Philipp Hyllus, Wiesław Laskowski, Roland Krischek, Christian Schwemmer, Witlef Wieczorek, Harald Weinfurter, Luca Pezzé, Augusto Smerzi
The Fisher information $F$ gives a limit to the ultimate precision achievable
in a phase estimation protocol. It has been shown recently that the Fisher
information for a linear two-mode interferometer cannot exceed the number of
particles if the input state is separable. As a direct consequence, with such
input states the shot-noise limit is the ultimate limit of precision. In this
work, we go a step further by deducing bounds on $F$ for several multiparticle
entanglement classes. These bounds imply that genuine multiparticle
entanglement is needed for reaching the highest sensitivities in quantum
interferometry. We further compute similar bounds on the average Fisher
information $\bar F$ for collective spin operators, where the average is
performed over all possible spin directions. We show that these criteria detect
different sets of states and illustrate their strengths by considering several
examples, also using experimental data. In particular, the criterion based on
$\bar F$ is able to detect certain bound entangled states.
View original:
http://arxiv.org/abs/1006.4366
No comments:
Post a Comment