707 research outputs found
Nonlinear Phenomena in Canonical Stochastic Quantization
Stochastic quantization provides a connection between quantum field theory
and statistical mechanics, with applications especially in gauge field
theories. Euclidean quantum field theory is viewed as the equilibrium limit of
a statistical system coupled to a thermal reservoir. Nonlinear phenomena in
stochastic quantization arise when employing nonlinear Brownian motion as an
underlying stochastic process. We discuss a novel formulation of the Higgs
mechanism in QED.Comment: 8 pages, invited talk at the International Workshop ``Critical
Phenomena and Diffusion in Complex Systems'', Dec. 5-7, 2006, Nizhni
Novgorod, Russi
Einstein-Podolsky-Rosen-like correlation on a coherent-state basis and inseparability of two-mode Gaussian states
The strange property of the Einstein-Podolsky-Rosen (EPR) correlation between
two remote physical systems is a primitive object on the study of quantum
entanglement. In order to understand the entanglement in canonical
continuous-variable systems, a pair of the EPR-like uncertainties is an
essential tool. Here, we consider a normalized pair of the EPR-like
uncertainties and introduce a state-overlap to a classically correlated mixture
of coherent states. The separable condition associated with this state-overlap
determines the strength of the EPR-like correlation on a coherent-state basis
in order that the state is entangled. We show that the coherent-state-based
condition is capable of detecting the class of two-mode Gaussian entangled
states. We also present an experimental measurement scheme for estimation of
the state-overlap by a heterodyne measurement and a photon detection with a
feedforward operation.Comment: 9 pages, 5 figures. A part of the materials in Sec. VI B of previous
versions was moved into another paper: Journal of Atomic, Molecular, and
Optical Physics, 2012, 854693 (2012).
http://www.hindawi.com/journals/jamop/2012/854693
Continuous Variable Quantum Cryptography using Two-Way Quantum Communication
Quantum cryptography has been recently extended to continuous variable
systems, e.g., the bosonic modes of the electromagnetic field. In particular,
several cryptographic protocols have been proposed and experimentally
implemented using bosonic modes with Gaussian statistics. Such protocols have
shown the possibility of reaching very high secret-key rates, even in the
presence of strong losses in the quantum communication channel. Despite this
robustness to loss, their security can be affected by more general attacks
where extra Gaussian noise is introduced by the eavesdropper. In this general
scenario we show a "hardware solution" for enhancing the security thresholds of
these protocols. This is possible by extending them to a two-way quantum
communication where subsequent uses of the quantum channel are suitably
combined. In the resulting two-way schemes, one of the honest parties assists
the secret encoding of the other with the chance of a non-trivial superadditive
enhancement of the security thresholds. Such results enable the extension of
quantum cryptography to more complex quantum communications.Comment: 12 pages, 7 figures, REVTe
Dynamical Semigroup Description of Coherent and Incoherent Particle-Matter Interaction
The meaning of statistical experiments with single microsystems in quantum
mechanics is discussed and a general model in the framework of non-relativistic
quantum field theory is proposed, to describe both coherent and incoherent
interaction of a single microsystem with matter. Compactly developing the
calculations with superoperators, it is shown that the introduction of a time
scale, linked to irreversibility of the reduced dynamics, directly leads to a
dynamical semigroup expressed in terms of quantities typical of scattering
theory. Its generator consists of two terms, the first linked to a coherent
wavelike behaviour, the second related to an interaction having a measuring
character, possibly connected to events the microsystem produces propagating
inside matter. In case these events breed a measurement, an explicit
realization of some concepts of modern quantum mechanics ("effects" and
"operations") arises. The relevance of this description to a recent debate
questioning the validity of ordinary quantum mechanics to account for such
experimental situations as, e.g., neutron-interferometry, is briefly discussed.Comment: 22 pages, latex, no figure
Angular distributions of H-induced HD and D2 desorptions from the Si(100) surfaces
We measured angular distributions of HD and D2 molecules desorbed via the reactions H+D/Si 100 âHD abstraction ABS and H+D/Si 100 âD2 adsorption-induced-desorption AID , respectively. It was found that the angular distribution of HD molecules desorbed alongABS is broader than that of D2 molecules desorbed along AID, i.e., the former could be fit withcos2.0±0.2 , while the latter with cos5.0±0.5 . This difference of the angular distributions between thetwo reaction paths suggests that their dynamic mechanisms are different. The observed cos2 distribution for the ABS reaction was reproduced by the classical trajectory calculations over theLondon-Eyring-Polanyi-Sato potential-energy surfaces. The simulation suggests that the HDdesorption along the ABS path takes place along the direction of SiâD bonds, but the apparentangular distribution is comprised of multiple components reflecting the different orientations ofD-occupied Si dimers in the 2 1 and 1 2 double domain structures
A Massive Jet Ejection Event from the Microquasar SS 433 Accompanying Rapid X-Ray Variability
Microquasars occasionally exhibit massive jet ejections which are distinct
from the continuous or quasi-continuous weak jet ejections. Because those
massive jet ejections are rare and short events, they have hardly been observed
in X-ray so far. In this paper, the first X-ray observation of a massive jet
ejection from the microquasar SS 433 with the Rossi X-ray Timing Explorer
(RXTE) is reported. SS 433 undergoing a massive ejection event shows a variety
of new phenomena including a QPO-like feature near 0.1 Hz, rapid time
variability, and shot-like activities. The shot-like activity may be caused by
the formation of a small plasma bullet. A massive jet may be consist of
thousands of those plasma bullets ejected from the binary system. The size,
mass, internal energy, and kinetic energy of the bullets and the massive jet
are estimated.Comment: 21 pages including 5 figures, submitted to Ap
Modulated hydrogen beam study of adsorption-induced desorption of deuterium from Si(100)-3Ă1:D surfaces
We have studied the kinetic mechanism of the adsorption-induced-desorption (AID) reaction, H + D/Si(100)D2. Using a modulated atomic hydrogen beam, two different types of AID reaction are revealed: one is the fast AID reaction occurring only at the beam on-cycles and the other the slow AID reaction occurring even at the beam off-cycles. Both the fast and slow AID reactions show the different dependence on surface temperature Ts, suggesting that their kinetic mechanisms are different. The fast AID reaction overwhelms the slow one in the desorption yield for 300 KTs650 K. It proceeds along a first-order kinetics with respect to the incident H flux. Based on the experimental results, both two AID reactions are suggested to occur only on the 3Ă1 dihydride phase accumulated during surface exposure to H atoms. Possible mechanisms for the AID reactions are discussed
Hot-complex-mediated abstraction and desorption of D adatoms by H on Si(100)
The collision-induced associative desorption (CID) and abstraction (ABS) of D adatoms by H have been studied on the Si(100) surfaces. D2 CID exhibits a feature common to that of a thermal desorption from a dideuteride phase. HD ABS proceeds along an apparently second-order kinetics rather than a first-order kinetics with respect to surface D coverages. The ABS cross section is about 6 ïŸă»sup>2, extremely large compared to the theoretical values. Both of the direct Eley-Rideal mechanism and the hot-atom mechanism are ruled out. A hot-complex-mediated reaction model is proposed for ABS and CID
Dynamical decoherence in a cavity with a large number of two-level atoms
We consider a large number of two-level atoms interacting with the mode of a
cavity in the rotating-wave approximation (Tavis-Cummings model). We apply the
Holstein-Primakoff transformation to study the model in the limit of the number
of two-level atoms, all in their ground state, becoming very large. The unitary
evolution that we obtain in this approximation is applied to a macroscopic
superposition state showing that, when the coherent states forming the
superposition are enough distant, then the state collapses on a single coherent
state describing a classical radiation mode. This appear as a true dynamical
effect that could be observed in experiments with cavities.Comment: 9 pages, no figures. This submission substitutes paper
quant-ph/0212148 that was withdrawn. Version accepted for publication in
Journal of Physics B: Atomic, Molecular & Optical Physic
Timelapse
We discuss the existence in an arbitrary frame of a finite time for the
transformation of an initial quantum state into another e.g. in a decay.
This leads to the introduction of a timelapse in analogy with
the lifetime of a particle. An argument based upon the Heisenberg uncertainty
principle suggests the value of . Consequences for the
exponential decay formula and the modifications that introduces
into the Breit-Wigner mass formula are described.Comment: 5 pages [2 figs], ReV-Te
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