arXiv subjects

F. Brosens

Publications and source records attributed to F. Brosens.

27 records · Page 2Linked to original sources

arXiv1998

Switching Boundary Conditions in the Many-Body Diffusion Algorithm

In this paper we show how the transposition, the basic operation of the permutation group, can be taken into account in a diffusion process of identical particles. Whereas in an earlier approach the method was applied to systems in which the potential is invariant under interchanging the Cartesian components of the particle coordinates, this condition on the potential is avoided here. In general, the potential introduces a switching of the boundary conditions of the walkers. These transitions modelled by a continuous-time Markov chain generate sample paths for the propagator as a Feynman-Kac functional. A few examples, including harmonic fermions with an anharmonic interaction, and the ground-state energy of ortho-helium are studied to elucidate the theoretical discussion and to illustrate the feasibility of a sign-problem-free implementation scheme for the recently developed many-body diffusion approach.

cond-mat.stat-mech↗

arXiv1998

Statistical mechanics and path integrals for a finite number of bosons

Recent investigations show that the statistical mechanics of a finite number of particles in ideal harmonic systems predicts different results for the same physical properties, depending on the ensemble under consideration. Path integral methods for a finite number of bosons with equidistant energy levels give the same answers for the mean energy, the specific heat and the condensation temperature etc., irrespective whether their calculation results from the density of states, from the partition function or from the generating function. We show that this contradiction is due either to the use of approximate relations between quantum statistical expressions, or to a misinterpretation of the generating function.

cond-mat.stat-mech↗

arXiv1997

Note on the stability of a confined Bose gas: Comment on quant-ph/9712030 by L. Salasnich

We demonstrate analytically that a Bose-Einstein condensate confined in a harmonic trap with zero-range attractive interparticle interactions is unstable if there is more than 1 boson. Replacing the zero-range interaction by a short-range attractive interaction lifts the instability, and leads to a pronounced clustering, by which the particles leak out of the condensate.

quant-ph↗

arXiv1997

The many-body diffusion algorithm, harmonic fermions

A numerical implementation scheme is presented for the recently developed many-body diffusion approach for identical particles, in the case of harmonic potentials. The procedure is free of the sign problem, by the introduction of the appropriate absorption or reflection conditions for the walkers at the boundary of a state space. These conditions are imposed by the permutation symmetry. The outflow of the walkers at the boundary of the state space contributes substantially to the energy. Furthermore, the implementation of crossing/recrossing effects at absorbing boundaries proves indispensable to sample the antisymmetric states by discrete time steps.

cond-mat.stat-mech↗

arXiv1997

Confined Harmonically Interacting Spin-Polarised Fermions

The thermodynamical properties are calculated for a three-dimensional model of $N$ harmonically interacting spin-polarized fermions in a parabolic potential well. The obtained dependences of the chemical potential and of the internal energy on the complete range of the temperature and of the number of particles turn out to obey a scaling law, similar to the scaling from the continuum approximation for the density of states. The calculation technique is based on our path integral approach of symmetrized density matrices for identical particles in a parabolic confining well.

cond-mat.stat-mech↗

arXiv1997

Density and Pair Correlation Function of Confined Identical Particles: the Bose-Einstein Case

Two basic correlation functions are calculated for a model of $N$ harmonically interacting identical particles in a parabolic potential well. The density and the pair correlation function of the model are investigated for the boson case. The dependence of these static response properties on the complete range of the temperature and of the number of particles is obtained. The calculation technique is based on the path integral approach of symmetrized density matrices for identical particles in a parabolic confining well.

cond-mat.stat-mech↗

arXiv1997

Many-Body Diffusion and Path Integrals for Identical Particles

For distinguishable particles it is well known that Brownian motion and a Feynman-Kac functional can be used to calculate the path integral (for imaginary times) for a general class of scalar potentials. In order to treat identical particles, we exploit the fact that this method separates the problem of the potential, dealt with by the Feynman-Kac functional, from the process which gives sample paths of a non-interacting system. For motion in 1 dimension, we emphasize that the permutation symmetry of the identical particles completely determines the domain of Brownian motion and the appropriate boundary conditions: absorption for fermions, reflection for bosons. Further analysis of the sample paths for motion in 3 dimensions allows us to decompose these paths into a superposition of 1-dimensional sample paths. This reduction expresses the propagator (and consequently the energy and other thermodynamical quantities) in terms of well-behaved 1-dimensional fermion and boson diffusion processes and the Feynman-Kac functional.

cond-mat↗

arXiv1996

Rotational properties of trapped bosons

Based on the Hellman-Feynman theorem it is shown that the average square radius of a cloud of interacting bosons in a parabolic well can be derived from their free energy. As an application, the temperature dependence of the moment of inertia of non-interacting bosons in a parabolic trap is determined as a function of the number of bosons. Well below the critical condensation temperature, the Bose-Einstein statistics are found to substantially reduce the moment of inertia of this system, as compared to a gas of "distinguishable" particles in a parabolic well.

cond-mat↗

arXiv1996

Thermodynamics of Coupled Identical Oscillators within the Path Integral Formalism

A generalization of symmetrized density matrices in combination with the technique of generating functions allows to calculate the partition function of identical particles in a parabolic confining well. Harmonic two-body interactions (repulsive or attractive) are taken into account. Also the influence of a homogeneous magnetic field, introducing anisotropy in the model, is examined. Although the theory is developed for fermions and bosons, special attention is payed to the thermodynamic properties of bosons and their condensation.

cond-mat↗