143 research outputs found
Nose-Hoover dynamics for coherent states
The popular method of Nose and Hoover to create canonically distributed
positions and momenta in classical molecular dynamics simulations is
generalized to a genuine quantum system of infinite dimensionality. We show
that for the quantum harmonic oscillator, the equations of motion in terms of
coherent states can easily be modified in an analogous manner to mimic the
coupling of the system to a thermal bath and create a quantum canonical
ensemble. Possible applications to more complex systems, especially interacting
Fermion systems, are proposed.Comment: 13 pages, 3 figure
Nose-Hoover sampling of quantum entangled distribution functions
While thermostated time evolutions stand on firm grounds and are widely used
in classical molecular dynamics (MD) simulations, similar methods for quantum
MD schemes are still lacking. In the special case of a quantum particle in a
harmonic potential, it has been shown that the framework of coherent states
permits to set up equations of motion for an isothermal quantum dynamics. In
the present article, these results are generalized to indistinguishable quantum
particles. We investigate the consequences of the (anti-)symmetry of the
many-particle wavefunction which leads to quantum entangled distribution
functions. The resulting isothermal equations of motion for bosons and fermions
contain new terms which cause Bose-attraction and Pauli-blocking. Questions of
ergodicity are discussed for different coupling schemes.Comment: 15 pages, 4 figures, submitted to PHYSICA A. More information at
http://www.physik.uni-osnabrueck.de/makrosysteme
-pairing Interactions of Fermions in a Single- Shell
In this talk I shall introduce our recent works on general pairing
interactions and pair truncation approximations for fermions in a single-j
shell, including the spin zero dominance, features of eigenvalues of fermion
systems in a single-j shell interacting by a pairing interaction.Comment: 10 pages and 4 figures, international symposiu
Quantum dissipation
We address the question of the microscopic origin of dissipation in collective motion of a quantum many--body system in the framework of a parametric random matrix approach to the intrinsic dynamics. We show that the fluctuation--dissipation theorem is generally violated and, moreover, energy diffusion has a markedly non--Gaussian character and the corresponding distribution has very long tails. Such features do not support a Langevin or Fokker--Planck approach to dissipation in collective nuclear motion
Angular momentum I ground state probabilities of boson systems interacting by random interactions
In this paper we report our systematic calculations of angular momentum
ground state probabilities () of boson systems with spin in the
presence of random two-body interactions. It is found that the P(0) dominance
is usually not true for a system with an odd number of bosons, while it is
valid for an even number of bosons, which indicates that the P(0) dominance is
partly connected to the even number of identical particles. It is also noticed
that the 's of bosons with spin do not follow the 1/N (,
referring to the number of independent two-body matrix elements) relation. The
properties of the 's obtained in boson systems with spin are
discussed.Comment: 8 pages and 3 figure
Regular spectra in the vibron model with random interactions
The phenomenom of emerging regular spectral features from random interactions
is addressed in the context of the vibron model. A mean-field analysis links
different regions of the parameter space with definite geometric shapes. The
results that are, to a large extent, obtained in closed analytic form, provide
a clear and transparent interpretation of the high degree of order that has
been observed in numerical studies.Comment: 19 pages, 8 figures, 2 tables. Physical Review C, in pres
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