2,175 research outputs found
Two-photon nonlinearity in general cavity QED systems
We have investigated the two-photon nonlinearity at general cavity QED
systems, which covers both weak and strong coupling regimes and includes
radiative loss from the atom. The one- and two-photon propagators are obtained
in analytic forms. By surveying both coupling regimes, we have revealed the
conditions on the photonic wavepacket for yielding large nonlinearity depending
on the cavity Q-value. We have also discussed the effect of radiative loss on
the nonlinearity.Comment: 8 pages, 5 figure
Optimized phase switching using a single atom nonlinearity
We show that a nonlinear phase shift of pi can be obtained by using a single
two level atom in a one sided cavity with negligible losses. This result
implies that the use of a one sided cavity can significantly improve the pi/18
phase shift previously observed by Turchette et al. [Phys. Rev. Lett. 75, 4710
(1995)].Comment: 6 pages, 3 figures, added comments on derivation and assumption
Energy level statistics for models of coupled single-mode Bose--Einstein condensates
We study the distribution of energy level spacings in two models describing
coupled single-mode Bose-Einstein condensates. Both models have a fixed number
of degrees of freedom, which is small compared to the number of interaction
parameters, and is independent of the dimensionality of the Hilbert space. We
find that the distribution follows a universal Poisson form independent of the
choice of coupling parameters, which is indicative of the integrability of both
models. These results complement those for integrable lattice models where the
number of degrees of freedom increases with increasing dimensionality of the
Hilbert space. Finally, we also show that for one model the inclusion of an
additional interaction which breaks the integrability leads to a non-Poisson
distribution.Comment: 5 pages, 4 figures, revte
Remote generation of entanglement for individual atoms via optical fibers
The generation of atomic entanglement is discussed in a system that atoms are
trapped in separate cavities which are connected via optical fibers. Two
distant atoms can be projected to Bell-state by synchronized turning off the
local laser fields and then performing a single quantum measurement by a
distant controller. The distinct advantage of this scheme is that it works in a
regime that , which makes the scheme insensitive to
cavity strong leakage. Moreover, the fidelity is not affected by atomic
spontaneous emission.Comment: 4 pages, 3 figure
Autofeedback scheme for preservation of macroscopic coherence in microwave cavities
We present a scheme for controlling the decoherence of a linear superposition
of two coherent states with opposite phases in a high-Q microwave cavity, based
on the injection of appropriately prepared ``probe'' and ``feedback'' Rydberg
atoms, improving the one presented in [D. Vitali et al., Phys. Rev. Lett. 79,
2442 (1997)]. In the present scheme, the information transmission from the
probe to the feedback atom is directly mediated by a second auxiliary cavity.
The detection efficiency for the probe atom is no longer a critical parameter,
and the decoherence time of the superposition state can be significantly
increased using presently available technology.Comment: revtex, 15 pages, 4 eps figure
Influence of a classical homogeneous gravitational field on dissipative dynamics of the Jaynes-Cummings model with phase damping
In this paper, we study the dissipative dynamics of the Jaynes-Cummings model
with phase damping in the presence of a classical homogeneous gravitational
field. The model consists of a moving two-level atom simultaneously exposed to
the gravitational field and a single-mode traveling radiation field in the
presence of the phase damping. We present a quantum treatment of the internal
and external dynamics of the atom based on an alternative su(2) dynamical
algebraic structure. By making use of the super-operator technique, we obtain
the solution of the master equation for the density operator of the quantum
system, under the Markovian approximation. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, we investigate the influence of gravity on the
temporal evolution of collapses and revivals of the atomic population
inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting
statistics and quadrature squeezing of the radiation field in the presence of
phase damping.Comment: 25 pages, 15 figure
Algebraic Bethe ansatz method for the exact calculation of energy spectra and form factors: applications to models of Bose-Einstein condensates and metallic nanograins
In this review we demonstrate how the algebraic Bethe ansatz is used for the
calculation of the energy spectra and form factors (operator matrix elements in
the basis of Hamiltonian eigenstates) in exactly solvable quantum systems. As
examples we apply the theory to several models of current interest in the study
of Bose-Einstein condensates, which have been successfully created using
ultracold dilute atomic gases. The first model we introduce describes Josephson
tunneling between two coupled Bose-Einstein condensates. It can be used not
only for the study of tunneling between condensates of atomic gases, but for
solid state Josephson junctions and coupled Cooper pair boxes. The theory is
also applicable to models of atomic-molecular Bose-Einstein condensates, with
two examples given and analysed. Additionally, these same two models are
relevant to studies in quantum optics. Finally, we discuss the model of
Bardeen, Cooper and Schrieffer in this framework, which is appropriate for
systems of ultracold fermionic atomic gases, as well as being applicable for
the description of superconducting correlations in metallic grains with
nanoscale dimensions. In applying all of the above models to physical
situations, the need for an exact analysis of small scale systems is
established due to large quantum fluctuations which render mean-field
approaches inaccurate.Comment: 49 pages, 1 figure, invited review for J. Phys. A., published version
available at http://stacks.iop.org/JPhysA/36/R6
Nonlinear Decoherence in Quantum State Preparation of a Trapped Ion
We present a nonlinear decoherence model which models decoherence effect
caused by various decohereing sources in a quantum system through a nonlinear
coupling between the system and its environment, and apply it to investigating
decoherence in nonclassical motional states of a single trapped ion. We obtain
an exactly analytic solution of the model and find very good agreement with
experimental results for the population decay rate of a single trapped ion
observed in the NIST experiments by Meekhof and coworkers (D. M. Meekhof, {\it
et al.}, Phys. Rev. Lett. {\bf 76}, 1796 (1996)).Comment: 5 pages, Revte
Quantum State Protection in Cavities
We show how an initially prepared quantum state of a radiation mode in a
cavity can be preserved for a long time using a feedback scheme based on the
injection of appropriately prepared atoms. We present a feedback scheme both
for optical cavities, which can be continuously monitored by a photodetector,
and for microwave cavities, which can be monitored only indirectly via the
detection of atoms that have interacted with the cavity field. We also discuss
the possibility of applying these methods for decoherence control in quantum
information processing.Comment: RevTex, 9 figures, submitted to Phys. Rev.
Optimal squeezing, pure states, and amplification of squeezing in resonance fluorescence
It is shown that 100% squeezed output can be produced in the resonance
fluorescence from a coherently driven two-level atom interacting with a
squeezed vacuum. This is only possible for squeezed input, and is
associated with a pure atomic state, i.e., a completely polarized state. The
quadrature for which optimal squeezing occurs depends on the squeezing phase
the Rabi frequency and the atomic detuning . Pure
states are described for arbitrary not just or as in
previous work. For small values of there may be a greater degree of
squeezing in the output field than the input - i.e., we have squeezing
amplification.Comment: 6 pages & 7 figures, Submitted to Phys. Rev.
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