Influence Of Quantum Fluctuations Research Articles

Quantum Coherence of the Ground State of a Mesoscopic Ring

We discuss the phase coherence properties of a mesoscopic normal ring coupled to an electric environment via Coulomb interactions. This system can be mapped onto the Caldeira–Leggett model with a flux dependent tunneling amplitude. We show that depending on the strength of the coupling between the ring and the environment the free energy can be obtained either by a Bethe ansatz approch (for weak coupling) or by using a perturbative expression which we derive here (in the case of strong coupling). We demonstrate that the zero-point fluctuations of the environment can strongly suppress the persistent current of the ring below its value in the absence of the environment. This is an indication that the equilibrium fluctuations in the environment disturb the coherence of the wave functions in the ring. Moreover the influence of quantum fluctuations can induce symmetry breaking seen in the polarization of the ring and in the flux induced capacitance.

Influence of quantum fluctuations on the ground state of quasi-one-dimensional triangular antiferromagnet [formula omitted

55 Mn NMR in the quasi-1D triangular antiferromagnet CsMnI 3 was investigated. Six NMR modes corresponding to six spin orientations of Mn ions in elementary magnetic cell were observed. The difference between average values of the Mn spins 〈S〉 in magnetically nonequivalent antiferromagnetic chains was found. We have determined a new magnetic phase of CsMnI 3 in a magnetic field parallel to the hexagonal axis in the range 39– 52 kOe . Calculations indicate that the new phase is a result of the difference between the 〈S〉 values in neighbouring antiferromagnetic chains.

Vliyanie kvantovykh fluktuatsii na magnitnye svoistva kvaziodnomernykh treugol'nykh antiferromagnetikov

Влияние квантовых флуктуаций на магнитные свойства квазиодномерных треугольных антиферромагнетиков, Думеш Б.С.

Quantum control by compensation of quantum fluctuations

We show that the influence of quantum fluctuations in the electromagnetic field vacuum on a two level atom can be measured and consequently compensated by balanced homodyne detection and a coherent feedback field. This compensation suppresses the decoherence associated with spontaneous emissions for a specific state of the atomic system allowing complete control of the coherent state of the system.

Low-temperature phase diagrams: non-linearities due to quantum mechanical saturation of order parameters

At low temperatures, the behaviour of structural phase transitions is modified by the influence of quantum fluctuations. Such fluctuations enhance the stability of the high-symmetry phase, reducing the observed transition temperature. The effect on phase diagrams of temperature versus some other control parameter (e.g. pressure or chemical composition) is described. A simple low-temperature extension of Landau theory is used, where the extent of quantum mechanical effects is characterized by a saturation temperature . The theory is used to model the phase diagrams of the mineral anorthoclase , the ferroelectric materials ( for the 20 K transition), and SbSI . The saturation temperature is related to the extent to which changes in the hard phonon modes influence the transition mechanism.

Influence of quantum fluctuations on the Néel temperature of a dilute two-dimensional anisotropic antiferromagnet

A quantum Monte Carlo procedure is used to calculate the energy, sublattice magnetization, Neel temperature, and the slopes of the S=[1/TN(x=0)]dTN(x)/dx curves as functions of the hole concentration and the exchange anisotropy Δ=1−Jx,y/Jz in the Heisenberg model with anisotropic negative interactions between nearest neighbors in a square lattice with dilution among the lattice sites. The slope diverges in the limit Δ→0: S∼ln(6.5/Δ).

Path-Integral Monte Carlo Scheme for Rigid Tops: Application to the Quantum Rotator Phase Transition in Solid Methane.

A new quantum propagator for asymmetric tops, exact for free tops, is applied to path-integral Monte Carlo simulations of quantum rotors. The algorithm does not suffer from the sign problem if the full density matrix is considered or if the identity representation for the density matrix is chosen. The method is applied to simulation of crystalline ${\mathrm{CH}}_{4}$, where the influence of quantum fluctuations in the lowering of the transition temperature from a plastic phase to an orientational ordered state is investigated. The possibility of an inverse hysteresis occurring at that transition is predicted and related to spin-statistical exchange effects.

Monte Carlo investigation of head-tail ordering of CO monolayers on graphite

Heat capacity measurements recently showed that CO physisorbed on graphite undergoes a head-tail ordering transition at roughly 5 K. The present paper is a detailed Monte Carlo study of this phase transition and the ordered state. The simulations are based on an ab initio pair potential and rely crucially on a thorough finite-size scaling study of various quantities. In agreement with experiments we find that the transition belongs to the universality class of the Ising model in two dimensions. We go beyond experimental knowledge by revealing the particular ferrielectric structure of the ground state, and show that the transition is due to the molecule's shape asymmetry rather than to electrostatic dipole interactions. The influence of quantum fluctuations on the ground state and on the transition itself are also analyzed.

Quantum effects and orientational ordering in adsorbed layers of linear molecules

AbstractWe study the influence of quantum fluctuations on the herringbone transition in adsorbed complete √3‐mono‐layers of diatomic molecules. Using Path‐Integral Monte Carlo simulations for rotations, we can quantify the shift of the transition temperature for a highly realistic model to describe N2 on graphite. In addition, the zero‐point motion of the librating molecules depresses the ground‐state order parameter. We compare the benchmark data to quadratic Feynman‐Hibbs effective potential simulations and to a quasiharmonic approximation. Using a simplified model for this transition, we study systematically quantum effects being relevant for lighter molecules. Depending on the rotator's rotational constant, we find re‐entrant orientational quantum melting or even the suppression of orientational order.

Influence of quantum fluctuations on solitary-wave acoustic polaron motion

The theory of Wilson's solitary-wave acoustic polaron motion is generalized to include the effects of quantum fluctuations and the non-adiabatic behaviour of the electron-phonon coupling. The polaron dynamics are described quantum mechanically in terms of master equations for the electronic variables. As a final result, it emerges that due to the considered quantum effects for v<<c (v=polaron velocity, c=sound velocity) the polaron behaviour is determined by the well-known semiclassical non-linear Schrodinger equation, whereas for v<c the polaron motion is overdamped but shows by no means a divergent behaviour as obtained in semiclassical theories. In addition, for v=c the phonon cloud around the electron disappears and the electron motion becomes diffusive.

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.

Laser cooling and trapping

The basic physical effects leading to radiation-induced forces are reviewed. A simple derivation of the mathematical expressions for the classical light forces is given. The influence of quantum fluctuations is demonstrated and the possibilities for trapping neutral particles are discussed. Two recent successful laser cooling and trapping experiments are described to illustrate the applications of the basic principles.

Quantum fluctuations in an ising spin glass with transverse field

The influence of quantum fluctuations on the transition temperature of an Ising spin glass with transverse field is studied. The results are compared with the so-called static approximation used widely in the literature. It is shown that quantum fluctuations have a significant effect on the field dependent transition temperature although the qualitative behavior is similar to results obtained within the static approximation.

Monte Carlo calculations of switching-time statistics in a two-mode laser.

A two-mode laser operating in the bistable region switches spontaneously from one mode to the other under the influence of quantum fluctuations. We present here a Monte Carlo simulation of the coupled Langevin equations describing the dynamics of a two-mode laser. We present results on the variation of average switching time with pump parameter. We show that if fluctuations in the pump parameter are incorporated, the Monte Carlo estimates agree well with measured switching times. To further check this observation we reanalyze the results of a recent analytical study and show that by including the same pump parameter fluctuations, the agreement with measurements becomes much better.

On the quantum effects in helimagnets

The influence of quantum fluctuations on the magnon spectrum of helimagnets is investigated. It is shown that quantum effects result in the shift of the helix wavevector value, while the general structure of the spectrum, i.e. the existence of the two Goldstone modes, remains unchanged.

Ferroelectric properties of single crystals of solid solutions of tris-sarcosine calcium chloride-bromide

The concentration dependence of the ferroelectric transition temperature Tc of single crystals of the solid solution Tris-sarcosine calcium chloride1-x bromidex is studied experimentally by measurement of the static dielectric constant εb and described by the empirical relation Tc(x) = Tc(0) (1 x/xcc)1/2. The Ising model with transverse field and the model of coupled anharmonic oscillators are used to explain the concentration dependence of the transition temperature Tc. The influence of quantum fluctuations is discussed.

First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser

The distribution of first-passage times is calculated for a homogeneously broadened two-mode laser, that is characterized by a bistable potential. As a consequence of quantum fluctuations, such a system tends to switch spontaneously between the two metastable states. The results of the calculation are compared with first-passage-time measurements of a two-mode dye laser.

Experimental Investigation of the Influence of Quantum Fluctuations of Radiation on the Motion of Electrons in the 1.5-GeV Synchrotron at Tomsk Polytechnical Institute

Experimental Investigation of the Influence of Quantum Fluctuations of Radiation on the Motion of Electrons in the 1.5-GeV Synchrotron at Tomsk Polytechnical Institute