Malitesta, Marco — Distributed Quantum Sensing with Squeezed-Vacuum Light in a Configurable Network of Mach-Zehnder Interferometers

Mach-Zehnder interferometry using squeezed-vacuum light is an archetype of quantum-enhanced
single-phase sensing. Here we propose and study a direct generalization for the estimation of an
arbitrary number of phase shifts in d ≥ 1 distributed Mach-Zehnder interferometers (MZIs). In this
case, the squeezed-vacuum is split between the d modes of a linear (splitting) network, each output
of the network being one sensing mode of a MZI, the other input being a coherent state. We predict
i) the linear combination of phase shifts that can be estimated with optimal sensitivity, given a
specific splitting network; and ii) the splitting network that allows the estimation of a specific linear
combination of phase shifts with optimal sensitivity. Sub-shot-noise sensitivity up to the Heisenberg
limit is discussed, the multiphase estimation only requiring local photocounting. We show that the
distributed entangled state provides a better scaling of precision with respect to separable strategies.