212,206 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.
Evolutionary Computing for Operating Point Analysis of Nonlinear Circuits
The DC operating point of an electronic circuit is conventionally found using the Newton-Raphson method. This method is not globally convergent and can only find one solution of the circuit at a time. In this paper, evolutionary computing methods, including Genetic Algorithms, Evolutionary Programming, Evolutionary Strategies and Differential Evolution are explored as possible alternatives to Newton-Raphson. These techniques have been implemented in a trial simulator. Results are presented showing that Evolutionary Computing methods are globally convergent and can find multiple solutions to circuits. The CPU time for these new methods is poor compared with Newton-Raphson, but better implementations and the use of hybrid methods suggest that further work in this area would prove fruitful
Nature of Quasielectrons and the Continuum of Neutral Bulk Excitations in the Laughlin Quantum Hall Fluids
We construct model wavefunctions for a family of single-quasielectron states
supported by the fractional quantum Hall (FQH) fluid. The charge
= quasielectron state is identified as a composite of a
charge- quasiparticle and a quasihole, orbiting around their
common center of charge with relative angular momentum , and
corresponds precisely to the "composite fermion" construction based on a filled
Landau level plus an extra particle in level . An effective
three-body model (one quasiparticle and two quasiholes) is
introduced to capture the essential physics of the neutral bulk excitations.Comment: 4 pages, 3 figs, minor modifications for the published versio
A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length
Inspired by the low--density Lee-Yang expansion for the energy of a dilute
Fermi gas of density and momentum , we introduce here a
Skyrme--type functional that contains only -wave terms and provides, at the
mean--field level, (i) a satisfactory equation of state for neutron matter from
extremely low densities up to densities close to the equilibrium point, and
(ii) a good--quality equation of state for symmetric matter at density scales
around the saturation point. This is achieved by using a density--dependent
neutron-neutron scattering length ) which satisfies the low--density
limit (for Fermi momenta going to zero) and has a density dependence tuned in
such a way that the low--density constraint is satisfied
at all density scales.Comment: 5 figure
Phase Evolution in a Kondo Correlated System
The coherence and phase evolution of electrons in a mesoscopic system in the
Kondo correlated regime were studied. The Kondo effect, in turn, is one of the
most fundamental many-body effects where a localized spin interacts with
conduction electrons in a conductor. Results were obtained by embedding a
quantum dot (QD) in a double path electronic interferometer and measuring
interference of electron waves. The Phase was found to evolve in a range twice
as large as the theoretically predicted one. Moreover, the phase proved to be
highly sensitive to the onset of Kondo correlation, thus serving as a new
fingerprint of the Kondo effect.Comment: 4 pages, 4 figures. typos corrected. Changed to APS PRL styl
From dilute matter to the equilibrium point in the energy--density--functional theory
Due to the large value of the scattering length in nuclear systems, standard
density--functional theories based on effective interactions usually fail to
reproduce the nuclear Fermi liquid behavior both at very low densities and
close to equilibrium. Guided on one side by the success of the Skyrme density
functional and, on the other side, by resummation techniques used in Effective
Field Theories for systems with large scattering lengths, a new energy--density
functional is proposed. This functional, adjusted on microscopic calculations,
reproduces the nuclear equations of state of neutron and symmetric matter at
various densities. Furthermore, it provides reasonable saturation properties as
well as an appropriate density dependence for the symmetry energy.Comment: 4 figures, 2 table
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