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 $\alpha$ 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 ($\alpha$=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 $5.2\times10^{33}$, $3.9\times10^{33}$ and $3.7\times10^{32}$ erg for the October 28, November 2 and 4 bursts, which are 131, 76 and 4 times as large as the thermal energies of $2.9\times10^{31}$, $2.1\times10^{31}$ and $5.2\times10^{31}$ 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)$\otimes$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 $\Lambda$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