Quantum temperature fluctuations in the magnetization of antiferromagnetic semimetals

It is shown that in semimetallic, low-temperature antiferromagnetic materials located in a quantizing magnetic field, the part of the band magnetization M _∼ which oscillates in H can have a nonmonotonic temperature dependence. This non-Fermi liquid behavior will show up experimentally in the form of quantum temperature fluctuations of the magnetization when the decrease with rising temperature is oscillatory, rather than the usual monotonic decrease. It is shown that the magnetization from an individual spin electron (or hole) subband has the form of weakly damped periodic oscillations as a function of T ². This result makes it possible to develop an efficient method for studying the electronic structure of antiferromagnetic semimetals based on an examination of the quantum temperature fluctuations. Calculations show that quantum temperature fluctuations can be observed, for example, in the cerium monopnictides CeP and CeAs, which are strongly correlated, antiferromagnetic, compensated semimetals with low Neel temperatures. Fiz. Tverd. Tela (St. Petersburg) 40, 1674–1680 (September 1998)     

Quantum discreteness effects and flicker fluctuations in tunneling conductivity

An analysis of events in the tunneling junction shows that the interaction of one-electron processes in a many-electron system may be a source of scale-invariant low-frequency fluctuations of conductivity (the interaction consists in that the quantum probability of an electron transition depends on fast random changes in the environment in the course of the transition, including the changes caused by analogous transitions). The theory relates flicker fluctuations in the tunneling conductivity to the discrete character of the spectrum of electron states and explains the nonlinearity of the noise-current characteristic observed in nanocomposites.     

Quantum fluctuations in quantum lattice systems with continuous symmetry

We discuss conditions for the absence of spontaneous breakdown of continuous symmetries in quantum lattice systems atT=0. Our analysis is based on Pitaevskii and Stringari's idea that the uncertainty relation can be employed to show quantum fluctuations. For one-dimensional systems, it is shown that the ground state is invariant under a continuous transformation if a certain uniform susceptibility is finite. For the two- and three-dimensional systems, it is shown that truncated correlation functions cannot decay any more rapidly than|r| ^–d+1 whenever the continuous symmetry is spontaneously broken. Both of these phenomena occur owing to quantum fluctuations. Our theorems cover a wide class of quantum lattice systems having not-too-long-range interactions.     

Quantum fluctuations of thermal transport coefficients in mesoscopic systems

The quantum interference effects in small-size samples are discussed. Using a corrected Wiedemann-Franz law, we obtain the functional dependence of the relative thermal conductivity on the relative electrical conductivity. The results show that the fluctuations of thermal transport coefficients have a periodic oscillation corresponding to the electrical conductivity fluctuation, but the amplitudes of them are different for different materials.     

Quantum mechanical effects in non-inertial systems

An investigation is made into the possible quantum mechanical effects due to the inertial force effect in the non-inertial systems, e.g. in atoms and molecules moving with high acceleration. In accordance with Einstein's principle of equivalence similar effects should appear in the sufficiently strong permanent gravitational fields.     

Quantum fluctuations and inertia

One of the three key assumptions involved in the stochastic formulation of quantum mechanics, the inverse proportionality of the quantum diffusion constant to the inertial mass, is shown to be amenable to experimental test. By relaxing this assumption, a non-linear generalization of the Schrödinger equation is found. The present experimental uncertainty in the measurement of the Lamb shift is then used to bound the deviation from the aforementioned inverse proportionality to be less than 4 × 10⁻¹³.     

Quantum vacuum fluctuations

The existence of irreducible field fluctuations in vacuum is an important prediction of quantum theory. These fluctuations have many observable consequences, like the Casimir effect, which is now measured with good accuracy and agreement with theory, provided that the latter accounts for differences between real experiments and the ideal situation considered by Casimir. But the vacuum energy density calculated by adding field mode energies is much larger than the density observed around us through gravitational phenomena. This ‘vacuum catastrophe’ is one of the unsolved problems at the interface between quantum theory on one hand, inertial and gravitational phenomena on the other hand. It is however possible to put properly formulated questions in the vicinity of this paradox. These questions are directly connected to observable effects bearing upon the principle of relativity of motion in quantum vacuum.     

Quantum fluctuations,master equation and Fokker-Planck equation

In order to describe quantum fluctuations a general method is developed, which also may be applied to nonstationary systems as well as to states far from thermodynamic equilibrium. After a concise derivation of the master equation quantum mechanically determined dissipation and fluctuation coefficients are introduced, for which several theorems and relations are given. By using these coefficients there is set up a general Fokker-Planck equation for the diffusion of the statistical operator due to quantum fluctuations.     

Quantum statistical effects in nuclear reactions,fission, and open quantum systems

Quantum diffusion equations with time-dependent transport coefficients are derived from generalized non-Markovian Langevin equations. Generalized fluctuation-dissipation relations and analytical formulas for calculating friction and diffusion coefficients in nuclear processes are obtained. The asymptotics of the transport coefficients and of the correlation functions are investigated. The problem of correlation decay in quantum dissipative systems is studied. A comparative analysis of diffusion coefficients for the harmonic and inverted oscillators is performed. The role of quantum statistical effects during passage through a parabolic potential barrier is investigated. Sets of diffusion coefficient assuring the purity of states at any time instant are found in cases of non-Markovian dynamics. The influence of different sets of transport coefficients on the rate of decay from a metastable state is studied in the framework of the master equation for reduced density matrices describing open quantum systems. The approach developed is applied to investigation of fission processes and the processes of projectile-nuclei capture by target nuclei for bombarding energies in the vicinity of the Coulomb barrier. The influence of dissipation and fluctuation on these processes is taken into account in a self-consistent way. The evaporation residue cross sections for asymmetric fusion reactions are calculated from the derived capture probabilities averaged over all orientations of the deformed projectile and target nuclei.     

Quantum potts gauge-matter systems at finite temperature

A systematic large-N expansion for gauge-matter Potts systems at finite temperature is presented. This allows us to explore the interior of the phase diagrams, taking into account all terms in the hamiltonian. Calculations are carried out in 3 + 1 and 2 + 1 dimensions and the expansion parameter is $\text{1/N}{}^{\mathrm{<mtext>1</mtext><mtext>d</mtext>}}$, where d is the number of space dimensions. For singly charged matter the Higgs-confinement phase is analytically connected to a high-temperature plasma phase. When the matter fields are multiply charged, both Higgs and confinement phases undergo a finite-temperature phase transition. The free charge phase may or may not undergo a phase transition depending on the number of space-time dimensions. Implications for other models, both abelian and non-abelian are discussed. We also comment on applications to quantum spin systems.     

简单体系温度涨落的发散问题

平衡体系热力学推导涨落的前提是涨落必须很小，如果得到一个发散的结果说明这一涨落是不可靠的.对一些体系温度涨落的热力学结果，在温度趋于绝对零度时是发散的，这时必须用统计物理来处理.对这些体系进行统计物理处理的结果表明，涨落在温度趋于绝对零度时是趋于零的. 关键词： 热力学与统计物理 涨落     

Quantum coherent effects in multi-Zeeman-sublevel atomic systems

This paper reports the experimental results on electromagnetically induced absorption （EIA） spectra observed in the system which does not satisfy completely the conditions given by Lezama et al [1999 Phys. Rev. A 59 4732]. EIA signals on the transitions in the Cs D2 line are able to be observed, where Fg ←→ Fe = Fg-1 as open systems. Theoretical model of Lezama et al is good for the case Fg ←→ Fc = Fg ＋ 1, considering spontaneous transfer of atomic coherences or populations this model is not able to explain our experimental results obtained in the case Fg ←→ Fe = Fg - 1. This paper offers a theoretical model which is able to well explain the case Fg ←→ Fc = Fg - 1. It also uses this theoretical model to explain the split and shift of EIA peaks, which have been obtained in experiments.     

Quantum fluctuations in nonlinear optics

We consider nonlinear optical devices which are excited by coherent light from a laser and in which several other waves are generated by nonlinear processes. We develop a general theory to treat the noise properties of the generated waves. In particular a probability distribution function is found which in principle can be measured experimentally. This formulation allows a thermodynamic study of phase transitions.     

The effects of fluctuations and nonuniformities on line-reversal temperature measurements

An analysis of line-reversal temperature measurements in the presence of fluctuations and nonuniformities is presented. The theory provides a method for the measurement of mean temperatures and temperature fluctuation intensities in certain combustion flows. Experiments with controlled and random fluctuations are interpreted by means of the analysis.