A set of nearly good real numbers to specify the eigenstates of a medium-body system with two kinds of spin-1 cold atoms and with the Hamiltonian containing non-commutable terms

Abstract: A distinguished feature of multi-species boson systems is the appearance of the odd channel, in which the coupled spin of two different bosons is given by an odd number. Through exact numerical solutions of the Schr\"{o}dinger equation for a medium-body cold system containing two types of spin-1 atoms, the effect of the odd channel has been studied. It was found that, due to the odd channel, the terms in the Hamiltonian are no longer all commutable. Accordingly, the combined spin of a single species is no longer conserved. However, when the parameters of interactions lie in some specific and broad domains, instead of a set of good quantum numbers, the ground-state (g.s.) can be specified by a set of nearly good real numbers. Each of them is not exactly a number but a very narrow interval on the positive real axis. The widths of the intervals would tend to zero when the particle numbers tend to infinity. When the parameters vary, the nearly good numbers can jump suddenly from one narrow interval to another well-separated narrow interval. Since the results of this paper are extracted from the exact solution of a medium-body system and not from a many-body approach as usual, for general many-body systems with Hamiltonians containing non-commutable terms, it remains to be clarified whether specific domains exist in the parameter space in which a set of nearly good real numbers can be used to specify the eigenstates.