Classical limit of master equation for harmonic oscillator coupled to oscillator bath with separable initial conditions

The equation for the Wigner function describing the reduced dynamics of a single harmonic oscillator, coupled to an oscillator bath, was obtained by Karrlein and Grabert [Phys. Rev. E, vol. 55, 153 (1997)]. It was shown that for some special correlated initial conditions the equation reduces, in the classical limit, to the corresponding classical Fokker-Planck equation obtained by Adelman [J. Chem Phys., vol. 64, 124 (1976)]. However for separable initial conditions the Adelman equations were not recovered. We resolve this problem by showing that, for separable initial conditions, the classical Langevin equation obtained from the oscillator bath model is somewhat different from the one considered by Adelman. We obtain the corresponding Fokker-Planck equation and show that it exactly matches the classical limit of the equation for the Wigner function obtained from the master equation for separable initial conditions. We also discuss why the special correlated initial conditions correspond to Adelman's solution.Comment: 12 page

Quantum eigenstate tomography with qubit tunneling spectroscopy

Measurement of the energy eigenvalues (spectrum) of a multi-qubit system has recently become possible by qubit tunneling spectroscopy (QTS). In the standard QTS experiments, an incoherent probe qubit is strongly coupled to one of the qubits of the system in such a way that its incoherent tunneling rate provides information about the energy eigenvalues of the original (source) system. In this paper, we generalize QTS by coupling the probe qubit to many source qubits. We show that by properly choosing the couplings, one can perform projective measurements of the source system energy eigenstates in an arbitrary basis, thus performing quantum eigenstate tomography. As a practical example of a limited tomography, we apply our scheme to probe the eigenstates of a kink in a frustrated transverse Ising chain.Comment: 8 pages, 4 figure

Importance of reaction volume in hadronic collisions: Canonical enhancement

We study the canonical flavor enhancement arising from exact conservation of strangeness, and charm flavor. Both the theoretical motivation, and the practical consequences are explored. We argue using qualitative theoretical arguments and quantitative evaluation, that this proposal to reevaluate strangeness signature of quark--gluon plasma is not able to explain the majority of available experimental results.Comment: 14 pages including 6 figures, submitted to Journal of Physics G Presented at: Strange Quark Matter, September 2001, Frankfur

Optimal Energy Dissipation in Sliding Friction Simulations

Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the removal of the frictionally generated Joule heat. Building upon general pre-existing formulation, we implement a fully microscopic dissipation approach which, based on a parameter-free, non-Markovian, stochastic dynamics, absorbs Joule heat equivalently to a semi-infinite solid and harmonic substrate. As a test case, we investigate the stick-slip friction of a slider over a two-dimensional Lennard-Jones solid, comparing our virtually exact frictional results with approximate ones from commonly adopted dissipation schemes. Remarkably, the exact results can be closely reproduced by a standard Langevin dissipation scheme, once its parameters are determined according to a general and self-standing variational procedure

Two-bath model for activated surface diffusion of interacting adsorbates

The diffusion and low vibrational motions of adsorbates on surfaces can be well described by a purely stochastic model, the so-called interacting single adsorbate model, for low-moderate coverages (\theta \lesssim 0.12). Within this model, the effects of thermal surface phonons and adsorbate-adsorbate collisions are accounted for by two uncorrelated noise functions which arise in a natural way from a two-bath model based on a generalization of the one-bath Caldeira-Leggett Hamiltonian. As an illustration, the model is applied to the diffusion of Na atoms on a Cu(001) surface with different coverages.Comment: 7 pages, 3 figure

Relativistic Brownian motion: From a microscopic binary collision model to the Langevin equation

The Langevin equation (LE) for the one-dimensional relativistic Brownian motion is derived from a microscopic collision model. The model assumes that a heavy point-like Brownian particle interacts with the lighter heat bath particles via elastic hard-core collisions. First, the commonly known, non-relativistic LE is deduced from this model, by taking into account the non-relativistic conservation laws for momentum and kinetic energy. Subsequently, this procedure is generalized to the relativistic case. There, it is found that the relativistic stochastic force is still \gd-correlated (white noise) but does \emph{no} longer correspond to a Gaussian white noise process. Explicit results for the friction and momentum-space diffusion coefficients are presented and discussed.Comment: v2: Eqs. (17c) and (28) corrected; v3: discussion extended, Eqs. (33) added, thereby connection to earlier work clarified; v4: final version, accepted for publication in Phys. Rev.

Creation and manipulation of entanglement in spin chains far from equilibrium

We investigate creation, manipulation, and steering of entanglement in spin chains from the viewpoint of quantum communication between distant parties. We demonstrate how global parametric driving of the spin-spin coupling and/or local time-dependent Zeeman fields produce a large amount of entanglement between the first and the last spin of the chain. This occurs whenever the driving frequency meets a resonance condition, identified as "entanglement resonance". Our approach marks a promising step towards an efficient quantum state transfer or teleportation in solid state system. Following the reasoning of Zueco et al. [1], we propose generation and routing of multipartite entangled states by use of symmetric tree-like structures of spin chains. Furthermore, we study the effect of decoherence on the resulting spin entanglement between the corresponding terminal spins.Comment: 10 pages, 8 figure

On a Possible Melting Curve of C60 Fullerite

We study thermodynamic properties of the high-temperature modification of fullerites on the basis of the Girifalco intermolecular potential. In the present work, using the Lindemann's melting criterion we estimate a possible melting curve Tm(P) of C60 fullerite. To take into account the lattice anharmonicity that has strong effect at T >700 K, we use the correlative method of unsymmetrized self-consistent field. The melting curve for C60 fullerite has been calculated from the melting point at normal pressure estimated at 1500 K up to 15 kbar which corresponds to 4000 K. The temperature dependence of the melting pressure is approximated very well by the Simon equation. We have calculated its parameters for C60. The temperature dependence of the molar volume along the melting curve is discribed by logarithmic function.Comment: 5 pages, 1 figure, pd

Pion Multiplicity Distribution in Proton-Antiproton Annihilation at Rest

The pion multiplicity distribution is widely believed to reflect the statistical aspects of $\bar{p}p$ annihilation at rest. We try to reproduce it in a grand canonical picture with explicit conservation of electric charge, isospin, total angular momentum, and the parity quantum numbers $P$, $C$, and $G$ via the projection operator formalism. Bose statistics is found to be non-negligible, particularly in fixing the interaction volume. The calculated pion multiplicity distribution for $\left\langle n_{\pi} \right\rangle = 5$ turns out to depend strongly on the conservation of the angular momentum and connected quantum numbers, as well as on the spin state occupation in S-wave annihilation. However, the empirical Gaussian pion multiplicity distribution cannot be reproduced. This calls in question either the statistical ansatz or the rather old data themselves.Comment: 13pages, TPR-94-3