Double-Fock Superposition Interferometry for Differential Diagnosis of Decoherence

TL;DR

This paper introduces a formalism using double-Fock superpositions in interferometry to differentiate between types of decoherence processes—dephasing, mixing, and distinguishability—in a single experiment, improving diagnostic capabilities.

Contribution

The authors develop a versatile many-boson interferometry formalism based on double-sided Feynman diagrams for differential decoherence diagnosis using specific Fock states.

Findings

Twin-Fock states reveal path distinguishability and mixing effects.

Double-Fock superpositions additionally quantify dephasing.

Single-experiment differential diagnosis of decoherence processes.

Abstract

Interferometric signals are degraded by decoherence, which encompasses dephasing, mixing and any distinguishing which-path information. These three paradigmatic processes are fundamentally different, but, for coherent, single-photon and $N00N$-states, they degrade interferometric visibility in the very same way, which impedes the diagnosis of the cause for reduced visibility in a single experiment. We introduce a versatile formalism for many-boson interferometry based on double-sided Feynman diagrams, which we apply to a protocol for differential decoherence diagnosis: Twin-Fock states |N,N> with $N \ge 2$ reveal to which extent decoherence is due to path distinguishability or to mixing, while double-Fock superpositions $|N:M> = (|N,M> + |M,N>)/\sqrt{2} $ with $N > M >0$ additionally witness the degree of dephasing. Hence, double-Fock superposition interferometry permits the differential diagnosis of decoherence processes in a single experiment, indispensable for the assessment of interferometers.