Activation of metrologically useful genuine multipartite entanglement

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Activation of useful multipartite entanglement
2024. 03. 08. 10:15
BME building F, seminar room of the Dept. of Theoretical Physics
Róbert Trényi (Bilbao/Wigner)
Trényi Róbert  (UPV Bilbao/Wigner FK)
Activation of metrologically useful genuine multipartite entanglement
The metrological usefulness of a quantum state can be measured by the amount it outperforms the most useful fully separable state. It is known that maximal metrological usefulness necessitates genuine multipartite entanglement (GME). In contrast, however, not all GME states exhibit utility for metrology. In this work[1], to make non-useful entangled states useful we consider an activation scheme by employing multiple copies of the state. With this scheme, we identify a broad class of practically important GME states that can attain the maximal metrological performance in the limit of many copies, even though in the single copy case these states can be non-useful. Thus, we essentially activate quantum metrologically useful GME. Moreover, this maximal usefulness is reached exponentially fast with the number of copies and the necessary measurements are simple correlation observables. We also provide examples of states not living in the above mentioned class that improve their usefulness. Our scheme can also be used to protect certain quantum states against certain types of errors without the use of full-fledged quantum error correction techniques.
[1] R Trényi, Á Lukács, P Horodecki, R Horodecki, T Vértesi, G Tóth, New J. Phys. 26 023034 (2024)