6,127 research outputs found
Spin-correlation functions in ultracold paired atomic-fermion systems: sum rules, self-consistent approximations, and mean fields
The spin response functions measured in multi-component fermion gases by
means of rf transitions between hyperfine states are strongly constrained by
the symmetry of the interatomic interactions. Such constraints are reflected in
the spin f-sum rule that the response functions must obey. In particular, only
if the effective interactions are not fully invariant in SU(2) spin space, are
the response functions sensitive to mean field and pairing effects. We
demonstrate, via a self-consistent calculation of the spin-spin correlation
function within the framework of Hartree-Fock-BCS theory, how one can derive a
correlation function explicitly obeying the f-sum rule. By contrast, simple
one-loop approximations to the spin response functions do not satisfy the sum
rule. As we show, the emergence of a second peak at higher frequency in the rf
spectrum, as observed in a recent experiment in trapped , can be
understood as the contribution from the paired fermions, with a shift of the
peak from the normal particle response proportional to the square of the BCS
pairing gap.Comment: 7 pages, 1 figure, content adde
Unitary Fermi gas at finite temperature in the epsilon expansion
Thermodynamics of the unitary Fermi gas at finite temperature is investigated
from the perspective of the expansion over epsilon=4-d with d being the
dimensionality of space. We show that the thermodynamics is dominated by
bosonic excitations in the low temperature region T<<Tc. Analytic formulas for
the thermodynamic functions as functions of the temperature are derived to the
lowest order in epsilon in this region. In the high temperature region where T
Tc, bosonic and fermionic quasiparticles are excited. We determine the critical
temperature Tc of the superfluid phase transition and the thermodynamic
functions around Tc to the leading and next-to-leading orders in epsilon.Comment: 13 pages, 7 figures, revtex4; version to appear in Phys. Rev.
EVIDENCE OF THE EFFECTS OF WATER QUALITY ON RESIDENTIAL LAND PRICES
We use hedonic techniques to show that water quality has a significant effect on property values along the Chesapeake Bay. Mindful of the limitations of using hedonic methods for welfare analysis, we calculate the potential benefits from an illustrative (but limited) water quality improvement. Past hedonic studies have almost entirely ignored the potential for omitted variables bias -- the possibility that pollution sources, in addition to emitting undesirable substances, are likely to be unpleasant neighbors. We discuss the implications of this oversight, and we provide an application that addresses the problem head-on.water quality, hedonic models, residential land prices, Environmental Economics and Policy,
Conversion of LARSYS III.1 to an IBM 370 computer
A software system for processing multispectral aircraft or satellite data (LARSYS) was designed and written at the Laboratory for Applications of Remote Sensing at Purdue University. This system, being implemented on an IBM 360/67 computer utilizing the Cambridge Monitor System, is of an interactive nature. TAMU LARSYS maintains the essential capabilities of Purdue's LARSYS. The machine configuration for which it has been converted is an IBM-compatible Amdahl 470V/6 computer utilizing the time sharing option of the currently implemented OS/VS2 Operating System. Due to TSO limitations, the NASA-JSC deliverable TAMU LARSYS is comprised of two parts. Part one is a TSO Control Card Checker for LARSYS control cards, and part two is a batch version of LARSYS. Used together, they afford most of the capabilities of the original LARSYS III.1. Additionally, two programs have been written by TAMU to support LARSYS processing. The first is an ERTS-to-MIST conversion program used to convert ERTS data to the LARSYS input form, the MIST tape. The second is a system runtable code which maintains tape/file location information for the MIST data sets
Short-distance and short-time structure of a unitary Fermi gas
We consider the operator product expansions for unitarity fermions. We
compute the dynamic structure factor S(q,w) at large frequency and wavenumber
away from the one-particle peak. The overall normalization of S(q,w) is
determined by Tan's contact parameter, and the dependence on q and w is
obtained in closed analytic form. We also find energy deposited into the system
by small, rapid variations of the inverse scattering length.Comment: 11 pages, 8 figure
Tuning Rashba and Dresselhaus spin-orbit couplings: Effects on singlet and triplet condensation with Fermi atoms
We investigate the pair condensation of a two-spin-component Fermi gas in the
presence of both Rashba and Dresselhaus spin-orbit couplings. We calculate the
condensate fraction in the BCS-BEC crossover both in two and in three
dimensions by taking into account singlet and triplet pairings. These
quantities are studied by varying the spin-orbit interaction from the case with
the only Rashba to the equal-Rashba-Dresselhaus one. We find that, by mixing
the two couplings, the singlet pairing decreases while the triplet pairing is
suppressed in the BCS regime and increased in the BEC regime, both in two and
three dimensions. At fixed spin-orbital strength, the greatest total condensate
fraction is obtained when only one coupling (only Rashba or only Dresselhaus)
is present.Comment: 9 pages, 6 figures, final versio
Even-Odd Correlation Functions on an Optical Lattice
We study how different many body states appear in a quantum gas microscope,
such as the one developed at Harvard [Bakr et al. Nature 462, 74 (2009)], where
the site-resolved parity of the atom number is imaged. We calculate the spatial
correlations of the microscope images, corresponding to the correlation
function of the parity of the number of atoms at each site. We produce analytic
results for a number of well-known models: noninteracting bosons, the large U
Bose-Hubbard model, and noninteracting fermions. We find that these parity
correlations tend to be less strong than density-density correlations, but they
carry similar information.Comment: 8 pages, 4 figures. Published versio
Zero Temperature Thermodynamics of Asymmetric Fermi Gases at Unitarity
The equation of state of a dilute two-component asymmetric Fermi gas at
unitarity is subject to strong constraints, which affect the spatial density
profiles in atomic traps. These constraints require the existence of at least
one non-trivial partially polarized (asymmetric) phase. We determine the
relation between the structure of the spatial density profiles and the T=0
equation of state, based on the most accurate theoretical predictions
available. We also show how the equation of state can be determined from
experimental observations.Comment: 10 pages and 7 figures. (Minor changes to correspond with published
version.
Statistical analysis of the growth and morphology of the filamentous microbe Streptomyces coelicolor
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
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