14,045 research outputs found
Dynamical invariants and nonadiabatic geometric phases in open quantum systems
We introduce an operational framework to analyze non-adiabatic Abelian and
non-Abelian, cyclic and non-cyclic, geometric phases in open quantum systems.
In order to remove the adiabaticity condition, we generalize the theory of
dynamical invariants to the context of open systems evolving under arbitrary
convolutionless master equations. Geometric phases are then defined through the
Jordan canonical form of the dynamical invariant associated with the
super-operator that governs the master equation. As a by-product, we provide a
sufficient condition for the robustness of the phase against a given decohering
process. We illustrate our results by considering a two-level system in a
Markovian interaction with the environment, where we show that the
non-adiabatic geometric phase acquired by the system can be constructed in such
a way that it is robust against both dephasing and spontaneous emission.Comment: 9 pages, 3 figures. v2: minor corrections and subsection IV.D added.
Published versio
Quantum Nonlocal Boxes Exhibit Stronger Distillability
The hypothetical nonlocal box (\textsf{NLB}) proposed by Popescu and Rohrlich
allows two spatially separated parties, Alice and Bob, to exhibit stronger than
quantum correlations. If the generated correlations are weak, they can
sometimes be distilled into a stronger correlation by repeated applications of
the \textsf{NLB}. Motivated by the limited distillability of \textsf{NLB}s, we
initiate here a study of the distillation of correlations for nonlocal boxes
that output quantum states rather than classical bits (\textsf{qNLB}s). We
propose a new protocol for distillation and show that it asymptotically
distills a class of correlated quantum nonlocal boxes to the value , whereas in contrast, the optimal non-adaptive
parity protocol for classical nonlocal boxes asymptotically distills only to
the value 3.0. We show that our protocol is an optimal non-adaptive protocol
for 1, 2 and 3 \textsf{qNLB} copies by constructing a matching dual solution
for the associated primal semidefinite program (SDP). We conclude that
\textsf{qNLB}s are a stronger resource for nonlocality than \textsf{NLB}s. The
main premise that develops from this conclusion is that the \textsf{NLB} model
is not the strongest resource to investigate the fundamental principles that
limit quantum nonlocality. As such, our work provides strong motivation to
reconsider the status quo of the principles that are known to limit nonlocal
correlations under the framework of \textsf{qNLB}s rather than \textsf{NLB}s.Comment: 25 pages, 7 figure
Photon-induced oxidation of graphene/Ir(111) by SO<sub>2</sub> adsorption
We prepare a single layer of graphene oxide by adsorption and subsequent photo-dissociation of SO2 on graphene/Ir(111). Epoxidic oxygen is formed as the main result of this process on graphene, as judged from the appearance of characteristic spectroscopic features in the C 1s and O 1s core level lines. The different stages of decomposition of SO2 into its photo-fragments are examined during the oxidation process. NEXAFS at the carbon K edge reveals a strong disturbance of the graphene backbone after oxidation and upon SO adsorption. The oxide phase is stable up to room temperature, and is fully reversible upon annealing at elevated temperatures. A band gap opening of 330 ± 60 meV between the valence and conduction bands is observed in the graphene oxide phase
Heshbon Expedition: The Second Campaign at Tell Hesban
The first campaign at Tell Hesban was carried out in 1968,\u27 and the second season was planned for the summer of 1970. The outbreak of the first phase of the Jordanian civil war in June of that year, however, forced a cancellation of the expedition, although some staff members, including the director, were already in Amman and most others were en route to Jordan. \u27 Rescheduled for the next summer, the second campaign was successfully conducted from July 5 to August 20, 1971. I Heshbon\u27s history from literary sources,2 and a description of , Tell Hesban and its geographical location3 have already been covered. For this reason these will not be discussed in this report
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Principles of Laser Micro Sintering
Laser Micro Sintering was introduced to the international community of freeform fabrication
engineers in 2003 and has since been employed for a variety of applications. It owes its unique
features to certain effects of q-switched pulses that formerly had been considered detrimental in
selective laser sintering. Besides sub-micrometer sized powders also materials with grain sizes
of 1-10 micrometers can be sintered. Surface and morphology of the product are influenced by
grain size and process environment. First results have been achieved with processing ceramic
materials.
A comprehensive overview of the process and the features is given supported by
experimental evidence. Routes of further development are indicated.Mechanical Engineerin
Multiphoton entanglement through a Bell multiport beam splitter
Multiphoton entanglement is an important resource for linear optics quantum
computing. Here we show that a wide range of highly entangled multiphoton
states, including W-states, can be prepared by interfering single photons
inside a Bell multiport beam splitter and using postselection. A successful
state preparation is indicated by the collection of one photon per output port.
An advantage of the Bell multiport beam splitter is that it redirects the
photons without changing their inner degrees of freedom. The described setup
can therefore be used to generate polarisation, time-bin and frequency
multiphoton entanglement, even when using only a single photon source.Comment: 8 pages, 2 figures, carefully revised version, references adde
CORE Technology and Exact Hamiltonian Real-Space Renormalization Group Transformations
The COntractor REnormalization group (CORE) method, a new approach to solving
Hamiltonian lattice systems, is presented. The method defines a systematic and
nonperturbative means of implementing Kadanoff-Wilson real-space
renormalization group transformations using cluster expansion and contraction
techniques. We illustrate the approach and demonstrate its effectiveness using
scalar field theory, the Heisenberg antiferromagnetic chain, and the
anisotropic Ising chain. Future applications to the Hubbard and t-J models and
lattice gauge theory are discussed.Comment: 65 pages, 9 Postscript figures, uses epsf.st
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