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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E.
Заглавие : On the short duration limit for the correlation-functions of 2 distant spins at high-temperatures
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz. - 1991. - Vol. 99, Is. 3. - P.809-815. - ISSN 0044-4510
Примечания : Cited References: 15
Предметные рубрики: DYNAMICS
Аннотация: The first term in the expansion in powers of time is found for the correlation function of two spins separated by a large distance in the case of an anisotropic Heisenberg paramagnet.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Averyanov E. M.
Заглавие : Orientation ordering and critical behavior of discoid nematics
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1996. - Vol. 110, Is. 5. - P1820-1840. - ISSN 0044-4510
Примечания : Cited References: 55
Предметные рубрики: LIQUID-CRYSTALS
PHASE-TRANSITION
ISOTROPIC-PHASE
LOCAL FIELD
SMECTIC-A
MOLECULES
SUSCEPTIBILITY
CONFORMATION
PARAMETER
DYNAMICS
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : On the radius of convergence of series in powers of time for spin correlation functions of the Heisenberg magnet at high temperature
Место публикации : Theor. Math. Phys.: PLENUM PUBL CORP, 1997. - Vol. 112, Is. 3. - P1182-1191. - ISSN 0040-5779, DOI 10.1007/BF02583049
Примечания : Cited References: 22
Предметные рубрики: AUTO-CORRELATION FUNCTION
INFINITE-TEMPERATURE
PARAMAGNET
DYNAMICS
MODEL
Аннотация: The convergence of series in powers of time for spin autocorrelation functions of the Heisenberg magnet are investigated at infinite temperatures on lattices of different dimensions d. The calculation data available at the present time for the coefficients of these series are used to estimate the corresponding radii of convergence, whose growth with decreasing d is revealed and explained in a self-consistent approximation. To this end, a simplified nonlinear equation corresponding to this approximation is suggested and solved for the autocorrelation function of a system with an arbitrary number Z of nearest neighbors. The coefficients of the expansion in powers of time for the solution are represented in the form of trees on the Bethe lattice with the coordination number Z. A computer simulation method is applied to calculate the expansion coefficients for trees embedded in square, triangular, and simple cubic lattices under the condition that the intersection of tree branches is forbidden. It is found that the excluded volume effect that manifests itself in a decrease in these coefficients and in an increase in the coordinate and exponent of the singularity of the autocorrelation function on the imaginary time axis is intensified with decreasing lattice dimensions.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Berman G. P., Campbell D. K., Tsifrinovich V. I.
Заглавие : Error correction for a spin quantum computer
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1997. - Vol. 55, Is. 9. - P5929-5936. - ISSN 0163-1829, DOI 10.1103/PhysRevB.55.5929
Примечания : Cited References: 26
Предметные рубрики: SYSTEMS
COMPUTATION
UNIVERSAL
DYNAMICS
LOGIC
Аннотация: The problems of error correction in a spin quantum computer are discussed. For digital processing in the Ising and Heisenberg chains driven by a resonant electromagnetic field, the simple schemes are suggested which provide correction of errors caused by imperfect pi pulses, and prevent the most significant errors caused by the nonresonant action of rr pulses. The probability of error caused by the Heisenberg interaction during the action of rr pulses is estimated. For quantum computations in spin systems a principal opportunity to correct the phase errors, based on Steane's three quantum-bits scheme, is described.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the magnetic properties of weakly interacting antiferromagnetic chains with an alternating exchange interaction with spin S=1/2
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2000. - Vol. 90, Is. 1. - P194-201. - ISSN 1063-7761, DOI 10.1134/1.559075
Примечания : Cited References: 35
Предметные рубрики: PEIERLS COMPOUND CUGEO3
MAGNON DISPERSION
BI2CUO4
EXCITATIONS
RESONANCE
SYSTEMS
SCATTERING
DYNAMICS
NEUTRON
PHASE
Аннотация: An approximation dependence of the spontaneous magnetic moment at a site, sigma/sigma(0) - 1 = 0.71(6)delta(2.5(2)), and the antiferromagnet-singlet state phase boundary, J(2)/J(1) = 0.52(3)delta, are determined by the quantum Monte Carlo method in the self-consistent sublattice molecular field approximation for weakly interacting (J(2)) antiferromagnetic chains with spin S = 1/2 and alternating exchange interaction (J(1) +/- delta). The Neel temperature and a number of critical temperatures which could be related with the filling energy of two singlets (Delta S-z = 0) and one triplet (Delta S-z= 1) spin bands, each of which is split by the sublattice field (h(x,y)not equal h(z)) into two subbands, are determined on the basis of the computed correlation radii of the two- and four-spin correlation function, the squared total spin (S-z)(2) with respect to the longitudinal components, the dimerization parameter, and the correlation functions between the nearest neighbors with respect to longitudinal and transverse spin components. On the basis of the Monte Carlo calculations, the critical temperatures and possible energy gaps at the band center are determined for the antiferromagnets CuWO4 and Bi2CuO4 and for the singlet compounds (VO)(2)P2O7 and CuGeO3 , agreeing satisfactorily with existing results, and new effects are also predicted. (C) 2000 MAIK "Nauka / Interperiodica".
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Alekseev K. N., Alekseeva N. V., Perina J.
Заглавие : Quantum-classical correspondence and nonclassical state generation in dissipative quantum optical systems
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2000. - Vol. 90, Is. 4. - P592-599. - ISSN 1063-7761, DOI 10.1134/1.559142
Примечания : Cited References: 32
Предметные рубрики: 2ND-HARMONIC GENERATION
STATISTICAL PROPERTIES
HARMONIC-GENERATION
SQUEEZED STATES
CHAOS
LIGHT
NONLINEARITIES
INSTABILITIES
DYNAMICS
ATOMS
Аннотация: We develop a semiclassical method to determine the nonlinear dynamics of dissipative quantum optical systems in the limit of large number of photons N; it is based on the 1/N-expansion and the quantum-classical correspondence. The method is used to tackle two problems: the study of the dynamics of nonclassical state generation in higher order anharmonic dissipative oscillators and the establishment of the difference between the quantum and classical dynamics of the second-harmonic generation in a self-pulsing regime. In addressing the first problem, we obtain an explicit time dependence of the squeezing and the Fano factor for an arbitrary degree of anharmonism in the short-time approximation. For the second problem, we analytically find a characteristic time scale at which the quantum dynamics differs insignificantly from the classical one. (C) 2000 MAIK "Nauka/Interperiodica".
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Alekseev K. N., Perina J.
Заглавие : The 1/N-expansion, quantum-classical correspondence and nonclassical states generation in dissipative higher-order anharmonic oscillators
Место публикации : Phys. Scr.: ROYAL SWEDISH ACAD SCIENCES, 2000. - Vol. 61, Is. 1. - P7-16. - ISSN 0281-1847, DOI 10.1238/Physica.Regular.061a00007
Примечания : Cited References: 38
Предметные рубрики: 2ND-HARMONIC GENERATION
HARMONIC-GENERATION
SQUEEZED STATES
CHAOS
LIGHT
MECHANICS
DYNAMICS
STATISTICS
SYSTEMS
OPTICS
Аннотация: We develop a method for the determination of the dynamics of dissipative quantum systems in the limit of large number of quanta N, based on the 1/N-expansion of Heidmann et al. [Opt. Commun. 54, 189 (1985)] and the quantum-classical correspondence. Using this method, we End analytically the dynamics of nonclassical states generation in the higher-order anharmonic dissipative oscillators for an arbitrary temperature of a reservoir. We show that the quantum correction to the classical motion increases with time quadratically up to some maximal value, which is dependent on the degree of nonlinearity and a damping constant, and then it decreases. Similarities and differences with the corresponding behavior of the quantum corrections to the classical motion in the Hamiltonian chaotic systems are discussed. We also compare our results obtained for some limiting cases with the results obtained by using other semiclassical tools and discuss the conditions for validity of our approach.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pichugin K., Schanz H., Seba P.
Заглавие : Effective coupling for open billiards
Место публикации : Phys. Rev. E: AMERICAN PHYSICAL SOC, 2001. - Vol. 64, Is. 5. - Ст.56227. - ISSN 1063-651X, DOI 10.1103/PhysRevE.64.056227
Примечания : Cited References: 30
Предметные рубрики: QUANTUM CHAOTIC SCATTERING
MICROWAVE CAVITY
RESONANCE POLES
QUANTIZATION
STATISTICS
DYNAMICS
FORMULA
SYSTEMS
STATES
Аннотация: We derive an explicit expression for the coupling constants of individual eigenstates of a closed billiard that is opened by attaching a waveguide. The Wigner time delay and the resonance positions resulting from the coupling constants are compared to an exact numerical calculation. Deviations can be attributed to evanescent modes in the waveguide and to the finite number of eigenstates taken into account. The influence of the shape of the billiard and of the boundary conditions at the mouth of the waveguide are also discussed. Finally we show that the mean value of the dimensionless coupling constants tends to the critical value when the eigenstates of the billiard follow random-matrix theory.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nazmitdinov R. G., Pichugin K. N., Rotter I., Seba P.
Заглавие : Conductance of open quantum billiards and classical trajectories
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2002. - Vol. 66, Is. 8. - Ст.85322. - ISSN 1098-0121, DOI 10.1103/PhysRevB.66.085322
Примечания : Cited References: 46
Предметные рубрики: BALLISTIC MICROSTRUCTURES
CHAOTIC SCATTERING
FLUCTUATIONS
DOTS
TRANSPORT
DYNAMICS
STATES
MAGNETOTRANSPORT
STATISTICS
RESONANCES
Аннотация: We analyze the transport phenomena of two-dimensional quantum billiards with convex boundary of different shape. The quantum mechanical analysis is performed by means of the poles of the S matrix while the classical analysis is based on the motion of a free particle inside the cavity along trajectories with a different number of bounces at the boundary. The value of the conductance depends on the manner in which the leads are attached to the cavity. The Fourier transform of the transmission amplitudes is compared with the length of the classical paths. There is good agreement between classical and quantum mechanical results when the conductance is achieved mainly by special short-lived states such as whispering gallery modes and bouncing ball modes. In these cases, also the localization of the wave functions agrees with the picture of the classical paths. The S matrix is calculated classically and compared with the transmission coefficients of the quantum mechanical calculations for five modes in each lead. The number of modes coupled to the special states is effectively reduced.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Second moment of multiple-quantum NMR and a time-dependent growth of the number of multispin correlations in solids
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 103, Is. 6. - P904-916. - ISSN 1063-7761, DOI 10.1134/S1063776106120089
Примечания : Cited References: 39
Предметные рубрики: NUCLEAR-MAGNETIC-RESONANCE
LINE-SHAPE
SPIN SYSTEMS
DYNAMICS
SPECTRA
COHERENCES
STATE
BEHAVIOR
CRYSTAL
MODEL
Ключевые слова (''Своб.индексиров.''): correlation methods--mathematical models--nuclear magnetic resonance spectroscopy--spectrum analysis--time series analysis--four-spin time correlation--multispin correlations--second moment--time power series--quantum theory
Аннотация: The time evolution of multispin correlations (the growth of the number of correlated spins as a function of time) can be observed directly using the multiple-quantum nuclear magnetic resonance spectroscopy of solids. A quantity related to this number, namely, the second moment n(2)(t) of the intensity distribution of coherences of different orders in the multiple-quantum spectrum can be calculated using the theory proposed in this work. An approach to the calculation of the four-spin time correlation function through which this moment is expressed is developed. The main sequences of contributions in the expansion of this function into a time power series are summed using the approximation of a large number of neighbors both for systems with a secular dipole-dipole interaction and for systems with a nonsecular effective interaction. An exponential dependence of n(2)(t) is obtained. The value of n(2)(t) is additionally calculated using an expansion in terms of orthogonal operators for three model examples corresponding to different limiting realizations of spin systems. It is shown that the results of the microscopic theory at least qualitatively agree with both the results obtained for model examples and experimental results obtained recently for adamantane.
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