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Journal of Physics B Atomic Molecular and Optical Physics

Quantum oscillator in a Kerr-nonlinear blackbody

Zixia Wu, Ze Cheng

Published Oct 14, 2009• 0 citations
Publisher

Abstract

In the present paper, a charged oscillator in a harmonic potential well interacting with a Kerr-nonlinear blackbody is investigated. A quantum Langevin equation is derived. It is shown that below a transition temperature Tc, the memory function is a decreasing function of the Kerr-nonlinear coefficient. In the large-cutoff limit, the free-energy shift is a complicated function of temperature which is no longer a simply T2-dependent function. The energy level shift of an oscillator in a normal blackbody is negative, while in our Kerr-nonlinear blackbody, only near zero temperature is the corresponding energy level shift negative. As the temperature increases to the transition temperature Tc, the corresponding energy level shift becomes a large positive value. Above Tc, our results are the same as those found in a normal blackbody.

DOI
10.1088/0953-4075/42/21/215501

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Journal of Physics B Atomic Molecular and Optical Physics•Jul 20, 2009•1 citation
In the present paper, a charged oscillator in a harmonic potential well interacting with a Kerr-nonlinear blackbody is investigated. A quantum Langevin equation is derived. It is shown that below a transition temperature Tc, the memory function is a decreasing function of the Kerr-nonlinear coefficient. In the large-cutoff limit, the free-energy shift is a complicated function of temperature which is no longer a simply T2-dependent function. The energy level shift of an oscillator in a normal blackbody is negative, while in our Kerr-nonlinear blackbody, only near zero temperature is the corresponding energy level shift negative. As the temperature increases to the transition temperature Tc, the corresponding energy level shift becomes a large positive value. Above Tc, our results are the same as those found in a normal blackbody.
The Lamb shift in a Kerr nonlinear blackbody (KNB) is studied in the framework of nonrelativistic quantum electrodynamics theory. It is found that the Lamb shift in a KNB depends on the absolute temperature and the Kerr nonlinear coefficient. Below a transition temperature Tc{T}_{c}Tc​, the Lamb shift is larger than that in a nonabsorbing linear medium. Under some conditions, the Lamb shift in a KNB can become much larger than that in a nonabsorbing linear medium or in free space. Above Tc{T}_{c}Tc​, the Lamb shift equals that in a nonabsorbing linear medium. The application of our theory is also discussed.
Within the framework of quantum field theory, we show that the photon system in a blackbody whose interior is filled by a Kerr nonlinear crystal is in a condensation state. In the condensation state, bare photons with opposite wave vectors and helicities are bound into pairs and unpaired bare photons are transformed into a new kind of quasiparticle, the nonpolariton. The photon-pair system is a condensate and the nonpolariton system is a boson gas. At zero temperature the condensate possesses a largest persistent energy density. The persistent energy density of the condensate is a monotonically decreasing function of temperature and Kerr nonlinear coefficient. The QQQ function of a Kerr nonlinear blackbody at any temperature is derived analytically. In the transition from the normal to the condensation state, the phase symmetry of the photon system is spontaneously broken.
A reservoir theory has been used to investigate the spontaneous emission of a two-level atom in a Kerr nonlinear blackbody. It is found that the atomic decay rate is a monotonically increasing function of absolute temperature. Below a transition temperature Tc{T}_{c}Tc​, the spontaneous emission is always inhibited compared to that in a nonabsorbing linear medium. It is also found that the inhibition of spontaneous emission is a monotonically decreasing function of the Kerr nonlinear coefficient. The inhibition of spontaneous emission is interpreted on the basis of a physical mechanism.
A photon blackbody field in Kerr nonlinear crystal is a squeezed thermal radiation state in which there is a new kind of quasi particle, the nonpolariton. A nonpolariton is a condensate of virtual nonpolar phonons, with a bare photon acting as the nucleus of condensation. The propagation velocity of nonpolaritons is a monotonically increasing function of temperature, and the noise of one quadrature phase in the squeezed thermal radiation state can be below the noise level in the vacuum state. The photon system undergoes a second-order phase transition from the normal to the squeezed thermal radiation state.
We investigate the dynamic Stark shift and atomic depopulation rate induced by real photons in a Kerr nonlinear blackbody. We found that the dynamic Stark shift and atomic depopulation rate are equally modified by a nonlinear contribution factor and a linear contribution factor under a transition temperature Tc. The nonlinear contribution factor depends on the Kerr nonlinear coefficient as well as the absolute temperature. Below Tc, the absolute values of the dynamic Stark shift and depopulation rate of a single atomic state (not the ground state) are correspondingly larger than those in a normal blackbody whose interior is filled with a nonabsorbing linear medium. Above Tc, the dynamic Stark shift and atomic depopulation rate are correspondingly equal to those in a normal blackbody with a nonabsorbing linear medium in its interior.