157 research outputs found
Two point correlations of a trapped interacting Bose gas at finite temperature
We develop a computationally tractable method for calculating correlation
functions of the finite temperature trapped Bose gas that includes the effects
of s-wave interactions. Our approach uses a classical field method to model the
low energy modes and treats the high energy modes using a Hartree-Fock
description. We present results of first and second order correlation
functions, in position and momentum space, for an experimentally realistic
system in the temperature range of to . We also characterize
the spatial coherence length of the system. Our theory should be applicable in
the critical region where experiments are now able to measure first and second
order correlations.Comment: 9 pages, 4 figure
Imaging the phase of an evolving Bose-Einstein condensate wavefunction
We demonstrate a spatially resolved autocorrelation measurement with a
Bose-Einstein condensate (BEC) and measure the evolution of the spatial profile
of its quantum mechanical phase. Upon release of the BEC from the magnetic
trap, its phase develops a form that we measure to be quadratic in the spatial
coordinate. Our experiments also reveal the effects of the repulsive
interaction between two overlapping BEC wavepackets and we measure the small
momentum they impart to each other
Elastic scattering loss of atoms from colliding Bose-Einstein condensate wavepackets
Bragg diffraction of atoms by light waves has been used to create high
momentum components in a Bose-Einstein condensate. Collisions between atoms
from two distinct momentum wavepackets cause elastic scattering that can remove
a significant fraction of atoms from the wavepackets and cause the formation of
a spherical shell of scattered atoms. We develop a slowly varying envelope
technique that includes the effects of this loss on the condensate dynamics
described by the Gross-Pitaevski equation. Three-dimensional numerical
calculations are presented for two experimental situations: passage of a moving
daughter condensate through a non-moving parent condensate, and four-wave
mixing of matter waves.Comment: Phys. Rev. Lett, in pres
Lambda's, V's and optimal cloning with stimulated emission
We show that optimal universal cloning of the polarization state of photons
can be achieved via stimulated emission in three-level systems, both of the
Lambda and the V type. We establish the equivalence of our systems with coupled
harmonic oscillators, which permits us to analyze the structure of the cloning
transformations realized. These transformations are shown to be equivalent to
the optimal cloning transformations for qubits discovered by Buzek and Hillery,
and Gisin and Massar. The down-conversion cloner discovered previously by some
of the authors is obtained as a limiting case. We demonstrate an interesting
equivalence between systems of Lambda atoms and systems of pairwise entangled V
atoms. Finally we discuss the physical differences between our photon cloners
and the qubit cloners considered previously and prove that the bounds on the
fidelity of the clones derived for qubits also apply in our situation.Comment: 10 page
Mach-Zehnder Bragg interferometer for a Bose-Einstein Condensate
We construct a Mach-Zehnder interferometer using Bose-Einstein condensed
rubidium atoms and optical Bragg diffraction. In contrast to interferometers
based on normal diffraction, where only a small percentage of the atoms
contribute to the signal, our Bragg diffraction interferometer uses all the
condensate atoms. The condensate coherence properties and high phase-space
density result in an interference pattern of nearly 100% contrast. In
principle, the enclosed area of the interferometer may be arbitrarily large,
making it an ideal tool that could be used in the detection of vortices, or
possibly even gravitational waves.Comment: 10 pages, 3 figures, Quantum Electronics and Laser Science Conference
1999, Postdeadline papers QPD12-
Logarithmic two-loop corrections to the Lamb shift in hydrogen
Higher order logarithmic corrections to the
hydrogen Lamb shift are calculated. The results obtained show the two-loop
contribution has a very peculiar behavior, and significantly alter the
theoretical predictions for low lying S-states.Comment: 14 pages, including 2 figures, submitted to Phys. Rev. A, updated
with minor change
Quantum carpet interferometry for trapped atomic Bose-Einstein condensates
We propose an ``interferometric'' scheme for Bose-Einstein condensates using
near-field diffraction. The scheme is based on the phenomenon of intermode
traces or quantum carpets; we show how it may be used in the detection of weak
forces.Comment: 4 figures. Submitted to Phys. Rev.
Experimental observation of the Bogoliubov transformation for a Bose-Einstein condensed gas
Phonons with wavevector were optically imprinted into a
Bose-Einstein condensate. Their momentum distribution was analyzed using Bragg
spectroscopy with a high momentum transfer. The wavefunction of the phonons was
shown to be a superposition of +q and -q free particle momentum states, in
agreement with the Bogoliubov quasiparticle picture.Comment: 4 pages, 3 figures, please take postscript version for the best
version of Fig
Coherence properties of an atom laser
We study the coherence properties of an atom laser, which operates by
extracting atoms from a gaseous Bose-Einstein condensate via a two-photon Raman
process, by analyzing a recent experiment. We obtain good agreement with the
experimental data by solving the time-dependent Gross-Pitaevskii equation in
three dimensions both numerically and with a Thomas-Fermi model. The coherence
length is strongly affected by the space-dependent phase developed by the
condensate when the trapping potential is turned off.Comment: 11 pages, 2 Postscript figure
Measuring the temporal coherence of an atom laser beam
We report on the measurement of the temporal coherence of an atom laser beam
extracted from a Rb Bose-Einstein condensate. Reflecting the beam from a
potential barrier creates a standing matter wave structure. From the contrast
of this interference pattern, observed by magnetic resonance imaging, we have
deduced an energy width of the atom laser beam which is Fourier limited by the
duration of output coupling. This gives an upper limit for temporal phase
fluctuations in the Bose-Einstein condensate.Comment: 4 pages, 3 figure
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