How two spins can thermalize a third spin

TL;DR

This paper demonstrates that a single spin-1/2 system can be fully thermalized through interaction with just two entangled bath spins, revealing minimal bath size requirements for quantum thermalization.

Contribution

The study shows that a minimal bath of two entangled spins can thermalize a single spin-1/2, extending understanding of quantum thermalization with minimal resources.

Findings

A single spin-1/2 can be thermalized by two entangled bath spins.

The thermalization process requires a specific time-dependent coupling.

Generalization to multiple spin pairs is possible.

Abstract

We consider thermalization of a microscopic quantum system by interaction with a thermal bath. Our interest is the minimal size the bath can have while still being able to thermalize the system. Within a specific thermalization scheme we show that a single spin-1/2 can be fully thermalized by interaction with a bath that consists of just two other spin-1/2. The two bath spins are initially in a pure, entangled state, and the thermalizing interaction is a Heisenberg exchange-interaction of the system-spin with one of the bath spins. The time dependent coupling strength has to obey a single integral constraint. We also present a simple generalization of this minimal model in which the bath consists of an arbitrary number of spin-1/2 pairs.