2,879 research outputs found
Instanton infra-red stabilization in the nonperturbative QCD vacuum
The influence of nonperturbative fields on instantons in quantum
chromodynamics is studied. Nonperturbative vacuum is described in terms of
nonlocal gauge invariant vacuum averages of gluon field strength. Effective
action for instanton is derived in bilocal approximation and it is demonstrated
that stochastic background gluon fields are responsible for infra-red
(IR)stabilization of instantons. Comparison of obtained instanton size
distribution with lattice data is made.Comment: 3 pages, 2 figures. Talk given at 5th International Conference on
Quark Confinement and the Hadron Spectrum, Gargnano, Brescia, Italy, 10-14
Sep 200
Instanton IR stabilization in the nonperturbative confining vacuum
The influence of nonperturbative fields on instantons in quantum
chromodynamics is studied. Nonperturbative vacuum is described in terms of
nonlocal gauge invariant vacuum averages of gluon field strength. Effective
action for instanton is derived in bilocal approximation and it is demonstrated
that stochastic background gluon fields are responsible for infra-red (IR)
stabilization of instantons. Dependence of characteristic instanton size on
gluon condensate and correlation length in nonperturbative vacuum is found. It
is shown that instanton size in QCD is of order of 0.25 fm. Comparison of
obtained instanton size distribution with lattice data is made.Comment: 10 pages, 4 figures; v2: minor corrections, to appear in JHE
Stability, effective dimensions, and interactions for bosons in deformed fields
The hyperspherical adiabatic method is used to derive stability criteria for
Bose-Einstein condensates in deformed external fields. An analytical
approximation is obtained. For constant volume the highest stability is found
for spherical traps. Analytical approximations to the stability criterion with
and without zero point motion are derived. Extreme geometries of the field
effectively confine the system to dimensions lower than three. As a function of
deformation we compute the dimension to vary continuously between one and
three. We derive a dimension-dependent effective radial Hamiltonian and
investigate one choice of an effective interaction in the deformed case.Comment: 7 pages, 5 figures, submitted to Phys. Rev. A. In version 2 figures 2
and 5 are added along with more discussions and explanations. Version 3
contains added comments and reference
Condensates and correlated boson systems
We study two-body correlations in a many-boson system with a hyperspherical
approach, where we can use arbitrary scattering length and include two-body
bound states. As a special application we look on Bose-Einstein condensation
and calculate the stability criterium in a comparison with the experimental
criterium and the theoretical criterium from the Gross-Pitaevskii equation.Comment: 6 pages, 4 figures. Contribution to Workshop on Critical Stability
III in Trento. Submitted to Few-Body System
Teleportation in an indivisible quantum system
Teleportation protocol is conventionally treated as a method for quantum
state transfer between two spatially separated physical carriers. Recent
experimental progress in manipulation with high-dimensional quantum systems
opens a new framework for implementation of teleportation protocols. We show
that the one-qubit teleportation can be considered as a state transfer between
subspaces of the whole Hilbert space of an indivisible eight-dimensional
system. We explicitly show all corresponding operations and discuss an
alternative way of implementation of similar tasks.Comment: 4 pages, 1 figure, 1 tabl
Bidirectional imperfect quantum teleportation with a single Bell state
We present a bidirectional modification of the standard one-qubit
teleportation protocol, where both Alice and Bob transfer noisy versions of
their qubit states to each other by using single Bell state and auxiliary
(trigger) qubits. Three schemes are considered: the first where the actions of
parties are governed by two independent quantum random triggers, the second
with single random trigger, and the third as a mixture of the first two. We
calculate the fidelities of teleportation for all schemes and find a condition
on correlation between trigger qubits in the mixed scheme which allows us to
overcome the classical fidelity boundary of 2/3. We apply the Choi-Jamiolkowski
isomorphism to the quantum channels obtained in order to investigate an
interplay between their ability to transfer the information,
entanglement-breaking property, and auxiliary classical communication needed to
form correlations between trigger qubits. The suggested scheme for
bidirectional teleportation can be realized by using current experimental
tools.Comment: 8 pages, 4 figures; published versio
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