Linear optical quantum metrology with single photons: Experimental errors, resource counting, and quantum Cramér-Rao bounds
Jonathan P. Olson, Keith R. Motes, Patrick M. Birchall, Nick M. Studer, Margarite L. LaBorde, Todd Moulder, Peter P. Rohde, Jonathan P. Dowling · Physical Review A · 2017
Quantum number-path entanglement is a resource for supersensitive quantum metrology and in particular provides for sub-shot-noise or even Heisenberg-limited sensitivity. However, such number-path entanglement is thought to have been resource intensive to create in the first place, typically requiring either very strong nonlinearities or nondeterministic preparation schemes with feedforward, which are difficult to implement. Recently [K. R. Motes et al., Phys. Rev. Lett. 114, 170802 (2015)], it was shown that number-path entanglement from a BosonSampling inspired interferometer can be used to beat the shot-noise limit. In this paper we compare and contrast different interferometric schemes, discuss resource counting, calculate exact quantum Cram\'er-Rao bounds, and study details of experimental errors.