37 research outputs found
A momentum filter for atomic gas
We propose and demonstrate a momentum filter for atomic gas based on a
designed Talbot-Lau interferometer. It consists in two identical optical
standing wave pulses separated by a delay equal to odd multiples of the half
Talbot time. The one dimensional momentum width along the long direction of a
cigar shape condensate is rapidly and greatly purified to a minimum, which
corresponds to the ground state energy of the confining trap in our experiment.
We find good agreement between theoretical analysis and experimental results.
The filter is also effective for non-condensed cold atoms and could be applied
widely.Comment: 9 pages, 6 figures, accepted by New Journal of Physic
Imprinting Light Phase on Matter Wave Gratings in Superradiance Scattering
Superradiance scattering from a Bose-Einstein condensate is studied with a
two-frequency pumping beam. We demonstrate the possibility of fully tuning the
backward mode population as a function of the locked initial relative phase
between the two frequency components of the pumping beam. This result comes
from an imprinting of this initial relative phase on two matter wave gratings,
formed by the forward mode or backward mode condensate plus the condensate at
rest, so that cooperative scattering is affected. A numerical simulation using
a semiclassical model agrees with our observations.Comment: 6 pages, 11 figure
Critical correlations in an ultracold Bose gas revealed by means of a temporal Talbot-Lau interferometer
We study experimentally the critical correlation in an ultra-cold Bose gas
with a temporal Talbot-Lau (TL) interferometer. Near the critical temperature,
we observe a bi-modal density distribution in an ultra-cold Bose gas after the
application of the TL interferometer. The measured fraction of the narrower
peak in the density distribution displays a clear peak within the critical
regime. The peak position agrees with the critical temperature calculated with
the finite-size and interaction corrections. The critical exponents are
extracted from the peak and they agree with the critical exponents for the
correlation length.Comment: 5 pages, 3 figures and supplemental materia
The observation of diffraction phases in matter wave scattering
We study the diffraction phase of different orders via the Dyson expansion
series, for ultracold atomic gases scattered by a standing-wave pulse. As these
diffraction phases are not observable in a single pulse scattering process, a
temporal Talbot-Lau interferometer consisting of two standing-wave pulses is
demonstrated experimentally with a Bose-Einstein condensate to explore this
physical effect. The role of the diffraction phases is clearly shown by the
second standing-wave pulse in the relative population of different momentum
states. Our experiments demonstrate obvious effects beyond the Raman-Nath
method, while agree well with our theory by including the diffraction phases.
In particular, the observed asymmetry in the dependence of the relative
population on the interval between two standing-wave pulses reflects the
diffraction phase differences. The role of interatomic interaction in the
Talbot-Lau interferometer is also discussed.Comment: 7 pages, 3 figures, accepted by Phys. Rev.
Effective preparation and collisional decay of atomic condensate in excited bands of an optical lattice
We present a method for the effective preparation of a Bose-Einstein
condensate (BEC) into the excited bands of an optical lattice via a
standing-wave pulse sequence. With our method, the BEC can be prepared in
either a single Bloch state in a excited-band, or a coherent superposition of
states in different bands. Our scheme is experimentally demonstrated by
preparing a Rb BEC into the -band and the superposition of - and
-band states of a one-dimensional optical lattice, within a few tens of
microseconds. We further measure the decay of the BEC in the -band state,
and carry an analytical calculation for the collisional decay of atoms in the
excited-band states. Our theoretical and experimental results consist well.Comment: 9 pages, 5 figures, Accepted by Phys. Rev.
Manipulating the momentum state of a condensate by sequences of standing wave pulses
We analyze the effects of sequences of standing wave pulses on a
Bose-Einstein condensate (BEC). Experimental observations are in good agreement
with a numerical simulation based on the band structure theory in the optical
lattice. We also demonstrate that a coherent control method based on such
sequences of pulses is very efficient for experimentally designing specific
momentum states.Comment: 6 pages; 5 figures; submitted to PR
Exploring multi-band excitations of interacting Bose gases in a 1D optical lattice by coherent scattering
We use a coherent Bragg diffraction method to impart an external momentum to
ultracold bosonic atoms trapped in a one-dimensional optical lattice. This
method is based on the application of a single light pulse, with conditions
where scattering of photons can be resonantly amplified by the atomic density
grating. An oscillatory behavior of the momentum distribution resulting from
the time evolution in the lattice potential is then observed. By measuring the
oscillating frequencies, we extract multi-band energy structures of
single-particle excitations with zero pseudo-momentum transfer for a wide range
of lattice depths. The excitation energy structures reveal the interaction
effect through the whole range of lattice depth.Comment: 6 pages, 5 figure