# Supremacy of incoherent sudden cycles

## TL;DR

This paper demonstrates that a two-level quantum system can function as a refrigerator in sudden cycles without quantum coherence, and coherence generation can hinder cooling, with practical implementation suggested using superconducting qubits.

## Contribution

It shows that incoherent sudden cycles can achieve refrigeration at high frequencies, contrasting with coherence-generating cycles that cause heating, and proposes a coherence-avoiding driving method.

## Key findings

- Incoherent sudden cycles produce finite cooling power.
- Quantum coherence in cycles leads to heating of baths.
- A practical superconducting qubit implementation is discussed.

## Abstract

We investigate theoretically a refrigerator based on a two-level system (TLS) coupled alternately to two different heat baths. Modulation of the coupling is achieved by tuning the level spacing of the TLS. We find that the TLS, which avoids quantum coherences, creates finite cooling power for one of the baths in sudden cycles, i.e. acts as a refrigerator even in the limit of infinite operation frequency. By contrast, the cycles that create quantum coherence in the sudden expansions and compressions lead to heating of both the baths. We propose a driving method that avoids creating coherence and thus restores the cooling in this system. We also discuss a physical realization of the cycle based on a superconducting qubit coupled to dissipative LC-resonators.