A parameter whose coupling to a quantum probe of n constituents includes all two-body interactions between the constituents can be measured with an uncertainty that scales as 1/n3/2, even when the constituents are initially unentangled. We devise a protocol that achieves the 1/n3/2 scaling without generating any entanglement among the constituents, and we suggest that the protocol might be implemented in a two-component Bose-Einstein condensate.
@article{arxiv.0805.2180,
title = {Quantum Metrology: Dynamics vs. Entanglement},
author = {Sergio Boixo and Animesh Datta and Matthew J. Davis and Steven T. Flammia and Anil Shaji and Carlton M. Caves},
journal= {arXiv preprint arXiv:0805.2180},
year = {2009}
}