Quantum asymmetry and noisy multi-mode interferometry

TL;DR

This paper explores how quantum asymmetry can increase despite decreasing coherence within degenerate subspaces, demonstrated through a three-mode interferometric experiment with noisy reference arms, revealing counterintuitive resource behavior.

Contribution

It uncovers a counterintuitive phenomenon where quantum asymmetry increases as coherence decreases, supported by experimental evidence and theoretical analysis in entanglement resource theory.

Findings

Asymmetry can increase with decreasing coherence in degenerate subspaces.

Experimental demonstration with three-mode single-photon interferometry.

Reduction of correlations between phase fluctuations enhances sensitivity.

Abstract

Quantum asymmetry is a physical resource which coincides with the amount of coherence between the eigenspaces of a generator responsible for phase encoding in interferometric experiments. We highlight an apparently counter-intuitive behavior that the asymmetry may \emph{increase} as a result of a \emph{decrease} of coherence inside a degenerate subspace. We intuitively explain and illustrate the phenomena by performing a three-mode single-photon interferometric experiment, where one arm carries the signal and two noisy reference arms have fluctuating phases. We show that the source of the observed sensitivity improvement is the reduction of correlations between these fluctuations and comment on the impact of the effect when moving from the single-photon quantum level to the classical regime. Finally, we also establish the analogy of the effect in the case of entanglement resource theory.