Multimode Metrology via Scattershot Sampling

Scattershot photon sources are known to have useful properties for optical quantum computing purposes, in particular for scaling to large numbers of photons. This paper investigates the application of these scattershot sources towards the metrological task of estimating an unknown phase shift. In this regard, we introduce three different scalable multimode interferometers, and quantify their quantum Fisher information performance using scattershot sources with arbitrary system sizes. We show that two of the interferometers need the probing photons to be in certain input configurations to beat the classical shot-noise precision limit, while the remaining interferometer has the necessary symmetry which allows it to always beat the classical limit no matter the input configuration. However, we can prove all three interferometers gives the same amount of information on average, which can be shown to beat the classical precision limit. We also perform Monte Carlo simulations to compare the interferometers in different experimentally relevant regimes, as a function of the number of samples.