1,420 research outputs found
Analysis of measurement errors for a superconducting phase qubit
We analyze several mechanisms leading to errors in a course of measurement of
a superconducting flux-biased phase qubit. Insufficiently long measurement
pulse may lead to nonadiabatic transitions between qubit states and
, before tunneling through a reduced barrier is supposed to distinguish
the qubit states. Finite (though large) ratio of tunneling rates for these
states leads to incomplete discrimination between and .
Insufficiently fast energy relaxation after the tunneling of state may
cause the repopulation of the quantum well in which only the state is
supposed to remain. We analyze these types of measurement errors using
analytical approaches as well as numerical solution of the time-dependent
Schr\"{o}dinger equation.Comment: 14 pages, 14 figure
Bound and resonance states of the nonlinear Schroedinger equation in simple model systems
The stationary nonlinear Schroedinger equation, or Gross-Pitaevskii equation,
is studied for the cases of a single delta potential and a delta-shell
potential. These model systems allow analytical solutions, and thus provide
useful insight into the features of stationary bound, scattering and resonance
states of the nonlinear Schroedinger equation. For the single delta potential,
the influence of the potential strength and the nonlinearity is studied as well
as the transition from bound to scattering states. Furthermore, the properties
of resonance states for a repulsive delta-shell potential are discussed.Comment: 19 pages, 10 figure
Quantum Hamilton-Jacobi Theory
Quantum canonical transformations have attracted interest since the beginning
of quantum theory. Based on their classical analogues, one would expect them to
provide a powerful quantum tool. However, the difficulty of solving a nonlinear
operator partial differential equation such as the quantum Hamilton-Jacobi
equation (QHJE) has hindered progress along this otherwise promising avenue. We
overcome this difficulty. We show that solutions to the QHJE can be constructed
by a simple prescription starting from the propagator of the associated
Schroedinger equation. Our result opens the possibility of practical use of
quantum Hamilton-Jacobi theory. As an application we develop a surprising
relation between operator ordering and the density of paths around a
semiclassical trajectory.Comment: 7 page
Model Analysis of the Electroproduction Reaction on the Proton
Recent CLAS data on the electroproduction off protons at
1.3W1.57 GeV and 0.250.6 GeV have been analyzed using
a meson-baryon phenomenological model. By fitting nine 1-fold differential
cross section data for each and bin, the charged double pion
electroproduction mechanisms are identified from their manifestations in the
observables. We have extracted the cross sections from amplitudes of each of
the considered isobar channels as well as from their coherent sum. We also
obtained non-resonant partial wave amplitudes of all contributing isobar
channels which could be useful for advancing a complete coupled-channel
analysis of all meson electroproduction data.Comment: Experiment Numbers: E93-006, E94-005 Group: Hall
Search for via the transition at LHCb and factory
It is interesting to study the characteristics of the whole family of
which contains two different heavy flavors. LHC and the proposed factory
provide an opportunity because a large database on the family will be
achieved. and its excited states can be identified via their decay modes.
As suggested by experimentalists, is not easy to be
clearly measured, instead, the trajectories of and occurring in
the decay of () can be unambiguously
identified, thus the measurement seems easier and more reliable, therefore this
mode is more favorable at early running stage of LHCb and the proposed
factory. In this work, we calculate the rate of
in terms of the QCD multipole-expansion and the numerical results indicate that
the experimental measurements with the luminosity of LHC and factory are
feasible.Comment: 12 pages, 1 figures and 4 tables, acceptted by SCIENCE CHINA Physics,
Mechanics & Astronomy (Science in China Series G
Flavor and Charge Symmetry in the Parton Distributions of the Nucleon
Recent calculations of charge symmetry violation(CSV) in the valence quark
distributions of the nucleon have revealed that the dominant symmetry breaking
contribution comes from the mass associated with the spectator quark
system.Assuming that the change in the spectator mass can be treated
perturbatively, we derive a model independent expression for the shift in the
parton distributions of the nucleon. This result is used to derive a relation
between the charge and flavor asymmetric contributions to the valence quark
distributions in the proton, and to calculate CSV contributions to the nucleon
sea. The CSV contribution to the Gottfried sum rule is also estimated, and
found to be small
Nucleon spin-flavor structure in SU(3) breaking chiral quark model
The SU(3) symmetric chiral quark model, which describes interactions between
quarks, gluons and the Goldstone bosons, explains reasonably well many aspects
of the flavor and spin structure of the proton, except for the values of
and . Introducing the SU(3)-breaking effect
suggested by the mass difference between the strange and nonstrange quarks, we
find that this discrepancy can be removed and better overall agreement
obtained.Comment: 18 pages, Latex, 4 tables. Phys. Rev. D (in press, submitted/revised
in June/Nov 1996
Effective s- and p-Wave Contact Interactions in Trapped Degenerate Fermi Gases
The structure and stability of dilute degenerate Fermi gases trapped in an
external potential is discussed with special emphasis on the influence of s-
and p-wave interactions. In a first step an Effective Contact Interaction for
all partial waves is derived, which reproduces the energy spectrum of the full
potential within a mean-field model space. Using the s- and p-wave part the
energy density of the multi-component Fermi gas is calculated in Thomas-Fermi
approximation. On this basis the stability of the one- and two-component Fermi
gas against mean-field induced collapse is investigated. Explicit stability
conditions in terms of density and total particle number are given. For the
single-component system attractive p-wave interactions limit the density of the
gas. In the two-component case a subtle competition of s- and p-wave
interactions occurs and gives rise to a rich variety of phenomena. A repulsive
p-wave part, for example, can stabilize a two-component system that would
otherwise collapse due to an attractive s-wave interaction. It is concluded
that the p-wave interaction may have important influence on the structure of
degenerate Fermi gases and should not be discarded from the outset.Comment: 18 pages, 11 figures (using RevTEX4
Heavy Quarkonia in Quark-Gluon Plasma
Using the color-singlet free energy F_1 and total internal energy U_1
obtained by Kaczmarek et al. for a static quark Q and an antiquark Qbar in
quenched QCD, we study the binding energies and wave functions of heavy
quarkonia in a quark-gluon plasma. By minimizing the grand potential in a
simplified schematic model, we find that the proper color-singlet Q-Qbar
potential can be obtained from the total internal energy U_1 by subtracting the
gluon internal energy contributions. We carry out this subtraction in the local
energy-density approximation in which the gluon energy density can be related
to the local gluon pressure by the quark-gluon plasma equation of state. We
find in this approximation that the proper color-singlet Q-Qbar potential is
approximately F_1 for T ~ T_c and it changes to (3/4)F_1+(1/4)U_1 at high
temperatures. In this potential model, the J/psi is weakly bound above the
phase transition temperature T_c, and it dissociates spontaneously above 1.62
T_c, while chi_c and psi' are unbound in the quark-gluon plasma. The bottomium
states Upsilon, chi_b and Upsilon' are bound in the quark-gluon plasma and they
dissociate at 4.10 T_c, 1.18 T_c, and 1.38 T_c respectively. For comparison, we
evaluate the heavy quarkonium binding energies also in other models using the
free energy F_1 or the total internal energy U_1 as the Q-Qbar potential. The
comparison shows that the model with the new Q-Qbar potential proposed in this
manuscript gives dissociation temperatures that agree best with those from
spectral function analyses. We evaluate the cross section for
sigma(g+J/psi->c+cbar) and its inverse process, in order to determine the J/psi
dissociation width and the rate of J/psi production by recombining c and cbar
in the quark gluon plasma.Comment: 30 pages, in Late
Chiral Transparency
Color transparency is the vanishing of initial and final state interactions,
predicted by QCD to occur in high momentum transfer quasielastic nuclear
reactions. For specific reactions involving nucleons, the initial and final
state interactions are expected to be dominated by exchanges of pions. We argue
that these interactions are also suppressed in high momentum transfer nuclear
quasielastic reactions; this is ``chiral transparency". We show that studies of
the reaction could reveal the influence of chiral
transparency.Comment: 20 pages, three figures available by fax from
[email protected]; submitted to Phys. Rev.
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