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Vladislav S. Olkhovsky

Publications and source records attributed to Vladislav S. Olkhovsky.

14 recordsLinked to original sources
arXiv2013

A fully quantum model of Big Bang

In the paper the closed Friedmann-Robertson-Walker model with quantization in the presence of the positive cosmological constant and radiation is studied. For analysis of tunneling probability for birth of an asymptotically deSitter, inflationary Universe as a function of the radiation energy a new definition of a "free" wave propagating inside strong fields is proposed. On such a basis, tunneling boundary condition is corrected, penetrability and reflection concerning to the barrier are calculated in fully quantum stationary approach. For the first time non-zero interference between the incident and reflected waves has been taken into account which turns out to play important role inside cosmological potentials and could be explained by non-locality of barriers in quantum mechanics. Inside whole region of energy of radiation the tunneling probability for the birth of the inflationary Universe is found to be close to its value obtained in semiclassical approach. The reflection from the barrier is determined for the first time (which is essentially differs on 1 at the energy of radiation close to the barrier height). The proposed method could be easily generalized on the cosmological models with the barriers of arbitrary shape, that has been demonstrated for the FRW-model with included Chaplygin gas. Result is stable for variations of the studied barriers, accuracy are found to be 11--18 digits for all coefficients and energies below the barrier height.

gr-qc↗
arXiv2009

On non-selfadjoint operators for observables in quantum mechanics and quantum field theory

Aim of this paper is to show the possible significance, and usefulness, of various non-selfadjoint operators for suitable Observables in non relativistic and relativistic quantum mechanics, and in quantum electrodynamics. More specifically, this work starts dealing with: (i) the maximal hermitian (but not selfadjoint) Time operator in non-relativistic quantum mechanics and in quantum electrodynamics; and with: (ii) the problem of the four-position and four-momentum operators, each one with its hermitian and anti-hermitian parts, for relativistic spin-zero particles. Afterwards, other physically important applications of non-selfadjoint (and even non-hermitian) operators are discussed: In particular, (iii) we reanalyze in detail the interesting possibility of associating quasi-hermitian Hamiltonians with (decaying) unstable states in nuclear physics. Finally, we briefly mention the cases of quantum dissipation, as well as of the nuclear optical potential. [PACS numbers: 03.65.Ta; 03.65.-w; 03.65.Pm; 03.70.+k; 03.65.Xp; 11.10.St; 11.10.-z; 11.90.+t; 02.00.00; 03.00.00; 24.10.Ht; 03.65.Yz; 21.60.-u; 11.10.Ef; 03.65.Fd. Keywords: time operator in quantum mechanics; space-time operator; time-"Hamiltonian"; non-selfadjoint operators; non-hermitian operators; bilinear operators; time operator for discrete energy spectra; time-energy uncertainty relations; unstable states; quasi-hermitian Hamiltonians; Klein-Gordon equation; quantum dissipation; nuclear optical model].

quant-ph↗
arXiv2008

Bremsstrahlung emission during $α$-decay of $^{226}{\rm Ra}$

We obtained the spectrum of probability of the bremsstrahlung emission accompanying the $α$-decay of $^{226}{\rm Ra}$ (E$_α$=4.8 MeV) by measuring the $α$-$γ$ coincidences and using the model presented in our previous study on the $α-$decay of $^{214}{\rm Po}$ (E$_α$=7.7 MeV). We compare the experimental data with the quantum mechanical calculation and find a good agreement between theory and experiment. We discuss the differences between the photon spectra connected with the $α$-decay of the $^{226}{\rm Ra}$ and $^{214}{\rm Po}$ nuclei. For the two mentioned nuclei we analyze the bremsstrahlung emission contributions from the tunneling and external regions of the nucleus barrier into the total spectrum, and we find the destructive interference between these contributions. We also find that the emission of photons during tunneling of the $α$-particle gives an important contribution to the bremsstrahlung spectrum in the whole E$_γ$ energy range of the studied $^{226}$Ra nucleus.

nucl-ex↗
arXiv2006

Angular analysis of bremsstrahlung in alpha decay

A new quantum electrodynamical method of calculations of bremsstrahlung spectra in the $α$-decay of heavy nuclei taking into account the angle between the directions of $α$-particle motion (or its tunneling) and photon emission is presented. The angular bremsstrahlung spectra for $^{210}{Po}$ have been obtained for the first time. According to calculations, the bremsstrahlung in the $α$-decay of this nucleus depends extremely weakly on the angle. Taking into account nuclear forces, such dependence is not changed visibly. An analytical formula of the angular dependence of the bremsstrahlung spectra is proposed and gives its harmonic behavior. The extremal values of the angle, at which the bremsstrahlung has maximal and minimal values, has been found.

nucl-th↗
arXiv2004

Resonant and non-resonant Tunneling through a double barrier

An explicit expression is obtained for the phase-time corresponding to tunneling of a (non-relativistic) particle through two rectangular barriers, both in the case of resonant and in the case of non-resonant tunneling. It is shown that the behavior of the transmission coefficient and of the tunneling phase-time near a resonance is given by expressions with "Breit-Wigner type" denominators. By contrast, it is shown that, when the tunneling probability is low (but not negligible), the non-resonant tunneling time depends on the barrier width and on the distance between the barriers only in a very weak (exponentially decreasing) way: This can imply in various cases, as well-known, the highly Superluminal tunneling associated with the so-called "generalized Hartman Effect"; but we are now able to improve and modify the mathematical description of such an effect, and to compare more in detail our results with the experimental data for non-resonant tunneling of photons. Finally, as a second example, the tunneling phase-time is calculated, and compared with the available experimental results, in the case of the quantum-mechanical tunneling of neutrons through two barrier-filters at the resonance energy of the set-up.

quant-ph↗
arXiv2004

Method of multiple internal reflections in description of nuclear alpha-decay

A spatial-time method of description of alpha-decay of a nucleus is presented. The method is based on the quantum mechanical model of the alpha-decay of a compound nuclear system with the barrier. alpha-decay dynamics is described on the basis of multiple internal reflections of wave packets from boundaries of the decay barrier. The method allows to study this process in details at any time moment or point of space. According to the method, some time before the time moment of the nuclear decay the nucleus makes oscilations. In the calculations of the time duration of the alpha-decay of the compound nucleus we propose to take into account the time durations of these oscillations. The method of the multiple internal reflections allows to calculate the time of such oscillations before the alpha-decay and the total alpha-decay time.

nucl-th↗
arXiv2004

The method of multiple internal reflections in a description of tunneling evolution of nonrelativistic particles and photons

A non-stationary method for tunneling description of non-relativistic particles and photons through a barrier on the basis of consideration of the multiple internal reflections of vawe packets in relation of barrier boundaries is presented. The method is described in details and proved in the case of the one-dimentional tunneling of the particle through the rectangular barrier. For problems of the tunneling of the particle through the spherically symmetric barrier and of the photon through the one-dimensional barrier the amplitudes of transmitted and reflected wave packets in relation to the barrier, times of the tunneling and the reflection are found using of the method. Hartman's and Fletcher's effect is analysed.

nucl-th↗
arXiv2004

Does Sub-Barrier Bremsstrahlung in alpha-decay of 210Po Exist?

A quantum mechanical model for the description of the alpha-decay of heavy nuclei with accompanying photons emission is presented. The model is based on a quantum mechanical one-particle model of alpha-decay through a decay barrier. The bremsstrahlung spectrum calculation employs multipole expansion of the vector potential of the Coulomb field of the daughter nucleus and takes into account the dependence on the angle between the directions of the alpha-particle propagation and the photon emission. Spectra of 210Po are obtained for the angles 25 and 90, and the best agreement with the experimental data in the 90 case in a comparison with other existing models is achieved. From the angular analysis, the model gives monotonic behavior of the bremsstrahlung spectrum for any value of the angle. We find that sub-barrier photon emission (i. e. bremsstrahlung photon emission during alpha-particle tunneling through decay barrier) exists but gives a small contribution to the total bremsstrahlung spectrum.

nucl-th↗
arXiv2004

Method of multiple internal reflections in description of tunneling evolution through barriers

A method of a non-stationary description of tunneling of a particle through the one-dimensional and spherically symmetric rectangular barriers on the basis of analisis of multiple internal reflections of wave packets in relation on the barrier boundaries, named as the Method of multiple internal reflections, is presented at the first time. For the one-dimensional problem the applicability of this method is proved, its specific features are analyzed. For the spherically symmetric problem the amplitudes of the transmitted and reflected wave packets, times of tunneling and reflection in relation to the barrier are calculated using this method. The effect of Hartman-Fletcher is analyzed.

nucl-th↗
arXiv2002

Superluminal effects for quantum tunneling through two successive barriers

We study the phenomenon of one-dimensional non-resonant tunnelling through two successive potential barriers, separated by an intermediate free region R, by analyzing the relevant solutions to the Schroedinger equation. We find that the total traversal time is INDEPENDENT not only of the barrier widths (the so-called "Hartman effect"), but also of the R-width: so that the effective velocity in the region R, between the two barriers, can be regarded as infinite. This agrees with the results known from the corresponding waveguide experiments, which simulated the tunnelling experiment herein considered because of the formal identity between the Schroedinger and the Helmholtz equation [PACS numbers: 73.40.Gk; 03.65.-w; 03.30.+p; 41.20.Jb; 84.40.Az].

quant-ph↗
arXiv2001

Unified time analysis of photon and (nonrelativistic) particle Tunnelling, and the Superluminal group-velocity problem

A unified approach to the time analysis of tunnelling of nonrelativistic particles is presented, in which Time is regarded as a quantum-mechanical observable, canonically conjugated to Energy. The validity of the Hartman effect (independence of the Tunnelling Time of the opaque barrier width, with Superluminal group velocities as a consequence) is verified for ALL the known expressions of the mean tunnelling time. Moreover, the analogy between particle and photon tunnelling is suitably exploited. On the basis of such an analogy, an explanation of some recent microwave and optics experimental results on tunnelling times is proposed. Attention is devoted to some aspects of the causality problem for particle and photon tunnelling.

quant-ph↗
arXiv1998

Tunneling Times and "Superluminal" Tunneling: A brief Review

In the First Part of this paper [that was submitted for pub. in 1991 and appeared in print in Phys. Reports 214 (1992) 339] we critically review the main theoretical definitions and calculations of the sub-barrier tunnelling and reflection times. Moreover, within conventional QM, we propose a new definition of such durations, on the basis of a recent general formalism of ours. At last, we discuss a surprising result: that QM predicts tunnelling through opaque barriers to take place with Superluminal group-velocities. In the Second Part [that appeared in print later, in J. de Physique-I 5 (1995) 1351] we, e.g., present the results of some numerical calculations (based on our equations) on the penetration and return times during tunnelling INSIDE a rectangular potential barrier, and set forth suitable definitions also of the variances, or dispersions, for the transmission and reflection time-durations. The numerical evaluations confirm that our approach implied, and implies, the existence of Superluminal tunnelling (that we called "Hartman effect"): an effect that in these days is receiving --at Cologne, Berkeley, Florence and Vienna-- indirect, but interesting, experimental verifications. More detailed reviews of the same topics are in the LANL Archive cond-mat/9802126 (and in an Appendix to physics/9712051, where the data are summarized of the experiments that --in four different sectors of physics-- seem to indicate the existence of Superluminal motions).

cond-mat↗
arXiv1998

Tempi di Tunnelling (Tunneling Times)

In this review (in Italian) we critically and detaily examine various definitions existing in the literature for the tunnelling times: namely, the phase-time; the centroid-based times; the Buttiker and Landauer times; the Larmor times; the complex (path-integral and Bohm) times; the dwell time, and the generalized (Olkhovsky and Recami) dwell time, with some numerical evaluations. Then, we pass to examine the equivalence between quantum tunnelling and "photon tunnelling" (evanescent waves propagation), with particular attention to tunnellings with Superluminal group-velocities ("Hartman effect"). At last, the main (Cologne, Berkeley, Florence, Vienna) experimental data about Superluminal evanescent wave propagation are briefly reviewed.

cond-mat↗