10,370 research outputs found
Pairing and Vortex Lattices for Interacting Fermions in Optical Lattices with a Large Magnetic Field
We study the structure of pairing order parameter for spin-1/2 fermions with
attractive interactions in a square lattice under a uniform magnetic field.
Because the magnetic translation symmetry gives a unique degeneracy in the
single-particle spectrum, the wave function has both zero and finite momentum
components co-existing, and their relative phases are determined by a
self-consistent mean-field theory. We present a microscopic calculation that
can determine the vortex lattice structure in the superfluid phase for
different flux densities. Phase transition from a Hofstadter insulator to a
superfluid phase is also discussed.Comment: 4 pages, 3 figures, one table, published versio
Rubidium resonant squeezed light from a diode-pumped optical-parametric oscillator
We demonstrate a diode-laser-pumped system for generation of quadrature
squeezing and polarization squeezing. Due to their excess phase noise, diode
lasers are challenging to use in phase-sensitive quantum optics experiments
such as quadrature squeezing. The system we present overcomes the phase noise
of the diode laser through a combination of active stabilization and
appropriate delays in the local oscillator beam. The generated light is
resonant to the rubidium D1 transition at 795nm and thus can be readily used
for quantum memory experiments.Comment: 6 pages 4 figure
Superfluidity in Three-species Mixture of Fermi Gases across Feshbach Resonances
In this letter a generalization of the BEC-BCS crossover theory to a
multicomponent superfluid is presented by studying a three-species mixture of
Fermi gas across two Feshbach resonances. At the BEC side of resonances, two
kinds of molecules are stable which gives rise to a two-component Bose
condensate. This two-component superfluid state can be experimentally
identified from the radio-frequency spectroscopy, density profile and short
noise measurements. As approaching the BCS side of resonances, the
superfluidity will break down at some point and yield a first-order quantum
phase transition to normal state, due to the mismatch of three Fermi surfaces.
Phase separation instability will occur around the critical regime.Comment: 4 pages, 3 figures, revised versio
Expanded microchannel heat exchanger: design, fabrication and preliminary experimental test
This paper first reviews non-traditional heat exchanger geometry, laser
welding, practical issues with microchannel heat exchangers, and high
effectiveness heat exchangers. Existing microchannel heat exchangers have low
material costs, but high manufacturing costs. This paper presents a new
expanded microchannel heat exchanger design and accompanying continuous
manufacturing technique for potential low-cost production. Polymer heat
exchangers have the potential for high effectiveness. The paper discusses one
possible joining method - a new type of laser welding named "forward conduction
welding," used to fabricate the prototype. The expanded heat exchanger has the
potential to have counter-flow, cross-flow, or parallel-flow configurations, be
used for all types of fluids, and be made of polymers, metals, or
polymer-ceramic precursors. The cost and ineffectiveness reduction may be an
order of magnitude or more, saving a large fraction of primary energy. The
measured effectiveness of the prototype with 28 micron thick black low density
polyethylene walls and counterflow, water-to-water heat transfer in 2 mm
channels was 72%, but multiple low-cost stages could realize the potential of
higher effectiveness
Valley-dependent Brewster angles and Goos-Hanchen effect in strained graphene
We demonstrate theoretically how local strains in graphene can be tailored to
generate a valley polarized current. By suitable engineering of local strain
profiles, we find that electrons in opposite valleys (K or K') show different
Brewster-like angles and Goos-H\"anchen shifts, exhibiting a close analogy with
light propagating behavior. In a strain-induced waveguide, electrons in K and
K' valleys have different group velocities, which can be used to construct a
valley filter in graphene without the need for any external fields.Comment: 5 pages, 4 figure
The quantum probability ranking principle for information retrieval
While the Probability Ranking Principle for Information Retrieval provides the basis for formal models, it makes a very strong assumption regarding the dependence between documents. However, it has been observed that in real situations this assumption does not always hold. In this paper we propose a reformulation of the Probability Ranking Principle based on quantum theory. Quantum probability theory naturally includes interference effects between events. We posit that this interference captures the dependency between the judgement of document relevance. The outcome is a more sophisticated principle, the Quantum Probability Ranking Principle, that provides a more sensitive ranking which caters for interference/dependence between documents’ relevanc
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