On the transmission rate of classical information through quantum communication channels

The coding of quantum communication channels in real time is considered as applied to the situation when information is coded into continuous quantum degrees of freedom (into the shape of the amplitude of quantum states with an arbitrary number of photons). It is shown that the nonlocalizability of states in quantum field theory requires that the identity of particles should be taken into account. This, together with the finiteness of the limit speed of propagation, leads to the fact that the formulas for the transmission rate of nonrelativistic communication channels have an asymptotic character; i.e., these formulas are formally valid only when the separation between messages is infinite (when the identity of particles can be neglected) and, hence, when the transmission rate in [bit/message s] is infinitely small. A real-time information capacity of a sequential relativistic quantum communication channel is obtained that takes into account the identity of particles for pure signal states with an arbitrary number of photons. An explicit analytic expression is obtained for the transmission rate of a quantum channel of finite bandwidth for one-photon input states.     

On a collective attack on the key in quantum cryptography on two nonorthogonal states

A “collective” attack on the key is considered, and its connection with the classical capacity of a quantum communication channel is analyzed. It has been shown that the allowable error probability for legitimate users to which the secure key can be extracted is less than half the value for “translucent” eavesdropping and individual measurements.     

A new approach to unconditional security in relativistic quantum cryptography

A principally new approach ensuring secure key distribution via an open quantum communication channel is proposed. In contrast to the existing schemes, in which the security is based upon special properties of nonorthogonal states in the Hilbert space, the security of the proposed scheme relies on a spacetime structure of states and on certain constraints imposed by special relativity. Using these factors, it is possible to provide for secure key transmission using practically arbitrary quantum states.     

Relativistic quantum cryptography on “Arrested” photons

A new relativistic quantum cryptosystem is proposed in which the information is carried by the extended single-photon states with orthogonal polarizations and effective length exceeding the communication channel length. The light “arrest” effect is used as a procedure for the detection and preparation of extended states. The cryptosystem is secure against any eavesdropping attempts, because its states are quantized and the propagation velocity is limited. In this scheme, the preparation and detection procedures are local in space but require a finite time, depending on the extension of the states. The preparation for detecting at the receiver end begins before the state left the source at the input end.     

Modified synthesis of Ru–Rh heterobimetallic metallacarboranes based on ruthenium exo-nido complexes and not accompanied by exo-nido → closo rearrangement

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Kinetic Theory of Boson Gas

Theoretical and Mathematical Physics - We construct a quantum kinetic theory of a weakly interacting critical boson gas using the expectation values of products of Heisenberg field operators in the...     

Quantum Key Distribution with Untrusted Detectors Accessible to an Eavesdropper

JETP Letters - A simple fundamental modification of quantum key distribution protocols has been proposed: it is not required to protect the results of avalanche detectors from an eavesdropper, but...     

Investigation of the dispersion equations of a free,transversally isotropic,elastic layer

To investigate the propagation of normal waves in a free, transversally isotropic, elastic layer it is necessary to determine the roots of the corresponding dispersion equation. It is shown that with increasing wave number the roots move monotonically along the axis of the phase velocity. The initial and final points of the roots are found. Examples of computations of the roots are given.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 99, pp. 85–103, 1980.     

An Effective Model of a Layered Medium in Which Alternating Porous and Elastic Layers Are in Slide Contact

For a medium in which porous and elastic layers alternate and there is slide contact on the interfaces, an effective model is established. This model is of three phases and includes two elastic phases and one fluid phase. Specific features of this effective model are that two waves with triangular front sets propagate and the second (slow) longitudinal wave is absent in it. In the special case where the thickness of elastic layers is very small but they continue to work as barriers for fluid particles from porous layers, the effective model is of two phases, and one of the triangular front sets disappears. Bibliography: 14 titles.