Bosons Bound in Strong Potentials

Abstract

This book would remain incomplete without a discussion of the behaviour of Bose particles in supercritical external fields. Indeed, the physics explored in the following sections differs fundamentally from the conclusions reached for fermions in arbitrarily strong external potentials. It is important to observe here that our intuition, sharpened by experience with classical physics, leads to a reasonably correct picture for bosons, contrary to the case for Fermi particles. Namely, the behaviour of condensed Bose particles is similar to that of classical, rather than quantum mechanical systems. In particular, we describe how in supercritical external potentials the stability of the vacuum state is assured by the appearance of a Bose condensate whose role is to screen the effective interaction down to a subcritical strength. When a very substantial screening of an extremely strong applied field occurs, a large number of condensed Bose particles form a macroscopic coherent state, similar in nature to the electromagnetic laser field. However, the validity of this analogy is limited, as in our case the condensed particles are bound and remain near the source of the supercritical interaction.