title: Efficient use of quantum resources for the transmission of a reference frame.
abstract: We propose a covariant protocol for transmitting reference frames encoded on N spins, achieving sensitivity N-2 without the need of a preestablished reference frame and without using entanglement between sender and receiver. The protocol exploits the use of equivalent representations that were overlooked in the previous literature.
authors.affiliation: QUIT Quantum Information Theory Group of the INFM, unità di Pavia, Dipartimento di Fisica A. Volta, via Bassi 6, I-27100 Pavia, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Chiribella
authors.forename: G M
authors.initials: GM
authors.lastname: D'Ariano
authors.forename: P
authors.initials: P
authors.lastname: Perinotti
authors.forename: M F
authors.initials: MF
authors.lastname: Sacchi