Exciton Spin Dynamics in Semiconductor Quantum Wells

In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum Wells. The spin properties of excitons in nanostructures are determined by their fine structure. We will mainly focus in this review on GaAs and InGaAs quantum wells which are model systems.Comment: 55 pages, 27 figure

Symmetry-breaking Effects for Polariton Condensates in Double-Well Potentials

We study the existence, stability, and dynamics of symmetric and anti-symmetric states of quasi-one-dimensional polariton condensates in double-well potentials, in the presence of nonresonant pumping and nonlinear damping. Some prototypical features of the system, such as the bifurcation of asymmetric solutions, are similar to the Hamiltonian analog of the double-well system considered in the realm of atomic condensates. Nevertheless, there are also some nontrivial differences including, e.g., the unstable nature of both the parent and the daughter branch emerging in the relevant pitchfork bifurcation for slightly larger values of atom numbers. Another interesting feature that does not appear in the atomic condensate case is that the bifurcation for attractive interactions is slightly sub-critical instead of supercritical. These conclusions of the bifurcation analysis are corroborated by direct numerical simulations examining the dynamics of the system in the unstable regime.MICINN (Spain) project FIS2008- 0484

Analog time machine in a photonic system

International audienceAnalog physics has successfully tackled the problems of gauge theories, event horizons, Big Bang and Universe expansion, and many others. Here, we suggest a photonic model system for a “time machine” based on the paraxial beam approximation. We demonstrate how the closed timelike curves and the well-known grandfather paradox can be studied experimentally in this system. We show how Novikov's self-consistency principle is realized in quantum mechanics owing to Heisenberg's uncertainty principle

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

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

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

Effective Theory of Non-Adiabatic Quantum Evolution Based on the Quantum Geometric Tensor

International audienceWe study the role of the quantum geometric tensor (QGT) in the evolution of quantum systems. We show that all its components play an important role on the extra phase acquired by a spinor and on the trajectory of an accelerated wavepacket in any realistic finite-duration experiment. While the adiabatic phase is determined by the Berry curvature (the imaginary part of the tensor), the non-adiabaticity is determined by the quantum metric (the real part of the tensor) and allows to determine corrections in the regimes where Landau-Zener approach is inapplicable. The particular case of a planar microcavity in the strong coupling regime allows to extract the QGT components by direct light polarization measurements and to check their effects on the quantum evolution

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

Quantum analogue of a Kerr black hole and the Penrose effect in a Bose-Einstein condensate

International audienceAnalogue physics became very popular in recent decades. It allows simulating inaccessible physical phenomena, such as black holes, in the laboratory. The first success of analogue physics is in fact much older being due to Maxwell, who derived his equations for the electromagnetic field by analogy with fluid dynamics in presence of vortices. Here we propose to use vortices for analogue gravity. We implement an acoustic Kerr black hole with quantized angular momentum in a Bose-Einstein condensate. We show that the condensate's metric is equivalent to the Kerr's one, exhibiting a horizon and an ergosphere. We confirm that this metric is obeyed not only by weak density waves, but also by quantum vortices which behave as massive test particles. We use these topological defects to demonstrate a quantum Penrose effect, extracting the rotation energy of the black hole by quanta of angular momentum. The particle trajectories are well described by the timelike geodesics of the Kerr metric, confirming the potential of analogue quantum gravity

Anisotropic polariton scattering and spin dynamics of cavity polaritons.

We describe the spin-dynamics of exciton–polaritons in semiconductor microcavities in the strong coupling regime. Using the Liouville equation for the spin-density matrix in the Born–Markov approximation we obtain kinetic equations taking into account polariton–acoustic phonon and polariton–polariton scattering. We describe both the ‘polariton laser’ regime (non-resonant excitation) and ‘optical parametric oscillator’ regime (resonant excitation at the magic angle). We obtain a good agreement with experimental data on the dynamics of polarization of light emitted by microcavities