Rostock 2019 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 54: Precision Measurements and Metrology III

Q 54.3: Vortrag

Donnerstag, 14. März 2019, 14:45–15:00, S SR 111 Maschb.

Optimal mixed states for quantum metrology — •Lukas Fiderer¹, Julien Mathieu Elias Fraïsse², and Daniel Braun¹ — ¹Eberhard Karls University Tübingen, Germany — ²Seoul National University, South Korea

The optimal initial state for estimating a parameter encoded to the state through unitary dynamics has been known since long: an equal superposition of eigenstates corresponding to the largest and smallest eigenvalue of the generator of the unitary dynamics. In principle, such an optimal initial state can be prepared by applying an appropriate unitary transformation to an available pure state. However, access to pure states is not always granted in realistic measurement setups, for instance, due to noise or interactions with an environment. In the present work, we answer the following question: Given a mixed state, what is the optimal initial state that can be prepared with the help of a unitary transformation? We give the quantum Fisher information for this optimal initial state and extend results for optimal quantum metrology with pure states to the regime of mixed states.