Information-Theoretic Features of Many Fermion Systems: An Exploration Based on Exactly Solvable Models

Abstract

Finite quantum many fermion systems are essential for our current understanding of Nature. They are at the core of molecular, atomic, and nuclear physics. In recent years, the application of information and complexity measures to the study of diverse types of many-fermion systems has opened a line of research that elucidates new aspects of the structure and behavior of this class of physical systems. In this work we explore the main features of information and information-based complexity indicators in exactly soluble many-fermion models of the Lipkin kind. Models of this kind have been extremely useful in shedding light on the intricacies of quantum many body physics. Models of the Lipkin kind play, for finite systems, a role similar to the one played by the celebrated Hubbard model of solid state physics. We consider two many fermion systems and show how their differences can be best appreciated by recourse to information theoretic tools. We appeal to information measures as tools to compare the structural details of different fermion systems. We will discover that few fermion systems are endowed by a much larger complexity-degree than many fermion ones. The same happens with the coupling-constants strengths. Complexity augments as they decrease, without reaching zero. Also, the behavior of the two lowest lying energy states are crucial in evaluating the system’s complexity.

Quasi-Magical Fermion Numbers and Thermal Many-Body Dynamics

“…As we use statistical mechanics theory throughout, we need a special formalism that is provided in [21]. Statistical mechanics quantifiers are derived from the partition function Z [16] which one constructs employing probabilities linked to the microscopic states involved, whose energies are E i [16].…”

“…We will place a strong emphasis on the so-called disequilibrium D AFP (quantities with sub-index L refer to the Lipkin model). For more details, see [21]. One deals with…”

Magic Numbers and Mixing Degree in Many-Fermion Systems

“…The quantum N-fermion system exhibits various properties, some of them indeed intricate [10,[19][20][21][22][23][24][25][26][27][28][29][30][31]. We will study manifestations of quantum properties at a very low finite temperature.…”

“…We construct Z using probabilities assigned to the models' microscopic states. Their energies are E i [19]. Some important macroscopic quantifiers are computed as in [19].…”

“…Their energies are E i [19]. Some important macroscopic quantifiers are computed as in [19]. These indicators, together with Z, derive from the canonical probability distributions [19] P n (v, J, β).…”