1,140 research outputs found
Non-Markovian entanglement dynamics in coupled superconducting qubit systems
We theoretically analyze the entanglement generation and dynamics by coupled
Josephson junction qubits. Considering a current-biased Josephson junction
(CBJJ), we generate maximally entangled states. In particular, the entanglement
dynamics is considered as a function of the decoherence parameters, such as the
temperature, the ratio between the reservoir cutoff
frequency and the system oscillator frequency , % between
the characteristic frequency of the %quantum system of interest, and
the cut-off frequency of %Ohmic reservoir and the energy levels
split of the superconducting circuits in the non-Markovian master equation. We
analyzed the entanglement sudden death (ESD) and entanglement sudden birth
(ESB) by the non-Markovian master equation. Furthermore, we find that the
larger the ratio and the thermal energy , the shorter the
decoherence. In this superconducting qubit system we find that the entanglement
can be controlled and the ESD time can be prolonged by adjusting the
temperature and the superconducting phases which split the energy
levels.Comment: 13 pages, 3 figure
Stochastic Quantization of the Chern-Simons Theory
We discuss Stochastic Quantization of =3 dimensional non-Abelian
Chern-Simons theory. We demonstrate that the introduction of an appropriate
regulator in the Langevin equation yields a well-defined equilibrium limit,
thus leading to the correct propagator. We also analyze the connection between
=3 Chern-Simons and =4 Topological Yang-Mills theories showing the
equivalence between the corresponding regularized partition functions. We study
the construction of topological invariants and the introduction of a
non-trivial kernel as an alternative regularization.Comment: 30 page
Resummation of QCD Corrections to the eta_c Decay Rate
We examine the ratio of the decay rate of the eta_c into light hadrons to the
decay rate into photons and find that most of the large next-to-leading-order
(NLO) correction is associated with running of the strong coupling alpha_s. We
resum such contributions by analyzing final-state chains of vacuum-polarization
bubbles. We show that the nonperturbative parts of the bubble chains can be
absorbed into a color-octet matrix element, once one has used contour
deformations of the phase-space integrals to cancel certain contributions. We
argue that these contributions are incompatible with the uncertainty principle.
We also argue that perturbation theory is reliable only if one carries out the
phase-space integrations before the perturbation summation. Our results are in
good agreement with experiment and differ considerably from those that one
obtains by applying the scale-setting method of Brodsky, Lepage, and Mackenzie
to the NLO result.Comment: 41 pages, REVTEX, corrected minor typos in tex
Effects of decoherence and errors on Bell-inequality violation
We study optimal conditions for violation of the Clauser-Horne-Shimony-Holt
form of the Bell inequality in the presence of decoherence and measurement
errors. We obtain all detector configurations providing the maximal Bell
inequality violation for a general (pure or mixed) state. We consider local
decoherence which includes energy relaxation at the zero temperature and
arbitrary dephasing. Conditions for the maximal Bell-inequality violation in
the presence of decoherence are analyzed both analytically and numerically for
the general case and for a number of important special cases. Combined effects
of measurement errors and decoherence are also discussed.Comment: 18 pages, 5 figure
The Field Perturbation Theory of the Double Correlated Phase in High Temperature Superconductors
The Double-Correlated phase in HTSC, and its treatment by field perturbation
theory, is established. In particular, we define the ground state, the
quasi-particle excitations, and construct an appropriate field. We also derive
the unperturbed Hamiltonian, and the propagators for the unperturbed state.
Then we discuss the perturbation Hamiltonian, and show that the Hartree diagram
is significant for both the pseudogap and the superconductive order parameter,
and suggest that it yields the major contribution to these parameters.Comment: 23 pages Of MSWord in PDF format, 1 figur
Ab Initio Evidence for the Formation of Impurity d(3z^2-r^2) Holes in Doped La_{2-x}Sr_xCuO_4
Using the spin unrestricted Becke-3-Lee-Yang-Parr density functional, we
computed the electronic structure of explicitly doped La_{2-x}Sr_xCuO_4 (x =
0.125, 0.25, and 0.5). At each doping level, an impurity hole band is formed
within the undoped insulating gap. This band is well-localized to CuO_6
octahedra adjacent to the Sr impurities. The nature of the impurity hole is
A_{1g} in symmetry, formed primarily from the z^2 orbital on the Cu and p_z
orbitals on the apical O's. There is a strong triplet coupling of this hole
with the intrinsic B_{1g} Cu x^2-y^2/O1 p_{sigma} hole on the same site.
Optimization of the c coordinate of the apical O's in the doped CuO_6
octahedron lead to an asymmetric anti-Jahn-Teller distortion of the O2 atoms
toward the central Cu. In particular, the O2 atom between the Cu and Sr is
displaced 0.26 A while the O2 atom between the Cu and La is displaced 0.10 A.
Contrary to expectations, investigation of a 0.1 A enhanced Jahn-Teller
distortion of this octahedron does not force formation of an x^2-y^2 hole, but
instead leads to migration of the z^2 hole to the four other CuO_6 octahedra
surrounding the Sr impurity. This latter observation offers a simple
explanation for the bifurcation of the Sr-O2 distance revealed in x-ray
absorption fine structure data.Comment: Submitted to Phys. Rev. B. See http://www.firstprinciples.com for
more informatio
Particle Production and Gravitino Abundance after Inflation
Thermal history after inflation is studied in a chaotic inflation model with
supersymmetric couplings of the inflaton to matter fields. Time evolution
equation is solved in a formalism that incorporates both the back reaction of
particle production and the cosmological expansion. The effect of the
parametric resonance gives rise to a rapid initial phase of the inflaton decay
followed by a slow stage of the Born term decay. Thermalization takes place
immediately after the first explosive stage for a medium strength of the
coupling among created particles. As an application we calculate time evolution
of the gravitino abundance that is produced by ordinary particles directly
created from the inflaton decay, which typically results in much more enhanced
yield than what a naive estimate based on the Born term would suggest.Comment: 23 pages + 13 figure
Spin-orbital gapped phase with least symmetry breaking in the one-dimensional symmetrically coupled spin-orbital model
To describe the spin-orbital energy gap formation in the one-dimensional
symmetrically coupled spin-orbital model, we propose a simple mean field theory
based on an SU(4) constraint fermion representation of spins and orbitals. A
spin-orbital gapped phase is formed due to a marginally relevant spin-orbital
valence bond pairing interaction. The energy gap of the spin and orbital
excitations grows extremely slowly from the SU(4) symmetric point up to a
maximum value and then decreases rapidly. By calculating the spin, orbital, and
spin-orbital tensor static susceptibilities at zero temperature, we find a
crossover from coherent to incoherent magnetic excitations as the spin-orbital
coupling decreasing from large to small values.Comment: 10 pages, Revtex file, 5 figure
Robust stationary entanglement of two coupled qubits in independent environments
The dissipative dynamics of two interacting qubits coupled to independent
reservoirs at nonzero temperatures is investigated, paying special attention to
the entanglement evolution. The counter-rotating terms in the qubit-qubit
interaction give rise to stationary entanglement, traceable back to the ground
state structure. The robustness of this entanglement against thermal noise is
thoroughly analyzed, establishing that it can be detected at reasonable
experimental temperatures. Some effects linked to a possible reservoir
asymmetry are brought to light.Comment: 8 pages, 6 figures; version accepted for publication on Eur. Phys. J.
Vertical transport and electroluminescence in InAs/GaSb/InAs structures: GaSb thickness and hydrostatic pressure studies
We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double
heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness
between 0-1200 \AA. A negative differential resistance (NDR) is observed for
all DHETs with GaSb thickness 60 \AA below which a dramatic change in the
shape of the I-V and a marked hysteresis is observed. The temperature
dependence of the I-V is found to be very strong below this critical GaSb
thickness. The I-V characteristics of selected DHETs are also presented under
hydrostatic pressures up to 11 kbar. Finally, a mid infra-red
electroluminescence is observed at 1 bar with a threshold at the NDR valley
bias. The band profile calculations presented in the analysis are markedly
different to those given in the literature, and arise due to the positive
charge that it is argued will build up in the GaSb layer under bias. We
conclude that the dominant conduction mechanism in DHETs is most likely to
arise out of an inelastic electron-heavy-hole interaction similar to that
observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding,
and not out of resonant electron-light-hole tunnelling as proposed by Yu et al.
A Zener tunnelling mechanism is shown to contribute to the background current
beyond NDR.Comment: 8 pages 12 fig
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