Negative temperature is cool for cooling

TL;DR

This paper investigates the use of negative temperature reservoirs in a three-qubit autonomous refrigerator, demonstrating their superior cooling capabilities and analyzing the limits of cooling close to absolute zero.

Contribution

It provides a detailed analysis of negative temperature reservoirs in quantum refrigerators and compares their effectiveness to positive temperature reservoirs.

Findings

Negative temperature reservoirs enable lower qubit temperatures than positive ones.

The lowest achievable qubit temperature is characterized for various parameters.

Reservoirs at negative temperatures outperform positive ones in cooling efficiency.

Abstract

In this work, we study an autonomous refrigerator composed of three qubits [Phys. Rev. Lett. 105, 130401 (2010)] operating with one of the reservoirs at negative temperatures, which has the purpose of cooling one of the qubits. We find the values of the lowest possible temperature that the qubit of interest reaches when fixing the relevant parameters, and we also study the limit for cooling the qubit arbitrarily close to absolute zero. We thus proceed to a comparative study showing that reservoirs at effective negative temperatures are more powerful than those at positive temperatures for cooling the qubit of interest.