158 research outputs found
Generation of Superposition Spin States in an Atomic Ensemble
A method for generating a mesoscopic superposition state of the collective
spin variable of a gas of atoms is proposed. The state consists of a
superposition of the atomic spins pointing in two slightly different
directions. It is obtained by using off resonant light to carry out Quantum Non
Demolition Measurements of the spins. The relevant experimental conditions,
which require very dense atomic samples, can be realized with presently
available techniques. Long-lived atomic superposition states may become useful
as an off-line resource for quantum computing with otherwise linear operations.Comment: 5 pages, 2 figures, accepted in Phys. Rev. Let
1D Bose gases in an optical lattice
We report on the study of the momentum distribution of a one-dimensional Bose gas in an optical lattice. From the momentum distribution we extract the condensed fraction of the gas and thereby measure the depletion of the condensate and compare it with a theoretical estimate. We have measured the coherence length of the gas for systems with average occupation n̄>1 and n̄<1 per lattice sit
1D Bose Gases in an Optical Lattice
We report on the study of the momentum distribution of a one-dimensional Bose
gas in an optical lattice. From the momentum distribution we extract the
condensed fraction of the gas and thereby measure the depletion of the
condensate and compare it with a theorical estimate. We have measured the
coherence length of the gas for systems with average occupation and
per lattice site.Comment: 4 pages, 3 figure
Storing and releasing light in a gas of moving atoms
We propose a scheme of storing and releasing pulses or cw beams of light in a
moving atomic medium illuminated by two stationary and spatially separated
control lasers. The method is based on electromagnetically induced transparency
(EIT) but in contrast to previous schemes, storage and retrieval of the probe
pulse can be achieved at different locations and without switching off the
control laser.Comment: 4 pages, 3 figures, revised versio
Bichromatic Local Oscillator for Detection of Two-Mode Squeezed States of Light
We present a new technique for the detection of two-mode squeezed states of
light that allows for a simple characterization of these quantum states. The
usual detection scheme, based on heterodyne measurements, requires the use of a
local oscillator with a frequency equal to the mean of the frequencies of the
two modes of the squeezed field. As a result, unless the two modes are close in
frequency, a high-frequency shot-noise-limited detection system is needed. We
propose the use of a bichromatic field as the local oscillator in the
heterodyne measurements. By the proper selection of the frequencies of the
bichromatic field, it is possible to arbitrarily select the frequency around
which the squeezing information is located, thus making it possible to use a
low-bandwidth detection system and to move away from any excess noise present
in the system.Comment: 11 pages, 3 figure
Superfluid to Mott insulator transition in one, two, and three dimensions
No Heading: We have created one-, two-, and three-dimensional quantum gases and study the superfluid to Mott insulator transition. Measurements of the transition using Bragg spectroscopy show that the excitation spectra of the low-dimensional superfluids differ significantly from the three-dimensional cas
Mapping a quantum state of light onto a long-lived atomic spin state: towards quantum memory
We report an experiment on mapping a quantum state of light onto the ground
state spin of an ensemble of Cs atoms with the life time of 2 milliseconds.
Quantum memory for one of the two quadrature phase operators of light is
demonstrated with vacuum and squeezed states of light. The sensitivity of the
mapping procedure at the level of approximately one photon/sec per Hz is shown.
The results pave the road towards complete (storing both quadrature phase
observables) quantum memory for Gaussian states of light. The experiment also
sheds new light on fundamental limits of sensitivity of the magneto-optical
resonance method.Comment: 5 pages, 4 figures, RevTe
Characterizing the spin state of an atomic ensemble using the magneto-optical resonance method
Quantum information protocols utilizing atomic ensembles require preparation
of a coherent spin state (CSS) of the ensemble as an important starting point.
We investigate the magneto-optical resonance method for characterizing a spin
state of cesium atoms in a paraffin coated vapor cell. Atoms in a constant
magnetic field are subject to an off-resonant laser beam and an RF magnetic
field. The spectrum of the Zeeman sub-levels, in particular the weak quadratic
Zeeman effect, enables us to measure the spin orientation, the number of atoms,
and the transverse spin coherence time. Notably the use of 894nm pumping light
on the D1-line, ensuring the state F=4, m_F=4 to be a dark state, helps us to
achieve spin orientation of better than 98%. Hence we can establish a CSS with
high accuracy which is critical for the analysis of the entangled states of
atoms.Comment: 12 pages ReVTeX, 6 figures, in v2 added ref. and corrected typo
Collapse and revival of oscillations in a parametrically excited Bose-Einstein condensate in combined harmonic and optical lattice trap
In this work, we study parametric resonances in an elongated cigar-shaped BEC
in a combined harmonic trap and a time dependent optical lattice by using
numerical and analytical techniques. We show that there exists a relative
competition between the harmonic trap which tries to spatially localize the BEC
and the time varying optical lattice which tries to delocalize the BEC. This
competition gives rise to parametric resonances (collapse and revival of the
oscillations of the BEC width). Parametric resonances disappear when one of the
competing factors i.e strength of harmonic trap or the strength of optical
lattice dominates. Parametric instabilities (exponential growth of Bogoliubov
modes) arise for large variations in the strength of the optical lattice.Comment: 9 pages, 20 figure
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