Using entanglement against noise in quantum metrology [1]
نویسندگان
چکیده
FIG. 1. Quantum metrology strategies. The maps Λφ encode the parameter φ to be estimated. (i) sequential scheme: Λφ acts n times sequentially on N/n input probes ρ (this is an entanglement-free classical scheme) ; (ii) entangled parallel scheme: an entangled state of N probes ρN goes through N maps Λφ in parallel; (iii) passive ancilla scheme: the N probes are also entangled with M noiseless ancillas; (iv) active ancilla-assisted scheme: the action of N channels Λφ is interspersed with arbitrary unitaries Ui representing interactions of the probe with ancillas. [All the other schemes can be derived from (iv) choosing swap or identity unitaries Ui].
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