SYSTEMS OF IMPENETRABLE BOSONS AND FERIONS WITH SPIN 1/2 IN ONE DIMENSION

P. Bocchieri, F. Miglietta

Patrizia Vignolo, Anna Minguzzi, M. P. Tosi

Developments in the realization and study of ultracold atomic gases inside elongated magnetic traps and atom waveguides have stimulated calculations of equilibrium properties and excitation spectra for mesoscopic clouds of hard-core bosons and of spin-polarized fermions moving under an external harmonic potential in one dimension. A rigorous correspondence exists between the wave functions of these two types of system, allowing a number of exact results to be obtained. The main theoretical techniques and results are reviewed in this article, with emphasis on their relevance in regard to tests of the Thomas–Fermi approximation for confined Fermi fluids and to the foundations of density functional theory for inhomogeneous quantum systems.

Marcos Rigol, ALEJANDRO MURAMATSU

We review recent exact results for the free expansion of impenetrable bosons on one-dimensional lattices, after switching off a confining potential. When the system is initially in a superfluid state, far from the regime in which the Mott-insulator appears in the middle of the trap, the momentum distribution of the expanding bosons rapidly approaches the momentum distribution of non-interacting fermions. Remarkably, no loss in coherence is observed in the system as reflected by a large occupation of the lowest eigenstate of the one-particle density matrix. In the opposite limit, when the initial system is a pure Mott insulator with one particle per lattice site, the expansion leads to the emergence of quasicondensates at finite momentum. In this case, one-particle correlations like the ones shown to be universal in the equilibrium case develop in the system. We show that the out-of-equilibrium behavior of the Shannon information entropy in momentum space, and its contrast with one of non-interacting fermions, allows to differentiate the two different regimes of interest. It also helps in understanding the crossover between them.

Alexander Rudol'fovich Its, Anatoli G. Izergin, V. E. Korepin

A.S. DAVYDOV

Dietrich E. Wolf, J. Zittartz