title: Using entanglement improves the precision of quantum measurements.
abstract: We show how entanglement can be used to improve the estimation of an unknown transformation. Using entanglement is always of benefit in improving either the precision or the stability of the measurement. Examples relevant for applications are illustrated, for either qubits or continuous variables.
authors.affiliation: Quantum Optics & Information Group, Istituto Nazionale di Fisica della Materia, Dipartimento di Fisica A. Volta, Università di Pavia, via Bassi 6, I-27100 Pavia, Italy. dariano@unipv.it
authors.forename: G M
authors.initials: GM
authors.lastname: D'Ariano
authors.forename: P
authors.initials: P
authors.lastname: Lo Presti
authors.forename: M G
authors.initials: MG
authors.lastname: Paris