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“Cooperative effects in excited electronic systems on multiquantum interaction with bosonic field


Author: Vitalie Eremeev
Degree:doctor of physics and mathematics
Speciality: 01.04.02 - Theoretical and mathematical physics
Year:2006
Scientific adviser: Nicolae Enache
doctor habilitat, professor, Institute of Applied Physics of the
Institution:
Scientific council:

Status

The thesis was presented on the 24 November, 2006
Approved by NCAA on the 21 December, 2006

Abstract

Adobe PDF document – 0.42 Mb / in romanian

Thesis

CZU 530.145 (043.3)

Adobe PDF document 0.88 Mb / in romanian
103 pages

Keywords

cooperative biquantum effects, two-photon superradiance, EMF-electromagnetic field, phase transition, biphonon superconductivity, critical temperature, order parameter, optical resonator, twophoton quantum generator, entangled photons, biphotons, biphonons, coherent light, quantum fluctuations

Summary

The thesis is dedicated to the cooperative-biquantum effects which occur in optical or solid systems and these effects are described in statistical and thermodynamic manner of treatment.

In this study is investigated the quantum phase transition of the system of N radiators in case of two-photon exchange interaction with single mode of cavity electromagnetic field. It is shown that for this system the atom-field exchange integral increases with the increase of temperature because this integral is direct proportional to the average number of photons in the cavity thermostat. This effect generates important physical peculiarities in phase transition picture. The process of nonlinear exchange between the quasi-spins leads to the increase of critical temperature as compared to traditional second order phase transition of quasi-spin system.

The example of superconductivity, where the Cooper pairs are created due to the simultaneous two-phonon exchange between electrons is studied. This effect occurs when the one-phonon exchange integral between the band electrons is smaller than that of the two-phonon exchange. This is possible in many-band superconducting materials, in which the two-phonon exchange integral arises through virtual levels of bands. In two-phonon processes, a more complicated temperature dependence of the order parameter is expected, so that the critical temperature increases.

It is proposed a model of quantum generator of coherent light based on two-photon processes.Taking into account the big number of resonator bimodes in which the photon pairs with fixed energy and phase are generated, it is demonstrated that the coherence between the pairs of photons remains larger than the coherence between individual photons. It is shown that the ignition of twophoton lasing from vacuum fluctuations increases with the increase in the number of resonator modes. This effect can be regarded as a collective phenomenon between the resonator bimodes in which the pairs of entangled photons are generated. A particular case, when two types of biphotons generated in cavity are possible, is studied too. For this case it is shown that the coherence between the biphotons remains larger than the coherence between the uncorrelated photons and the ignition of lasing from vacuum of cavity field is possible.

The main results of the thesis were published in 20 scientific papers (10 articles and 10 abstracts).

The thesis consists from 103 text pages, 17 figures and 100 references.