350 research outputs found
Statistical comparison of ensemble implementations of Grover's search algorithm to classical sequential searches
We compare pseudopure state ensemble implementations, quantified by their
initial polarization and ensemble size, of Grover's search algorithm to
probabilistic classical sequential search algorithms in terms of their success
and failure probabilities. We propose a criterion for quantifying the resources
used by the ensemble implementation via the aggregate number of oracle
invocations across the entire ensemble and use this as a basis for comparison
with classical search algorithms. We determine bounds for a critical
polarization such that the ensemble algorithm succeeds with a greater
probability than the probabilistic classical sequential search. Our results
indicate that the critical polarization scales as N^(-1/4) where N is the
database size and that for typical room temperature solution state NMR, the
polarization is such that the ensemble implementation of Grover's algorithm
would be advantageous for N > 10^2
The effect of an imaginary part of the Schwinger-Dyson equation at finite temperature and density
We examined the effect of an imaginary part of the ladder approximation
Schwinger-Dyson equation. We show the imaginary part enhances the effect of the
first order transition, and affects a tricritical point. In particular, a
chemical potential at a tricritical point is moved about 200(MeV). Thus, one
should not ignore the imaginary part. On the other hand, since an imaginary
part is small away from a tricritical point, one should be able to ignore an
imaginary part. In addition, we also examined the contribution of the wave
function renormalization constant.Comment: 12 pages, 14 figure
High temperature limit in static backgrounds
We prove that the hard thermal loop contribution to static thermal amplitudes
can be obtained by setting all the external four-momenta to zero before
performing the Matsubara sums and loop integrals. At the one-loop order we do
an iterative procedure for all the 1PI one-loop diagrams and at the two-loop
order we consider the self-energy. Our approach is sufficiently general to the
extent that it includes theories with any kind of interaction vertices, such as
gravity in the weak field approximation, for space-time dimensions. This
result is valid whenever the external fields are all bosonic.Comment: 15 pages, 11 figures. To be published in Physical Review
Quark Propagation in the Quark-Gluon Plasma
It has recently been suggested that the quark-gluon plasma formed in
heavy-ion collisions behaves as a nearly ideal fluid. That behavior may be
understood if the quark and antiquark mean-free- paths are very small in the
system, leading to a "sticky molasses" description of the plasma, as advocated
by the Stony Brook group. This behavior may be traced to the fact that there
are relatively low-energy resonance states in the plasma leading to
very large scattering lengths for the quarks. These resonances have been found
in lattice simulation of QCD using the maximum entropy method (MEM). We have
used a chiral quark model, which provides a simple representation of effects
due to instanton dynamics, to study the resonances obtained using the MEM
scheme. In the present work we use our model to study the optical potential of
a quark in the quark-gluon plasma and calculate the quark mean-free-path. Our
results represent a specific example of the dynamics of the plasma as described
by the Stony Brook group.Comment: 17 pages, 4 figures, revtex
Photon Production from a Quark-Gluon-Plasma at Finite Baryon Chemical Potential
We compute the photon production of a QCD plasma at leading order in the
strong coupling with a finite baryon chemical potential. Our approach starts
from the real time formalism of finite temperature field theory. We identify
the class of diagrams contributing at leading order when a finite chemical
potential is added and resum them to perform a full treatment of the LPM effect
similar to the one performed by Arnold, Moore, and Yaffe at zero chemical
potential. Our results show that the contribution of and processes grows as the chemical potential grows.Comment: 28 pages, 14 figure
Gluon propagators and center vortices in gluon plasma
We study electric and magnetic components of the gluon propagators in
quark-gluon plasma in terms of center vortices by using a quenched simulation
of SU(2) lattice theory. In the Landau gauge, the magnetic components of the
propagators are strongly affected in the infrared region by removal of the
center vortices, while the electric components are almost unchanged by this
procedure. In the Coulomb gauge, the time-time correlators, including an
instantaneous interaction, also have an essential contribution from the center
vortices. As a result, one finds that magnetic degrees of freedom in the
infrared region couple strongly to the center vortices in the deconfinement
phase.Comment: 12 pages, 11 figure
Thermal momentum distribution from path integrals with shifted boundary conditions
For a thermal field theory formulated in the grand canonical ensemble, the
distribution of the total momentum is an observable characterizing the thermal
state. We show that its cumulants are related to thermodynamic potentials. In a
relativistic system for instance, the thermal variance of the total momentum is
a direct measure of the enthalpy. We relate the generating function of the
cumulants to the ratio of (a) a partition function expressed as a Matsubara
path integral with shifted boundary conditions in the compact direction, and
(b) the ordinary partition function. In this form the generating function is
well suited for Monte-Carlo evaluation, and the cumulants can be extracted
straightforwardly. We test the method in the SU(3) Yang-Mills theory and obtain
the entropy density at three different temperatures.Comment: 4 pages, 1 figure, minor revisions; version accepted in PR
Thermal Effective Lagrangian of Static Gravitational Fields
We compute the effective Lagrangian of static gravitational fields
interacting with thermal fields. Our approach employs the usual imaginary time
formalism as well as the equivalence between the static and space-time
independent external gravitational fields. This allows to obtain a closed form
expression for the thermal effective Lagrangian in space-time dimensions.Comment: Accepted for publication in the Physical Review
The role of energy-momentum conservation in emission of Cherenkov gluons
The famous formula for the emission angle of Cherenkov radiation should be
modified when applied to hadronic reactions because of recoil effects. They
impose the upper limit on the energy of the gluon emitted at a given angle.
Also, it leads to essential corrections to the nuclear refractive index value
as determined from the angular position of Cherenkov rings.Comment: 6
Effective actions at finite temperature
This is a more detailed version of our recent paper where we proposed, from
first principles, a direct method for evaluating the exact fermion propagator
in the presence of a general background field at finite temperature. This can,
in turn, be used to determine the finite temperature effective action for the
system. As applications, we discuss the complete one loop finite temperature
effective actions for 0+1 dimensional QED as well as for the Schwinger model in
detail. These effective actions, which are derived in the real time (closed
time path) formalism, generate systematically all the Feynman amplitudes
calculated in thermal perturbation theory and also show that the retarded
(advanced) amplitudes vanish in these theories. Various other aspects of the
problem are also discussed in detail.Comment: 9 pages, revtex, 1 figure, references adde
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