4,037 research outputs found
Fragilities of Liquids Predicted from the Random First Order Transition Theory of Glasses
A microscopically motivated theory of glassy dynamics based on an underlying
random first order transition is developed to explain the magnitude of free
energy barriers for glassy relaxation. A variety of empirical correlations
embodied in the concept of liquid "fragility" are shown to be quantitatively
explained by such a model. The near universality of a Lindemann ratio
characterizing the maximal amplitude of thermal vibrations within an amorphous
minimum explains the variation of fragility with a liquid's configurational
heat capacity density. Furthermore the numerical prefactor of this correlation
is well approximated by the microscopic calculation. The size of heterogeneous
reconfiguring regions in a viscous liquid is inferred and the correlation of
nonexponentiality of relaxation with fragility is qualitatively explained. Thus
the wide variety of kinetic behavior in liquids of quite disparate chemical
nature reflects quantitative rather than qualitative differences in their
energy landscapes.Comment: 10 pages including 4 eps figure
Investigation of pre and post plating surface roughness of electroless nickel phosphorus coated substrate for diamond turning application
In an overarching project to reduce the number of defects found in electroless nickel phosphorus alloy (EN-P) coatings on large
diamond-turned components used in the next generation of reel-to-reel (R2R) printing stations, the significance of the coating
surface on achieving a wear resistant and optically smooth surface has been investigated. This paper presents an investigation that
focuses on the substrate roughness variation achieved through different pre-treatment methods prior to coating using a
commercial plating solution. It looks at the number of features observed pre and post plating. The results provide some suggestions
with respect to the diamond machining of a 100 micron thick EN-P coating
Finite temperature phase diagram of a spin-polarized ultracold Fermi gas in a highly elongated harmonic trap
We investigate the finite temperature properties of an ultracold atomic Fermi
gas with spin population imbalance in a highly elongated harmonic trap.
Previous studies at zero temperature showed that the gas stays in an exotic
spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid
state at the trap center; while moving to the edge, the system changes into
either a non-polarized Bardeen-Cooper-Schriffer superfluid () or a fully
polarized normal gas (), depending on the smallness of the spin
polarization , relative to a critical value . In this work, we show how
these two phase-separation phases evolve with increasing temperature, and
thereby construct a finite temperature phase diagram. For typical interactions,
we find that the exotic FFLO phase survives below one-tenth of Fermi degeneracy
temperature, which seems to be accessible in the current experiment. The
density profile, equation of state, and specific heat of the polarized system
have been calculated and discussed in detail. Our results are useful for the
on-going experiment at Rice University on the search for FFLO states in
quasi-one-dimensional polarized Fermi gases.Comment: 9 pages and 8 figures; Published version in Phys. Rev.
Exact few-body results for strongly correlated quantum gases in two dimensions
The study of strongly correlated quantum gases in two dimensions has
important ramifications for understanding many intriguing pheomena in solid
materials, such as high- superconductivity and the fractional quantum
Hall effect. However, theoretical methods are plagued by the existence of
significant quantum fluctuations. Here, we present two- and three-body exact
solutions for both fermions and bosons trapped in a two-dimensional harmonic
potential, with an arbitrary -wave scattering length. These few-particle
solutions link in a natural way to the high-temperature properties of
many-particle systems via a quantum virial expansion. As a concrete example,
using the energy spectrum of few fermions, we calculate the second and third
virial coefficients of a strongly interacting Fermi gas in two dimensions, and
consequently investigate its high-temperature thermodynamics. Our thermodynamic
results may be useful for ongoing experiments on two-dimensional Fermi gases.
These exact results also provide an unbiased benchmark for quantum Monte Carlo
simulations of two-dimensional Fermi gases at high temperatures.Comment: 11 pages, 6 figure
Static structure factor of a strongly correlated Fermi gas at large momenta
We theoretically investigate the static structure factor of an interacting
Fermi gas near the BEC-BCS crossover at large momenta. Due to short-range
two-body interactions, we predict that the structure factor of unlike spin
correlations falls off as in a universal
scaling region with large momentum and large scattering length. The
scaling coefficient is determined by the celebrated Tan's contact parameter,
which links the short-range behavior of many-body systems to their universal
thermodynamic properties. By implementing this new Tan relation together with
the random-phase approximation and the virial expansion theory in various
limiting cases, we show how to calculate at zero
and finite temperatures for arbitrary interaction strengths, at momentum
transfer higher than the Fermi momentum. Our results provide a way to
experimentally confirm a new Tan relation and to accurately measure the value
of contact parameter.Comment: 8 pages, 3 figures; revised according to the Referee's suggestions;
publised versio
Cavity-free nondestructive detection of a single optical photon
Detecting a single photon without absorbing it is a long standing challenge
in quantum optics. All experiments demonstrating the nondestructive detection
of a photon make use of a high quality cavity. We present a cavity free scheme
for nondestructive single-photon detection. By pumping a nonlinear medium we
implement an inter-field Rabi-oscillation which leads to a ?pi phase shift on
weak probe coherent laser field in the presence of a single signal photon
without destroying the signal photon. Our cavity-free scheme operates with a
fast intrinsic time scale in comparison with similar cavity-based schemes. We
implement a full real-space multimode numerical analysis of the interacting
photonic modes and confirm the validity of our nondestructive scheme in the
multimode case.Comment: 4 figures, 5 page
Mean-field study of itinerant ferromagnetism in trapped ultracold Fermi gases: Beyond the local density approximation
We theoretically investigate the itinerant ferromagnetic transition of a
spherically trapped ultracold Fermi gas with spin imbalance under strongly
repulsive interatomic interactions. Our study is based on a self-consistent
solution of the Hartree-Fock mean-field equations beyond the widely used local
density approximation. We demonstrate that, while the local density
approximation holds in the paramagnetic phase, after the ferromagnetic
transition it leads to a quantitative discrepancy in various thermodynamic
quantities even with large atom numbers. We determine the position of the phase
transition by monitoring the shape change of the free energy curve with
increasing the polarization at various interaction strengths.Comment: 7 pages, 5 figures; published version in Phys. Rev.
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