260 research outputs found
Weak force detection using a double Bose-Einstein condensate
A Bose-Einstein condensate may be used to make precise measurements of weak
forces, utilizing the macroscopic occupation of a single quantum state. We
present a scheme which uses a condensate in a double well potential to do this.
The required initial state of the condensate is discussed, and the limitations
on the sensitivity due to atom collisions and external coupling are analyzed.Comment: 12 pages, 2 figures, Eq.(41) has been correcte
Bose-Einstein condensate collapse: a comparison between theory and experiment
We solve the Gross-Pitaevskii equation numerically for the collapse induced
by a switch from positive to negative scattering lengths. We compare our
results with experiments performed at JILA with Bose-Einstein condensates of
Rb-85, in which the scattering length was controlled using a Feshbach
resonance. Building on previous theoretical work we identify quantitative
differences between the predictions of mean-field theory and the results of the
experiments. Besides the previously reported difference between the predicted
and observed critical atom number for collapse, we also find that the predicted
collapse times systematically exceed those observed experimentally. Quantum
field effects, such as fragmentation, that might account for these
discrepancies are discussed.Comment: 4 pages, 2 figure
Optimally squeezed spin states
We consider optimally spin-squeezed states that maximize the sensitivity of
the Ramsey spectroscopy, and for which the signal to noise ratio scales as the
number of particles . Using the variational principle we prove that these
states are eigensolutions of the Hamiltonian
and that, for large , the states become equivalent to the quadrature
squeezed states of the harmonic oscillator. We present numerical results that
illustrate the validity of the equivalence
Ground State and Quasiparticle Spectrum of a Two Component Bose-Einstein Condensate
We consider a dilute atomic Bose-Einstein condensate with two non-degenerate
internal energy levels. The presence of an external radiation field can result
in new ground states for the condensate which result from the lowering of the
condensate energy due to the interaction energy with the field. In this
approach there are no instabilities in the quasiparticle spectrum as was
previously found by Goldstein and Meystre (Phys. Rev. A \QTR{bf}{55}, 2935
(1997)).Comment: 20 pages, 2 figures RevTex. Submitted to Phys. Rev. A; Revised
versio
Dissipative Dynamics of a Josephson Junction In the Bose-Gases
The dissipative dynamics of a Josephson junction in the Bose-gases is
considered within the framework of the model of a tunneling Hamiltonian. The
effective action which describes the dynamics of the phase difference across
the junction is derived using functional integration method. The dynamic
equation obtained for the phase difference across the junction is analyzed for
the finite temperatures in the low frequency limit involving the radiation
terms. The asymmetric case of the Bose-gases with the different order
parameters is calculated as well
Evolution of the macroscopically entangled states in optical lattices
We consider dynamics of boson condensates in finite optical lattices under a
slow external perturbation which brings the system to the unstable equilibrium.
It is shown that quantum fluctuations drive the condensate into the maximally
entangled state. We argue that the truncated Wigner approximation being a
natural generalization of the Gross-Pitaevskii classical equations of motion is
adequate to correctly describe the time evolution including both collapse and
revival of the condensate.Comment: 14 pages, 10 figures, Discussion of reversibility of entanglement is
adde
Dynamics and Berry phase of two-species Bose-Einstein condensates
In terms of exact solutions of the time-dependent Schrodinger equation for an
effective giant spin modeled from a coupled two-mode Bose-Einstein condensate
(BEC) with adiabatic and cyclic time-varying Raman coupling between two
hyperfine states of the BEC, we obtain analytic time-evolution formulas of the
population imbalance and relative phase between two components with various
initial states, especially the SU(2)coherent state. We find the Berry phase
depending on the number parity of atoms, and particle number dependence of the
collapse revival of population-imbalance oscillation. It is shown that
self-trapping and phase locking can be achieved from initial SU(2) coherent
states with proper parameters.Comment: 18 pages,5 figure
Decoherence in Bose-Einstein Condensates: towards Bigger and Better Schroedinger Cats
We consider a quantum superposition of Bose-Einstein condensates in two
immiscible internal states. A decoherence rate for the resulting Schroedinger
cat is calculated and shown to be a significant threat to this macroscopic
quantum superposition of BEC's. An experimental scenario is outlined where the
decoherence rate due to the thermal cloud is dramatically reduced thanks to
trap engineering and "symmetrization" of the environment which allow for the
Schroedinger cat to be an approximate pointer states.Comment: 12 pages in RevTex; improved presentation; a new comment on
decoherence-free pointer subspaces in BEC; accepted in Phys.Rev.
Testing Broken U(1) Symmetry in a Two-Component Atomic Bose-Einstein Condensate
We present a scheme for determining if the quantum state of a small trapped
Bose-Einstein condensate is a state with well defined number of atoms, a Fock
state, or a state with a broken U(1) gauge symmetry, a coherent state. The
proposal is based on the observation of Ramsey fringes. The population
difference observed in a Ramsey fringe experiment will exhibit collapse and
revivals due to the mean-field interactions. The collapse and revival times
depend on the relative strength of the mean-field interactions for the two
components and the initial quantum state of the condensate.Comment: 20 Pages RevTex, 3 Figure
Quantum corrections to the dynamics of interacting bosons: beyond the truncated Wigner approximation
We develop a consistent perturbation theory in quantum fluctuations around
the classical evolution of a system of interacting bosons. The zero order
approximation gives the classical Gross-Pitaevskii equations. In the next order
we recover the truncated Wigner approximation, where the evolution is still
classical but the initial conditions are distributed according to the Wigner
transform of the initial density matrix. Further corrections can be
characterized as quantum scattering events, which appear in the form of a
nonlinear response of the observable to an infinitesimal displacement of the
field along its classical evolution. At the end of the paper we give a few
numerical examples to test the formalism.Comment: published versio
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