Double-Fock superposition interferometry for differential diagnosis of decoherence

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 $\mid N,N\rangle $ with $N\geqslant 2$ reveal to what extent decoherence is due to path distinguishability or to mixing, while double-Fock superpositions $\mid N:M\rangle =\left( \mid N,M\rangle +\mid M,N\rangle \right)/\sqrt{2}$ with $N\gt M\gt 0$ 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.

Keywords

• decoherence
• entangled states
• interferometry
• non-classical states of photons
• photon counting and statistics
• 42.50.Ar