Effect of time reversal in the magnetization of an atom by a resonant light pulse

It is shown that the even dependence of the light-induced magnetic moment on the detuning ω-ω _ba from resonance in the case of a circularly polarized pulse and an isotropic initial state of the atom and the odd dependence on ω-ω _ba in the case of a linearly polarized pulse and an anisotropic initial state in the form of alignment of the atom are consequences of the symmetry under time reversal t→−t and of the initial conditions at time t=0. In a number of cases, this fundamental law makes it possible to determine the vector properties of a light-induced magnetic moment and its dependence on the time t and ω-ω _ba without solving the equation for the density matrix in detail and without calculating the sum over the projections of the angular momenta in the formula for the magnetization of an atom by light. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 231–236 (10 February 1997)     

Critical current of an inhomogeneous Josephson junction at an intergrain boundary with a random distribution of dislocations

The critical current J _c(θ) of an intergrain boundary is calculated as a function of the contact misorientation angle θ of the granules. It is assumed that the ordering parameter is suppressed in regions near boundaries with an enhanced mechanical stress induced by randomly distributed surface dislocations. The stress distribution function is determined using a probabilistic approach. Assuming that the weak coupling at the boundary is Josephson coupling, an analytic expression is found for the angular dependence J _c(θ) (for tilt and twist boundaries). The magnitude of the residual critical current of a boundary in a strong magnetic field is estimated. Fiz. Tverd. Tela (St. Petersburg) 40, 393–402 (March 1998)     

Evolution of large-scale correlations in a strongly nonequilibrium Bose condensation process

The evolution of off-diagonal correlation functions (for the example of a single-particle density matrix) in the process of Bose condensation of an initially nonequilibrium interacting gas is discussed. Special attention is given to the character of the decay of the density matrix at distances much greater than the size of the quasicondensate region. Specifically, it is shown that the exponential decay of the density matrix necessarily presupposes the presence of a chaotic vortex structure — a tangle of vortex lines — in the system. When topological order is established but there is no off-diagonal long-range order, the density matrix decays with distance according to a power law. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 495–501 (10 April 1998)     

Magnetization of optically polarized gas atoms by an optical pulse train

The properties of the density matrix and the multipole moments arising in oriented and aligned atoms with zero nuclear spin through the interaction with strong resonant ultrashort pulses with wave vector k ₀ and circular or linear polarization have been found. Calculations have been made for the time-dependent light-induced magnetization μ(t′) of a gas of pre-oriented and prealigned atoms following the passage of a weak resonant elliptically polarized pulse with frequency ω and wave vector k collinear with k ₀. It is shown that for oriented atoms, μ(t′) is an even function of the detuning from resonance, ω-ω _ba, and can be split into two terms whose directions are a consequence of symmetry and are determined by the vectors k ₀ and k as well as by the direction of rotation of the electric fields corresponding to the pulses. For aligned atoms the vector μ(t′) is collinear with k, and the first term is an even function of ω-ω _ba. However, the second term is an odd function of ω-ω _ba and reverses direction when the sign of ω-ω _ba changes, as well as when the orientation of the axes of the polarization ellipse is changed. It is shown that if a series of weak linearly polarized pulses pass through the gas, the light-induced magnetization of the oriented and aligned gas atoms can be decomposed into three factors: the first determines the direction and is a consequence of the symmetry; the second (with the dimensions of magnetic moment) depends on the characteristics of the resonant transitions; and the third is a universal function of t′ and ω-ω _ba that does not depend on the underlying characteristics of the resonant transition. These vector factors and the universal functions are in principle different for oriented and aligned atoms. Zh. éksp. Teor. Fiz. 111, 63–92 (January 1997)     

Nonlinear collapse of an isolated,homogeneously broadened,spectral line as a result of coherent collisions

The collisional exchange between an off-diagonal element of the density matrix and its complex conjugate results in the collapse of a homogeneously broadened spectral line. The case when such exchange is due to the polarization of the heat bath on account of two-photon absorption is studied. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 599–603 (10 November 1996)     

Effect of the state of a quantized electromagnetic field on the interaction with an atom with allowance for the continuum

This paper studies the effect of a transition into the continuous spectrum on the “collapse” and “revival” of population oscillations in an atom. It is shown that at large values of the mean number of photons in a radiation field and in conditions of weak ionization the phenomena of collapse and revival can still be observed, but the amplitude of population oscillations decreases exponentially because of the damping of the level. The interaction of a quantized electromagnetic field with a Λ system of an atom when one state is continuous is examined. Expressions are derived for the probability of “survival” of the atom when the quantized field was initially in a state with a given number of photons and when it was in a coherent state. An approximate calculation of the sum in averaging over the photon number distribution in the case of a coherent field leads to expressions for the probabilities of survival of the atom that transform into expressions, as the mean number of photons tends to infinity, corresponding to the case of a field in the representation of a fixed number of photons. The possibility of a stable state existing in a coherent quantized field is examined. It is found that for a Λ system the condition for the existence of a stable state remains valid in the case of a coherent state of the field when the photon number is large. Zh. éksp. Teor. Fiz. 113, 1193–1205 (April 1998)     

An eigenvalue-based approach for the design of reflector systems and prisms with a specified image orientation change

The image orientation change (IOC) of an object following its reflection by a system comprising an arbitrary number of flat boundary surfaces can be described using a merit function (Γ) expressed in the form of a 3×3 matrix. The present study proposes a design methodology for stable-IOC reflector and prism systems in which the merit function is solved using an eigenvalue-based approach. It is shown that a reflector system remains IOC-stable following its rotation about the eigenvector of the IOC merit function, provided that the image can still physically enter the system’s aperture. Furthermore, it is shown that an IOC-stable prism can be obtained by adding two refracting flat boundary surfaces at the entrance and exit positions of the light ray in an optical system comprising multiple reflectors provided that the condition n _n =Γn ₁ is maintained. Illustrative examples are provided to demonstrate the validity of the proposed design approach.     

On a precise check of the standard model in an experiment with a 90Sr beta source

A discussion is given on the prospects for making a precise determination of the value of sin²θ _W (θ_W is the Weinberg angle) and for improving the sensitivity of the search for the antineutrino magnetic moment to ≈1.5×10⁻¹¹μ_B and for the mixing parameter to sin²2θ ≈10⁻² by measuring in a single experiment the cross sections for scattering for the reaction . Such an experiment with ∼100 000 events/yr detected for each reaction can be carried out, for example, using the BOREXINO detector and an approximately 10 MCi ⁹⁰Sr source. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 435–439 (10 April 1998)     

On the Spectrum of the Generator of an Infinite System of Interacting Diffusions

We study the spectrum of the operator

A modified Jaynes-Cummings model for an atom interacting with a classical multifrequency field

An open quantum system, which consists of a “dressed” two-level atom, i.e., an atom interacting with a classical multifrequency field, and a single quantized mode of an electromagnetic field, is examined. It is shown that when the frequency of the quantized mode coincides with one of the transition frequencies between the quasienergy levels, two interaction mechanisms, which differ in the dynamics of the populations of the quasienergy states, can be realized. Zh. éksp. Teor. Fiz. 112, 818–827 (September 1997)     

Motion of an electronic wave packet in an electromagnetic field

An equation is derived for the matrix of the parameters of a small Gaussian wave packet moving in arbitrary fixed electromagnetic fields. The equation can be used to describe the evolution of wave packets in a wide class of vacuum devices. A simple example of the evolution of a packet in a constant magnetic field is studied. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 515–520 (25 October 1996)     

Lattice dynamics of ionic crystals in a model of “breathing” and polarizable ions

An expression is written down for the dynamic matrix of ionic crystals in terms of a microscopic, parameterless model of “breathing” and polarizable ions. Results from a calculation of the complete spectrum of the lattice vibrations of ionic crystals having an NaCl structure are presented as an illustration. Fiz. Tverd. Tela (St. Petersburg) 40, 350–354 (February 1998)     

Shape of the magnetic resonance line in a thin film on the surface of an anisotropic superconductor

The shape of the EPR line in a thin (=λ/2, where λ is the London penetration depth of the magnetic field in the superconductor) paramagnetic film deposited on the surface of an anisotropic superconductor is calculated in an oblique magnetic field with allowance for the inhomogeneity of the local magnetic field of the Abrikosov vortex lattice. It is shown that, as the tilt angle of the external magnetic field is varied, the shape of the EPR line changes noticeably. This fact can give additional information about the superconductor parameters (the symmetry type of the vortex lattice and the anisotropy parameter of the superconductor). Fiz. Tverd. Tela (St. Petersburg) 41, 386–388 (March 1999)     

Coherent effects in regular three-dimensional lattices of insulator nanocrystals in an opal matrix

Samples of the nanocomposite opal + NaCl with 100% filling of first-order voids in the opal by NaCl have been obtained. The thermal conductivity of the nanocomposite has been measured in the temperature interval 4.2–300 K. It is shown that NaCl, introduced into opal, forms a regular “matrix quasilattice” of microcrystals, which leads to suppression of coherent effects and, as a consequence, of properties characteristic of massive crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 348–353 (February 1999)     

Scaling function near a transition to an insulator state

Analysis of experimental results yields a scaling function of the form β(g)=121/g near the metal-insulator transition in three-dimensional systems. In two-dimensional electronic systems demonstrating a transition to an insulator state, the same relation holds for the function νβ, where ν is the critical exponent characterizing the divergence of the correlation length. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 807–811 (10 December 1998)     

Effective permittivity of a discrete random medium with anisotropic inclusions

We use the method of substitution of field variables in the bilocal approximation to find the effective permittivity of a two-phase composite random medium in the form of an ensemble of small, arbitrarily anisotropic spherical inclusions distributed inside an isotropic matrix. To illustrate the results we calculate the damping of the plane waves of the mean field in such a medium. Zh. éksp. Teor. Fiz. 114, 1188–1201 (October 1998)     

Propagation of a transient electromagnetic disturbance in an inhomogeneous, collisional, Magnetized plasma

Summary The time response of an anisotropic, inhomogeneous magnetized plasma to a time-dependent externally applied electric field is studied. The plasma is considered as a conducting medium embedded in a static magnetic fieldB _o, with finite and constant parallel conductivity σ_∥ and normal conductivity σ_⊥ exponentially varying; a constant ion polarization conductivity (σ_pol) normal toB ₀ is also included. The driving termE ₀ is assumed to be normal to the ambient magnetic field, with a space dependence only in the (E ₀, B₀)-plane (two-dimensional case). The problem is treated as an initial (in time) and boundary (in space) value problem, and an analytic solution is obtained for the time response of the system to a unit step of electric field; the solution for any other driving field is then given via a convolution integral. This model can be used in particular to study the propagation through the ionosphere of ULF waves generated by the motion of an artificially created ion cloud in the upperF region. Moreover, the mathematical technique is rather general, so it may be used also for different plasma models.

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Riassunto Si presenta lo studio della risposta temporale (transitorio) di un plasma magnetizzato, anisotropo e inomogeneo ad un campo elettrico esterno impresso. Il plasma è trattato come un mezzo conduttore, immerso in un campo magnetico staticoB ₀, la cui conducibilità elettrica parallela al campo magnetico σ_∥ è costante, mentre la conducibilità normale σ_⊥ varia esponenzialmente nello spazio; si considera inoltre una conducibilità dovuta alla polarizzazione degli ioni (σ_pol) costante e normale aB ₀. Il campo impressoE ₀ è assunto normale al campo magnetico ambiente con dipendenza spaziale solo nel piano (E ₀, B₀) (caso bidimensionale). In queste ipotesi si perviene ad un problema ai valori iniziali e al contorno, e si deriva una soluzione analitica per la risposta transitoria del sistema ad un gradino di campo elettrico impresso; la soluzione per una qualsiasi funzione di campo applicato è data come integrale di convoluzione con la risposta al gradino. Questo modello può essere usato, in particolare, per studiare la propagazione attraverso la ionosfera di un'onda ULF generata dal moto di una nuvola ionica creata artificialmente nella parte superiore della regioneF. Un ulteriore interesse deriva dal fatto che, essendo la tecnica matematica utilizzata molto generale, questa può essere applicata pure a differenti modelli di plasma.

     

Possibility of the appearance of spin autowaves in a model of a ferromagnet with nonuniform dissipation

A model of a ferromagnet with nonuniform dissipation is introduced for the Landau-Lifshitz equations. It is shown that in this model a ferromagnet can be regarded as an oscillating active medium where the formation of autowave structures — spin autowaves, pacemakers, and spiral waves — is possible. Their wave characteristics, expressed in terms of the parameters of the medium, are found for a special case. Fiz. Tverd. Tela (St. Petersburg) 39, 513–515 (March 1997)     

Electroproduction of an isobar as a background from the beam-residual-gas interaction in φ factories

It is shown that the electroproduction of the isobar Δ(1232) occurs in φ factories when the beams interact with the residual gas. In one effective year (10⁷ s) the decay of this isobar over an interaction length of one meter gives ∼10⁷ pions, moving predominantly in a direction transverse to the axis of the beams, with a resonance energy distribution having a 120-MeV wide peak near 265 MeV. Formulas required for modeling the process under discussion, giving the distributions over the momentum transfer, angles, energies, and momenta of the decay products are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 295–300 (25 February 1997)