5,820 research outputs found
Theory of the cold collision frequency shift in 1S--2S spectroscopy of Bose-Einstein-condensed and non-condensed hydrogen
We show that a correct formulation of the cold collision frequency shift for
two photon spectroscopy of Bose-condensed and cold non-Bose-condensed hydrogen
is consistent with experimental data. Our treatment includes transport and
inhomogeneity into the theory of a non-condensed gas, which causes substantial
changes in the cold collision frequency shift for the ordinary thermal gas, as
a result of the very high frequency (3.9kHz) of transverse trap mode. For the
condensed gas, we find substantial corrections arise from the inclusion of
quasiparticles, whose number is very large because of the very low frequency
(10.2Hz) of the longitudinal trap mode. These two effects together account for
the apparent absence of a "factor of two" between the two possibilities.
Our treatment considers only the Doppler-free measurements, but could be
extended to Doppler-sensitive measurements. For Bose-condensed hydrogen, we
predict a characteristic "foot" extending into higher detunings than can arise
from the condensate alone, as a result of a correct treatment of the statistics
of thermal quasiparticles.Comment: 16 page J Phys B format plus 6 postscript figure
Helix or Coil? Fate of a Melting Heteropolymer
We determine the probability that a partially melted heteropolymer at the
melting temperature will either melt completely or return to a helix state.
This system is equivalent to the splitting probability for a diffusing particle
on a finite interval that moves according to the Sinai model. When the initial
fraction of melted polymer is f, the melting probability fluctuates between
different realizations of monomer sequences on the polymer. For a fixed value
of f, the melting probability distribution changes from unimodal to a bimodal
as the strength of the disorder is increased.Comment: 4 pages, 5 figure
Normal mode splitting in a coupled system of nanomechanical oscillator and parametric amplifier cavity
We study how an optical parametric amplifier inside the cavity can affect the
normal mode splitting behavior of the coupled movable mirror and the cavity
field. We work in the resolved sideband regime. The spectra exhibit a
double-peak structure as the parametric gain is increased. Moreover, for a
fixed parametric gain, the double-peak structure of the spectrum is more
pronounced with increasing the input laser power. We give results for mode
splitting. The widths of the split lines are sensitive to parametric gain.Comment: 7 pages,9 figure
Chaotic dynamics in superconducting nanocircuits
The quantum kicked rotator can be realized in a periodically driven
superconducting nanocircuit. A study of the fidelity allows the experimental
investigation of exponential instability of quantum motion inside the Ehrenfest
time scale, chaotic diffusion and quantum dynamical localization. The role of
noise and the experimental setup to measure the fidelity is discussed as well.Comment: 4 pages, 4 figure
Unusual light spectra from a two-level atom in squeezed vacuum
We investigate the interaction of an atom with a multi-channel squeezed
vacuum. It turns out that the light coming out in a particular channel can have
anomalous spectral properties, among them asymmetry of the spectrum, absence of
the central peak as well as central hole burning for particular parameters. As
an example plane-wave squeezing is considered. In this case the above phenomena
can occur for the light spectra in certain directions. In the total spectrum
these phenomena are washed out.Comment: 16 pages, LaTeX, 3 figures (included via epsf
Multiplicativity of maximal output purities of Gaussian channels under Gaussian inputs
We address the question of the multiplicativity of the maximal p-norm output
purities of bosonic Gaussian channels under Gaussian inputs. We focus on
general Gaussian channels resulting from the reduction of unitary dynamics in
larger Hilbert spaces. It is shown that the maximal output purity of tensor
products of single-mode channels under Gaussian inputs is multiplicative for
any p>1 for products of arbitrary identical channels as well as for a large
class of products of different channels. In the case of p=2 multiplicativity is
shown to be true for arbitrary products of generic channels acting on any
number of modes.Comment: 9 page
Three-body recombination of ultracold Bose gases using the truncated Wigner method
We apply the truncated Wigner method to the process of three-body
recombination in ultracold Bose gases. We find that within the validity regime
of the Wigner truncation for two-body scattering, three-body recombination can
be treated using a set of coupled stochastic differential equations that
include diffusion terms, and can be simulated using known numerical methods. As
an example we investigate the behaviour of a simple homogeneous Bose gas.Comment: Replaced paper same as original; correction to author list on
cond-mat mad
Implementation of the three-qubit phase-flip error correction code with superconducting qubits
We investigate the performance of a three qubit error correcting code in the
framework of superconducting qubit implementations. Such a code can recover a
quantum state perfectly in the case of dephasing errors but only in situations
where the dephasing rate is low. Numerical studies in previous work have
however shown that the code does increase the fidelity of the encoded state
even in the presence of high error probability, during both storage and
processing. In this work we give analytical expressions for the fidelity of
such a code. We consider two specific schemes for qubit-qubit interaction
realizable in superconducting systems; one -coupling and one
cavity mediated coupling. With these realizations in mind, and considering
errors during storing as well as processing, we calculate the maximum operation
time allowed in order to still benefit from the code. We show that this limit
can be reached with current technology.Comment: 10 pages, 8 figure
Bose-Einstein Condensation from a Rotating Thermal Cloud: Vortex Nucleation and Lattice Formation
We develop a stochastic Gross-Pitaveskii theory suitable for the study of
Bose-Einstein condensation in a {\em rotating} dilute Bose gas. The theory is
used to model the dynamical and equilibrium properties of a rapidly rotating
Bose gas quenched through the critical point for condensation, as in the
experiment of Haljan et al. [Phys. Rev. Lett., 87, 21043 (2001)]. In contrast
to stirring a vortex-free condensate, where topological constraints require
that vortices enter from the edge of the condensate, we find that phase defects
in the initial non-condensed cloud are trapped en masse in the emerging
condensate. Bose-stimulated condensate growth proceeds into a disordered vortex
configuration. At sufficiently low temperature the vortices then order into a
regular Abrikosov lattice in thermal equilibrium with the rotating cloud. We
calculate the effect of thermal fluctuations on vortex ordering in the final
gas at different temperatures, and find that the BEC transition is accompanied
by lattice melting associated with diminishing long range correlations between
vortices across the system.Comment: 15 pages, 12 figure
Characterization of tomographically faithful states in terms of their Wigner function
A bipartite quantum state is tomographically faithful when it can be used as
an input of a quantum operation acting on one of the two quantum systems, such
that the joint output state carries a complete information about the operation
itself. Tomographically faithful states are a necessary ingredient for
tomography of quantum operations and for complete quantum calibration of
measuring apparatuses. In this paper we provide a complete classification of
such states for continuous variables in terms of the Wigner function of the
state. For two-mode Gaussian states faithfulness simply resorts to correlation
between the modes.Comment: 9 pages. IOPAMS style. Some improvement
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