272 research outputs found
Spin noise spectroscopy to probe quantum states of ultracold fermionic atomic gases
Ultracold alkali atoms provide experimentally accessible model systems for
probing quantum states that manifest themselves at the macroscopic scale.
Recent experimental realizations of superfluidity in dilute gases of ultracold
fermionic (half-integer spin) atoms offer exciting opportunities to directly
test theoretical models of related many-body fermion systems that are
inaccessible to experimental manipulation, such as neutron stars and
quark-gluon plasmas. However, the microscopic interactions between fermions are
potentially quite complex, and experiments in ultracold gases to date cannot
clearly distinguish between the qualitatively different microscopic models that
have been proposed. Here, we theoretically demonstrate that optical
measurements of electron spin noise -- the intrinsic, random fluctuations of
spin -- can probe the entangled quantum states of ultracold fermionic atomic
gases and unambiguously reveal the detailed nature of the interatomic
interactions. We show that different models predict different sets of
resonances in the noise spectrum, and once the correct effective interatomic
interaction model is identified, the line-shapes of the spin noise can be used
to constrain this model. Further, experimental measurements of spin noise in
classical (Boltzmann) alkali vapors are used to estimate the expected signal
magnitudes for spin noise measurements in ultracold atom systems and to show
that these measurements are feasible
A quantitative study of spin noise spectroscopy in a classical gas of K atoms
We present a general derivation of the electron spin noise power spectrum in
alkali gases as measured by optical Faraday rotation, which applies to both
classical gases at high temperatures as well as ultracold quantum gases. We
show that the spin-noise power spectrum is determined by an electron spin-spin
correlation function, and we find that measurements of the spin-noise power
spectra for a classical gas of K atoms are in good agreement with the
predicted values. Experimental and theoretical spin noise spectra are directly
and quantitatively compared in both longitudinal and transverse magnetic fields
up to the high magnetic field regime (where Zeeman energies exceed the
intrinsic hyperfine energy splitting of the K ground state)
Dynamics of broken symmetry lambda phi^4 field theory
We study the domain of validity of a Schwinger-Dyson (SD) approach to
non-equilibrium dynamics when there is broken symmetry. We perform exact
numerical simulations of the one- and two-point functions of lambda phi^4 field
theory in 1+1 dimensions in the classical domain for initial conditions where <
phi(x) > not equal to 0. We compare these results to two self-consistent
truncations of the SD equations which ignore three-point vertex function
corrections. The first approximation, which sets the three-point function to
one (the bare vertex approximation (BVA)) gives an excellent description for <
phi(x) > = phi(t). The second approximation which ignores higher in 1/N
corrections to the 2-PI generating functional (2PI -1/N expansion) is not as
accurate for phi(t). Both approximations have serious deficiencies in
describing the two-point function when phi(0) > .4.Comment: 10 pages, 6 figure
Acoustic attenuation rate in the Fermi-Bose model with a finite-range fermion-fermion interaction
We study the acoustic attenuation rate in the Fermi-Bose model describing a
mixtures of bosonic and fermionic atom gases. We demonstrate the dramatic
change of the acoustic attenuation rate as the fermionic component is evolved
through the BEC-BCS crossover, in the context of a mean-field model applied to
a finite-range fermion-fermion interaction at zero temperature, such as
discussed previously by M.M. Parish et al. [Phys. Rev. B 71, 064513 (2005)] and
B. Mihaila et al. [Phys. Rev. Lett. 95, 090402 (2005)]. The shape of the
acoustic attenuation rate as a function of the boson energy represents a
signature for superfluidity in the fermionic component
Density and spin response functions in ultracold fermionic atom gases
We propose a new method of detecting the onset of superfluidity in a
two-component ultracold fermionic gas of atoms governed by an attractive
short-range interaction. By studying the two-body correlation functions we find
that a measurement of the momentum distribution of the density and spin
response functions allows one to access separately the normal and anomalous
densities. The change in sign at low momentum transfer of the density response
function signals the transition between a BEC and a BCS regimes, characterized
by small and large pairs, respectively. This change in sign of the density
response function represents an unambiguous signature of the BEC to BCS
crossover. Also, we predict spin rotational symmetry-breaking in this system
Paper presented at the 11th International School on Vacuum Electron and Ion Technologies
Abstract An investigation in the afterglow of a Cd}Ne positive column at low and intermediate pressure is presented. The model is based on numerical solution of the time-dependent Boltzmann equation and a system of particle balance equations for the electrons, excited atoms and ions. By this model all discharge properties of interest (electron energy distribution function, electron and ion densities and the populations of both Cd and Ne excited states) are calculated in the afterglow. The populations of the excited Cd (5pP ) atoms are measured using time-resolved optical absorption spectroscopy. The electron density is derived by probes measurements. Model predictions are in fair agreement with measured electron density and excitedstate populations
Phases in Strongly Coupled Electronic Bilayer Liquids
The strongly correlated liquid state of a bilayer of charged particles has
been studied via the HNC calculation of the two-body functions. We report the
first time emergence of a series of structural phases, identified through the
behavior of the two-body functions.Comment: 5 pages, RevTEX 3.0, 4 ps figures; Submitted to Phys. Rev. Let
An O(N) symmetric extension of the Sine-Gordon Equation
We discuss an O(N) exension of the Sine-Gordon (S-G)equation which allows us
to perform an expansion around the leading order in large-N result using
Path-Integral methods. In leading order we show our methods agree with the
results of a variational calculation at large-N. We discuss the striking
differences for a non-polynomial interaction between the form for the effective
potential in the Gaussian approximation that one obtains at large-N when
compared to the N=1 case. This is in contrast to the case when the classical
potential is a polynomial in the field and no such drastic differences occur.
We find for our large-N extension of the Sine-Gordon model that the unbroken
ground state is unstable as one increases the coupling constant (as it is for
the original S-G equation) and we determine the stability criteria.Comment: 21 pages, Latex (Revtex4) v3:minor grammatical changes and addition
Angle-resolved photoemission and first-principles electronic structure of single-crystalline -uranium (001)
Continuing the photoemission study begun with the work of Opeil et al. [Phys.
Rev. B \textbf{73}, 165109 (2006)], in this paper we report results of an
angle-resolved photoemission spectroscopy (ARPES) study performed on a
high-quality single-crystal -uranium at 173 K. The absence of
surface-reconstruction effects is verified using X-ray Laue and low-energy
electron diffraction (LEED) patterns. We compare the ARPES intensity map with
first-principles band structure calculations using a generalized gradient
approximation (GGA) and we find good correlations with the calculated
dispersion of the electronic bands
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