Modeling the Singlet State with Local Variables

A local-variable model yielding the statistics from the singlet state is presented for the case of inefficient detectors and/or lowered visibility. It has independent errors and the highest efficiency at perfect visibility is 77.80%, while the highest visibility at perfect detector-efficiency is 63.66%. Thus, the model cannot be refuted by measurements made to date.Comment: 15 pages, 13 figure

Quantum optics with bosons and fermions

Atom optics, a field which takes much inspiration from traditional optics, has advanced to the point that some of the fundamental experiments of quantum optics, involving photon correlations, have found atomic analogs. We discuss some recent experiments on atom bunching and anti-bunching as well as some prospects for extending them to the field of many body physics.Comment: English version of "Optique atomique quantique : apr\`es les bosons, les fermions

Operational Characterization of Simultaneous Measurements in Quantum Mechanics

Quantum mechanics predicts the joint probability distribution of the outcomes of simultaneous measurements of commuting observables, but, in the state of the art, has lacked the operational definition of simultaneous measurements. The question is answered as to when the consecutive applications of measuring apparatuses give a simultaneous measurement of their observables. For this purpose, all the possible state reductions caused by measurements of an observable is also characterized by their operations.Comment: 9 pages, REVTe

Decoherence at absolute zero

We present an analytical study of the loss of quantum coherence at absolute zero. Our model consists of a harmonic oscillator coupled to an environment of harmonic oscillators at absolute zero. We find that for an Ohmic bath, the offdiagonal elements of the density matrix in the position representation decay as a power law in time at late times. This slow loss of coherence in the quantum domain is qualitatively different from the exponential decay observed in studies of high temperature environments.Comment: Published in Physics Letters

Testing temporal Bell inequalities through repeated measurements in rf-SQUIDs

Temporal Bell-like inequalities are derived taking into account the influence of the measurement apparatus on the observed magnetic flux in a rf-SQUID. Quantum measurement theory is shown to predict violations of these inequalities only when the flux states corresponding to opposite current senses are not distinguishable. Thus rf-SQUIDs cannot help to discriminate realism and quantum mechanics at the macroscopic level.Comment: 12 pages, 4 Postscript figures in an uuencoded file figures.uu, uses revtex.st

Bell's inequalities I: An explanation for their experimental violation

Derivations of two Bell's inequalities are given in a form appropriate to the interpretation of experimental data for explicit determination of all the correlations. They are arithmetic identities independent of statistical reasoning and thus cannot be violated by data that meets the conditions for their validity. Two experimentally performable procedures are described to meet these conditions. Once such data are acquired, it follows that the measured correlations cannot all equal a negative cosine of angular differences. The relation between this finding and the predictions of quantum mechanics is discussed in a companion paper.Comment: 15 pages, 2 figure

Spontaneous parity breaking of graphene in the quantum Hall regime

We propose that the inversion symmetry of the graphene honeycomb lattice is spontaneously broken via a magnetic field dependent Peierls distortion. This leads to valley splitting of the $n=0$ Landau level but not of the other Landau levels. Compared to quantum Hall valley ferromagnetism recently discussed in the literature, lattice distortion provides an alternative explanation to all the currently observed quantum Hall plateaus in graphene.Comment: 4 pages, to appear in Phys. Rev. Let