The folklore notion of the "Non-Locality of Quantum Mechanics" is examined from the point of view of hidden-variables theories according to Belinfante's classification in his Survey of Hidden Variables Theories. It is here shown that in the case of EPR, there exist hidden variables theories that successfully reproduce quantum-mechanical predictions, but which are explicitly local. Since such theories do not fall into Belinfante's classification, we propose an expanded classification which includes similar theories, which we term as theories of the "third" kind. Causal implications of such theories are explored. -Pacs: 03.65.Bz

Open Access June 2, 2014

The Mean King's Problem: Spin

Yakir Aharonov, Berthold-Georg Englert

Page range: 16-19

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Abstract

We show how one can ascertain the values of four mutually complementary observables of a spin-1 degree of freedom. -Pacs: 03.65.Bz

Open Access June 2, 2014

Sending Signals to Space-Like Separated Regions

Y. Aharonov, L. Vaidman

Page range: 20-26

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Abstract

Two recent works suggest a possibility of sending signals to a space-like separated region, contrary to the spirit of special relativity. In the first work (J. Grunhaus, S. Popescu, and D. Rohrlich, Phys. Rev. A 53, 3781 (1996)) it has been shown that sending signals to a particular union of space-like separated regions cannot cause causality paradoxes. Another work (Y. Aharonov and L. Vaidman, Phys. Rev. A 61, 052108 (2000)) showed that the relative phase of the quantum superposition of a particle at two separate locations can be measured locally. Together with the possibility of changing the relative phase in a nonlocal way using the potential effect we, apparently, have a method of sending signals to space-like separated regions. These arguments are critically analyzed in this paper.

Open Access June 2, 2014

Verifying Atom Entanglement Schemes by Testing Bell's Inequality

Dimitris G. Angelakis, Almut Beigea, Peter L. Knight, William J. Munro, Ben Tregenn

Page range: 27-34

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Abstract

Recent experiments to test B ell's inequality using entangled photons and ions aimed at tests of basic quantum mechanical principles. Interesting results have been obtained and many loopholes could be closed. In this paper we want to point out that tests of Bell's inequality also play an important role in verifying atom entanglement schemes. We describe as an example a scheme to prepare arbitrary entangled states of N two-level atoms using a leaky optical cavity and a scheme to entangle atoms inside a photonic crystal. During the state preparation no photons are emitted, and observing a violation of B ell's inequality is the only way to test whether a scheme works with a high precision or not.

Open Access June 2, 2014

Spin Squeezing in Degenerate and Non-degenerate Atomic Vapors: Some Approaches to Atomic Entanglement

Nicholas P. Bigelow

Page range: 35-40

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Abstract

In this paper we discuss our recent work on the creation of spin-squeezed states in both thermal (room temperature) gasses and in spinor Bose-Einstein condensates.

Open Access June 2, 2014

Young's Experiment, Schrödinger's Spread and Spontaneous Intrinsic Decoherence

R. Bonifacio, S. Olivares

Page range: 41-47

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Abstract

The two slits interference pattern for single particle is revisited, showing its strict relation to the free particle Schrödinger’s spread and describing the optical analogy. We explicitly show the possibility that spontaneous intrinsic decoherence (SID) can destroy interference pattern and that decoherence becomes stronger at the macroscopic limit.

Open Access June 2, 2014

Unusual Bound or Localized States

M. A. Cirone, G. Metikas, W. P. Schleicha

Page range: 48-60

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Abstract

We summarize unusual bound or localized states in quantum mechanics. Our guide through these intriguing phenomena is the classical physics of the upside-down pendulum, taking advantage of the analogy between the corresponding Newton’s equation of motion and the time independent Schrödinger equation. We discuss the zero-energy ground state in a three-dimensional, spatially oscillating, potential. Moreover, we focus on the effect of the attractive quantum anti-centrifugal potential that only occurs in a two-dimensional situation.

Open Access June 2, 2014

Multiparticle Quantum Superposition and Stimulated Entanglement by Parity Selective Amplification of Entangled States

Francesco De Martini, Giovanni Di Giuseppe

Page range: 61-66

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Abstract

A multiparticle quantum superposition state has been generated by a novel phase-selective parametric amplifier of an entangled two-photon state. This realization is expected to open a new field of investigations on the persistence of the validity of the standard quantum theory for systems of increasing complexity, in a quasi decoherence-free environment. Because of its nonlocal structure the new system is expected to play a relevant role in the modem endeavor on quantum information and in the basic physics of entanglement. - Pacs: 03.65.Bz, 03.67.-a, 42.50.Ar, 89.70.+C

Open Access June 2, 2014

The Inconsistency of the Usual Galilean Transformation in Quantum Mechanics and How To Fix It

Daniel M. Greenberger

Page range: 67-75

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Abstract

It is shown that the generally accepted statement that one cannot superpose states of different mass in non-relativistic quantum mechanics is inconsistent. It is pointed out that the extra phase induced in a moving system, which was previously thought to be unphysical, is merely the non-relativistic residue of the "twin-paradox" effect. In general, there are phase effects due to proper time differences between moving frames that do not vanish non-relativistically. There are also effects due to the equivalence of mass and energy in this limit. The remedy is to include both proper time and rest energy non-relativis-tically. This means generalizing the meaning of proper time beyond its classical meaning, and introduc ing the mass as its conjugate momentum. The result is an uncertainty principle between proper time and mass that is very general, and an integral role for both concepts as operators in non-relativistic physics.

Open Access June 2, 2014

Quantum Physics and Reality

Rudolf Haag

Page range: 76-82

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Abstract

Apparent paradoxes in Quantum Physics demand a sharp distinction between a "real part of the world" and the realm of possibilities. In the former we may distinguish individual elements (coarse events) relating to space-time, with causal connections between them respecting the relativistic locality principle. The latter, quantitatively described by probability assignments conditioned on existing facts and depending on the definition of equivalence classes of situations, cannot be subdivided in space-time categories. There are global correlations (Pauli principle...). The cut between the realms of facts and possibilities implies an evolutionary picture of the "real world" in which the (generalized) arrow of time assumes basic significance. Some deficiencies of existing theory are pointed out.

Open Access June 2, 2014

Frequent Observations Accelerate Decay: The anti-Zeno Effect

A. G. Kofman, G. Kurizki

Page range: 83-90

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Abstract

The quantum Zeno effect (QZE) is the striking prediction that the decay of any unstable quan tum state can be inhibited by sufficiently frequent observations (measurements). The consensus

Open Access June 2, 2014

Entanglement Capability of Two-qubit Operations

B. Kraus, W. Dür, G. Vidal, J. I. Cirac, M. Lewenstein, N. Linden, S. Popescu

Page range: 91-99

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Abstract

We study the optimal way of creating bi-partite entanglement using a general two-qubit in teraction. On the one hand, we analyze the entanglement capability of an arbitrary non-local Hamiltonian acting on two qubits. We explicitly calculate the state which maximizes the entangle ment produced per time step 81 during the non-local evolution. On the other hand, we determine the maximal amount of entanglement which can be produced by an arbitrary two-qubit gate. We also give the separable state which leads to the output state containing this amount of entanglement. Furthermore, we consider the situation where auxiliary systems are present. Finally, we determine the non-unitary processes which are able to create entanglement from an initially separable state of two systems.

Open Access June 2, 2014

The Paradoxes of the Interaction-free Measurements

L. Vaidman

Page range: 100-107

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Abstract

Interaction-free measurements introduced by Elitzur and Vaidman [Found. Phys. 23,987 (1993)] allow finding infinitely fragile objects without destroying them. Paradoxical features of these and related measurements are discussed. The resolution of the paradoxes in the framework of the Many-Worlds Interpretation is proposed.

Open Access June 2, 2014

A Cavity QED Source for Entangled Photons

David Vitali, Giacomo Ciaramicoli, Paolo Tombesi

Page range: 108-116

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Abstract

We study the possible limitations and sources of decoherence of a scheme for the deterministic generation of polarization-entangled photons based on an appropriately driven single atom trapped within an optical cavity. -Pacs: 03.67.Hk, 42.50.Gy, 32.80.Qk

Open Access June 2, 2014

Generation and Detection of Fock-States of the Radiation Field

Herbert Walther

Page range: 117-123

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Abstract

In this paper we give a survey of our experiments performed with the micromaser on the generation of Fock states. Three methods can be used for this purpose: the trapping states leading to Fock states in a continuous wave operation, state reduction of a pulsed pumping beam, and finally using a pulsed pumping beam to produce Fock states on demand where trapping states stabilize the photon number.

Open Access June 2, 2014

Decoherence, Classical Properties and Entanglement of Quantum Systems

Ph. Blanchard, R. Olkiewicz

Page range: 124-127

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Abstract

We discuss the properties of decoherence and its role in the appearance of classical properties in open quantum systems. In particular, it is used for classification of pure states with respect to their ability to persist despite the environmental monitoring.

Open Access June 2, 2014

Bell States, Bell Operators, and Total Teleportation

E. DelRe, B. Crosignani, P. Di Porto

Page range: 128-132

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Abstract

We identify the operators and the corresponding physical quantities whose measurement allows in principle to obtain total teleportation of the unknown spin state of a single electron. We introduce an analogous scheme for a single photon and discuss its experimental implementation.

Open Access June 2, 2014

Quantum Criticality

P. D. Drummond, S. Chaturvedi, K. Dechoum, J. Comey

Page range: 133-139

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Abstract

We investigate the theory of quantum fluctuations in non-equilibrium systems having large critical fluctuations. This allows us to treat the limits imposed by nonlinearities to quantum squeezing and noise reduction, and also to envisage future tests of quantum theory in regions of macroscopic quantum fluctuations. A long-term objective of this research is to identify suitable physical systems in which macroscopic 'Schrödinger cat'-like behaviour may be observed. We investigate two systems in particular of much current experimental interest, namely the degenerate parametric oscillator near threshold, and the evaporatively cooled (BEC). We compare the results obtained in the positive-P representation, as a fully quantum mechanical calculation, with the truncated Wigner phase space equation, also known as semi-classical theory. We show when these results agree and differ in calculations taken beyond the linearized approximation. In the region where the largest quantum fluctuations and Schrödinger cat-like behaviour might be expected, we find that the quantum predictions correspond very closely to the semi-classical theory. Nature abhors observing a Schrödinger cat. -Pacs: 03.65.Bz

Open Access June 2, 2014

On the Observation of Decoherence with a Movable Mirror

R. Folman, J. Schmiedmayer, H. Ritsch, D. Vitali

Page range: 140-144

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Abstract

Recently it has been proposed to use parity as a measure of the mechanism behind decoherence or the transformation from quantum to classical. Here, we show that the proposed experiment is more feasible than previously thought, as even an initial thermal state would exhibit the hypothesized symmetry breaking. - Pacs: 03.75.Be, 03.65.Nk

Open Access June 2, 2014

Entangled State Reconstruction of an Electron in the Penning Trap

Mauro Fortunato, Michol Massini, Stefano Mancini, Paolo Tombesi

Page range: 145-151

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Abstract

We apply a tomographic method we have recently proposed to the reconstruction of the full entangled quantum state for the cyclotron and spin degrees of freedom of a trapped electron. Our numerical simulations show that the entangled state is accurately reconstructed. -Pacs: 03.65.

Open Access June 2, 2014

Maximally Entangled Mixed States and the Bell Inequality

W. J. Munro, K. Nemoto

Page range: 152-154

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Abstract

Recently a class of maximally entangled states has been proposed that has the maximum amount of entanglement for a given purity. We investigate how much such states violate the conventional Bell inequality and discuss its implication.

Open Access June 2, 2014

Interaction-Free Which-Path Information and Some of Its Consequences

Luiz Carlos Ryff

Page range: 155-159

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Abstract

Let us consider a single particle in an interferometer. If one of the two possible paths is blocked and the particle is detected, we know that the particle has followed the path which is not blocked. This would be an interference-free "which-path" information experiment. However, we no longer have an interferometer, since one path is blocked. An alternative is to interact with the particle, but this would change its momentum and as a consequence the interference fringes would disappear, as discussed by Feynman. We can also consider two particles entangled in direction. Knowing the path followed by one of the particles, it is possible to know the path followed by the other. On the other hand, when this information is erased, interference can be observed. However, this is a two particle interference: no single particle interference can be observed. Retrodiction experiments are also possible, but these are not conclusive. Here we propose a much less intuitive experiment in which, without blocking one path or directly interacting with the particle, it is possible to know the path which is being followed by the particle in the interferometer. According to quantum mechanics, this is sufficient to lose the single particle interference. The same idea can be used to test the local pilot wave interpretation, to test quantum nonlocality under new conditions, and to devise an interferometer for a two-photon wave packet. This last result strongly suggests that there must be some connection between the deBroglie wavelength of an N-particle wave packet and entanglement. Wavelength of an /V-particle Wave Packet.

Open Access June 2, 2014

Evolution of an Atom Impeded by Measurement: The Quantum Zeno Effect

Chr. Wunderlich, Chr. Balzer, P. E. Toschek

Page range: 160-164

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Abstract

A quantum system being observed evolves more slowly. This "quantum Zeno effect" is reviewed with respect to a previous attempt of demonstration, and to subsequent criticism of the significance of the findings. A recent experiment on an individual cold trapped ion has been capable of revealing the micro-state of this quantum system, such that the effect of measurement is indeed discriminated from dephasing of the quantum state by either the meter or the environment.

Open Access June 2, 2014

Non-Collinear Configuration for Dichromatic Squeezing

Alessandra Andreoni, Maria Bondani, G. Mauro D ’Ariano, Matteo G. A. Paris

Page range: 165-168

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Abstract

We propose a non-collinear experimental scheme for the joint generation of two amplitudesqueezed beams at the frequencies u\ and u>2, fundamental and second harmonics of a Nd:YAG laser pulse. The scheme consists of two successive steps, both involving second-order non-linear interactions in ß - BaB 2 O 4 non-linear crystals. One of the output beams show subPoissonian photon statistics, and this allows to use photodetection instead of homodyne detection for diagnostics

Open Access June 2, 2014

Laser Assisted Cherenkov Emission in Resonant Media

M. Artoni, I. Carusotto, G. C. La Rocca, F. Bassani

Page range: 169-172

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Abstract

We theoretically examine the behaviour of Cherenkov radiation in a lossy, dispersive and resonant medium when emission is assisted by an external electromagnetic field. Under the appropriate coherence conditions for Cherenkov emission, we anticipate a large increase of the emission yield at resonance. Our predictions are implemented by numerical estimates for cuprous oxide (Cu20 ). Pacs: 61.43.Fs, 77.22.Ch, 75.50.Lk

Open Access June 2, 2014

Transverse Momentum Distribution of Atoms in an Interferometer

Mirijana Božić, Dušan Arsenović, Lepša Vušković

Page range: 173-177

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Abstract

From the stationary solution of Schrödinger's equation in an interferometer we derive the wave functions of the longitudinal and the transverse motion. The former function is a plane wave. The wave function of the transverse motion is a one dimensional wave packet representing a super position of components with various values of the particles transverse momentum. The particles transverse momentum distribution in an interferometer is time independent and is determined by the aperture wave function. Consequently, it is independent of the distance from the slits. As such, it is a very important characteristic of the quantum state. Experimental determination of the mo mentum distribution would support the particle and wave interpretation of quantum interference in a new manner.

Open Access June 2, 2014

Local Realistic Theory for PDC Experiments Based on the Wigner Formalism

Alberto Casado, Ramón Risco-Delgado, Emilio Santos

Page range: 178-181

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Abstract

In this article we present a local hidden variables model for all experiments involving photon pairs produced in parametric down conversion, based on the Wigner representation of the radiation field. A modification of the standard quantum theory of detection is made in order to give a local realistic explanation of the counting rates in photodetectors. This model involves the existence of a real zeropoint field, such that the vacumm level of radiation lies below the threshold of the detectors.

Open Access June 2, 2014

Coherently Driven Micromaser Pumped by Atoms in Superposition States

F. Casagrande, A. Lulli, V. Santagostino

Page range: 182-185

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Abstract

By a Monte Carlo wave function approach we describe the dynamics of a coherently driven micromaser pumped by coherently prepared atoms. The system can exhibit nonclassical effects such as quadrature squeezing, sub-Poissonian photonstatistics, and Rabi oscillations revival. The interplay between driving field and polarised atoms allows manipulating both the photon number and the phase of the cavity field. By varying either the atomic transit time or the injected field intensity, the coherence of the system dynamics can be enhanced or even suppressed, whereas the induced cavity field phase can be shifted.

Open Access June 2, 2014

Against Quantum Nonlocality

W. De Baere, J. De Neve

Page range: 186-190

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Abstract

It is shown that all quantum “contradictions” disappear if one drops the assumption of unique initial conditions for a hidden variable theory for individual quantum processes. Our proposal corresponds with a deterministic world evolution such that local physical conditions are nonreproducible, in agreement with empirical observation

Open Access June 2, 2014

Nonlocal de Broglie Wavelength of a Two-Photon System

E. J. S. Fonseca, Zoltan Paulinia, P. Nussenzveig, C. H. Monkena, S. Padua

Page range: 191-196

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Abstract

We show that it is possible to associate a de Broglie wavelength to a composite system even when the constituent particles are separated spatially. The nonlocal de Broglie wavelength (A /2) of a two-photon system separated spatially is measured with an appropriate detection system. The two-photon system is prepared in an entangled state in space-momentum variables. - Pacs: 42.50.-p, 42.50.Ar

Open Access June 2, 2014

Flopping between Schrödinger's Cat States

Marco Frasca

Page range: 197-199

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Abstract

We show that for an atom in a cavity in the strong coupling regime, flopping between Schrödinger cat states, devised as a superposition of displaced number states, can be accomplished. Beside, the Rabi frequency can be set to zero, so that population trapping or localization can be accomplished. These states could be proved to be useful for quantum computation

Open Access June 2, 2014

A Coherent Approach to Spacetime Foam

R. Garattini

Page range: 200-201

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Abstract

A coherent superposition of N Schwarzschild wormholes is proposed as a model for space time foam. Following the subtraction procedure for manifolds with boundaries, we calculate by variational methods the Casimir energy. A proposal for an alternative foamy model formed by N

Open Access June 2, 2014

Delayed-choice Measurement and Temporal Nonlocality

Ilki Kim, Günter Mahler

Page range: 202-204

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Abstract

We study for a composite quantum system with a quantum Turing architecture the temporal non-locality of quantum mechanics by using the temporal Bell inequality, which will be derived for a discretized network dynamics by identifying the subsystem indices with (discrete) parameter time. However, the direct “observation” of the quantum system will lead to no violation of the temporal Bell inequality and to consistent histories of any subsystem. Its violation can be demonstrated, though, for a delayedchoice measurement

Open Access June 2, 2014

Bohm's Mysterious 'Quantum Force' and 'Active Information': Alternative Interpretation and Statistical Properties

Boon Leong Lan

Page range: 205-207

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Abstract

An alternative interpretation to Bohm’s ‘quantum force’ and ‘active information’ is proposed. Numerical evidence is presented, which suggests that the time series of Bohm’s ‘quantum force’ evaluated at the Bohmian position for non-stationary quantum states are typically non-Gaussian stable distributed with a flat power spectrum in classically chaotic Hamitonian systems. An important implication of these statistical properties is briefly mentioned

Open Access June 2, 2014

Chaos and Possible Underpinnings for Quantum Mechanics

Wm. C. McHarris

Page range: 208-211

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Abstract

Deterministic chaos with its nonlinearities can formally reproduce some of the counterintuitive idiosyncrasies of quantum mechanics. In this paper I raise the question as to whether chaos might possibly supply some of the “hidden variables” that have been sought as underpinnings at a deeper level of quantum mechanics

Open Access June 2, 2014

Decoherence and Universality of a Quantum Phase Gate

Stefano Mancini, Rodolfo Bonifacio

Page range: 212-215

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Abstract

We study the dephasing noisy effects on a Quantum Phase Gate and the consequences on its universality. To this end we employ two frameworks displaying their differences and analogies. Pacs: 03.67.Lx, 03.65.Bz

Open Access June 2, 2014

The Domain of the Quantum Matter Wave

B. Mills

Page range: 216-219

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Abstract

In quantum mechanics a particle is represented by a complex wave function. This is similar to the classical description of a distributed particle by a real valued density function. However, while classically the combined density of multiple particles can be decomposed into individual densities; the wave function of a multi-particle system can not always be decomposed into wave functions for the individual particles. Hence the classical assumption that density is a property of physical space, which is only possible because of the special topology of classical configuration space, does not work for quantum systems.

Open Access June 2, 2014

Bell Inequalities with Schrödinger Cats

M. D. Reid

Page range: 220-223

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Abstract

In the Schrödinger cat gedanken experiment a “cat” is in a quantum superposition of two macroscopically distinct states. There is the apparent interpretation that the “cat” is not in one state or the other, “alive” or “dead”. Here this interpretation is proved objectively. I propose the following definition of macroscopic reality: first, that the “cat” is either dead or alive, the measurement revealing which; second, that measurements on other “cats” some distance away cannot induce the macroscopic change, “dead” to “alive” and vice versa, to the “cat”. The predictions of quantum mechanics are shown to be incompatible with this premise.

Open Access June 2, 2014

Twin-beams Statistics for Strong Pumping

A. Porzio, F. Sciarrino, A. Chiummo, S. Solimeno

Page range: 224-227

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Abstract

Twin-beams generated by non degenerate optical parametric oscillators exhibit squeezing in the inten sity difference. Here we report intensity noise correlation and single beam spectra for pump power up to 14 times the threshold value. The degree of correlation of the two beams is practically independent of pump level. The single beam spectra confirm presence of relaxation oscillation.

Open Access June 2, 2014

QSES's and the Quantum Jump

David Salgado, José Luis Sánchez-Gómez

Page range: 228-229

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Abstract

The stochastic methods in Hilbert space have been used both from a fundamental and a practical point of view. The result reported here concerns the application of these methods to model the evolution of quantum systems and does not enter into the question of their fundamental or practical status. It can easily be stated as follows: Once a quantum stochastic evolution scheme is assumed, the incompatibility of the Markov property with the notion of quantum jumps is easily established

Open Access June 2, 2014

Brownian Motion: the Quantum Perspective

Bassano Vacchini

Page range: 230-234

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Abstract

We briefly go through the problem of the quantum description of Brownian motion, concentrating on recent results about the connection between the dynamics of the particle and dynamic structure factor of the medium. - 05.40.Jc, 05.30.Fk, 05.30.Jp, 03.65.Yz

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Objective
A Journal of Physical Sciences: Zeitschrift für Naturforschung A (ZNA) is an international scientific journal which publishes original research papers from all areas of experimental and theoretical physics. Authors are encouraged to pay particular attention to a clear exposition of their respective subject, addressing a wide readership. In accordance with the name of our journal, which means “Journal for Natural Sciences”, manuscripts submitted to ZNA should have a tangible connection to actual physical phenomena. In particular, we welcome experiment-oriented contributions.

Manuscripts considered for publication in A Journal of Physical Sciences: Zeitschrift für Naturforschung A undergo high-level refereeing. Mere formal correctness of a paper is not sufficient for its acceptance. Moreover, articles reporting a merely marginal extension of already existing knowledge are considered unsatisfactory. Instead, the key quality a publication in A Journal of Physical Sciences: Zeitschrift für Naturforschung A should possess is that it makes a genuine contribution to the advancement of its topic.

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Quantum Theory
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