32 research outputs found
A high frequency optical trap for atoms using Hermite-Gaussian beams
We present an experimental method to create a single high frequency optical
trap for atoms based on an elongated Hermite-Gaussian TEM01 mode beam. This
trap results in confinement strength similar to that which may be obtained in
an optical lattice. We discuss an optical setup to produce the trapping beam
and then detail a method to load a Bose-Einstein Condensate (BEC) into a TEM01
trap. Using this method, we have succeeded in producing individual highly
confined lower dimensional condensates.Comment: 9 pages, 5 figure
Vibronic "Rabi resonances" in harmonic and hard-wall ion-traps for arbitrary laser intensity and detuning
We investigate laser-driven vibronic transitions of a single two-level atomic
ion in harmonic and hard wall traps. In the Lamb-Dicke regime, for tuned or
detuned lasers with respect to the internal frequency of the ion, and weak or
strong laser intensities, the vibronic transitions occur at well isolated "Rabi
Resonances", where the detuning-adapted Rabi frequency coincides with the level
spacing of the vibrational modes. These vibronic resonances are characterized
as avoided crossings of the dressed levels (eigenvalues of the full
Hamiltonian). Their peculiarities due to symmetry constraints and trapping
potential are also examined.Comment: 7 pages, 4 figure
Bose Einstein Condensate in a Box
Bose-Einstein condensates have been produced in an optical box trap. This
novel optical trap type has strong confinement in two directions comparable to
that which is possible in an optical lattice, yet produces individual
condensates rather than the thousands typical of a lattice. The box trap is
integrated with single atom detection capability, paving the way for studies of
quantum atom statistics.Comment: 4 pages, 5 figure
Decay by tunneling of Bosonic and Fermionic Tonks-Girardeau Gases
We study the tunneling dynamics of bosonic and fermionic Tonks-Girardeau
gases from a hard wall trap, in which one of the walls is substituted by a
delta potential. Using the Fermi-Bose map, the decay of the probability to
remain in the trap is studied as a function of both the number of particles and
the intensity of the end-cap delta laser. The fermionic gas is shown to be a
good candidate to study deviations of the non-exponential decay of the
single-particle type, whereas for the bosonic case a novel regime of
non-exponential decay appears due to the contributions of different resonances
of the trap
Free expansion of impenetrable bosons on one-dimensional optical lattices
We review recent exact results for the free expansion of impenetrable bosons
on one-dimensional lattices, after switching off a confining potential. When
the system is initially in a superfluid state, far from the regime in which the
Mott-insulator appears in the middle of the trap, the momentum distribution of
the expanding bosons rapidly approaches the momentum distribution of
noninteracting fermions. Remarkably, no loss in coherence is observed in the
system as reflected by a large occupation of the lowest eigenstate of the
one-particle density matrix. In the opposite limit, when the initial system is
a pure Mott insulator with one particle per lattice site, the expansion leads
to the emergence of quasicondensates at finite momentum. In this case,
one-particle correlations like the ones shown to be universal in the
equilibrium case develop in the system. We show that the out-of-equilibrium
behavior of the Shannon information entropy in momentum space, and its contrast
with the one of noninteracting fermions, allows to differentiate the two
different regimes of interest. It also helps in understanding the crossover
between them.Comment: 21 pages, 14 figures, invited brief revie
Dynamics of a Tonks-Girardeau gas released from a hard-wall trap
We study the expansion dynamics of a Tonks-Girardeau gas released from a hard
wall trap. Using the Fermi-Bose map, the density profile is found analytically
and shown to differ from that one of a classical gas in the microcanonical
ensemble even at macroscopic level, for any observation time larger than a
critical time. The relevant time scale arises as a consequence of
fermionization.Comment: 4 pages, 6 figure
Collective Excitations of Bose-Einstein Condensates in a Double-Well Potential
We investigate collective excitations of Bose-Einstein condensates at
absolute zero in a double-well trap. We solve the Bogoliubov equations with a
double-well trap, and show that the crossover from the dipole mode to the
Josephson plasma mode occurs in the lowest energy excitation. It is found that
the anomalous tunneling property of low energy excitations is crucial to the
crossover.Comment: 14 pages, 6 figure
Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas
We report the direct observation of sub-Poissonian number fluctuation for a
degenerate Bose gas confined in an optical trap. Reduction of number
fluctuations below the Poissonian limit is observed for average numbers that
range from 300 to 60 atoms.Comment: 5 pages, 4 figure
Conduction of Ultracold Fermions Through a Mesoscopic Channel
In a mesoscopic conductor electric resistance is detected even if the device
is defect-free. We engineer and study a cold-atom analog of a mesoscopic
conductor. It consists of a narrow channel connecting two macroscopic
reservoirs of fermions that can be switched from ballistic to diffusive. We
induce a current through the channel and find ohmic conduction, even for a
ballistic channel. An analysis of in-situ density distributions shows that in
the ballistic case the chemical potential drop occurs at the entrance and exit
of the channel, revealing the presence of contact resistance. In contrast, a
diffusive channel with disorder displays a chemical potential drop spread over
the whole channel. Our approach opens the way towards quantum simulation of
mesoscopic devices with quantum gases
Matter-wave diffraction in time with a linear potential
Diffraction in time of matter waves incident on a shutter which is removed at
time is studied in the presence of a linear potential. The solution is
also discussed in phase space in terms of the Wigner function. An alternative
configuration relevant to current experiments where particles are released from
a hard wall trap is also analyzed for single-particle states and for a
Tonks-Girardeau gas.Comment: 11 pages, 6 figure