Atom interferometric detection of the pairing order parameter in a Fermi gas

We propose two interferometric schemes to experimentally detect the onset of pair condensation in a two spin-component Fermi gas. Two atomic wave-packets are coherently extracted from the gas at different positions and are mixed by a matter-wave beam splitter: we show that the spatial long range order of the atomic pairs in the gas then reflects in the atom counting statistics in the output channels of the beam splitter. Alternatively, the same long range order is also shown to create a matter-wave grating in the overlapping region of the two extracted wave-packets, grating that can be revealed by a light scattering experiment

Feshbach blockade: single-photon nonlinear optics using resonantly enhanced cavity-polariton scattering from biexciton states

We theoretically demonstrate how the resonant coupling between a pair of cavity-polaritons and a biexciton state can lead to a large single-photon Kerr nonlinearity in a semiconductor solid-state system. A fully analytical model of the scattering process between a pair of cavity-polaritons is developed, which explicitly includes the biexcitonic intermediate state. A dramatic enhancement of the polariton-polariton interactions is predicted in the vicinity of the biexciton Feshbach resonance. Application to the generation of non-classical light from polariton dots is discussed

Immunity of intersubband polaritons to inhomogeneous broadening

We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous effects originating from the presence of multiple quantum wells (MQWs). In a series of samples that exhibit mid-infrared ISB absorption transitions with broadenings varying by a factor of 5 (from 4 meV to 20meV), we have observed polariton linewidths always lying in the 4 - 7 meV range only. We have experimentally verified the dominantly inhomogeneous origin of the broadening of the ISB transition, and that the linewidth reduction effect of the polariton modes persists up to room-temperature. This immunity to inhomogeneous broadening is a direct consequence of the coupling of the large number of ISB oscillators to a single photonic mode. It is a precious tool to gauge the natural linewidth of the ISB plasmon , that is otherwise masked in such MQWs system , and is also beneficial in view of perspective applications such as intersubband polariton lasers

Evaporative cooling of an atomic beam

We present a theoretical analysis of the evaporative cooling of an atomic beam propagating in a magnetic guide. Cooling is provided by transverse evaporation. The atomic dynamics inside the guide is analyzed by solving the Boltzmann equation with two different approaches: an approximate analytical ansatz and a Monte-Carlo simulation. Within their domain of validity, these two methods are found to be in very good agreement with each other. They allow us to determine how the phase-space density and the flux of the beam vary along its direction of propagation. We find a significant increase for the phase-space density along the guide for realistic experimental parameters. By extrapolation, we estimate the length of the beam needed to reach quantum degeneracy.Comment: 13 pages, 7 figures, to be published in EPJ D, revised versio

Non-equilibrium Berezinskii-Kosterlitz-Thouless Transition in a Driven Open Quantum System

The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is mediated by the proliferation of topological defects, governs the critical behaviour of a wide range of equilibrium two-dimensional systems with a continuous symmetry, ranging from superconducting thin films to two-dimensional Bose fluids, such as liquid helium and ultracold atoms. We show here that this phenomenon is not restricted to thermal equilibrium, rather it survives more generally in a dissipative highly non-equilibrium system driven into a steady-state. By considering a light-matter superfluid of polaritons, in the so-called optical parametric oscillator regime, we demonstrate that it indeed undergoes a vortex binding-unbinding phase transition. Yet, the exponent of the power-law decay of the first order correlation function in the (algebraically) ordered phase can exceed the equilibrium upper limit -- a surprising occurrence, which has also been observed in a recent experiment. Thus we demonstrate that the ordered phase is somehow more robust against the quantum fluctuations of driven systems than thermal ones in equilibrium.Comment: 11 pages, 9 figure

Testing Hawking particle creation by black holes through correlation measurements

Hawking's prediction of thermal radiation by black holes has been shown by Unruh to be expected also in condensed matter systems. We show here that in a black hole-like configuration realised in a BEC this particle creation does indeed take place and can be unambiguously identified via a characteristic pattern in the density-density correlations. This opens the concrete possibility of the experimental verification of this effect.Comment: 13 pages, 2 figures. Honorable mention in the 2010 GRF Essay Competitio

An exact reformulation of the Bose-Hubbard model in terms of a stochastic Gutzwiller ansatz

We extend our exact reformulation of the bosonic many-body problem in terms of a stochastic Hartree ansatz to a stochastic Gutzwiller ansatz for the Bose Hubbard model. This makes the corresponding Monte Carlo method more efficient for strongly correlated bosonic phases like the Mott insulator phase or the Tonks phase. We present a first numerical application of this stochastic method to a system of impenetrable bosons on a 1D lattice showing the transition from the discrete Tonks gas to the Mott phase as the chemical potential is increased

Many-body physics of a quantum fluid of exciton-polaritons in a semiconductor microcavity

Some recent results concerning nonlinear optics in semiconductor microcavities are reviewed from the point of view of the many-body physics of an interacting photon gas. Analogies with systems of cold atoms at thermal equilibrium are drawn, and the peculiar behaviours due to the non-equilibrium regime pointed out. The richness of the predicted behaviours shows the potentialities of optical systems for the study of the physics of quantum fluids.Comment: Proceedings of QFS2006 conference to appear on JLT