Form factors,deformed Knizhnik-Zamolodchikov equations and finite-gap integration

We study the limit of asymptotically free massive integrable models in which the algebra of nonlocal charges turns into affine algebra. The form factors of fields in that limit are described by KZ equations on level 0. We show the limit to be connected with finite-gap integration of classical integrable equations.     

Magnetic measurement of transport AC losses in Bi-2223/Ag tapes

Magnetic nature of the losses in superconducting wire carrying AC current implies that it should be possible to determine these losses in a contactless way. Ribbon-like samples are quite favorable for such an experiment, because a notable portion of magnetic flux related to losses ‘escapes' the sample volume and can be detected by an appropriate pick-up coil. In this case, a model describing the AC current penetration into the tape, based, e.g., on the critical state model, allows one to derive the losses from the pick-up coil signal. Because this signal is proportional to the number of coil turns, extension of the accessible range of measured voltages (and losses) can be achieved. We demonstrate the data obtained on a 1 cm long portion of a low-loss multifilamentary tape carrying AC current with frequency 35 Hz. The pick-up coil technique allowed us to reach loss level more than one order below the experimental limit for direct measurements.     

Transients in all-optical bistability using transverse optical pumping: Observation of critical slowing down

We report on the transient response of an all-optical bistable device to step-inputs of light. The nonlinear mechanism used for bistable switching relies on transverse optical pumping within the Zeeman sublevels of the sodium ground state. Our measurements demonstrate the crucial role of critical slowing down for switching time. We also find that time-dependent diffusion processes can strongly affect the dynamics of this bistable device. Numerical calculations are shown to yield results in satisfactory agreement with experimental data.     

Distant measurement

Distant correlations are investigated within the framework of quantum mechanics. They are inherent to any physical situation in which two separated quantal systems are described by one composite state vector. Owing to correlations of this kind one can perform a measurement on one of the systems, thereby measuring a certain observable on the other (distant) system without interacting with it. Necessary and sufficient conditions are given for such a distant measurement to take place. It is found which are the observables that can be measured distantly, and which are the states of the distant system obtainable in this way. Solution of these problems is achieved by replacing the composite state vector by two entities equivalent to it: the reduced statistical operator of the system which is directly measured and a correlation operator. The latter gives a connection between states, observables, and probabilities of the two systems. Experimental evidence for distant measurement is discussed.