10,888 research outputs found
Quasi-Hamiltonian Method for Computation of Decoherence Rates
For many implementations of quantum computing, 1/f and other types of
broad-spectrum noise are an important source of decoherence. An important step
forward would be the ability to back out the characteristics of this noise from
qubit measurements and to see if it leads to new physical effects. For certain
types of qubits, the working point of the qubit can be varied. Using a new
mathematical method that is suited to treat all working points, we present
theoretical results that show how this degree of freedom can be used to extract
noise parameters and to predict a new effect: noise-induced looping on the
Bloch sphere. We analyze data on superconducting qubits to show that they are
very near the parameter regime where this looping should be observed.Comment: 15 pages, 4 figure
Robust entanglement between a movable mirror and atomic ensemble and entanglement transfer in coupled optomechanical system
We propose a scheme for the creation of robust entanglement between a movable
mirror and atomic ensemble at the macroscopic level in coupled optomechanical
system. In experimentally accessible parameter regimes, we show that critical
temperature of the bipartite continuous variable entanglement in our scheme can
be raised from previous 24 K [Vitali {\it et al.}, Phys. Rev. Lett.
\textbf{98}, 030405 (2007)] and 20 K [Genes {\it et al.}, Phys. Rev. A
\textbf{77}, 050307(R) (2008)] to 32 K. We also investigate the entanglement
transfer based on this coupled system. The scheme can be used for the
realization of quantum memories for continuous variable quantum information
processing and quantum-limited displacement measurements.Comment: 18 pages, 4 figure
Modulation of entanglement between two oscillators separated in space with an optical parametric amplifier
We propose a scheme to modulate the entanglement between two oscillators
separated in space via the squeezing cavity field generated by the optical
parametric amplifier instead of injecting the squeezing field directly with the
assistance of Coulomb interaction. We show that the Coulomb interaction between
the oscillators is the essential reason for the existence of entanglement. Due
to the gain of the optical parametric amplifier and the phase of the pump
driving the optical parametric amplifier can simultaneously modulate the
squeezing cavity field, the radiation pressure interaction between the cavity
field and the oscillator is modulated accordingly. We find that there is
competing effect between the radiation pressure interaction and the Coulomb
interaction for the oscillator which these two interactions act on
simultaneously. Therefore, the modulation of entanglement can be achieved with
the assistance of Coulomb interaction. The results of numerical simulation show
that the present scheme has stronger robustness against the temperature of
environment compared with previous schemes in experimentally feasible regimes.Comment: 19 pages, 5 figure
Steady-state mechanical squeezing in a double-cavity optomechanical system
We study the physical properties of double-cavity optomechanical system in
which the mechanical resonator interacts with one of the coupled cavities and
another cavity is used as an auxiliary cavity. The model can be expected to
achieve the strong optomechanical coupling strength and overcome the
optomechanical cavity decay, simultaneously. Through the coherent auxiliary
cavity interferences, the steady-state squeezing of mechanical resonator can be
generated in highly unresolved sideband regime. The validity of the scheme is
assessed by numerical simulation and theoretical analysis of the steady-state
variance of the mechanical displacement quadrature. The scheme provides a
platform for the mechanical squeezing beyond the resolved sideband limit and
addresses the restricted experimental bounds at present.Comment: 15 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1512.0653
Steady-state mechanical squeezing in a hybrid atom-optomechanical system with a highly dissipative cavity
Quantum squeezing of mechanical resonator is important for studying the
macroscopic quantum effects and the precision metrology of weak forces. Here we
give a theoretical study of a hybrid atom-optomechanical system in which the
steady-state squeezing of the mechanical resonator can be generated via the
mechanical nonlinearity and cavity cooling process. The validity of the scheme
is assessed by simulating the steady-state variance of the mechanical
displacement quadrature numerically. The scheme is robust against dissipation
of the optical cavity, and the steady-state squeezing can be effectively
generated in a highly dissipative cavity
Diagnostics From Three Rising Submillimeter Bursts
In the paper we investigate three novel rising submillimeter (THz) bursts
occurred sequentially in a super-Active Region NOAA 10486. The average rising
rate of the flux density above 200 GHz is only 20 sfu/GHz (corresponding
spectral index of 1.6) for the THz spectral components of 2003 October
28 and November 4 bursts, while it can attain values of 235 sfu/GHz
(=4.8) for 2003 November 2 burst. The steeply rising THz spectrum can
be produced by a population of high relativistic electrons with a low-energy
cutoff of 1 MeV , while it only requires a low-energy cutoff of 30 keV for the
two slowly rising THz bursts, via gyrosynchrotron (GS) radiation based on our
numerical simulations of burst spectra in the magnetic dipole field case. The
electron density variation is much larger in the THz source than that in
microwave (MW) one. It is interesting that the THz source radius decreased by
20--50 during the decay phase for the three events, but the MW one
increased by 28 for the 2003 November 2 event. In the paper we will present
a calculation formula of energy released by ultrarelativistic electrons,
accounting the relativistic correction for the first time. We find that the
energy released by energetic electrons in the THz source exceeds that in
microwave one due to the strong GS radiation loss at THz range, although the
modeled THz source area is 3--4 orders smaller than the modeled MW one. The
total energies released by energetic electrons via the GS radiation in radio
sources are estimated, respectively, to be ,
and erg for the October 28, November 2
and 4 bursts, which are 131, 76 and 4 times as large as the thermal energies of
, and erg estimated
from the soft x-ray GOES observations
Entanglements in Systems with Multiple Degrees of Freedom
We present the entanglement properties of the spin-orbital coupling systems
with multiple degrees of freedom. After constructing the maximally entangled
spin-orbital basis of bipartite, we find that the quantum entanglement length
in the noninteracting itinerant Fermion system with spin and orbit is
considerably larger than that in the system with only spin. In the
SU(2)SU(2) spin-orbital interacting system, the entanglement,
expressed in terms of the spin-orbital correlation functions, clearly manifests
the close relationship with the quantum phases in strongly correlated systems;
and the entanglement phase diagram of the finite-size systems is in agreement
with the magnetic and orbital phase diagram of the infinite systems. The
application of the present theory on nucleon systems is suggested.Comment: 4 pages, 2 figures, submitte
Inflation in de Sitter spacetime and CMB large scales anomaly
The influence of cosmological constant type dark energy in the early universe
is investigated. This is accommodated by a new dispersion relation in de Sitter
spacetime. We perform a global fitting to explore the cosmological parameters
space by using the CosmoMC package with the recently released Planck TT and
WMAP Polarization datasets. Using the results from global fitting, we compute a
new CMB temperature-temperature spectrum. The obtained TT spectrum has lower
power compared with the one based on CDM model at large scales.Comment: 4 pages, 1 table, 3 figure
CosmoMC Installation and Running Guidelines
CosmoMC is a Fortran 95 Markov-Chain Monte-Carlo (MCMC) engine to explore the
cosmological parameter space, plus a Python suite for plotting and presenting
results (see http://cosmologist.info/cosmomc/). This document describes the
installation of the CosmoMC on a Linux system (Ubuntu 14.04.1 LTS 64-bit
version). It is written for those who want to use it in their scientific
research but without much training on Linux and the program. Besides a
step-by-step installation guide, we also give a brief introduction of how to
run the program on both a desktop and a cluster. We share our way to generate
the plots that are commonly used in the references of cosmology. For more
information, one can refer to the CosmoCoffee forum
(http://cosmocoffee.info/viewforum.php?f=11) or contact the authors of this
document. Questions and comments would be much appreciated.Comment: 10 pages, 0 figures. Publicly distributed and availabl
Density of eigenvalues and its perturbation invariance in unitary ensembles of random matrices
We generally study the density of eigenvalues in unitary ensembles of random
matrices from the recurrence coefficients with regularly varying conditions for
the orthogonal polynomials. First we calculate directly the moments of the
density. Then, by studying some deformation of the moments, we get a family of
differential equations of first order which the densities satisfy (see Theorem
1.2), and give the densities by solving them. Further, we prove that the
density is invariant after the polynomial perturbation of the weight function
(see Theorem 1.5).Comment: 21page
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