2,558 research outputs found
Heating rates for an atom in a far-detuned optical lattice
We calculate single atom heating rates in a far detuned optical lattice, in
connection with recent experiments. We first derive a master equation,
including a realistic atomic internal structure and a quantum treatment of the
atomic motion in the lattice. The experimental feature that optical lattices
are obtained by superimposing laser standing waves of different frequencies is
also included, which leads to a micromotional correction to the light shift
that we evaluate. We then calculate, and compare to experimental results, two
heating rates, the "total" heating rate (corresponding to the increase of the
total mechanical energy of the atom in the lattice), and the ground bande
heating rate (corresponding to the increase of energy within the ground energy
band of the lattice).Comment: 11 pages, 3 figures, 1 tabl
Resonances for a Hydrogenic System or a Harmonic Oscillator Strongly Coupled to a Field
We calculate resonances which are formed by a particle in a potential which
is either Coulombian or quadratic when the particle is strongly coupled to a
massless boson, taking only two energy levels into consideration. From these
calculations we derive how the moving away of the particle from its attraction
center goes together with the energy lowering of hybrid states that this
particle forms with the field. We study the width of these states and we show
that stable states may also appear in the coupling.Comment: 17 pages, 6 figure
Decays in Quantum Hierarchical Models
We study the dynamics of a simple model for quantum decay, where a single
state is coupled to a set of discrete states, the pseudo continuum, each
coupled to a real continuum of states. We find that for constant matrix
elements between the single state and the pseudo continuum the decay occurs via
one state in a certain region of the parameters, involving the Dicke and
quantum Zeno effects. When the matrix elements are random several cases are
identified. For a pseudo continuum with small bandwidth there are weakly damped
oscillations in the probability to be in the initial single state. For
intermediate bandwidth one finds mesoscopic fluctuations in the probability
with amplitude inversely proportional to the square root of the volume of the
pseudo continuum space. They last for a long time compared to the non-random
case
Nonlinear Faraday Rotation and Superposition-State Detection in Cold Atoms
We report on the first observation of nonlinear Faraday rotation with cold
atoms at a temperature of ~100 uK. The observed nonlinear rotation of the light
polarization plane is up to 0.1 rad over the 1 mm size atomic cloud in
approximately 10 mG magnetic field. The nonlinearity of rotation results from
long-lived coherence of ground-state Zeeman sublevels created by a
near-resonant light. The method allows for creation, detection and control of
atomic superposition states. It also allows applications for precision
magnetometry with high spatial and temporal resolution.Comment: 5 pages, 6 figure
Decoherence and dephasing in strongly driven colliding Bose-Einstein condensates
We report on a series of measurements of decoherence and wavepacket dephasing
between two colliding, strongly coupled, identical Bose-Einstein condensates.
We measure, in the strong excitation regime, a suppression of the mean-field
shift, compared to the shift which is observed for a weak excitation. This
suppression is explained by applying the Gross-Pitaevskii energy functional. By
selectively counting only the non-decohered fraction in a time of flight image
we observe oscillations for which both inhomogeneous and Doppler broadening are
suppressed, in quantitative agreement with a full Gross-Pitaevskii equation
simulation. If no post selection is used, the decoherence rate due to
collisions can be extracted, and is in agreement with the local density average
calculated rate.Comment: 4 pages, 5 figure
Slow quench dynamics of periodically driven quantum gases
We study the evolution of bosons in a periodically driven optical lattice
during a slow change of the driving amplitude. Both the regime of high
frequency and low frequency driving are investigated. In the low frequency
regime, resonant absorption of energy is observed. In the high frequency
regime, the dynamics is compared to a system with an effective Hamiltonian in
which the atoms are `dressed' by the driving field. This `dressing' can
dramatically change the amplitude and sign of the effective tunneling. A
particular focus of this study is the investigation of the time-scales
necessary for the evolving quantum state to follow almost adiabatically to the
ground-state of the effective many body system.Comment: 10 pages, 8 figure
On the consequences of the fact that atomic levels have a certain width
This note presents two ideas. The first one is that quantum theory has a
fundamentally perturbative basis but leads to nonperturbative states which it
would seem natural to take into account in the foundation of a theory of
quantum phenomena. The second one consists in questioning the validity of the
present notion of time. Both matters are related to the fact that atomic levels
have a certain width. This note is presented qualitatively so as to evidence
its main points, independently of the models on which these have been tested.Comment: 8 page
Thermal breakdown of coherent backscattering: a case study of quantum duality
We investigate coherent backscattering of light by two harmonically trapped
atoms in the light of quantitative quantum duality. Including recoil and
Doppler shift close to an optical resonance, we calculate the interference
visibility as well as the amount of which-path information, both for zero and
finite temperature.Comment: published version with minor changes and an added figur
Measurement of the ac Stark shift with a guided matter-wave interferometer
We demonstrate the effectiveness of a guided-wave Bose-Einstein condensate
interferometer for practical measurements. Taking advantage of the large arm
separations obtainable in our interferometer, the energy levels of the 87Rb
atoms in one arm of the interferometer are shifted by a calibrated laser beam.
The resulting phase shifts are used to determine the ac polarizability at a
range of frequencies near and at the atomic resonance. The measured values are
in good agreement with theoretical expectations. However, we observe a
broadening of the transition near the resonance, an indication of collective
light scattering effects. This nonlinearity may prove useful for the production
and control of squeezed quantum states.Comment: 5 pages, three figure
Entanglement swapping between spacelike separated atoms
We show a mechanism that projects a pair of neutral two-level atoms from an
initially uncorrelated state to a maximally entangled state while they remain
spacelike separated. The atoms begin both excited in a common electromagnetic
vacuum, and the radiation is collected with a partial Bell-state analyzer. If
the interaction time is short enough and a certain two-photon Bell state is
detected after the interaction, a high degree of entanglement, even maximal,
can be generated while one atom is outside the light cone of the other, for
arbitrary large interatomic distances.Comment: v2: version accepted in Phys. Rev.
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