Decoherence - Fluctuation Relation and Measurement Noise

We discuss fluctuations in the measurement process and how these fluctuations are related to the dissipational parameter characterising quantum damping or decoherence. On the example of the measuring current of the variable-barrier or QPC problem we show there is an extra noise or fluctuation connected with the possible different outcomes of a measurement. This noise has an enhanced short time component which could be interpreted as due to ``telegraph noise'' or ``wavefunction collapses''. Furthermore the parameter giving the the strength of this noise is related to the parameter giving the rate of damping or decoherence.Comment: 6 pages, no figures, for Okun Festschrift, Physics Report

Lessons of Coherence and Decoherence--From Neutrinos to SQUIDS

We indicate some of the lessons learned from our work on coherence and decoherence in various fields and mention some recent work with sold state devices as elements of the ``quantum computer'', including the realization of simple logic gates controlled by adiabatic processes. We correct a commonly held misconception concerning decoherence for a free particle.Comment: 5 pages, 3 figures. Some clarification added, references added and updated. No change in essential conten

Simulations of "Decoherence" with Noise Pulses

A simulation of decoherence as random noise in the Hamiltonian is studied. The full Hamiltonian for the rf Squid is used, with the parameters chosen such that there is a double-potential well configuration where the two quasi-degenerate lowest levels are well separated from the rest. The results for these first two levels are in quantitative agreement with expectations from the ``spin 1/2'' picture for the behavior of a two-state system.Comment: Four pages, three figures. Contribution to special issue of Molecular Physics in honor of R. A. Harri

Inversion of the Photon Number Integral

We consider the behavior of the photon number integral under inversion, concentrating on euclidean space. The discussion may be framed in terms of an additive differential $I$ which arises under inversions. The quantity $\int \int I$ is an interesting integral invariant whose value characterizes different configurations under inversion.Comment: 13 pages, 3 figure

Neutrino Flight Times in Cosmology

If neutrinos have a small but non-zero mass, time-of-flight effects for neutrino bursts from distant sources can yield information on the large-scale geometry of the universe, the effects being proportional to the integral over time of the cosmological expansion parameter. In principle absolute physical determinations of the Hubble constant and the acceleration parameter are possible. Practical realization of these possibilities would depend on neutrino masses being in a favorable range and the future development of very large detectors.Comment: Three pages, no figure