2,230 research outputs found
Qubit Disentanglement and Decoherence via Dephasing
We consider whether quantum coherence in the form of mutual entanglement
between a pair of qubits is susceptible to decay that may be more rapid than
the decay of the coherence of either qubit individually. An instance of
potential importance for solid state quantum computing arises if embedded
qubits (spins, quantum dots, Cooper pair boxes, etc.) are exposed to global and
local noise at the same time. Here we allow separate phase-noisy channels to
affect local and non-local measures of system coherence. We find that the time
for decay of the qubit entanglement can be significantly shorter than the time
for local dephasing of the individual qubits.Comment: REVTeX, 9 pages, 1 figure, v2 with minor changes, reference adde
Spectral approach to linear programming bounds on codes
We give new proofs of asymptotic upper bounds of coding theory obtained
within the frame of Delsarte's linear programming method. The proofs rely on
the analysis of eigenvectors of some finite-dimensional operators related to
orthogonal polynomials. The examples of the method considered in the paper
include binary codes, binary constant-weight codes, spherical codes, and codes
in the projective spaces.Comment: 11 pages, submitte
An asymptotical von-Neumann measurement strategy for solid-state qubits
A measurement on a macroscopic quantum system does in general not lead to a
projection of the wavefunction in the basis of the detector as predicted by
von-Neumann's postulate. Hence, it is a question of fundametal interest, how
the preferred basis onto which the state is projected is selected out of the
macroscopic Hilbert space of the system. Detector-dominated von-Neumann
measurements are also desirable for both quantum computation and verification
of quantum mechanics on a macroscopic scale. The connection of these questions
to the predictions of the spin-boson modelis outlined. I propose a measurement
strategy, which uses the entanglement of the qubit with a weakly damped
harmonic oscillator. It is shown, that the degree of entanglement controls the
degree of renormalization of the qubit and identify, that this is equivalent to
the degree to which the measurement is detector-dominated. This measurement
very rapidly decoheres the initial state, but the thermalization is slow. The
implementation in Josephson quantum bits is described and it is shown that this
strategy also has practical advantages for the experimental implementation.Comment: 4 pages, 3 figures, accepted for publication as a rapid communication
in Phys. Rev.
Scattering of scalar particles by a black hole
The absorption cross section for scalar particle impact on a Schwarzschild
black hole is found. The process is dominated by two physical phenomena. One of
them is the well-known greybody factor that arises from the energy-dependent
potential barrier outside the horizon that filters the incoming and outgoing
waves. The other is related to the reflection of particles on the horizon
(Kuchiev 2003). This latter effect strongly diminishes the cross section for
low energies, forcing it to vanish in the infrared limit. It is argued that
this is a general property, the absorption cross section vanishes in the
infrared limit for scattering of particles of arbitrary spin.Comment: 7 pages, revtex, 1 figur
Modulated Entanglement Evolution Via Correlated Noises
We study entanglement dynamics in the presence of correlated environmental
noises. Specifically, we investigate the quantum entanglement dynamics of two
spins in the presence of correlated classical white noises, deriving Markov
master equation and obtaining explicit solutions for several interesting
classes of initial states including Bell states and X form density matrices. We
show how entanglement can be enhanced or reduced by the correlation between the
two participating noises.Comment: 9 pages, 4 figures. To be published in Quantum Information
Processing, special issue on Quantum Decoherence and Entanglemen
A REAL TIME MONITORING MODEL OF THE CALCIUM CARBONATE FOULING INDUCTION PERIOD BASED ON THE CONDUCTANCE TITRATION
A new method has been developed to monitor the calcium carbonate fouling induction period (CCFIP) in real time. Based on the conductance titration, this paper investigated the forming process of CCFIP by a staticdynamic combined simulation experiment unit. With the help of titration analysis (that is titrimetry), an accurate definition of CCFIP and the corresponding real time monitoring model were built up. The investigation results show that the proposed model applies not only to measure the CCFIP in real time, but also applies to an investigation of the influence of various factors on the CCFIP
1059-17 Prolongation of atrial effective refractory period by biatrial subthreshold stimulation
Low Temperature Measurements by Infrared Spectroscopy in CoFeO Ceramic
In this paper results of new far-infrared and middle-infrared measurements
(wavenumber range of 4000cm-1 - 100cm-1) in the range of the temperature from
300K to 8K of the CoFe2O4 ceramic are presented. The bands positions and their
shapes are the same in the wide temperature range. The quality of the sample
was investigated by X-ray, EDS and EPMA studies. The CoFe2O4 reveals the cubic
structure (Fd-3m) in the temperature range from 85K to 360 K without any traces
of distortion. On the current level of knowledge the polycrystalline CoFe2O4
does not exhibit phase transition in the temperature range from 8 K to 300 K.Comment: 10 pages, 6 figure
Reflection, radiation and interference for black holes
Black holes are capable of reflection: there is a finite probability for any
particle that approaches the event horizon to bounce back. The albedo of the
black hole depends on its temperature and the energy of the incoming particle.
The reflection shares its physical origins with the Hawking process of
radiation, both of them arise as consequences of the mixing of the incoming and
outgoing waves that takes place on the event horizon.Comment: 10 pages, 1 figure, Revte
Sub-Poissonian statistics in order-to-chaos transition
We study the phenomena at the overlap of quantum chaos and nonclassical
statistics for the time-dependent model of nonlinear oscillator. It is shown in
the framework of Mandel Q-parameter and Wigner function that the statistics of
oscillatory excitation number is drastically changed in order-to chaos
transition. The essential improvement of sub-Poissonian statistics in
comparison with an analogous one for the standard model of driven anharmonic
oscillator is observed for the regular operational regime. It is shown that in
the chaotic regime the system exhibits the range of sub- and super-Poissonian
statistics which alternate one to other depending on time intervals. Unusual
dependence of the variance of oscillatory number on the external noise level
for the chaotic dynamics is observed.Comment: 9 pages, RevTeX, 14 figure
- …