Abstract
We investigate the connection between the shot-noise limit in linear interferometers and particle entanglement. In particular, we ask whether sub-shot-noise sensitivity can be reached with all pure entangled input states of particles if they can be optimized with local operations. Results on the optimal local transformations allow us to show that for all pure entangled states can be made useful for sub-shot-noise interferometry while for this is not the case. We completely classify the useful entangled states available in a bosonic two-mode interferometer. We apply our results to several states, in particular to multiparticle singlet states and to cluster states. The latter turn out to be practically useless for sub-shot-noise interferometry. Our results are based on the Cramer-Rao bound and the Fisher information.
- Received 22 December 2009
DOI:https://doi.org/10.1103/PhysRevA.82.012337
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