965 research outputs found
The Generalized Hartle-Hawking Initial State: Quantum Field Theory on Einstein Conifolds
Recent arguments have indicated that the sum over histories formulation of
quantum amplitudes for gravity should include sums over conifolds, a set of
histories with more general topology than that of manifolds. This paper
addresses the consequences of conifold histories in gravitational functional
integrals that also include scalar fields. This study will be carried out
explicitly for the generalized Hartle-Hawking initial state, that is the
Hartle-Hawking initial state generalized to a sum over conifolds. In the
perturbative limit of the semiclassical approximation to the generalized
Hartle-Hawking state, one finds that quantum field theory on Einstein conifolds
is recovered. In particular, the quantum field theory of a scalar field on de
Sitter spacetime with spatial topology is derived from the generalized
Hartle-Hawking initial state in this approximation. This derivation is carried
out for a scalar field of arbitrary mass and scalar curvature coupling.
Additionally, the generalized Hartle-Hawking boundary condition produces a
state that is not identical to but corresponds to the Bunch-Davies vacuum on
de Sitter spacetime. This result cannot be obtained from the original
Hartle-Hawking state formulated as a sum over manifolds as there is no Einstein
manifold with round boundary.Comment: Revtex 3, 31 pages, 4 epsf figure
Husimi's function and quantum interference in phase space
We discuss a phase space description of the photon number distribution of non
classical states which is based on Husimi's function and does not
rely in the WKB approximation. We illustrate this approach using the examples
of displaced number states and two photon coherent states and show it to
provide an efficient method for computing and interpreting the photon number
distribution . This result is interesting in particular for the two photon
coherent states which, for high squeezing, have the probabilities of even and
odd photon numbers oscillating independently.Comment: 15 pages, 12 figures, typos correcte
Microtubule-dependent Organization of Vaccinia Virus Core-derivd Early mRNAs into Distinct Cytoplasmic Structures.
Vaccinia virus (vv) early transcription can be reconstituted in vitro from purified virions; in this assay mRNAs are made inside the viral core and subsequently extruded. Although the in vitro process has been extensively characterized, relatively little is known about vv early transcription in vivo. In the present study the fate of vv early mRNAs in infected HeLa cells was followed by BrUTP transfection and confocal and electron microscopy. The extruded vv early mRNAs were found to be organized into unique granular cytoplasmic structures that reached a size up to 1 ÎĽm. By EM these structures appeared as amorphous electron-dense cytoplasmic aggregates that were surrounded by ribosomes. Confocal images showed that the RNA structures were located some distance away from intracellular cores and that both structures appeared to be aligned on microtubules (MTs), implying that MT tracks connected mRNAs and cores. Accordingly, intact MTs were found to be required for the typical punctate organization of viral mRNAs. Biochemical evidence supported the notion that vv mRNAs were MT associated and that MT depletion severely affected viral (but not cellular) mRNA synthesis and stability. By confocal microscopy the viral mRNA structures appeared to be surrounded by molecules of the translation machinery, showing that they were active in protein synthesis. Finally, our data suggest a role for a MT and RNA-binding viral protein of 25 kDa (gene L4R), in mRNA targeting away from intracellular cores to their sites of cytoplasmic accumulation
The Beam Conditions Monitor of the LHCb Experiment
The LHCb experiment at the European Organization for Nuclear Research (CERN)
is dedicated to precision measurements of CP violation and rare decays of B
hadrons. Its most sensitive components are protected by means of a Beam
Conditions Monitor (BCM), based on polycrystalline CVD diamond sensors. Its
configuration, operation and decision logics to issue or remove the beam permit
signal for the Large Hadron Collider (LHC) are described in this paper.Comment: Index Terms: Accelerator measurement systems, CVD, Diamond, Radiation
detector
Wigner flow reveals topological order in quantum phase space dynamics
The behaviour of classical mechanical systems is characterised by their phase
portraits, the collections of their trajectories. Heisenberg's uncertainty
principle precludes the existence of sharply defined trajectories, which is why
traditionally only the time evolution of wave functions is studied in quantum
dynamics. These studies are quite insensitive to the underlying structure of
quantum phase space dynamics. We identify the flow that is the quantum analog
of classical particle flow along phase portrait lines. It reveals hidden
features of quantum dynamics and extra complexity. Being constrained by
conserved flow winding numbers, it also reveals fundamental topological order
in quantum dynamics that has so far gone unnoticed.Comment: 6 pages, 6 figure
Rydberg Wave Packets are Squeezed States
We point out that Rydberg wave packets (and similar ``coherent" molecular
packets) are, in general, squeezed states, rather than the more elementary
coherent states. This observation allows a more intuitive understanding of
their properties; e.g., their revivals.Comment: 7 pages of text plus one figure available in the literature, LA-UR
93-2804, to be published in Quantum Optics, LaTe
Photon-assisted entanglement creation by minimum-error generalized quantum measurements in the strong coupling regime
We explore possibilities of entangling two distant material qubits with the
help of an optical radiation field in the regime of strong quantum
electrodynamical coupling with almost resonant interaction. For this purpose
the optimum generalized field measurements are determined which are capable of
preparing a two-qubit Bell state by postselection with minimum error. It is
demonstrated that in the strong-coupling regime some of the recently found
limitations of the non-resonant weak-coupling regime can be circumvented
successfully due to characteristic quantum electrodynamical quantum
interference effects. In particular, in the absence of photon loss it is
possible to postselect two-qubit Bell states with fidelities close to unity by
a proper choice of the relevant interaction time. Even in the presence of
photon loss this strong-coupling regime offers interesting perspectives for
creating spatially well-separated Bell pairs with high fidelities, high success
probabilities, and high repetition rates which are relevant for future
realizations of quantum repeaters.Comment: 14 pages, 12 figure
Classical phase-space descriptions of continuous-variable teleportation
The nonnegative Wigner function of all quantum states involved in
teleportation of Gaussian states using the standard continuous-variable
teleportation protocol means that there is a local realistic phase-space
description of the process. This includes the coherent states teleported up to
now in experiments. We extend the phase-space description to teleportation of
non-Gaussian states using the standard protocol and conclude that teleportation
of non-Gaussian states with fidelity of 2/3 is a "gold standard" for this kind
of teleportation.Comment: New version contains minor changes requested by journal referee
NMR experiment factors numbers with Gauss sums
We factor the number 157573 using an NMR implementation of Gauss sums.Comment: 4 pages 5 figure
- …