein condensation of the polaritons is observed. Optomechanical induced amplification type of experiments with an additional weak laser probe clearly identify the coupling of these Bose-Einstein condensates to 20~GHz breathing-like vibrations confined in the same cavities. With single continuous wave non-resonant laser excitation, and once the laser power overpasses the threshold for Bose-Einstein condensation in trap arrays, mechanical self-oscillation similar to phonon ``lasing'' is induced with the concomitant observation of Mollow-triplet type mechanical sidebands on the Bose-Einstein condensate emission. High-resolution spectroscopic photoluminescence experiments evidence that these vibrational side-band resolved lines are enhanced when neighboring traps are red-detuned with respect to the BEC emission at overtones of the fundamental 20 GHz breathing mode frequency. These results constitute the first demonstration of coherent cavity polariton optomechanics and pave the way towards a novel type of hybrid devices for quantum technologies, phonon lasers, and phonon-photon bidirectional translators.

physics.optics↗

arXiv2019

Three dimensional trapping of light with light in semiconductor planar microcavities

When light is confined in all three directions and in dimensions of the order of the light wavelength, full discretization of the photon spectra and distinctive phenomena occur, the Purcell effect and the inhibition of emission of atoms being two paradigmatic examples. Diverse solid-state devices that confine light in all three dimensions have been developed and applied. Typically the confinement volume, operating wavelength, and quality factor of these resonators are set by construction, and small variations of these characteristics with external perturbations are targeted for applications including light modulation and control. Here we describe full 3D light trapping, that is set and tuned by laser excitation in an all-optical scheme. The proposed device is based on a planar distributed Bragg reflector GaAs semiconductor microcavity operated at room temperature. Lateral confinement is generated with an attractive effective photonic potential tailored by the increase in the cavity spacer refractive index, induced by carriers photoexcited by a focused laser. Strong three dimensional trapping of light is evidenced by the laser-induced changes on the spectral, spatial, and k-space distribution of the emission. The dynamics of the laser induced photonic potential is studied using modulated optical excitation, highlighting the central role of thermal effects at the origin of the observed phenomena.

physics.optics↗

arXiv2018

Quantum well photoelastic comb for ultra-high frequency cavity optomechanics

Optomechanical devices operated at their quantum limit open novel perspectives for the ultrasensitive determination of mass and displacement, and also in the broader field of quantum technologies. The access to higher frequencies implies operation at higher temperatures and stronger immunity to environmental noise. We propose and demonstrate here a new concept of quantum well photoelastic comb for the efficient coupling of light to optomechanical resonances at hundreds of GHz in semiconductor hybrid resonators. A purposely designed ultra-high resolution Raman spectroscopy set-up is exploited to evidence the transfer of spectral weight from the mode at 60 GHz to modes at 190-230 GHz, corresponding to the $8^{th}$ and $10^{th}$ overtone of the fundamental breathing mode of the light-sound cavities. The coupling to mechanical frequencies two orders of magnitude larger than alternative approaches is attained without reduction of the optomechanical constant $g_0$. The wavelength dependence of the optomechanical coupling further proves the role of resonant photoelastic interaction, highlighting the potentiality to access strong-coupling regimes. The experimental results show that electrostrictive forces allow for the design of devices optimized to selectively couple to specific mechanical modes. Our proposal opens up exciting opportunities towards the implementation of novel approaches applicable in quantum and ultra-high frequency information technologies.

physics.optics↗

arXiv2018

Dimensional crossover of acoustic phonon lifetime in $2H$-MoSe$_2$

A time-resolved observation of coherent interlayer longitudinal acoustic phonons in 2$H$-MoSe$_2$ is reported. A femtosecond pump-probe technique is used to investigate the evolution of the energy loss of these vibrational modes in a wide selection of MoSe$_2$ flakes with different thicknesses ranging from bilayer up to the bulk limit. By directly analysing the temporal decay of the modes, we can clearly distinguish an abrupt crossover related to the acoustic mean free path of the phonons in a layered system, and the constraints imposed to the acoustic decay channels when reducing the dimensionality. Loses intrinsic to the low dimensionality of single or few layer materials impose critical limitations for their use in optomechanical and optoelectronic devices.

cond-mat.mes-hall↗

arXiv2018

Optoelectronic forces with quantum wells for cavity optomechanics in GaAs/AlAs semiconductor microcavities

Radiation pressure, electrostriction, and photothermal forces have been investigated to evidence backaction, non-linearities and quantum phenomena in cavity optomechanics. We show here through a detailed study of the relative intensity of the cavity mechanical modes observed when exciting with pulsed lasers close to the GaAs optical gap that optoelectronic forces involving real carrier excitation and deformation potential interaction are the strongest mechanism of light-to-sound transduction in semiconductor GaAs/AlAs distributed Bragg reflector optomechanical resonators. We demonstrate that the ultrafast spatial redistribution of the photoexcited carriers in microcavities with massive GaAs spacers leads to an enhanced coupling to the fundamental 20 GHz vertically polarized mechanical breathing mode. The carrier diffusion along the growth axis of the device can be enhanced by increasing the laser power, or limited by embedding GaAs quantum wells in the cavity spacer, a strategy used here to prove and engineer the optoelectronic forces in phonon generation with real carriers. The wavelength dependence of the observed phenomena provide further proof of the role of optoelectronic forces. The optical forces associated to the different intervening mechanisms and their relevance for dynamical backaction in optomechanics are evaluated using finite-element methods. The results presented open the path to the study of hitherto seldom investigated dynamical backaction in optomechanical solid-state resonators in the presence of optoelectronic forces.

physics.optics↗

arXiv2017

Optomechanical properties of GaAs/AlAs micropillar resonators operating in the 18 GHz range

Recent experiments demonstrated that GaAs-AlAs based micropillar cavities are promising systems for quantum optomechanics, allowing the simultaneous three-dimensional confinement of near-infrared photons and acoustic phonons in the 18-100 GHz range. Here, we investigate through numerical simulations the optomechanical properties of this new platform. We evidence how the Poisson's ratio and semiconductor-vacuum boundary conditions lead to very distinct features in the mechanical and optical three dimensional confinement. We find a strong dependence of the mechanical quality factor and strain distribution on the micropillar radius, in great contrast to what is predicted and observed in the optical domain. The derived optomechanical coupling constants g_0 reach ultra-large values in the 10^6 rad/s range.

cond-mat.mes-hall↗

arXiv2016

Time-Resolved Cavity Nano-Optomechanics in the 20-100 GHz range

Applications of cavity optomechanics span from gravitational wave detection to the study of quantum motion states in mesoscopic mechanical systems. The engineering of resonators supporting strongly interacting mechanical and optical modes is central to these developments. However, current technological and experimental approaches limit the accessible mechanical frequencies to a few GHz, imposing hard constraints on quantum mechanical studies. Here we demonstrate the optical control of 20-100~GHz mechanical modes confined in the three dimensions within semiconductor nano-optomechanical pillar cavities. We use a time-resolved transient optical reflectivity technique and access both the energy spectrum and dynamics of the mechanical modes at the picosecond timescale. A strong increase of the optomechanical coupling upon reducing the pillar size is observed together with unprecedent room temperature Q-frequency products above $10^{14}$. The measurements also reveal sideband generation in the optomechanical response. Such resonators can naturally integrate quantum wells and quantum dots, enabling novel applications in cavity quantum electrodynamics and high frequency nanomechanics.

physics.optics↗