Abstract

We provide a detailed study of the properties of a few interacting spin 1 / 2 fermions trapped in a one-dimensional harmonic oscillator potential. The interaction is assumed to be well represented by a contact delta potential. Numerical results obtained by means of direct diagonalization techniques are combined with analytical expressions for both the non-interacting and strongly interacting regime. The N = 2 case is used to benchmark our numerical techniques with the known exact solution of the problem. After a detailed description of the numerical methods, in a tutorial-like manner, we present the static properties of the system for N = 2 , 3 , 4 and 5 particles, e.g., low-energy spectrum, one-body density matrix, ground-state densities. Then, we consider dynamical properties of the system exploring first the excitation of the breathing mode, using the dynamical structure function and corresponding sum-rules, and then a sudden quench of the interaction strength.

Highlights

  • The theoretical study of one-dimensional systems has always attracted a lot of attention

  • They are looking at those systems as a very versatile laboratory where they apply ab-initio techniques, without the complexity of the inter-particle interactions that appear in other fields, as for instance in nuclear physics [18,19]

  • In this chapter we describe the method named direct diagonalization to find an approximate solution of the many-body Schrödinger equation

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Summary

Introduction

The theoretical study of one-dimensional systems has always attracted a lot of attention. The groundbreaking experiments of Jochim’s group in Heildelberg, have opened new theoretical challenges to study one-dimensional fermionic systems They have been able to precisely control the number of atoms and the strength of the interactions [11]. Mathematics 2020, 8, 1196 phenomena in few-fermion systems [15], the behaviour of two fermions in a double-well potential [16], the realization of an antiferromagnetic spin chain of few cold atoms [17], all belong to the long list of theoretical challenges that the experimental advances are offering to theoreticians They are looking at those systems as a very versatile laboratory where they apply ab-initio techniques, without the complexity of the inter-particle interactions that appear in other fields, as for instance in nuclear physics [18,19].

Theoretical Approach
The Hamiltonian of the System
Non-Interacting and Infinite Interaction Limits
Non-Interacting Case
Infinite Interaction Case
Second Quantization
Creation and Annihilation Operators
Fock Space
Operators in Second Quantization
The Hamiltonian in Second Quantization
Numerical Methods
Direct Diagonalization
The Two-Body Matrix Elements of the Interaction
A Benchmark for the Two-Particle Case
Theoretical Spectrum for Two Particles
Comparison of Analytical and Numerical Results
Ground State Properties
Energy and Virial Theorem
One Body Density Matrix
Density Profile
Natural Orbits
Low-Energy Excited States
Energy Spectrum
Spin Determination
Dynamical Excitation
Sudden Change in the Trap Frequency
Dynamic Structure Function
Sum Rules
Interaction Quench
Time Evolution of the Perturbed System
Central Density Oscillations
Summary and Conclusions
Full Text
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