arXiv subjects
Publications and source records attributed to Constantin V. Usenko.
The analysis of uniformly longitudinally extended detector is performed and it is shown that the response of such a detector does not differ from the response of the Unruh detector, but the its excitation is caused not by the thermal bath, but by interaction with the fluctuations of the quantum field by virtual quanta.
The problem of quantum state reduction in the process of measurement has attracted attention of almost everyone who created, developed or explained quantum physics to the students. Absence of a solution is the basis for the statement that the physical laws alone are not enough to describe the reduction of state of the measured particle. In the presented study, it is taken into account that the measurement of all properties of quantum particles can not be carried out in one physical process (the no-cloning theorem). For such a measurement several series of incompatible observations are needed, each series is to be carried out by means of a separate measuring instrument. Each event of measurement is a separate physical process; combination of different measurement events is performed by the Measurer - a subject capable of recognizing or not recognizing different events as similar depending on the purpose of the measurement, and capable as well of planning the measurements, of obtaining results and making conclusions. Several strategies for measuring the quantum state of photon polarization are considered; it is shown that modeling of a mixed state by a set of photon pure states is possible only if for this set in all the measurements the same measuring devices are used. It is also shown that the reduction of the quantum state is determined by the parameters of interaction of the measuring device with the measured particle. This fact removes the restrictions on the magnitudes of correlations of different observables, known as Bell's inequalities.
In the direct communication quantum channels the authorized recipient (Bob) and the non-authorized recipient (Eve) have different abilities for verification of received information. Bob can apply the feedback to commit the sender (Alice) to perform verification. Eve has to use for verification an indirect method based on the measurement of a set of incompatible observables enough for determination of the coding basis used by Alice. In the protocol of direct communication regular modification of coding basis and masking it with an equilibrium in average information carrier density matrix prevents reconstruction of coding basis by the results of Eve's measurements of an arbitrary set of observables. This provides unconditional security of the channel.
Analysis of the process of accumulation of the results of measurements shows that the success of this process substantially depends on the possibility of coordination of actions of two participants of the process - preparator who prepares the series of the states being measured and registrator who chooses in each event of measurement one of incompatible observables. A new value, the complexity of measurement of a state, is used, this characterizes the number of the measurement events needed for solution of the reconstruction problem. By means of this value it is shown that the dependence of the upper limit of the needed number of measurements on the permissible error is a square law one, so a twofold decrease of permissible error corresponds to a fourfold increase of needed number of measurements.
We address the process of generation of the photon-number entangled states of light in the stimulated nonlinear parametric down conversion process and build the simple model describing the generation, not involving the traditional parametric approximation. The motion equations for the system of pumping and two-mode outgoing field are solved for the case of the strong correlation between two modes, the evolution of the state parameters of the generated modes is obtained. The solution is briefly analyzed for particular types of photon-number entangled states.
Problem of classification of parallel quantum channels for information transfer is studied by method of ladder operators. Detailed compared to http://arxiv.org/abs/quant-ph/0702076 presentation of method of ladder operators is given. Examples of paired channel and qubit-qunit pair are added. Relations between eigenvalues of density matrices of composite channel and its subchannels determining presence/absence of entanglement of arbitrary mixed state of channel are obtained.
Classification of states of quantum channels of information transfer is built on the basis of unreducible representations of qubit state space group of symmetry and properties of density matrix spectrum. It is shown that pure disentangled states form two-dimensional surface, and the reason of state disentanglement is in degeneration of non-zero density matrix eigenvalues
It is shown that relative coordinate and momentum of coherent electron pair have the meaning of observables with the help of quadrupole and magnetic moments. Distributions of quadrupole terms of scalar potential are shown. These distributions have nonclassical properties.
Classification of states of two-particle quantum channels of information transfer is built on the basis of irreducible representations of qubit state space group of symmetry and properties of density matrix spectrum. It is shown that the reason of state disentanglement can be in degeneration of non-zero density matrix eigenvalues. Among the states with non-degenerate density matrix disentangled states form two-dimensional surface of special states.
Problem of classification of all the set of entangled states is considered. Invariance of entangled states relative to transformations from a group of symmetry of qubit space leads to classification of all states of the system through irreducible representations from that group. Excess of entropy of a subsystem over entropy of the whole system indicates the presence of entaglement in the system.
This report is about contradiction between fidelity needed to determine the entanglement and concomitant noise that always accompanies precise measurement. Account of quantum properties of field leads to additional noise caused by multiple particle creation through nonunitarity of quantum field representation in embedded sections of space (Unruh noise). Causes of quantum noise vanish at leaving off assumption about statistical independence of detectors. Smearing of detector leads to elimination of causes of Unruh noise and to emergence of imaginary entanglement of few mode states caused by overlap of detector sections.
Identity of electrons leads to description of their states by symmetrical or anti-symmetrical combination of free coherent states. Due to the coordinate uncertainty potential energy of the Coulomb repulsing is limited from above and so when energy of electrons is large enough, electrons go through each other, without noticing one another. We show existence of set of coherent states for which wave packages recession vanish - electrons remain close regardless of Coulomb repulsion.
This work is the development and analysis of the recently proposed quantum cryptographic protocol, based on the use of the two-mode coherently correlated states. The protocol is supplied with the cyrptographic control procedures. The channel error properties and stability against eavesdropping are examined. State detection features are proposed.
The Wigner function of quantum systems is an effective instrument to construct the approximate classical description of the systems for which the classical approximation is possible. During the last time, the Wigner function formalism is applied as well to seek indications of specific quantum properties of quantum systems leading to impossibility of the classical approximation construction. Most of all, as such an indication the existence of negative values in Wigner function for specific states of the quantum system being studied is used. The existence of such values itself prejudices the probabilistic interpretation of the Wigner function, though for an arbitrary observable depending jointly on the coordinate and the momentum of the quantum system just the Wigner function gives an effective instrument to calculate the average value and the other statistical characteristics. In this paper probabilistic interpretation of the Wigner function based on coordination of theoretical-probabilistic definition of the probability density, with restrictions to a physically small domain of phase space due to the uncertainty principle, is proposed.
This work is the development and analysis of the recently proposed quantum cryptographic protocol, based on the use of the two-mode coherently correlated states. The protocol is supplied with the cryptographic control procedures. The quantum noise influence on the channel error properties is examined. State detection features are proposed.
The data transmission protocol, based on the use of a strongly correlated pair of laser beams, is proposed. The properties of the corresponding states are described in detail. The protocol is based on the strong correlation of photon numbers in both beams in each measurement. The protocol stability against the interception attempts is analyzed.