Radio emission of Shakhbazian Compact Galaxy Groups

Three hundred fifty three radio sources from the NRAO VLA Sky Survey (NVSS) (Condon et al. 1998) and the FIRST Survey (White et al. 1997}, are detected in the areas of 179 Shakhbazian Compact Groups (ShCGs) of galaxies. Ninety three of them are identified with galaxies in 74 ShCGs. Six radio sources have complex structure. The radio spectra of 22 sources are determined. Radio luminosities of galaxies in ShCGs are in general higher than that of galaxies in Hickson Compact Groups (HCGs). The comparison of radio (at 1.4 GHz) and FIR (at 60 $\mu$m) fluxes of ShCG galaxies with that of HCG galaxies shows that galaxies in ShCGs are relatively stronger emitters at radio wavelengths, while galaxies in HCGs have relatively stronger FIR emission. The reasons of such difference is discussed.Comment: 35 pages, 6 Postscript figures, ApJS in pres

Decoherence induced deformation of the ground state in adiabatic quantum computation

Despite more than a decade of research on adiabatic quantum computation (AQC), its decoherence properties are still poorly understood. Many theoretical works have suggested that AQC is more robust against decoherence, but a quantitative relation between its performance and the qubits' coherence properties, such as decoherence time, is still lacking. While the thermal excitations are known to be important sources of errors, they are predominantly dependent on temperature but rather insensitive to the qubits' coherence. Less understood is the role of virtual excitations, which can also reduce the ground state probability even at zero temperature. Here, we introduce normalized ground state fidelity as a measure of the decoherence-induced deformation of the ground state due to virtual transitions. We calculate the normalized fidelity perturbatively at finite temperatures and discuss its relation to the qubits' relaxation and dephasing times, as well as its projected scaling properties.Comment: 10 pages, 3 figure

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

Motional effects on the efficiency of excitation transfer

Energy transfer plays a vital role in many natural and technological processes. In this work, we study the effects of mechanical motion on the excitation transfer through a chain of interacting molecules with application to biological scenarios of transfer processes. Our investigation demonstrates that, for various types of mechanical oscillations, the transfer efficiency is significantly enhanced over that of comparable static configurations. This enhancement is a genuine quantum signature, and requires the collaborative interplay between the quantum-coherent evolution of the excitation and the mechanical motion of the molecules; it has no analogue in the classical incoherent energy transfer. This effect may not only occur naturally, but it could be exploited in artificially designed systems to optimize transport processes. As an application, we discuss a simple and hence robust control technique.Comment: 25 pages, 11 figures; completely revised; version accepted for publicatio

Entanglement in helium

Using a configuration-interaction variational method, we accurately compute the reduced, single-electron von Neumann entropy for several low-energy, singlet and triplet eigenstates of helium atom. We estimate the amount of electron-electron orbital entanglement for such eigenstates and show that it decays with energy.Comment: 5 pages, 2 figures, added references and discussio

Accessible quantification of multiparticle entanglement

Entanglement is a key ingredient for quantum technologies and a fundamental signature of quantumness in a broad range of phenomena encompassing many-body physics, thermodynamics, cosmology and life sciences. For arbitrary multiparticle systems, entanglement quantification typically involves nontrivial optimisation problems, and it may require demanding tomographical techniques. Here, we develop an experimentally feasible approach to the evaluation of geometric measures of multiparticle entanglement. Our framework provides analytical results for particular classes of mixed states of N qubits, and computable lower bounds to global, partial, or genuine multiparticle entanglement of any general state. For global and partial entanglement, useful bounds are obtained with minimum effort, requiring local measurements in just three settings for any N. For genuine entanglement, a number of measurements scaling linearly with N are required. We demonstrate the power of our approach to estimate and quantify different types of multiparticle entanglement in a variety of N-qubit states useful for uantum information processing and recently engineered in laboratories with quantum optics and trapped ion setups

Finite-time destruction of entanglement and non-locality by environmental influences

Entanglement and non-locality are non-classical global characteristics of quantum states important to the foundations of quantum mechanics. Recent investigations have shown that environmental noise, even when it is entirely local in influence, can destroy both of these properties in finite time despite giving rise to full quantum state decoherence only in the infinite time limit. These investigations, which have been carried out in a range of theoretical and experimental situations, are reviewed here.Comment: 27 pages, 6 figures, review article to appear in Foundations of Physic