arXiv subjects

A. Nalitov

Publications and source records attributed to A. Nalitov.

16 recordsLinked to original sources

arXiv2026

Probing intermittent polariton vortex dynamics with two-point correlations

Superconducting single-photon detectors with time resolution of 80 ps have been used to study the spatiotemporal dynamics of a trapped bosonic condensate of exciton-polaritons. Both second- and first-order correlation functions are found to exhibit pronounced oscillations in time governed by the dynamics of the polariton condensate in the trap. We have identified the intermittent regime of stochastic transitions between stationary and limit-cycle regimes near the Andronov-Hopf bifurcation manifested in asymmetric distortions of the correlation function. This rich interplay of deterministic and stochastic condensate dynamics is explained theoretically as a manifestation of mutually compensating self-repulsion and reservoir-mediated attraction.

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arXiv2026

Collective Excitations and Stability of Nonequilibrium Polariton Supersolids

Formation of nonequilibrium counterparts of supersolids, simultaneously characterized with spontaneous superfluid and crystalline order, was recently reported in incoherently pumped polariton condensates. We investigate collective excitation spectra of this phase and explicitly demonstrate the emergence of gapless Nambu-Goldstone modes due to spontaneously broken continuous phase and translation symmetries. For the recent implementation of the polariton nonequilibrium supersolidity in semiconductor metasurfaces [D. Trypogeorgos et al., Nature 639, 337 (2025)], we demonstrate the key role of attractive polariton interactions, mediated by the excitonic reservoir, for stability of the supersolid phase. Performing a thorough numerical investigation, we identify the conditions for existence of the diagonal and off-diagonal long-range order in negative-mass nonequilibrium supersolids.

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arXiv2025

Kardar-Parisi-Zhang universality in optically induced lattices of exciton-polariton condensates

We investigate space-time coherence in one-dimensional lattices of exciton-polariton condensates formed by fully reconfigurable non-resonant optical pumping. Starting from an open-dissipative Gross-Pitaevskii equation with deterministic reservoir kinetics and stochastic condensate noise, we derive a discrete complex-field model that incorporates coherent tunnelling, reservoir-mediated dissipative coupling and gain-saturation non-linearity. Adiabatic elimination of fast density fluctuations reveals a wedge-shaped region in the complex hopping plane where the coarse-grained phase dynamics reduces to the Kardar-Parisi-Zhang (KPZ) equation. By computing high-resolution phase diagrams of the temporal and spatial scaling exponents we pinpoint the boundaries separating the KPZ domain from the Edwards-Wilkinson (EW) regime. Large-scale graphics processing unit (GPU) simulations of chains containing up to $N=2000$ condensates confirm these predictions: inside the wedge the exponents converge to $β_{N}=\textbf{0.329}(3)\!\approx\!1/3$ and $χ_{N}=\textbf{0.504}(4)\!\approx\!1/2$, whereas outside it the dynamics moves away from KPZ and ultimately flows toward the EW fixed point, although finite system size and finite observation time may yield intermediate effective exponents. These results pave the way to the implementation of ultrafast KPZ-simulators based on one-dimensional arrays of exciton-polariton condensates.

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arXiv2025

Ultra-small Mode Volume Polariton Condensation via Precision $He^+$ Ion Implantation

We present a novel method for generating potential landscapes in GaAs microcavities through focused $He^{+}$ implantation. The ion beam imprints micron-scale patterns of non-radiative centers that deplete the exciton reservoir and form a loss-defined potential minimum. Under non-resonant pumping, the resulting traps have a lateral size $\le 1.2 ~\mathrm{μm}$ and a three-dimensional mode volume of only $\approx 0.6 ~ \mathrm{μm^3}$, small enough to to support a single polariton condensate mode. The implantation process maintains strong coupling and provides lithographic ($ < 300 ~ \mathrm{nm}$) resolution. These loss-engineered traps effectively overcome the micrometer-scale limitations of conventional microcavity patterning techniques, opening new avenues for device development and polariton research within the quantum regime.

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arXiv2024

Giant effective $g$-factor due to spin bifurcations in polariton condensates

We predict giant susceptibility of spin-bifurcating polariton condensates to externally applied permanent magnetic field. In the presence of spin-anisotropic polariton-polariton interactions, the condensate spontaneously takes an elliptically polarised state, {whose perturbation dynamics can be interpreted in terms of the presence of strong effective magnetic field} significantly surpassing the external one. Surprisingly, this behaviour of the addressed strongly out-of-equilibrium system in the vicinity of a critical point exhibits intriguing analogy with the second-order phase transition. The predicted field-enhancement effect can be utilized for creation of topologically nontrivial states of Bogoliubov's excitations existing on top of the polariton condensate.

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arXiv2024

Non-adiabatic polariton condensation in annular optical traps

We explore formation and dynamics of nonequilibrium bosonic exciton-polariton condensates in annular optically induced traps. For the vicinity of condensation pumping threshold, we develop the two-mode model, accounting for counter-rotating quantized vortices and corresponding angular harmonics in the incoherent excitonic reservoir density. Identifying the range of parameter, in which adiabatic elimination of the reservoir is valid, we extend the analytic model beyond the adiabatic approximation. In the circularly symmetric case, we predict a neutral equilibrium phase due to spontaneous breaking of the continuous symmetry, condensate multistability and limit cycle dynamics. We also account for weak trap asymmetry to show that non-adiabaticity of the coupled condensate-reservoir system prevents formation of giant vortices and outline experimental conditions for their observation.

cond-mat.quant-gas↗

arXiv2021

Kibble-Zurek mechanism in polariton graphene

We study the formation of topological defects (quantum vortices) during the formation of a 2D polariton condensate at the $Γ$ point of a honeycomb lattice via the Kibble-Zurek mechanism. The lattice modifies the single-particle dispersion. The typical interaction energies at the quench time correspond to the linear part of the dispersion. The resulting scaling exponent for the density of topological defects is numerically found as $0.95\pm0.05$. This value differs from the one expected for 2D massive particles (1/2), but is indeed compatible with the one expected for a linear dispersion. We moreover demonstrate that the vortices can be pinned to the lattice, which prevents their recombination and could facilitate their observation and counting in continuous wave experiments.

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arXiv2021

Pseudo-conservative dynamics of coupled polariton condensates

Open-dissipative systems obeying parity-time ($\mathcal{PT}$) symmetry are capable of demonstrating oscillatory dynamics akin to the conservative systems. In contrast to limit cycle solutions characteristic of nonlinear systems, the $\mathcal{PT}$-symmetric oscillations form a continuum of non-isolated orbits. However, precise sculpturing of the real potential and the gain-loss spatial profiles required for establishing of the $\mathcal{PT}$-symmetry is practically challenging. The optical devices, such as lasers, exhibit relaxation dynamics and do not operate as the $\mathcal{PT}$-symmetric systems. Here we demonstrate how these constraints can be overcome. We predict that a pair of optically trapped polariton condensates (a polariton dimer) can be excited and operated in the oscillating regime typical of the isolated systems. This regime can be realized in the presence of both dissipative and conservative coupling between the condensates and can be maintained at an arbitrary external pump intensity. Every orbit is characterised by a frequency comb appearing in the spectrum of a dimer in the presence of the conservative nonlinearity. Our results pave the way for the creation of the optical computing devices operating under the constant-wave external pumping.

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arXiv2020

Quantum metric and wavepackets at exceptional points in non-Hermitian systems

The usual concepts of topological physics, such as the Berry curvature, cannot be applied directly to non-Hermitian systems. We show that another object, the quantum metric, which often plays a secondary role in Hermitian systems, becomes a crucial quantity near exceptional points in non-Hermitian systems, where it diverges in a way that fully controls the description of wavepacket trajectories. The quantum metric behaviour is responsible for a constant acceleration with a fixed direction, and for a non-vanishing constant velocity with a controllable direction. Both contributions are independent of the wavepacket size.

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arXiv2017

Observation of macroscopic valley-polarized monolayer exciton-polaritons at room temperature

In this letter, we address the chiral properties of valley exciton-polaritons in a monolayer of WS2 in the regime of strong light-matter coupling with a Tamm-Plasmon resonance. We observe that the valley polarization, which manifests in the circular polarization of the emitted photoluminescence, is strongly enhanced in comparison to bare WS2 monolayers, and can even be observed under non-resonant excitation at ambient conditions. We study the relaxation and decay dynamics of exciton-polaritons in our device, and present a microscopic model to explain the wave vector-dependent valley depolarization as an interplay of bright and dark states, electron-hole exchange interaction and the linear polarization splitting inherent to the microcavity.

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arXiv2017

Chiral modes at exceptional points in exciton-polariton quantum fluids

We demonstrate generation of chiral modes -- vortex flows with fixed handedness in exciton-polariton quantum fluids. The chiral modes arise in the vicinity of exceptional points (non-Hermitian spectral degeneracies) in an optically-induced resonator for exciton polaritons. In particular, a vortex is generated by driving two dipole modes of the non-Hermitian ring resonator into degeneracy. Transition through the exceptional point in the space of the system's parameters is enabled by precise manipulation of real and imaginary parts of the closed-wall potential forming the resonator. As the system is driven to the vicinity of the exceptional point, we observe the formation of a vortex state with a fixed orbital angular momentum (topological charge). Our method can be extended to generate high-order orbital angular momentum states through coalescence of multiple non-Hermitian spectral degeneracies, which could find application in integrated optoelectronics.

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arXiv2017

Valley polarized relaxation and upconversion luminescence from Tamm-Plasmon Trion-Polaritons with a MoSe2 monolayer

Transition metal dichalcogenides represent an ideal testbed to study excitonic effects, spin-related phenomena and fundamental light-matter coupling in nanoscopic condensed matter systems. In particular, the valley degree of freedom, which is unique to such direct band gap monolayers with broken inversion symmetry, adds fundamental interest in these materials. Here, we implement a Tamm-plasmon structure with an embedded MoSe2 monolayer and study the formation of polaritonic quasi-particles. Strong coupling conditions between the Tamm-mode and the trion resonance of MoSe2 are established, yielding bright luminescence from the polaritonic ground state under non-resonant optical excitation. We demonstrate, that tailoring the electrodynamic environment of the monolayer results in a significantly increased valley polarization. This enhancement can be related to change in recombination dynamics shown in time-resolved photoluminescence measurements. We furthermore observe strong upconversion luminescence from resonantly excited polariton states in the lower polariton branch. This upconverted polariton luminescence is shown to preserve the valley polarization of the trion-polariton, which paves the way towards combining spin-valley physics and exciton scattering experiments.

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arXiv2016

Influence of magnetic quantum confined Stark effect on the spin lifetime of indirect excitons

We report on the unusual and counter-intuitive behaviour of spin lifetime of excitons in coupled semiconductor quantum wells (CQWs) in the presence of in-plane magnetic field. Instead of conventional acceleration of spin relaxation due to the Larmor precession of electron and hole spins we observe a strong increase of the spin relaxation time at low magnetic fields followed by saturation and decrease at higher fields. We argue that this non-monotonic spin relaxation dynamics is a fingerprint of the magnetic quantum confined Stark effect. In the presence of electric field along the CQW growth axis, an applied magnetic field efficiently suppresses the exciton spin coherence, due to inhomogeneous broadening of the $g$-factor distribution.

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arXiv2015

Exciton-polaritons in van der Waals heterostructures embedded in tunable microcavities

Layered materials can be assembled vertically to fabricate a new class of van der Waals (VDW) heterostructures a few atomic layers thick, compatible with a wide range of substrates and optoelectronic device geometries, enabling new strategies for control of light-matter coupling. Here, we incorporate molybdenum diselenide/boron nitride (MoSe$_2$/hBN) quantum wells (QWs) in a tunable optical microcavity. Part-light-part-matter polariton eigenstates are observed as a result of the strong coupling between MoSe$_2$ excitons and cavity photons, evidenced from a clear anticrossing between the neutral exciton and the cavity modes with a splitting of 20 meV for a single MoSe$_2$ monolayer QW, enhanced to 29 meV in MoSe$_2$/hBN/MoSe$_2$ double-QWs. The splitting at resonance provides an estimate of the exciton radiative lifetime of 0.4 ps. Our results pave the way for room temperature polaritonic devices based on multiple-QW VDW heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realised.

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arXiv2014

Nonlinear optical spectroscopy of indirect excitons in biased coupled quantum wells

Indirect excitons in coupled quantum wells are long-living quasi-particles, explored in the studies of collective quantum states. We demonstrate, that despite the extremely low oscillator strength, their spin and population dynamics can by addressed by time-resolved pump-probe spectroscopy. Our experiments make it possible to unravel and compare spin dynamics of direct excitons, indirect excitons and residual free electrons in coupled quantum wells. Measured spin relaxation time of indirect excitons exceeds not only one of direct excitons, but also one of free electrons by two orders of magnitude.

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arXiv2014

Engineering spin-orbit coupling for photons and polaritons in microstructures

One of the most fundamental properties of electromagnetism and special relativity is the coupling between the spin of an electron and its orbital motion. This is at the origin of the fine structure in atoms, the spin Hall effect in semiconductors, and underlies many intriguing properties of topological insulators, in particular their chiral edge states. Configurations where neutral particles experience an effective spin-orbit coupling have been recently proposed and realized using ultracold atoms and photons. Here we use coupled micropillars etched out of a semiconductor microcavity to engineer a spin-orbit Hamiltonian for photons and polaritons in a microstructure. The coupling between the spin and orbital momentum arises from the polarisation dependent confinement and tunnelling of photons between micropillars arranged in the form of a hexagonal photonic molecule. Dramatic consequences of the spin-orbit coupling are experimentally observed in these structures in the wavefunction of polariton condensates, whose helical shape is directly visible in the spatially resolved polarisation patterns of the emitted light. The strong optical nonlinearity of polariton systems suggests exciting perspectives for using quantum fluids of polaritons11 for quantum simulation of the interplay between interactions and spin-orbit coupling.

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