Faithful extraction of quantum coherence

TL;DR

This paper introduces two coherence-preserving extraction protocols for quantum systems, demonstrating their effectiveness and limits, including an improved method over previous catalytic coherence techniques.

Contribution

The authors develop two faithful, coherence-preserving extraction protocols and analyze their performance, including implementation with harmonic oscillator reservoirs and comparison with existing methods.

Findings

One protocol outperforms catalytic coherence in single extraction scenarios.

Protocols successfully implement coherence extraction with harmonic oscillator reservoirs.

Limits of repeatable extraction are characterized.

Abstract

Coherence, a strictly quantum phenomenon, has found many applications, from quantum information theory and thermodynamics to quantum foundations and biology. When physical constraints are taken into consideration creation of coherence in a system is usually impossible and must therefore be extracted from another system acting as a reservoir. In this article we present two faithful extraction protocols in the sense that the interaction involved between the system and reservoir is coherence preserving. As an example we implement both in the case where the reservoir is a quantum harmonic oscillator in a coherent and a squeezed state respectively, and study the limits of repeatable extraction. For a single extraction onto qubits it is demonstrated that, perhaps surprisingly, one of the protocols manages to outperform a previous method, known as catalytic coherence, which allows the creation of an extra amount of coherence between degenerate energy eigenstates of the combined system.