arXiv subjects

G. Malpuech

Publications and source records attributed to G. Malpuech.

At least 19 recordsLinked to original sources

arXiv2026

Mode-locking instability and multiple soliton formation in GaN polariton waveguide cavities

We study the emergence of multi-soliton regimes in 1D ridge polariton waveguides of two different lengths. We show that by varying the position of the gain, which in out-of-equilibrium polariton systems is provided by the pumping laser and its associated excitonic reservoir, it is possible to tune the regime of soliton formation between single and multiple solitons. This soliton dynamics can be quantitatively reproduced by solving the Gross-Pitaevskii equations of the coupled exciton-photon system, which show that the soliton splitting mechanism is governed by the exciton reservoir dynamics.

cond-mat.mes-hall↗

arXiv2026

Analogue black hole merger in a polariton condensate

Analogue studies represent an important tool in modern Physics. In particular, analogue gravity had a strong success in the recent years with the demonstrations of Hawking radiation and superradiance of analogue black holes in classical and quantum fluids. So far, the metric of the analogue black holes was mostly fixed by the conditions of the experiment, preventing the simulation of any significant evolution of their properties, such as the change of their mass, their spatial motion, gravitation attraction to other bodies, and, ultimately, black hole mergers. Polariton condensates represent a perfect setting for the analogue simulation of black hole evolution and mergers because of the velocity-dependent losses creating a convergent flow associated with each quantum vortex, which thus becomes an analogue black hole capable of spatial motion. We show that while two vortices are unable to form a common horizon, four or more vortices can exhibit a complete black hole merger, with the radius of the common horizon given by a simple geometrical law. We also discuss the difference between the horizon and the apparent horizon in these analogue black holes with quantized constituents.

cond-mat.mes-hall↗

arXiv2025

Soliton formation in a bound state in the continuum GaN waveguide polariton laser

We study polaritonic bound states in the continuum (BIC) created in GaN waveguides. The existence of symmetry-protected BICs is confirmed by the suppression of light emission and the observation of a polarization vortex in momentum space. Upon increasing the pumping, polariton population accumulates at the BIC and we observe polariton lasing from the blueshifted BIC states. The assessment of the polariton BIC emission energy and of its real and momentum space wavefunctions as a function of pumping power, i.e. of polariton density, indicates the formation of a bright soliton above the lasing threshold. Soliton formation at the BIC is induced by the combination of negative mass BIC and of repulsive polariton-polariton and polariton-reservoir interactions.

cond-mat.mes-hall↗

arXiv2025

Dirac points annihilation and its obstruction characterized by Euler number and quaternionic charges in kagome lattice

We investigate the topological phenomenon of Dirac point annihilation and its obstruction in three-band, real symmetric Hamiltonians with time-reversal symmetry, and their relation to the Euler number, a well-known topological invariant. For this purpose, we study the example of the kagome lattice using a simple tight-binding model. By tuning the parameters of the lattice continuously, we illustrate situations where two Dirac points are able to annihilate, and others, where this annihilation is topologically obstructed. For a system with no gaps between the three bands, like in the kagome lattice, the Euler number of two bands is ill-defined on the whole Brillouin zone, which requires the introduction of the so-called ``patch" Euler number on a subregion without additional degeneracies coming from the third band. A non-zero patch Euler number means that the annihilation of the Dirac points is impossible. We also illustrate another point of view, using homotopy theory, associating the Dirac points with quaternionic charges. We prove that the non-abelian braiding of the Dirac points in k-space conjugates their quaternionic charge and explains the possible obstruction to the annihilation of Dirac points. Finally, we show that the proposed deformation of the kagome lattice can be achieved in realistic photonic systems.

cond-mat.mes-hall↗

arXiv2024

Mode-locked GaN waveguide polariton laser

So far, exciton-polariton (polariton) lasers were mostly single mode lasers based on microcavities. Despite the large repulsive polariton-polariton interaction, pulsed mode-locked polariton laser was never reported. Here, we use a $60 \ μm-$long GaN-based waveguide surrounded by distributed Bragg reflectors forming a multi-mode horizontal cavity. We demonstrate experimentally and theoretically a polariton mode-locked micro-laser operating in the blue-UV, at room temperature, with a 300$\ GHz$ repetition rate and 100$\ fs$-long pulses. The mode locking is demonstrated by the compensation (linearization) of the mode dispersion by the self-phase modulation induced by the polariton-polariton interaction. It is also supported by the observation in experiment and theory of the typical envelope frequency profile of a bright soliton.

physics.optics↗

arXiv2024

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

Bound states in the continuum (BIC) are of special interest in photonics due to their theoretically infinite radiative lifetime. Here, we design a structure composed of a GaN layer with guided exciton-polaritons and a TiO$_2$ 1D photonic crystal slab. The photonic BIC hosted by the photonic crystal slab couples with the excitons of GaN to form a polaritonic BIC with a negative mass. This allows condensation to be reached with a low threshold in a structure suitable for electrical injection, paving the way for room-temperature polariton microdevices. We study in detail how the repulsive interaction between exciton-polaritons affects the condensate distribution in reciprocal space and, consequently, the condensate's overlap with the BIC resonance and, therefore, the condensate lifetime. We study an intrinsic contribution related to the formation of a bright soliton and the extrinsic contribution related to the interaction with an excitonic reservoir induced by spatially focused non-resonant pumping. We then study the peculiar dynamics of the condensation process in a BIC state for interacting particles using Boltzmann equations and hybrid Boltzmann-Gross Pitaevskii equations. We find optimal conditions allowing one to benefit from the long lifetime of the BIC for polariton condensation in a real structure.

physics.optics↗

arXiv2024

Topological moiré polaritons

The combination of an in-plane honeycomb potential and of a photonic spin-orbit coupling (SOC) emulates a photonic/polaritonic analog of bilayer graphene. We show that modulating the SOC magnitude allows to change the overall lattice periodicity, emulating any type of moiré-arranged bilayer graphene with a unique all-optical access to the moiré band topology. We show that breaking the time-reversal symmetry by an effective exciton-polariton Zeeman splitting opens a large topological gap in the array of moiré flat bands. This gap contains one-way topological edge states whose constant group velocity makes an increasingly sharp contrast with the flattening moiré bands.

cond-mat.mes-hall↗

arXiv2022

Simultaneous creation of multiple vortex-antivortex pairs in momentum space in photonic lattices

Engineering of the orbital angular momentum (OAM) of light due to interaction with photonic lattices reveals rich physics and motivates potential applications. We report the experimental creation of regularly-distributed quantized vortex arrays in momentum space by probing the honeycomb and hexagonal photonic lattices with a single focused Gaussian beam. For the honeycomb lattice, the vortices are associated with Dirac points and mimic the Berry curvature sources. However, we show that the resulting spatial patterns of vortices are strongly defined by the symmetry of the wave packet evolving in the optical lattice but not by lattice topological properties. Our findings reveal the underlying physics by connecting the symmetry and OAM conversion, and provide a simple and efficient method to create regularly-distributed multiple vortices by unstructured light.

physics.optics↗

arXiv2022

Design of a room-temperature topological exciton-polariton laser in a ZnO/TiO$_2$-photonic crystal slab

We propose theoretically a scheme to get a room-temperature 2D topological exciton-polariton laser with propagating topological lasing modes. The structure uses guided modes in a photonic crystal slab. A ZnO layer provides strong excitonic resonances stable at room temperature. It is capped by a TiO$_2$ layer pierced by a triangular lattice. The exciton-polariton modes of the 3D structure are computed by solving numerically Maxwell's equations including the excitonic response. The designed triangular lattice shows a transverse electric gap. The triangular lattice is shown to be the limit of a staggered honeycomb lattice when one of the sub-lattices vanishes. Its topology can be characterized by symmetry indicators. The interface between two shifted triangular lattices supports two counter-propagating modes lying in the gap of the bulk modes. The interface states are analogous to quantum pseudospin Hall interface states. These modes show orthogonal polarizations. They can be selectively excited using polarized excitation and are well-protected from back-scattering. These modes can benefit from the exciton-polariton gain at room temperature because of their sufficiently large exciton fraction and favorable position in energy. The strong localization of these propagating modes makes them suitable to host topological lasing triggered by a non-resonant pump localized on the interface.

cond-mat.mes-hall↗

arXiv2022

The Berry-Foucault Pendulum

The geometric phase is known to play a role both in the rotation of the Foucault pendulum and in the anomalous Hall effect (AHE) due to the Berry curvature. Here, we show that a 2D harmonic oscillator with AHE induced by Berry curvature behaves exactly like the Foucault pendulum: in both, the plane of the oscillations rotates with time. The rotating pendulum configuration enhances the AHE, simplifying its observation and allowing high-precision measurements of the Berry curvature. We also show how the non-adiabaticity and anharmonicity determine the maximal rotation angle and find the optimal conditions for the observations.

cond-mat.mes-hall↗

arXiv2022

Angular-dependent Andreev reflection on a polaritonic superfluid

We study analytically an analog of the Andreev reflection at a normal-superfluid interface. The polariton gapped superfluid region is achieved by quasi-resonant optical pumping. The interacting polaritons are described with the driven-dissipative Gross-Pitaevskii equation. We find analytical formulas for the angles and amplitudes of the reflected and transmitted particles. There are limit angles and energies, above which Andreev reflection/transmission cannot be observed anymore and where the Andreev wave becomes a surface mode, exponentially localized on the interface. These properties are confirmed by solving numerically the Gross-Pitaevskii equation in simulations reproducing realistic experimental conditions.

cond-mat.mes-hall↗

arXiv2022

Domain-wall topology induced by spontaneous symmetry breaking in polariton graphene

We present a numerical study of exciton-polariton (polariton) condensation in a staggered polariton graphene showing a gapped s-band at the $K$ and $K'$ valleys. The condensation occurs at $K$ or $K'$, at the kinetically-favorable negative mass extrema of the valence band. Considering attractive polariton-polariton interaction allows to generate a spatially extended condensate. Spontaneous symmetry breaking occurring during the condensate build-up leads to the formation of valley-polarized domains following the Kibble-Zurek scenario. The selection of a single valley breaks time-reversal symmetry and the walls separating domains exhibit a topologically-protected chiral current. This current therefore emerges as a result of the interplay between the non-trivial valley topology and the condensation-induced symmetry breaking.

cond-mat.mes-hall↗

arXiv2021

Annihilation of exceptional points from different Dirac valleys in a 2D photonic system

Topological physics relies on the existence of Hamiltonian's eigenstate singularities carrying a topological charge, such as quantum vortices, Dirac points, Weyl points and -- in non-Hermitian systems -- exceptional points (EPs), lines or surfaces. They appear only in pairs connected by a Fermi arc and are related to a Hermitian singularity, such as a Dirac point. The annihilation of 2D Dirac points carrying opposite charges has been experimentally reported. It remained elusive for Weyl points and second order EPs terminating different Fermi arcs. Here, we observe the annihilation of second order EPs issued from different Dirac points forming distinct valleys. We study a liquid crystal microcavity with voltage-controlled birefringence and TE-TM photonic spin-orbit-coupling. Two neighboring modes can be described by a two-band Hermitian Hamiltonian showing two topological phases with either two same-sign or four opposite-sign Dirac points (valleys). Non-Hermiticity is provided by polarization-dependent losses, which split Dirac points into pairs of EPs, connected by Fermi arcs. We measure their topological charges and control their displacement in reciprocal space by increasing the non-Hermiticity degree. EPs of opposite charges from different valleys meet and annihilate, connecting in a closed line the different Fermi arcs. This non-Hermitian topological transition occurs only when the Hermitian part of the Hamiltonian is topologically trivial (with four valleys), but is distinct from the Hermitian transition. Our results offer new perspectives of versatile manipulation of EPs, opening the new field of non-Hermitian valley-physics.

cond-mat.mes-hall↗

arXiv2021

Giant effective Zeeman splitting in a monolayer semiconductor realized by spin-selective strong light-matter coupling

Strong coupling between light and the fundamental excitations of a two-dimensional electron gas (2DEG) are of foundational importance both to pure physics and to the understanding and development of future photonic nanotechnologies. Here we study the relationship between spin polarization of a 2DEG in a monolayer semiconductor, MoSe$_2$, and light-matter interactions modified by a zero-dimensional optical microcavity. We find robust spin-susceptibility of the 2DEG to simultaneously enhance and suppress trion-polariton formation in opposite photon helicities. This leads to observation of a giant effective valley Zeeman splitting for trion-polaritons (g-factor >20), exceeding the purely trionic splitting by over five times. Going further, we observe robust effective optical non-linearity arising from the highly non-linear behaviour of the valley-specific strong light-matter coupling regime, and allowing all-optical tuning of the polaritonic Zeeman splitting from 4 to >10 meV. Our experiments lay the groundwork for engineering quantum-Hall-like phases with true unidirectionality in monolayer semiconductors, accompanied by giant effective photonic non-linearities rooted in many-body exciton-electron correlations.

cond-mat.mes-hall↗

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.

cond-mat.mes-hall↗

arXiv2021

Universal semiclassical equations based on the quantum metric

We derive semiclassical equations of motion for an accelerated wavepacket in a two-band system. We show that these equations can be formulated in terms of the static band geometry described by the quantum metric. We consider the specific cases of the Rashba Hamiltonian with and without a Zeeman term. The semiclassical trajectories are in full agreement with the ones found by solving the Schrödinger equation. This formalism successfully describes the adiabatic limit and the anomalous Hall effect traditionally attributed to Berry curvature. It also describes the opposite limit of coherent band superposition giving rise to a spatially oscillating Zitterbewegung motion. At $k=0$, such wavepacket exhibits a circular trajectory in real space, with its radius given by the square root of the quantum metric. This quantity appears as a universal length scale, providing a geometrical origin of the Compton wavelength.

cond-mat.mes-hall↗

arXiv2021

Topological gap solitons in a 1D non-Hermitian lattice

Nonlinear topological photonics is an emerging field aiming at extending the fascinating properties of topological states to the realm where interactions between the system constituents cannot be neglected. Interactions can indeed trigger topological phase transitions, induce symmetry protection and robustness properties for the many-body system. Moreover when coupling to the environment via drive and dissipation is also considered, novel collective phenomena are expected to emerge. Here, we report the nonlinear response of a polariton lattice implementing a non-Hermitian version of the Su-Schrieffer-Heeger model. We trigger the formation of solitons in the topological gap of the band structure, and show that these solitons demonstrate robust nonlinear properties with respect to defects, because of the underlying sub-lattice symmetry. Leveraging on the system non-Hermiticity, we engineer the drive phase pattern and unveil bulk solitons that have no counterpart in conservative systems. They are localized on a single sub-lattice with a spatial profile alike a topological edge state. Our results demonstrate a tool to stabilize the nonlinear response of driven dissipative topological systems, which may constitute a powerful resource for nonlinear topological photonics.

cond-mat.mes-hall↗

arXiv2020

Topological turbulence in spin-orbit-coupled driven-dissipative quantum fluids of light generates high angular momentum states

We demonstrate the formation of a high angular momentum turbulent state in an exciton-polariton quantum fluid with TE-TM Spin-Orbit Coupling (SOC). The transfer of particles from quasi-resonantly cw pumped \spl component to \sm component is accompanied with the generation of a turbulent gas of quantum vortices by inhomogeneities. We show that this system is unstable with respect to the formation of bogolons at a finite wave vector, controlled by the laser detuning. In a finite-size cavity, the domains with this wave vector form a ring-like structure along the border of a cavity, with a gas of mostly same-sign vortices in the center. The total angular momentum is imposed by the sign of TE-TM SOC, the wave vector of instability, and the cavity size. This effect can be detected experimentally via local dispersion measurements or by interference. The proposed configuration thus allows simultaneous experimental studies of quantum turbulence and high-angular momentum states in continuously-pumped exciton-polariton condensates.

cond-mat.quant-gas↗