PRLReadable/2004-06

Volume 92

Bell States of Atoms with Ultralong Lifetimes and Their Tomographic State Analysis

C. F. Roos, G. P. T. Lancaster, M. Riebe, H. Haffner, W. Hansel, S. Gulde, C. Becher, J. Eschner, F. Schmidt-Kaler, and R. Blatt
Institut fur Experimentalphysik, Universitat Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
(Received 28 July 2003; published 3 June 2004)

Arbitrary atomic Bell states with two trapped ions are generated in a deterministic and preprogrammed way. The resulting entanglement is quantitatively analyzed using various measures of entanglement. For this, we reconstruct the density matrix using single qubit rotations and subsequent measurements with near-unity detection efficiency. This procedure represents the basic building block for future process tomography of quantum computations. As a first application, the temporal decay of entanglement is investigated in detail. We observe ultralong lifetimes for the Bell states ±, close to the fundamental limit set by the spontaneous emission from the metastable upper qubit level and longer than all reported values by 3 orders of magnitude. ⓒ2004 The American Physical Society
- URL: http://link.aps.org/abstract/PRL/v92/e220402
- doi:10.1103/PhysRevLett.92.220402
- PACS: 03.65.Wj, 03.65.Ud, 03.67.Mn, 32.80.Pj

Stability of Atomic Clocks Based on Entangled Atoms

A. André, A. S. Sørensen, and M. D. Lukin
Physics Department and Institute for Theoretical Atomic and Molecular Physics, Harvard University, Cambridge, Massachusetts 02138, USA
(Received 19 January 2004; published 7 June 2004

We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of N atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as N1/6 compared to the atomic shot noise level. ©2004 The American Physical Society
- URL: http://link.aps.org/abstract/PRL/v92/e230801
- doi:10.1103/PhysRevLett.92.230801
- PACS: 06.30.Ft, 03.65.Yz, 03.67.Pp, 06.20.Dk