SAMOP 2021 – wissenschaftliches Programm

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QI: Fachverband Quanteninformation

QI 9: Quantum Metrology

QI 9.1: Hauptvortrag

Donnerstag, 23. September 2021, 10:45–11:15, H4

The true Heisenberg limit in optical interferometry — •Rafal Demkowicz-Dobrzanski — University of Warsaw, Poland

The concept of the Heisenberg limit represents the ultimate bound on estimation precision in quantum enhanced optical interferometry and in quantum metrology in general. In the context of optical interferometry it refers to the inverse-proportionality scaling of the phase estimation precision as a function of the number of photons used in the experiment---a quadratic improvement over the shot noise scaling. Even though at a first glance there should be no ambiguity as to the actual form of the limit, it comes in different variants depending on whether: (i) definite or indefinite photon number states are considered, (ii) reference beam is explicitly taken into account or not, (iii) multiple-repetition or single-shot scenarios are considered. This results in Heisenberg limits that differ by constant factors and a reasonable question to ask is: `which one is the actual operationally meaningful one?'.

This issue has an even more dramatic turn in case of multiple-arm interferometry where multiple relative phases are to be estimated simultaneously. In this case the actual scaling of the Heisenberg limit, in terms of the number of phases being estimated, may differ depending on the approach.