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arXiv:1211.2959

Universality in tightly bound 3-boson systems

Yanzhang He, Yizhong Fang, Bao Cheng-guang

Published Nov 13, 2012• 0 citations

Abstract

The effects of two distinct operations of the elements of the symmetry groups of a Hamiltonian on a quantum state might be equivalent in some specific zones of coordinate space. Making use of the matrix representations of the groups, the equivalence leads to a set of homogeneous linear equations imposing on the wave functions. When the matrix of the equations is non-degenerate, the wave functions will appear as nodal surfaces in these zones. Therefore, the equivalence leads to the existence of inherent nodal structure in the quantum states. In this paper, trapped 3-boson systems with different types of interactions are studied. The structures of the tightly bound eigenstates have been analyzed systematically. The emphasis is placed to demonstrate the universality arising from the common inherent nodal structures.

DOI: 10.48550/arxiv.1211.2959

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The effects of two distinct operations of the elements of the symmetry groups of a Hamiltonian on a quantum state might be equivalent in some specific zones of coordinate space. Making use of the matrix representations of the groups, the equivalence leads to a set of homogeneous linear equations imposing on the wave functions. When the matrix of the equations is non-degenerate, the wave functions will appear as nodal surfaces in these zones. Therefore, the equivalence leads to the existence of inherent nodal structure in the quantum states. In this paper, trapped 3-boson systems with different types of interactions are studied. The structures of the tightly bound eigenstates have been analyzed systematically. The emphasis is placed to demonstrate the universality arising from the common inherent nodal structures.

The presence of few-body bound states is an important issue in the study of interacting bosonic systems due to the instability it introduces into the condensation. The problem is more interesting in two dimensions because the system can host only a finite number of bound states, in contrast to the Efimov effect in three dimensions. The authors considered a two-component bosonic system in two dimensions, with repulsive intra- and attractive inter-species interactions. They found that there is only one three-particle bound state and the binding energies for various scattering lengths fall on an universal curve, where the microscopic details are of no relevance. Their conclusion is pertinent for various systems such as excitons in quantum well structures and bosonic dipoles in bilayer geometries. They developed an efficient renormalization group type method, capable of handling both short- and long- range physics and free of numerical instabilities. This method also makes use of the Hopf coordinates and running basis to reduce the proliferation of hyperspherical harmonics appearing in alternative approaches, yielding significant saving in numerical implementations.

In this chapter, we derived some elements of quantum mechanics, which are essential for the further development of our theory: the momentum of a system of Fermions in the second quantization, the coordinate and momentum of a harmonic oscillator as a unique operator at two different moments of time, Boson and Fermion operator algebra, coherent states, the electron-field interaction, the quantization of the electromagnetic field, Boson and Fermion distributions, and densities of states in a degenerate, or a non-degenerate system of Fermions. Our starting point is the wave nature of a quantum particle, the Hamiltonian equations were obtained as group velocities in the two conjugate spaces of the wave, of the coordinates and of the momentum. In this way, the Schr¨odinger equation and the electron-field potential of interaction are obtained from quantum equations generated by the particle wave function.

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