24,754 research outputs found
Preparation of n-qubit Greenberger-Horne-Zeilinger entangled states in cavity QED: An approach with tolerance to nonidentical qubit-cavity coupling constants
We propose a way for generating -qubit Greenberger-Horne-Zeilinger (GHZ)
entangled states with a three-level qubit system and (n-1) four-level qubit
systems in a cavity. This proposal does not require identical qubit-cavity
coupling constants, and thus is tolerant to qubit-system parameter
nonuniformity and nonexact placement of qubits in a cavity. The proposal does
not require adjustment of the qubit-system level spacings during the entire
operation. Moreover, it is shown that entanglement can be deterministically
generated using this method and the operation time is independent of the number
of qubits. The present proposal is quite general, which can be applied to
physical systems such as various types of superconducting devices coupled to a
resonator or atoms trapped in a cavity.Comment: 3 figures, accepted by Phys. Rev.
Disentangling the entangled: Observations and analysis of the triple non-coeval protostellar system VLA1623
Commonplace at every evolutionary stage, Multiple Protostellar Systems (MPSs)
are thought to be formed through fragmentation, but it is unclear when and how.
The youngest MPSs, which have not yet undergone much evolution, provide
important constraints to this question. It is then of interest to disentangle
early stage MPSs. In this letter we present the results of our work on VLA1623
using our observations and archival data from the Submillimeter Array (SMA).
Our continuum and line observations trace VLA1623's components, outflow and
envelope, revealing unexpected characteristics. We construct the SED for each
component using the results of our work and data from literature, as well as
derive physical parameters from continuum and perform a simple kinematical
analysis of the circumstellar material. Our results show VLA1623 to be a triple
non-coeval system composed of VLA1623A, B & W, with each source driving its own
outflow and unevenly distributed circumstellar material. From the SED, physical
parameters and IR emission we conclude that VLA1623A & W are Class 0 and I
protostars, respectively, and together drive the bulk of the observed outflow.
Furthermore, we find two surprising results, first the presence of a rotating
disk-like structure about VLA1623A with indications of pure Keplerian rotation,
which, if real, would make it one of the first evidence of Keplerian disk
structures around Class 0 protostars. Second, we find VLA1623B to be a bonafide
extremely young protostellar object between the starless core and Class 0
stages.Comment: 22 pages, 4 figures, 1 Table, Accepted to Ap
Nonlinear Schr\"odinger Equation for Superconductors
Using the Hartree-Fock-Bogoliubov factorization of the density matrix and the
Born-Oppenheimer approximation we show that the motion of the condensate
satisfies a nonlinear Schr\"odinger equation in the zero temperature limit. The
Galilean invariance of the equation is explicitly manifested. {}From this
equation some general properties of a superconductor, such as Josephson
effects, the Magnus force, and the Bogoliubov-Anderson mode can be obtained
readily.Comment: Latex, 12 page
- …