768 research outputs found
Time interval distributions of atoms in atomic beams
We report on the experimental investigation of two-particle correlations
between neutral atoms in a Hanbury Brown and Twiss experiment. Both an atom
laser beam and a pseudo-thermal atomic beam are extracted from a Bose-Einstein
condensate and the atom flux is measured with a single atom counter. We
determine the conditional and the unconditional detection probabilities for the
atoms in the beam and find good agreement with the theoretical predictions.Comment: 4 pages, 3 figure
Keldysh Green's function approach to coherence in a non-equilibrium steady state: connecting Bose-Einstein condensation and lasing
Solid state quantum condensates often differ from previous examples of
condensates (such as Helium, ultra-cold atomic gases, and superconductors) in
that the quasiparticles condensing have relatively short lifetimes, and so as
for lasers, external pumping is required to maintain a steady state. On the
other hand, compared to lasers, the quasiparticles are generally more strongly
interacting, and therefore better able to thermalise. This leads to questions
of how to describe such non-equilibrium condensates, and their relation to
equilibrium condensates and lasers. This chapter discusses in detail how the
non-equilibrium Green's function approach can be applied to the description of
such a non-equilibrium condensate, in particular, a system of microcavity
polaritons, driven out of equilibrium by coupling to multiple baths. By
considering the steady states, and fluctuations about them, it is possible to
provide a description that relates both to equilibrium condensation and to
lasing, while at the same time, making clear the differences from simple
lasers
Raman coupler for a trapped two-component quantum-degenerate Fermi gas
We investigate theoretically the Raman coupling between two internal states
of a trapped low-density quantum-degenerate Fermi gas. In general, the trap
frequencies associated with the two internal states can be different, leading
to the onset of collapses and revivals in the population difference of the two
internal states. This behavior can be changed drastically by two-body
collisions. In particular, we show that under appropriate conditions they can
suppress the dephasing leading to the collapse of the population difference,
and restore almost full Rabi oscillations between the two internal states.
These results are compared and contrasted to those for a quantum-degenerate
bosonic gas.Comment: 7 pages incl. 7 PostScript figures (.eps), LaTeX using RevTeX4,
submitted to Phys. Rev. A, modified versio
Higher-order mutual coherence of optical and matter waves
We use an operational approach to discuss ways to measure the higher-order
cross-correlations between optical and matter-wave fields. We pay particular
attention to the fact that atomic fields actually consist of composite
particles that can easily be separated into their basic constituents by a
detection process such as photoionization. In the case of bosonic fields, that
we specifically consider here, this leads to the appearance in the detection
signal of exchange contributions due to both the composite bosonic field and
its individual fermionic constituents. We also show how time-gated counting
schemes allow to isolate specific contributions to the signal, in particular
involving different orderings of the Schr\"odinger and Maxwell fields.Comment: 11 pages, 2 figure
Input-output theory for fermions in an atom cavity
We generalize the quantum optical input-output theory developed for optical
cavities to ultracold fermionic atoms confined in a trapping potential, which
forms an "atom cavity". In order to account for the Pauli exclusion principle,
quantum Langevin equations for all cavity modes are derived. The dissipative
part of these multi-mode Langevin equations includes a coupling between cavity
modes. We also derive a set of boundary conditions for the Fermi field that
relate the output fields to the input fields and the field radiated by the
cavity. Starting from a constant uniform current of fermions incident on one
side of the cavity, we use the boundary conditions to calculate the occupation
numbers and current density for the fermions that are reflected and transmitted
by the cavity
Continuous loading of a magnetic trap
We have realized a scheme for continuous loading of a magnetic trap (MT).
^{52}Cr atoms are continuously captured and cooled in a magneto-optical trap
(MOT). Optical pumping to a metastable state decouples atoms from the cooling
light. Due to their high magnetic moment (6 Bohr magnetons), low-field seeking
metastable atoms are trapped in the magnetic quadrupole field provided by the
MOT. Limited by inelastic collisions between atoms in the MOT and in the MT, we
load 10^8 metastable atoms at a rate of 10^8 atoms/s below 100 microkelvin into
the MT. After loading we can perform optical repumping to realize a MT of
ground state chromium atoms.Comment: 4 pages, 4 figures, version 2, modified references, included
additional detailed information, minor changes in figure 3 and in tex
Expansion of a Bose-Einstein Condensate in an atomic waveguide
The expansion of a Bose-Einstein condensate in an atomic waveguide is
analyzed. We study different regimes of expansion, and identify a transient
regime between one-dimensional and three-dimensional dynamics, in which the
properties of the condensate and its further expansion can be well explained by
reducing the transversal dynamics to a two-level system. The relevance of this
regime in current experiments is discussed.Comment: 4 pages, 3 figs, Accepted for publication in Phys. Rev.
Coherent dynamics of Bose-Einstein condensates in high-finesse optical cavities
We study the mutual interaction of a Bose-Einstein condensed gas with a
single mode of a high-finesse optical cavity. We show how the cavity
transmission reflects condensate properties and calculate the self-consistent
intra-cavity light field and condensate evolution. Solving the coupled
condensate-cavity equations we find that while falling through the cavity, the
condensate is adiabatically transfered into the ground state of the periodic
optical potential. This allows time dependent non-destructive measurements on
Bose-Einstein condensates with intriguing prospects for subsequent controlled
manipulation.Comment: 5 pages, 5 figures; revised version: added reference
Quantum Limits of Stochastic Cooling of a Bosonic Gas
The quantum limits of stochastic cooling of trapped atoms are studied. The
energy subtraction due to the applied feedback is shown to contain an
additional noise term due to atom-number fluctuations in the feedback region.
This novel effect is shown to dominate the cooling efficiency near the
condensation point. Furthermore, we show first results that indicate that
Bose--Einstein condensation could be reached via stochastic cooling.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Hydrodynamic behavior in expanding thermal clouds of Rb-87
We study hydrodynamic behavior in expanding thermal clouds of Rb-87 released
from an elongated trap. At our highest densities the mean free path is smaller
than the radial size of the cloud. After release the clouds expand
anisotropically. The cloud temperature drops by as much as 30%. This is
attributed to isentropic cooling during the early stages of the expansion. We
present an analytical model to describe the expansion and to estimate the
cooling. Important consequences for time-of-flight thermometry are discussed.Comment: 7 pages with 2 figure
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