Relativistic quantum bit commitment in real-time

A relativistic quantum exchange protocol making it possible to implement a bit commitment scheme is realized. The protocol is based on the idea that in the relativistic case the propagation of a field into a region of space accessible for measurement requires, in contrast to the nonrelativistic case, a finite time that depends on the structure of the states. The protocol requires one classical and several quantum communication channels. It turns out that it is possible in principle to preserve the secret bit for as long a period of time desired and with probability as close to 1 as desired.     

Effective models of stratified media containing porous biot layers

Periodic stratified media in which either two porous Biot layer, or an elastic and a porous layers, or a fluid and a porous layer alternate are considered. The effective models of these media are constructed and investigated. In the case of alternating porous layers, the effective model is a generalized transversely isotropic Biot medium. In this medium, the density of the fluid phase and the mean density acquire tensor character. It is shown that the effective model of a porous-fluid medium is, on the one hand, a generalized transversely isotropic Biot medium of special type and, on the other hand, a generalization of the effective model of a stratified elastic-fluid medium.Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 239, 1997, pp. 140–163.This work was supported by the Russian Foundation for Basic Research under grant Nos. 96-01-00666 and 96-05-66207.     

Measurement of the state of an individual spin using a “turnstile”

A scheme is proposed for measuring the state of an individual spin (system of spins). The scheme is based on the idea of a single-electron “turnstile” and the injection of single spin-polarized electrons from the magnetic metallic borders. Applications to the recently proposed scheme of quantum spin gates based on a silicon matrix are discussed (B. E. Kane, Nature 393, 133 (1998)). Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 141–147 (25 July 1999)     

Dynamics of macroparticles in a dusty plasma under microgravity conditions (First experiments on board the ISS)

The results of experimental investigation of macroparticle transport in the dusty plasma of a capacitive high-frequency discharge under microgravity conditions are considered. Experimental data were obtained for monodisperse polymer particles of radius a _p =1.7 mm in a wide range of plasma parameters on the International Space Station. Analysis of macroparticle dynamics for a strongly nonideal dusty plasma, including diffusion and dust vortex formation processes, is carried out.     

Macroscopic quantum tunneling in small magnetic particles

Macroscopic quantum tunneling of magnetization in small antiferromagnetic clusters is studied for the spin-1/2 anisotropic (J _z ≡ J, J _x =J _y ≡J _xy ) Heisenberg model with the use of both perturbation theory and an exact numerical diagonalization technique. Splitting of the two lowest levels due to the lifting of the degeneracy between them (in the case J _xy =0) by the in-plane exchange (J _xy ≠ 0) is found to occur in the N/2th order of perturbation theory. Tunneling is absent in systems with an odd number of sites, in which the levels are doubly degenerate in zero magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 688–693 (10 May 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

On an effective two-phase model of a medium with cracks of finite length

An effective two-phase model of media with cracks filled with liquid is generalized to the case of finite cracks. Wave propagation in a half-space and in a free layer, described by the new model, is investigated. The results are compared with experimental data and with corresponding results in the case of media with infinite cracks. Bibliography: 11 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 203, 1992, pp. 137–155. Translated by L. A. Molotkov.     

Real-time coding in a parallel quantum communication channel

Coding theorems formulated as exchange protocols in the space of states of quantum systems do not answer one of the basic questions of real-time information transmission rate. Expressions obtained for the transmission capacity of a binary quantum communication channel describe the real-time information transmission rate.     

Collective excitations in superconductors with structural transition

In this paper we have found new low-frequency collective excitations in superconductors with structural transformation. The connection between our results and the experiments on Raman scattering in 2H-NbSe₂ cDw- superconductor is discussed.     

Correlation between the strength and relaxation properties of polymers in the rubbery state

The molecular nature of the processes of fracture and relaxation of polymers in the rubbery state is examined. Allowance for the activating influence of mechanical stress and temperature leads to the obtaining of certain relaxations which describe, more accurately than the existing ones, the temperature-stress dependences of the rupture life and the activation energy of the various molecular processes.