Volume 78, Number 3, May 2007
Article Number 30004
Number of page(s) 6
Section General
Published online 27 April 2007
EPL, 78 (2007) 30004
DOI: 10.1209/0295-5075/78/30004

Sub shot-noise interferometric phase sensitivity with beryllium ions Schrödinger cat states

L. Pezzé and A. Smerzi

CNR-INFM BEC Center and Dipartimento di Fisica - Università di Trento, I-38050 Povo, Italy

received 20 November 2006; accepted in final form 19 March 2007; published May 2007
published online 27 April 2007

Interferometry with NOON quantum states can provide unbiased phase estimation with a sensitivity scaling as $\Delta \theta \sim 1/N_{T}$ given a prior knowledge that the true phase shift $\theta $ lies in the interval $-\pi \leqslant \theta \leqslant \pi $. The protocol requires a total of NT=2p-1 particles (unequally) distributed among p independent measurements and overcomes basic difficulties present in previously proposed approaches. We demonstrate the possibility to obtain a phase sensitivity beating the classical shot-noise limit using published probabilities retrieved experimentally for the creation of Schrödinger cat quantum states containing up to N=6 beryllium ions.

03.75.Dg - Atom and neutron interferometry.
03.65.Ud - Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.).
42.50.-p - Quantum optics.

© Europhysics Letters Association 2007