Europhys. Lett.
Volume 65, Number 2, January 2004
Page(s) 165 - 171
Section General
Published online 01 January 2004
Europhys. Lett., 65 (2) , pp. 165-171 (2004)
DOI: 10.1209/epl/i2003-10079-1

Quantum universal detectors

G. M. D'Ariano, P. Perinotti and M. F. Sacchi

Quantum Optics & Information Group, Unità INFM and Dipartimento di Fisica "A. Volta", Università di Pavia via A. Bassi 6, I-27100 Pavia, Italy

(Received 5 September 2003; accepted 18 November 2003)

We address the problem of achieving a universal measuring apparatus that allows to estimate the expectation value of any arbitrary operator by changing only the data processing of the outcomes. The "universal detector" performs a joint measurement on the system and on a suitably prepared ancilla. We characterize such universal detectors, and show how they can be obtained either via Bell measurements or via local measurements and classical communication between system and ancilla.

03.65.Ta - Foundations of quantum mechanics; measurement theory.
03.65.Wj - State reconstruction, quantum tomography.

© EDP Sciences 2004