Optimal scheme for estimating a pure qubit state via local measurements

Abstract

We present the optimal scheme for estimating a pure qubit state by means of local measurements on N identical copies. We give explicit examples for low N. For large N, we show that the fidelity saturates the collective measurement bound up to order 1/N. When the signal state lays on a meridian of the Bloch sphere, we show that this can be achieved without classical communication.

Version to appear in PRL (minor changes, title changed)

References in corpus (3)

• Fidelity trade-off for finite ensembles of identically prepared qubits
• Optimal encoding and decoding of a spin direction
• Communication of Spin Directions with Product States and Finite Measurements

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