Quantum Environments: Spin Baths, Oscillator Baths, and applications to Quantum Magnetism

TL;DR

This paper reviews how effective Hamiltonians with spin or oscillator baths model low-energy physics in quantum systems, demonstrating methods with examples from magnetism, superconductivity, and quantum tunneling in nanomagnets.

Contribution

It provides a comprehensive method for deriving and solving effective Hamiltonians involving baths, with applications to quantum relaxation and tunneling phenomena.

Findings

Effective Hamiltonian techniques are demonstrated for various quantum systems.

Applications to quantum relaxation and tunneling in nanomagnets are detailed.

The approach unifies modeling of spin and oscillator baths in low-energy physics.

Abstract

The low-energy physics of systems coupled to their surroundings is understood by truncating to effective Hamiltonians; these tend to reduce to a few canonical forms, involving coupling to "baths" of oscillators or spins. The method for doing this is demonstrated using examples from magnetism, superconductivity, and measurement theory, as is the way one then solves for the low-energy dynamics. Finally, detailed application is given to the exciting recent Quantum relaxation and tunneling work in naomagnets.