Effect of laser-amplitude fluctuations on the production of the stokes field

By means of the theory of multiplicative stochastic processes, we obtain an exact solution for the Stokes field build-up in the presence of a stochastic laser pump, and show that the fluctuations in the laser amplitude enhance the growth of the Stokes field.     

Protecting quantum coherence of two-level atoms from vacuum fluctuations of electromagnetic field

In the framework of open quantum systems, we study the dynamics of a static polarizable two-level atom interacting with a bath of fluctuating vacuum electromagnetic field and explore under which conditions the coherence of the open quantum system is unaffected by the environment. For both a single-qubit and two-qubit systems, we find that the quantum coherence cannot be protected from noise when the atom interacts with a non-boundary electromagnetic field. However, with the presence of a boundary, the dynamical conditions for the insusceptible of quantum coherence are fulfilled only when the atom is close to the boundary and is transversely polarizable. Otherwise, the quantum coherence can only be protected in some degree in other polarizable direction.     

Electron polarization in quantum wells in a strong variable field

The wave function of an electron in a symmetric double quantum well placed in a strong time-periodic electric field is found, expressions for quasienergy functions are derived, and the dependence of the dipole moment on the average electric field is analyzed for the case where the average field remains constant. In the case of slow monotonic variation of the “constant” component of the electric field, the Schro dinger equation is solved by the WKB method. It is found that the dependence of the dipole moment on the average field is of a clearly nonlinear almost-periodic nature and that in the event of adiabatic monotonic variation of the average field there is a periodic relocation of the electron density from well to well with a small frequency proportional to the rate of variation of the average field. Zh. éksp. Teor. Fiz. 116, 217–235 (July 1999)     

Spin polarization in quantum dots by radiation field with circular polarization

For circular quantum dot (QD), taking into account the Razhba spin-orbit interaction (SOI), an exact energy spectrum is obtained. For a small SOI constant, the eigenfunctions of the QD are found. It is shown that the application of a radiation field with circular polarization removes the Kramers degeneracy of the QD eigenstates. Effective spin polarization of electrons transmitted through the QD owing to a radiation field with circular polarization is demonstrated.     

Effects of quantum vacuum fluctuations of the electric field on DNA condensation

By assuming that not only counter-ions but DNA molecules as well are thermally distributed according to a Boltzmann law, we propose a modified Poisson-Boltzmann equation, at the classical level, as a starting point to compute the effects of quantum fluctuations of the electric field on the interaction among DNA-cation complexes. The latter are modeled here as infinite one-dimensional wires (δ-functions). Our goal is to single out such quantum-vacuum-driven interaction from the counterion-induced and water-related interactions. We obtain a universal, frustration-free Casimir-like (codimension 2) interaction that extensive numerical analysis show to be a good candidate to explain the formation and stability of DNA aggregates. Such Casimir energy is computed for a variety of configurations of up to 19 DNA strands in a hexagonal array. It is found to be many-body.     

Some connections between the classical theory of fluctuations and quantum field theory

A number of authors have noticed that the ground state of the harmonic oscillator can be represented as the motion of a classical charged particle under the influence of a fluctuating electromagnetic field, provided the effect of radiative reaction is taken into account. Their work is reviewed and some new results are obtained which extend the treatment to excited states.     

Dynamics of nuclear polarization in InGaAs quantum dots in a transverse magnetic field

The time-resolved Hanle effect is examined for negatively charged InGaAs/GaAs quantum dots. Experimental data are analyzed by using an original approach to separate behavior of the longitudinal and transverse components of nuclear polarization. This made it possible to determine the rise and decay times of each component of nuclear polarization and their dependence on transverse magnetic field strength. The rise and decay times of the longitudinal component of nuclear polarization (parallel to the applied field) were found to be almost equal (approximately 5 ms). An analysis of the transverse component of nuclear polarization shows that the corresponding rise and decay times differ widely and strongly depend on magnetic field strength, increasing from a few to tens of milliseconds with an applied field between 20 and 100 mT. Current phenomenological models fail to explain the observed behavior of nuclear polarization. To find an explanation, an adequate theory of spin dynamics should be developed for the nuclear spin system of a quantum dot under conditions of strong quadrupole splitting.     

Thermal 1/ω fluctuations of a quantum oscillator under a parametric effect of a random field

It is shown that the effect of a time-correlated Gaussian random field of sufficiently high intensity on the elasticity coefficient of a quantum oscillator manifests itself in the generation of thermal fluctuations with a 1/ω spectrum in the oscillator. It is also shown that, in any physical system described by the equation of an anharmonic oscillator, fluctuations with a 1/ω spectrum arise at an above-critical temperature.     

Mn55 NMR investigation of the suppression of quantum fluctuations in quasi-one-dimensional antiferromagnets by a magnetic field

The NMR of Mn⁵⁵ nuclei is measured in the quasi-one-dimensional antiferromagnets CsMnBr₃, RbMnBr₃, and CsMnI₃ in magnetic fields upto 8 T attemperatures in the range 1.3–4.2 K. The average moments of the magnetic sublattices and their field dependences, which turned out to be comparatively strong and different for magnetically non-equivalent Mn²⁺ ions, are determined from the hyperfine-field data obtained. As a result, the magnetizations of separate sublattices in an external magnetic field ∼8 T differ by more than 5%. The results obtained agree qualitatively with the theory of the suppression of quantum fluctuations by a magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 724–729 (10 December 1997) Deceased.     

The emergence of background geometry from quantum fluctuations

We show how the quantization of two-dimensional gravity leads to an (Euclidean) quantum space–time where the average geometry is that of constant negative curvature and where the Hartle–Hawking boundary condition arises naturally.     

Influence of quantum fluctuations on the motion of an electron in the field of a plane electromagnetic wave

The influence of radiation on the change in the energy, the longitudinal component of the momentum, and the shape of the orbit of an electron in the field of a wave is investigated. A comparison with the analogous quantities in the limiting case of high strength of a high-frequency electromagnetic field is made.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 95–97, February, 1991.     

Degree of polarization for quantum light field propagating through non-Kolmogorov turbulence

Nonclassical polarization properties of a quantum field propagating through non-Kolmogorov turbulence are studied in a turbulent atmosphere paraxial channel. The analytic equation for the quantum degree of polarization of linearly polarized light is obtained. It is shown by numerical simulation that the polarization fluctuations of the quantum field are a function of the turbulent strength, the photon number, the propagation distance, the fractal constant α and the coherence length ρ₀.     

Ultrafast time-resolved quantum beats in the polarization state of coherent emission from quantum wells

Dual-channel spectral interferometry is used to measure the ellipticity, the orientation of the polarization ellipse, and the sense of rotation of the four-wave-mixing signal from a GaAs-AlGaAs multiple quantum well. Each parameter is observed to oscillate dramatically at the heavy-hole-light-hole quantum beat frequency. During each beat period (in the strong quantum beat regime), the ellipticity oscillates twice between linear and almost-circular polarization, the orientation of the polarization ellipse rotates through a complete 180 degrees , and the sense of rotation changes from left- to right-circular polarization.