88 research outputs found
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 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
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