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Twist-untwist protocols for quantum sensing

Thursday November 18, 2021
3:30 pm

 Presenter:  Tyler Volkoff (Los Alamos)
 Series:  CQuIC Seminars
 Abstract:  Applying an unparameterized unitary after calling the parameter in a quantum estimation protocol does not change the quantum Cramer-Rao bound for an estimator of that parameter. However, when the probe state is spin-squeezed, such an operation can decrease the estimation error of an experimentally realistic measurement (such as a total spin component) far below the standard quantum limit, providing a route to near-optimal quantum sensing.
We will look at this phenomenon for the "twist-untwist" protocols, i.e., protocols in which one-axis twisting is applied before and after the parameter call, but with opposite sign. Under what conditions is twist-untwist optimal in the set of all protocols that apply one-axis twisting before and after the parameter call? This question will be answered for several physical settings. Extensions of the twist-untwist paradigm to displacement sensing with continuous variables, and iteration of twist-untwist protocols to amplify signal-to-noise ratio will also be discussed.
 Host:  Ivan Deutsch
 Location:  PAIS-2540, PAIS

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