908 research outputs found
Invariant quantum discord in qubit-qutrit systems under local dephasing
We investigate the dynamics of quantum discord and entanglement for a
class of mixed qubit-qutrit states assuming that only the qutrit is under the action of a dephasing channel. We demonstrate that even though the entanglement in the qubit-qutrit state disappears in a finite time interval, partial coherence left in the system enables quantum discord to remain invariant throughout the whole time evolution
Concept definition study for recovery of tumbling satellites. Volume 1: Executive summary, study results
The first assessment is made of the design requirements and conceptual definition of a front end kit to be transported on the currently defined Orbital Maneuvering Vehicle (OMV) and the Space Transportation System Shuttle Orbiter, to conduct remote, teleoperated recovery of disabled and noncontrollable, tumbling satellites. Previous studies did not quantify the dynamic characteristics of a tumbling satellite, nor did they appear to address the full spectrum of Tumbling Satellite Recovery systems requirements. Both of these aspects are investigated with useful results
Concept definition study for recovery of tumbling satellites. Volume 2: Supporting research and technology report
A number of areas of research and laboratory experiments were identified which could lead to development of a cost efficient remote, disable satellite recovery system. Estimates were planned of disabled satellite motion. A concept is defined as a Tumbling Satellite Recovery kit which includes a modular system, composed of a number of subsystem mechanisms that can be readily integrated into varying combinations. This would enable the user to quickly configure a tailored remote, disabled satellite recovery kit to meet a broad spectrum of potential scenarios. The capability was determined of U.S. Earth based satellite tracking facilities to adequately determine the orientation and motion rates of disabled satellites
Quantum correlations in a few-atom spin-1 Bose-Hubbard model
We study the thermal quantum correlations and entanglement in spin-1 Bose-Hubbard model with two and three particles. While we use negativity to calculate entanglement, more general non-classical correlations are quantified using a new measure based on a necessary and sufficient condition for zero-discord state. We demonstrate that the energy level crossings in the ground state of the system are signalled by both the behavior of thermal quantum correlations and entanglement
Dynamics of Atom-Atom Correlations in the Fermi problem
We present a detailed perturbative study of the dynamics of several types of
atom-atom correlations in the famous Fermi problem. This is an archetypal model
to study micro-causality in the quantum domain where two atoms, the first
initially excited and the second prepared in its ground state, interact with
the vacuum electromagnetic field. The excitation can be transferred to the
second atom via a flying photon and various kinds of quantum correlations
between the two are generated during this process. Among these, prominent
examples are given by entanglement, quantum discord and nonlocal correlations.
It is the aim of this paper to analyze the role of the light cone in the
emergence of such correlations.Comment: 14 pages, 7 figure
Two dimensional Ising spin glasses with non-zero ordering temperatures
We demonstrate numerically that for Ising spins on square lattices with
ferromagnetic second neighbour interactions and random near neighbour
interactions, two dimensional Ising spin glass order with a non-zero freezing
temperature can occur. We compare some of the physical properties of these spin
glasses with those of standard spin glasses in higher dimensions.Comment: 9 page latex file and 9 ps figures. To appear in Phys. Rev. Let
The High Voltage Feedthroughs for the ATLAS Liquid Argon Calorimeters
The purpose, design specifications, construction techniques, and testing
methods are described for the high voltage feedthrough ports and filters of the
ATLAS Liquid Argon calorimeters. These feedthroughs carry about 5000 high
voltage wires from a room-temperature environment (300 K) through the cryostat
walls to the calorimeters cells (89 K) while maintaining the electrical and
cryogenic integrity of the system. The feedthrough wiring and filters operate
at a maximum high voltage of 2.5 kV without danger of degradation by corona
discharges or radiation at the Large Hadron Collider
Bipartite Entanglement in Continuous-Variable Cluster States
We present a study of the entanglement properties of Gaussian cluster states,
proposed as a universal resource for continuous-variable quantum computing. A
central aim is to compare mathematically-idealized cluster states defined using
quadrature eigenstates, which have infinite squeezing and cannot exist in
nature, with Gaussian approximations which are experimentally accessible.
Adopting widely-used definitions, we first review the key concepts, by
analysing a process of teleportation along a continuous-variable quantum wire
in the language of matrix product states. Next we consider the bipartite
entanglement properties of the wire, providing analytic results. We proceed to
grid cluster states, which are universal for the qubit case. To extend our
analysis of the bipartite entanglement, we adopt the entropic-entanglement
width, a specialized entanglement measure introduced recently by Van den Nest M
et al., Phys. Rev. Lett. 97 150504 (2006), adapting their definition to the
continuous-variable context. Finally we add the effects of photonic loss,
extending our arguments to mixed states. Cumulatively our results point to key
differences in the properties of idealized and Gaussian cluster states. Even
modest loss rates are found to strongly limit the amount of entanglement. We
discuss the implications for the potential of continuous-variable analogues of
measurement-based quantum computation.Comment: 22 page
Quantum nature of laser light
All compositions of a mixed-state density operator are equivalent for the
prediction of the probabilities of future outcomes of measurements. For
retrodiction, however, this is not the case. The retrodictive formalism of
quantum mechanics provides a criterion for deciding that some compositions are
fictional. Fictional compositions do not contain preparation device operators,
that is operators corresponding to states that could have been prepared. We
apply this to Molmer's controversial conjecture that optical coherences in
laser light are a fiction and find agreement with his conjecture. We generalise
Molmer's derivation of the interference between two lasers to avoid the use of
any fictional states. We also examine another possible method for
discriminating between conerent states and photon number states in laser light
and find that it does not work, with the equivalence for prediction saved by
entanglement
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