117 research outputs found
The Faraday Quantum Clock and Non-local Photon Pair Correlations
We study the use of the Faraday effect as a quantum clock for measuring
traversal times of evanescent photons through magneto-refractive structures.
The Faraday effect acts both as a phase-shifter and as a filter for circular
polarizations. Only measurements based on the Faraday phase-shift properties
are relevant to the traversal time measurements. The Faraday polarization
filtering may cause the loss of non-local (Einstein-Podolsky-Rosen) two-photon
correlations, but this loss can be avoided without sacrificing the clock
accuracy. We show that a mechanism of destructive interference between
consecutive paths is responsible for superluminal traversal times measured by
the clock.Comment: 6 figure
Motion of a condensate in a shaken and vibrating harmonic trap
The dynamics of a Bose-Einstein condensate (BEC) in a time-dependent harmonic
trapping potential is determined for arbitrary variations of the position of
the center of the trap and its frequencies. The dynamics of the BEC wavepacket
is soliton-like. The motion of the center of the wavepacket, and the spatially
and temporally dependent phase (which affects the coherence properties of the
BEC) multiplying the soliton-like part of the wavepacket, are analytically
determined.Comment: Accepted for publication in J. Phys. B: At Mol Opt Phy
Experimental investigation of optical atom traps with a frequency jump
We study the evolution of a trapped atomic cloud subject to a trapping
frequency jump for two cases: stationary and moving center of mass. In the
first case, the frequency jump initiates oscillations in the cloud's momentum
and size. At certain times we find the temperature is significantly reduced.
When the oscillation amplitude becomes large enough, local density increases
induced by the anharmonicity of the trapping potential are observed. In the
second case, the oscillations are coupled to the center of mass motion through
the anharmonicity of the potential. This induces oscillations with even larger
amplitudes, enhancing the temperature reduction effects and leading to
nonisotropic expansion rates while expanding freely.Comment: 8 figures, Journal of Physics B: At. Mol. Op. Phy
Pulsed light beams in vacuum with superluminal and negative group velocities
Gouy's phase of transversally limited pulses can create a strong anomalous
dispersion in vacuum leading to highly superluminal and negative group
velocities. As a consequence, a focusing pulse can diverge beyond the focus
before converging into it. A simple experiment is proposed.Comment: 4 pages, 5 figure
Negative phase time for Scattering at Quantum Wells: A Microwave Analogy Experiment
If a quantum mechanical particle is scattered by a potential well, the wave
function of the particle can propagate with negative phase time. Due to the
analogy of the Schr\"odinger and the Helmholtz equation this phenomenon is
expected to be observable for electromagnetic wave propagation. Experimental
data of electromagnetic wells realized by wave guides filled with different
dielectrics confirm this conjecture now.Comment: 10 pages, 6 figure
Trapping cold atoms using surface-grown carbon nanotubes
We present a feasibility study for loading cold atomic clouds into magnetic
traps created by single-wall carbon nanotubes grown directly onto dielectric
surfaces. We show that atoms may be captured for experimentally sustainable
nanotube currents, generating trapped clouds whose densities and lifetimes are
sufficient to enable detection by simple imaging methods. This opens the way
for a novel type of conductor to be used in atomchips, enabling atom trapping
at sub-micron distances, with implications for both fundamental studies and for
technological applications
Dynamics of a Bose-Einstein Condensate in an Anharmonic Trap
We present a theoretical model to describe the dynamics of Bose-Einstein
condensates in anharmonic trapping potentials. To first approximation the
center-of-mass motion is separated from the internal condensate dynamics and
the problem is reduced to the well known scaling solutions for the Thomas-Fermi
radii. We discuss the validity of this approach and analyze the model for an
anharmonic waveguide geometry which was recently realized in an experiment
\cite{Ott2002c}
Improved Semiclassical Approximation for Bose-Einstein Condensates: Application to a BEC in an Optical Potential
We present semiclassical descriptions of Bose-Einstein condensates for
configurations with spatial symmetry, e.g., cylindrical symmetry, and without
any symmetry. The description of the cylindrical case is quasi-one-dimensional
(Q1D), in the sense that one only needs to solve an effective 1D nonlinear
Schrodinger equation, but the solution incorporates correct 3D aspects of the
problem. The solution in classically allowed regions is matched onto that in
classically forbidden regions by a connection formula that properly accounts
for the nonlinear mean-field interaction. Special cases for vortex solutions
are treated too. Comparisons of the Q1D solution with full 3D and Thomas-Fermi
ones are presented.Comment: 14 pages, 5 figure
Adiabatic Output Coupling of a Bose Gas at Finite Temperatures
We develop a general theory of adiabatic output coupling from trapped atomic
Bose-Einstein Condensates at finite temperatures. For weak coupling, the output
rate from the condensate, and the excited levels in the trap, settles in a time
proportional to the inverse of the spectral width of the coupling to the output
modes. We discuss the properties of the output atoms in the quasi-steady-state
where the population in the trap is not appreciably depleted. We show how the
composition of the output beam, containing condensate and thermal component,
may be controlled by changing the frequency of the output coupler. This
composition determines the first and second order coherence of the output beam.
We discuss the changes in the composition of the bose gas left in the trap and
show how nonresonant output coupling can stimulate either the evaporation of
thermal excitations in the trap or the growth of non-thermal excitations, when
pairs of correlated atoms leave the condensate.Comment: 22 pages, 6 Figs. To appear in Physical Review A All the typos from
the previous submission have been fixe
Coherent Tunneling of Atoms from Bose-condensed Gases at Finite Temperatures
Tunneling of atoms between two trapped Bose-condensed gases at finite
temperatures is explored using a many-body linear response tunneling formalism
similar to that used in superconductors. To lowest order, the tunneling
currents can be expressed quite generally in terms of the single-particle
Green's functions of the isolated Bose gases. A coherent first-order tunneling
Josephson current between two atomic Bose-condensates is found, in addition to
coherent and dissipative contributions from second-order
condensate-noncondensate and noncondensate-noncondensate tunneling. Our work is
a generalization of Meier and Zwerger, who recently treated tunneling between
uniform atomic Bose gases. We apply our formalism to the analysis of an
out-coupling experiment induced by light wave fields, using a simple
Bogoliubov-Popov quasiparticle approximation for the trapped Bose gas. For
tunneling into the vacuum, we recover the results of Japha, Choi, Burnett and
Band, who recently pointed out the usefulness of studying the spectrum of
out-coupled atoms. In particular, we show that the small tunneling current of
noncondensate atoms from a trapped Bose gas has a broad spectrum of energies,
with a characteristic structure associated with the Bogoliubov quasiparticle
u^2 and v^2 amplitudes.Comment: 26 pages, 5 figures, minor changes, to appear in PR
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