293 research outputs found
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
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