How small can thermal machines be? The smallest possible refrigerator

TL;DR

This paper explores the minimal size of quantum refrigerators, demonstrating that self-contained cooling devices can be constructed with only a few qubits or qutrits, and analyzing their fundamental performance limits.

Contribution

It introduces three models of minimal quantum refrigerators and investigates their ability to cool towards absolute zero, establishing fundamental size and performance limits.

Findings

Self-contained quantum refrigerators can be built with minimal qubits or qutrits.

Cooling towards absolute zero is theoretically achievable with these small systems.

Performance limits depend on the system's size and interaction structure.

Abstract

We investigate the fundamental dimensional limits to thermodynamic machines. In particular we show that it is possible to construct self-contained refrigerators (i.e. not requiring external sources of work) consisting of only a small number of qubits and/or qutrits. We present three different models, consisting of two qubits, a qubit and a qutrit with nearest-neighbour interactions, and a single qutrit respectively. We then investigate fundamental limits to their performance; in particular we show that it is possible to cool towards absolute zero.