124 research outputs found
Exploring the Kibble-Zurek mechanism with homogeneous Bose gases
Out-of-equilibrium phenomena is a subject of considerable interest in many
fields of physics. Ultracold quantum gases, which are extremely clean,
well-isolated and highly controllable systems, offer ideal platforms to
investigate this topic. The recent progress in tailoring trapping potentials
now allows the experimental production of homogeneous samples in custom
geometries, which is a key advance for studies of the emergence of coherence in
interacting quantum systems. Here we review recent experiments in which
temperature quenches have been performed across the Bose-Einstein condensation
(BEC) phase transition in an annular geometry and in homogeneous 3D and
quasi-2D gases. Combined, these experiments give a comprehensive picture of the
Kibble-Zurek (KZ) scenario through complementary measurements of correlation
functions and topological defects density. They also allow the measurement of
KZ scaling laws, the direct confirmation of the "freeze-out" hypothesis that
underlies the KZ theory, and the extraction of critical exponents of the
Bose-Einstein condensation transition.Comment: 11 pages, 6 figures; topical revie
Clock spectroscopy of interacting bosons in deep optical lattices
We report on high-resolution optical spectroscopy of interacting bosonic
Yb atoms in deep optical lattices with negligible tunneling. We prepare
Mott insulator phases with singly- and doubly-occupied isolated sites and probe
the atoms using an ultra-narrow "clock" transition. Atoms in singly-occupied
sites undergo long-lived Rabi oscillations. Atoms in doubly-occupied sites are
strongly affected by interatomic interactions, and we measure their inelastic
decay rates and energy shifts. We deduce from these measurements all relevant
collisional parameters involving both clock states, in particular the intra-
and inter-state scattering lengths
Non-linear Relaxation of Interacting Bosons Coherently Driven on a Narrow Optical Transition
We study the dynamics of a two-component Bose-Einstein condensate (BEC) of
Yb atoms coherently driven on a narrow optical transition. The
excitation transfers the BEC to a superposition of states with different
internal and momentum quantum numbers. We observe a crossover with decreasing
driving strength between a regime of damped oscillations, where coherent
driving prevails, and an incoherent regime, where relaxation takes over.
Several relaxation mechanisms are involved: inelastic losses involving two
excited atoms, leading to a non-exponential decay of populations; Doppler
broadening due to the finite momentum width of the BEC and inhomogeneous
elastic interactions, both leading to dephasing and to damping of the
oscillations. We compare our observations to a two-component Gross-Pitaevskii
(GP) model that fully includes these effects. For small or moderate densities,
the damping of the oscillations is mostly due to Doppler broadening. In this
regime, we find excellent agreement between the model and the experimental
results. For higher densities, the role of interactions increases and so does
the damping rate of the oscillations. The damping in the GP model is less
pronounced than in the experiment, possibly a hint for many-body effects not
captured by the mean-field description.Comment: 7 pages, 4 figures; supplementary material available as ancillary
fil
Recent progress on the manipulation of single atoms in optical tweezers for quantum computing
This paper summarizes our recent progress towards using single rubidium atoms
trapped in an optical tweezer to encode quantum information. We demonstrate
single qubit rotations on this system and measure the coherence of the qubit.
We move the quantum bit over distances of tens of microns and show that the
coherence is reserved. We also transfer a qubit atom between two tweezers and
show no loss of coherence. Finally, we describe our progress towards
conditional entanglement of two atoms by photon emission and two-photon
interferences.Comment: Proceedings of the ICOLS07 conferenc
Optimal approach to quantum communication using dynamic programming
Reliable preparation of entanglement between distant systems is an
outstanding problem in quantum information science and quantum communication.
In practice, this has to be accomplished via noisy channels (such as optical
fibers) that generally result in exponential attenuation of quantum signals at
large distances. A special class of quantum error correction protocols--quantum
repeater protocols--can be used to overcome such losses. In this work, we
introduce a method for systematically optimizing existing protocols and
developing new, more efficient protocols. Our approach makes use of a dynamic
programming-based searching algorithm, the complexity of which scales only
polynomially with the communication distance, letting us efficiently determine
near-optimal solutions. We find significant improvements in both the speed and
the final state fidelity for preparing long distance entangled states.Comment: 9 pages, 6 figure
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