1,068 research outputs found
Bistable behavior of a two-mode Bose-Einstein condensate in an optical cavity
We consider a two-component Bose-Einstein condensate in a one-dimensional
optical cavity. Specifically, the condensate atoms are taken to be in two
degenerate modes due to their internal hyperfine spin degrees of freedom and
they are coupled to the cavity field and an external transverse laser field in
a Raman scheme. A parallel laser is also exciting the cavity mode. When the
pump laser is far detuned from its resonance atomic transition frequency, an
effective nonlinear optical model of the cavity-condensate system is developed
under Discrete Mode Approximation (DMA), while matter-field coupling has been
considered beyond the Rotating Wave Approximation. By analytical and numerical
solutions of the nonlinear dynamical equations, we examine the mean cavity
field and population difference (magnetization) of the condensate modes. The
stationary solutions of both the mean cavity field and normalized magnetization
demonstrate bistable behavior under certain conditions for the laser pump
intensity and matter-field coupling strength.Comment: Proceeding of Laser Physics 201
Emergence of turbulence in an oscillating Bose-Einstein condensate
We report on the experimental observation of vortices tangle in an atomic BEC
of Rb-87 atoms when an external oscillatory perturbation is introduced in the
trap. The vortices tangle configuration is a signature of the presence of a
turbulent regime in the cloud. We also show that this turbulent cloud has
suppression of the aspect ratio inversion typically observed in quantum
degenerate bosonic gases during free expansion. Instead, the cloud expands
keeping the ratio between their axis constant. Turbulence in atomic superfluids
may constitute an alternative system to investigate decay mechanisms as well as
to test fundamental theoretical aspects in this field.Comment: accepted for Phys. Rev. Let
Phase 2 of the array automated assembly task for the low cost solar array project
The process sequence for the fabrication of dendritic web silicon into solar panels was modified to include aluminum back surface field formation. Plasma etching was found to be a feasible technique for pre-diffusion cleaning of the web. Several contacting systems were studied. The total plated Pd-Ni system was not compatible with the process sequence; however, the evaporated TiPd-electroplated Cu system was shown stable under life testing. Ultrasonic bonding parameters were determined for various interconnect and contact metals but the yield of the process was not sufficiently high to use for module fabrication at this time. Over 400 solar cells were fabricated according to the modified sequence. No sub-process incompatibility was seen. These cells were used to fabricate four demonstration modules. A cost analysis of the modified process sequence resulted in a selling price of $0.75/peak watt
Efficient all-optical production of large Li quantum gases using D gray-molasses cooling
We use a gray molasses operating on the D atomic transition to produce
degenerate quantum gases of Li with a large number of atoms. This
sub-Doppler cooling phase allows us to lower the initial temperature of 10
atoms from 500 to 40 K in 2 ms. We observe that D cooling remains
effective into a high-intensity infrared dipole trap where two-state mixtures
are evaporated to reach the degenerate regime. We produce molecular
Bose-Einstein condensates of up to 510 molecules and
weakly-interacting degenerate Fermi gases of 10 atoms at
with a typical experimental duty cycle of 11 seconds.Comment: 5 pages, 3 figure
Connecting dissipation and phase slips in a Josephson junction between fermionic superfluids
We study the emergence of dissipation in an atomic Josephson junction between
weakly-coupled superfluid Fermi gases. We find that vortex-induced phase
slippage is the dominant microscopic source of dissipation across the BEC-BCS
crossover. We explore different dynamical regimes by tuning the bias chemical
potential between the two superfluid reservoirs. For small excitations, we
observe dissipation and phase coherence to coexist, with a resistive current
followed by well-defined Josephson oscillations. We link the junction transport
properties to the phase-slippage mechanism, finding that vortex nucleation is
primarily responsible for the observed trends of conductance and critical
current. For large excitations, we observe the irreversible loss of coherence
between the two superfluids, and transport cannot be described only within an
uncorrelated phase-slip picture. Our findings open new directions for
investigating the interplay between dissipative and superfluid transport in
strongly correlated Fermi systems, and general concepts in out-of-equlibrium
quantum systems.Comment: 6 pages, 4 figures + Supplemental Materia
Creation and characterization of vortex clusters in atomic Bose-Einstein condensates
We show that a moving obstacle, in the form of an elongated paddle, can
create vortices that are dispersed, or induce clusters of like-signed vortices
in 2D Bose-Einstein condensates. We propose new statistical measures of
clustering based on Ripley's K-function which are suitable to the small size
and small number of vortices in atomic condensates, which lack the huge number
of length scales excited in larger classical and quantum turbulent fluid
systems. The evolution and decay of clustering is analyzed using these
measures. Experimentally it should prove possible to create such an obstacle by
a laser beam and a moving optical mask. The theoretical techniques we present
are accessible to experimentalists and extend the current methods available to
induce 2D quantum turbulence in Bose-Einstein condensates.Comment: 9 pages, 9 figure
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