45 research outputs found
Mach-Zehnder Bragg interferometer for a Bose-Einstein Condensate
We construct a Mach-Zehnder interferometer using Bose-Einstein condensed
rubidium atoms and optical Bragg diffraction. In contrast to interferometers
based on normal diffraction, where only a small percentage of the atoms
contribute to the signal, our Bragg diffraction interferometer uses all the
condensate atoms. The condensate coherence properties and high phase-space
density result in an interference pattern of nearly 100% contrast. In
principle, the enclosed area of the interferometer may be arbitrarily large,
making it an ideal tool that could be used in the detection of vortices, or
possibly even gravitational waves.Comment: 10 pages, 3 figures, Quantum Electronics and Laser Science Conference
1999, Postdeadline papers QPD12-
Resolved diffraction patterns from a reflection grating for atoms
We have studied atomic diffraction at normal incidence from an evanescent
standing wave with a high resolution using velocity selective Raman
transitions. We have observed up to 3 resolved orders of diffraction, which are
well accounted for by a scalar diffraction theory. In our experiment the
transverse coherence length of the source is greater than the period of the
diffraction grating.Comment: 8 pages, 4 figure
Diffraction of complex molecules by structures made of light
We demonstrate that structures made of light can be used to coherently
control the motion of complex molecules. In particular, we show diffraction of
the fullerenes C60 and C70 at a thin grating based on a standing light wave. We
prove experimentally that the principles of this effect, well known from atom
optics, can be successfully extended to massive and large molecules which are
internally in a thermodynamic mixed state and which do not exhibit narrow
optical resonances. Our results will be important for the observation of
quantum interference with even larger and more complex objects.Comment: 4 pages, 3 figure
Coherent Control of Atomic Beam Diffraction by Standing Light
Quantum interference is shown to deliver a means of regulating the
diffraction pattern of a thermal atomic beam interacting with two standing wave
electric fields. Parameters have been identified to enhance the diffraction
probability of one momentum component over the others, with specific
application to Rb atoms.Comment: 5 figure
Gravitational-wave Detection With Matter-wave Interferometers Based On Standing Light Waves
We study the possibility of detecting gravitational-waves with matter-wave
interferometers, where atom beams are split, deflected and recombined totally
by standing light waves. Our calculation shows that the phase shift is
dominated by terms proportional to the time derivative of the gravitational
wave amplitude. Taking into account future improvements on current
technologies, it is promising to build a matter-wave interferometer detector
with desired sensitivity.Comment: 7 pages, 3 figures. To be published in General Relativity and
Gravitatio
Bloch-Like Quantum Multiple Reflections of Atoms
We show that under certain circumstances an atom can follow an oscillatory
motion in a periodic laser profile with a Gaussian envelope. These oscillations
can be well explained by using a model of energetically forbidden spatial
regions. The similarities and differences with Bloch oscillations are
discussed. We demonstrate that the effect exists not only for repulsive but
also for attractive potentials, i.e. quantum multiple reflections are also
possible.Comment: LaTeX, 7 pages, 7 figure
Talbot Oscillations and Periodic Focusing in a One-Dimensional Condensate
An exact theory for the density of a one-dimensional Bose-Einstein condensate
with hard core particle interactions is developed in second quantization and
applied to the scattering of the condensate by a spatially periodic impulse
potential. The boson problem is mapped onto a system of free fermions obeying
the Pauli exclusion principle to facilitate the calculation. The density
exhibits a spatial focusing of the probability density as well as a periodic
self-imaging in time, or Talbot effect. Furthermore, the transition from single
particle to many body effects can be measured by observing the decay of the
modulated condensate density pattern in time. The connection of these results
to classical and atom optical phase gratings is made explicit
Planck's scale dissipative effects in atom interferometry
Atom interferometers can be used to study phenomena leading to
irreversibility and dissipation, induced by the dynamics of fundamental objects
(strings and branes) at a large mass scale. Using an effective, but physically
consistent description in terms of a master equation of Lindblad form, the
modifications of the interferometric pattern induced by the new phenomena are
analyzed in detail. We find that present experimental devices can in principle
provide stringent bounds on the new effects.Comment: 12 pages, plain-Te
High resolution amplitude and phase gratings in atom optics
An atom-field geometry is chosen in which an atomic beam traverses a field
interaction zone consisting of three fields, one having frequency propagating in the direction and the other two having
frequencies and propagating in the
- direction. For and , where and are positive integers and
is the pulse duration in the atomic rest frame, the atom-field interaction
results in the creation of atom amplitude and phase gratings having period . In this manner, one can use optical fields having
wavelength to produce atom gratings having periodicity much less
than .Comment: 11 pages, 14 figure
Activity of Bdellovibrio Hit Locus Proteins, Bd0108 and Bd0109, Links Type IVa Pilus Extrusion/Retraction Status to Prey-Independent Growth Signalling
Bdellovibrio bacteriovorus are facultatively predatory bacteria that grow within gram-negative prey, using pili to
invade their periplasmic niche. They also grow prey-independently on organic nutrients after undergoing a reversible
switch. The nature of the growth switching mechanism has been elusive, but several independent reports suggested
mutations in the hit (host-interaction) locus on the Bdellovibrio genome were associated with the transition to preyindependent
growth. Pili are essential for prey entry by Bdellovibrio and sequence analysis of the hit locus predicted
that it was part of a cluster of Type IVb pilus-associated genes, containing bd0108 and bd0109. In this study we have
deleted the whole bd0108 gene, which is unique to Bdellovibrio, and compared its phenotype to strains containing
spontaneous mutations in bd0108 and the common natural 42 bp deletion variant of bd0108. We find that deletion of
the whole bd0108 gene greatly reduced the extrusion of pili, whereas the 42 bp deletion caused greater pilus
extrusion than wild-type. The pili isolated from these strains were comprised of the Type IVa pilin protein; PilA.
Attempts to similarly delete gene bd0109, which like bd0108 encodes a periplasmic/secreted protein, were not
successful, suggesting that it is likely to be essential for Bdellovibrio viability in any growth mode. Bd0109 has a
sugar binding YD- repeat motif and an N-terminus with a putative pilin-like fold and was found to interact directly with
Bd0108. These results lead us to propose that the Bd0109/Bd0108 interaction regulates pilus production in
Bdellovibrio (possibly by interaction with the pilus fibre at the cell wall), and that the presence (and possibly retraction
state) of the pilus feeds back to alter the growth state of the Bdellovibrio cell. We further identify a novel small RNA
encoded by the hit locus, the transcription of which is altered in different bd0108 mutation background