arXiv subjects

A. V. Kavokin

Publications and source records attributed to A. V. Kavokin.

At least 19 recordsLinked to original sources

arXiv2026

Sharp Coherence Crossover and Multimode Phase Control in Coupled Exciton-Polariton Condensates

We investigate the formation of mutual coherence and deterministic phase control in a multimode exciton-polariton system realized in two optically induced traps with tunable intertrap coupling. As the coupling channel between the traps is progressively opened, the mutual first-order coherence rises sharply from nearly zero to values close to unity, revealing a threshold-like crossover from weakly correlated to highly coherent dynamics. We demonstrate deterministic multimode phase control with a short spatially localized nonresonant pulse, which allows the phase relations between selected polariton condensate modes to be set while keeping their amplitudes nearly unchanged. The induced phase transformation is read out directly from time-resolved interferograms and realized for different sets of modes in both intermediate- and high-coherence regimes. Within a reduced four-mode description, the control pulse implements an effective phase operator on the coherent multimode field with a fidelity exceeding 0.995. The same approach can be extended to larger networks of coupled traps, offering a route to optical control over phase relations in increasingly complex multimode polariton states.

physics.optics↗

arXiv2026

Generating entangled polaritonic condensates by pumping with entangled pairs of photons

We investigate the steady state of two single-mode uniform spatially separated polaritonic conden- sates exposed to resonant pumping with entangled pairs of photons. We demonstrate the principal possibility of driving the system to an entangled state despite its exposure to noises arising from the excitonic reservoir and photon leakage through the microcavity mirrors. Estimates are provided for the flux of entangled particles required to drive the system into a steady state that violates the partial-transpose criterion for entanglement. Furthermore, we trace the evolution of the system after a sudden disappearance of the entangled pumping. Our analysis provides estimates for the entanglement lifetime in a system of two exciton-polariton condensates

quant-ph↗

arXiv2026

Geometric oscillations of local Hall and Nernst effects in ballistic graphene at weak magnetic fields

We predict a novel class of magnetotransport oscillations in ballistic graphene specific for a ring-shape geometry. Using the Büttiker-Landauer formalism, we analytically obtain the local Hall and Nernst coefficients in the weak-field ballistic regime. These coefficients exhibit pronounced oscillations as functions of both the magnetic field and the angular positions of the measurement probes. The oscillations originate from the discrete set of skipping orbits that geometrically connect the contacts, with resonances occurring when the angular separation between contacts times the radius of the disk equals an integer number of cyclotron diameters. Unlike conventional quantum oscillations in conductivity, this effect is robust at room temperature and can dominate local thermoelectric signals. This geometric control of ballistic flow provides a platform for studying electron hydrodynamics and engineering phase-coherent devices, with potential applications in sensitive terahertz detectors and thermal management systems.

cond-mat.mes-hall↗

arXiv2025

Digital-Alloy Bragg Mirrors in High-Q Microcavities for Polariton Lasing

We present an approach to the molecular-beam epitaxy of high-Q planar GaAs-based microcavities in which the AlGaAs high-index layers of the distributed Bragg reflectors (DBRs) are replaced by short-period GaAs/AlAs superlattices (digital alloys) with similar optical properties. This design enables a significant reduction of interface roughness, precise control of the quarter-wavelength optical thickness and the effective Al content, suppression of the propagation of structural defects, and efficient tuning of intrinsic absorption at the polariton emission wavelength via optimization of the superlattice parameters. Using this approach, we fabricate a microcavity with a low polariton-lasing threshold of approximately 570 W/cm$^2$ and a high experimental quality factor of about 5.4 x $10^4$. This value exceeds by almost a factor of two the theoretical estimate obtained within an equivalent ternary-alloy model. We demonstrate that accurate modeling of the stop-band characteristics and the Q factor requires incorporating the modified electronic density of states in the superlattice, including quantum-confinement and excitonic effects.

cond-mat.mtrl-sci↗

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.

cond-mat.mes-hall↗

arXiv2025

Classical and single photon memory devices based on polariton lasers

Stimulated scattering of incoherent excitons into an exciton-polariton mode leads to the build-up of a polariton condensate whose polarization is sensitive to a small seeded population that triggers the stimulated process. We show, within a semiclassical stochastic Gross-Pitaevskii model, that this mechanism enables a robust polarization memory operation: the condensate tends to align its Stokes vector with that of the seed and to maintain it for times far exceeding an individual polariton lifetime. Importantly, this single-photon-seeded regime is modeled as an initial weak excitation of the condensate mode. We quantify the memory performance by a classical polarization-alignment metric and find that the seed polarization can remain well preserved on a nanosecond timescale under realistic parameters.

cond-mat.mes-hall↗

arXiv2025

Supersolidity in Optically Trapped Polariton Condensates

Superfluids under specific conditions can exhibit spontaneous breaking of continuous translation symmetries and form exotic spatially ordered states of matter known as supersolids. Despite its early theoretical prediction, it took over half-a-centrury to experimentally demonstrate the supersolid phase in ultracold atomic Bose-Einstein condensates, forming due to long-range interatomic interactions. Here we propose as a promising new platform for supersolidity exciton-polariton superfluids, confined in annular optically induced traps. The supersolid phase emerges due to effective attractive interactions, mediated by the normal excitonic component of the system. Experimental demonstration of spontaneously formed spatially ordered phase is in agreement with detailed mean-field theoretical analysis and numerical simulation. The spontaneous character of the observed supersolid transition is further evidenced by the formation of specific zero-energy Nambu-Goldstone modes in the collective excitation spectrum.

cond-mat.mes-hall↗

arXiv2025

Quantum beats of a macroscopic polariton condensate in real space

We experimentally observe harmonic oscillations in a bosonic condensate of exciton-polaritons confined within an elliptical trap. These oscillations arise from quantum beats between two size-quantized states of the condensate, split in energy due to the trap's ellipticity. By precisely targeting specific spots inside the trap with nonresonant laser pulses, we control frequency, amplitude, and phase of these quantum beats. The condensate wave function dynamics is visualized on a streak camera and mapped to the Bloch sphere, demonstrating Hadamard and Pauli-Z operations. We conclude that a qubit based on a superposition of these two polariton states would exhibit a coherence time exceeding the lifetime of an individual exciton-polariton by at least two orders of magnitude.

cond-mat.mes-hall↗

arXiv2025

Thermoelectric effects in two-dimensional topological insulators

We explore the nontrivial thermoelectric properties of two-dimensional topological systems. For the Chern insulator, we show that the Seebeck coefficient is fully determined by the Kelvin formula, while the Nernst coefficient vanishes. For a two-dimensional electron gas with Rashba spin-orbit interactions we reveal how the Berry curvature affects the thermoelectric coefficients, and derive the Mott-like equation for thermopower. We predict a strong variation of the thermopower of a two-dimensional topological insulator with time-reversal symmetry in the ballistic and dissipative regimes. The Kelvin formula applies in the ballistic regime, while the Mott formula holds in the dissipative regime. Importantly, in a system with trapezoidal geometry, the combination of ballistic and dissipative regimes leads to the anomalous Nernst effect. Finally, we analyze a two-dimensional Anderson insulator, where edge modes show distinct temperature behavior of the Seebeck coefficient near the weak localization-strong localization transition temperatures. In the trivial phase, the thermopower exhibits a strong power law temperature dependence, while in the topological phase both power law and exponential dependences coexist.

cond-mat.mes-hall↗

arXiv2024

Failure of the Mott's formula for the Thermopower in Carbon Nanotubes

Well-known Mott's formula links the thermoelectric power characterised by Seebeck coefficient to conductivity. We calculate analytically the thermoelectric current and Seebeck coefficient in one-dimensional systems and show that, while the prediction of Mott's formula is valid for Dirac fermions, it is misleading for the carriers having a parabolic dispersion. We apply the developed formalism to metallic single wall carbon nanotubes and obtain a non-trivial non-monotonic dependence of the Seebeck coefficient on the chemical potential. We emphasize that, in contrast to Mott's formula, the classical Kelvin's formula that links thermoelectric power to the temperature derivative of the chemical potential is perfectly valid in carbon nanotubes in the ballistic regime. Interestingly, however, the Kelvin's formula fails in two- and three-dimensional systems in the ballistic regime.

cond-mat.mes-hall↗

arXiv2024

Anomalous Seebeck effect and counter-propagating ballistic currents in graphene

The Seebeck effect consists in the induction of a voltage drop due to the temperature difference in a conductor. In the middle of XIXth century, Lord Kelvin has proposed a relation between the Seebeck coefficient and the derivative of the chemical potential over temperature in the broken circuit regime. This relation appears to be nearly universal as it equally well applies to metals, semimetals and semiconductors. We show that it may fail, however, in graphene, due to the non-locality effects in the ballistic electronic transport regime. The correction to the Kelvin's formula emerges due to the coexistence of counter-propagating non-dissipative currents of cold and hot electrons. The external magnetic field normal to the graphene sample allows separating hot and cold currents in real space. The developed formalism may help interpreting the recent experimental data on ballistic edge currents in graphene bi-layers in the quantum Hall regime [1].

cond-mat.mes-hall↗

arXiv2023

Persistent polarization oscillations in ring-shape polariton condensates

We predict the limit cycle solution for a ring-shape bosonic condensate of exciton-polaritons confined in an optically induced rotating trap. The limit cycle manifests itself with polarization oscillations on a characteristic timescale of tens of picoseconds. The effect arises due to the interplay between orbital motion and the polarization degree of freedom. It is specific to spinor bosonic condensates and would be absent in a scalar case, where a bi-stability of stationary solutions would be observed instead. This work offers a tool of initialisation and control of qubits based on superpositions of polariton condensates characterised by different topologic charges.

physics.optics↗

arXiv2023

Vorticity of polariton condensates in rotating traps

This work is inspired by recent experiments on the formation of vortices in exciton-polariton condensates placed in rotating optical traps. We study theoretically the dynamics of formation of such vortices and elucidate the fundamental role of the mode competition effect in determining the properties of stationary polariton states triggered by stimulated scattering of exciton-polaritons. The interplay between linear and non-linear effects is shown to result in a peculiar polariton dynamics. However, near the lasing threshold, the predominant contribution of the nonlinear effects is the saturation of the linear gain.

physics.optics↗

arXiv2022

Spin resonance induced by a mechanical rotation of a polariton condensate

We study theoretically the polarization dynamics in a ring-shape bosonic condensate of exciton-polaritons confined in a rotating trap. The interplay between the rotating potential and TE-TM splitting of polariton modes offers a tool of control over the spin state and the angular momentum of the condensate. Specific selection rules describing the coupling of pseudospin and angular momentum are formulated. The resonant coupling between states having linear and circular polarizations leads to the polarization beats. The effect may be seen as a polariton analogy to the electronic magnetic resonance in the presence of constant and rotating magnetic fields. Remarkably, spin beats are induced by a purely mechanical rotation of the condensate.

physics.optics↗

arXiv2021

Terahertz transitions in finite carbon chains

We predict an optical effect associated with systems which exhibit topologically protected states separated by a finite distance. We develop a tight-binding model to calculate the optical selection rules in linear chains of atoms of different lengths, and show the crucial importance of edge states. For long enough molecules the interband transitions involving these edge states are in the highly sought-after THz frequency range. Although we have specifically considered finite carbon chains terminated by gold nanoparticles, the main results of our work can be generalized to various systems which exhibit topologically protected states separated by a finite distance.

cond-mat.mes-hall↗

arXiv2021

Dynamics and control of nonradiative excitons - free carriers mixture in GaAs/AlGaAs quantum wells

Dynamics of nonradiative excitons with large in-plane wave vectors forming a so-called reservoir is experimentally studied in a high-quality semiconductor structure containing a 14-nm shallow GaAs/Al$_{0.03}$Ga$_{0.97}$As quantum well by means of the non-degenerate pump-probe spectroscopy. The exciton dynamics is visualized via the dynamic broadening of the heavy-hole and light-hole exciton resonances caused by the exciton-exciton scattering. Under the non-resonant excitation free carriers are optically generated. In this regime the exciton dynamics is strongly affected by the exciton-carrier scattering. In particular, if the carriers of one sign are prevailing, they efficiently deplete the reservoir of the nonradiative excitons inducing their scattering into the light cone. A simple model of the exciton dynamics is developed, which considers the energy relaxation of photocreated electrons and holes, their coupling into excitons, and exciton scattering into the light cone. The model well reproduces the exciton dynamics observed experimentally both at the resonant and nonresonant excitation. Moreover, it correctly describes the profiles of the photoluminescence pulses studied experimentally. The efficient exciton-electron interaction is further experimentally verified by the control of the exciton density in the reservoir when an additional excitation creates electrons depleting the reservoir.

cond-mat.mes-hall↗

arXiv2021

Nernst and Ettingshausen effects in the Laughlin geometry

The ideal reversible thermodynamic cycle visualization of the Nernst effect in Laughlin geometry, excluding the kinetic contribution is proposed. The Ettingshausen effect is also treated in the fashion using the reverse cycle. The corresponding values of the off-diagonal thermoelectric coefficients are expressed through the ratio of the entropy budget per magnetic flux. Our approach enlightens the profound thermodynamic origin of the relation between the Nernst effect and magnetization currents.

cond-mat.mes-hall↗

arXiv2021

Anomalous Exciton Hall Effect

It is well known that electrically neutral excitons can still be affected by crossed electric and magnetic fields that make them move in a direction perpendicular to both fields. We show that a similar effect appears in the absence of external electric fields, in the case of scattering of an exciton flow by charged impurities in the presence of the external magnetic field. As a result, the exciton flow changes the direction of its propagation that may be described in terms of the Hall conductivity for excitons. We develop a theory of this effect, which we refer to as the anomalous exciton Hall effect, to distinguish it from the exciton Hall effect that arises due to the valley selective exciton transport in transition metal dichalcogenides. According to our estimations, the effect is relatively weak for optically active or bright excitons in conventional GaAs quantum wells, but it becomes significant for optically inactive or dark excitons, because of the difference of the lifetimes. This makes the proposed effect a convenient tool for spatial separation of dark and bright excitons.

cond-mat.mes-hall↗