45 research outputs found
Entanglement and squeezing in continuous-variable systems
We introduce a multi-mode squeezing coefficient to characterize entanglement
in -partite continuous-variable systems. The coefficient relates to the
squeezing of collective observables in the -dimensional phase space and can
be readily extracted from the covariance matrix. Simple extensions further
permit to reveal entanglement within specific partitions of a multipartite
system. Applications with nonlinear observables allow for the detection of
non-Gaussian entanglement.Comment: 11 pages, 2 figure
Quantum metrology with nonclassical states of atomic ensembles
Quantum technologies exploit entanglement to revolutionize computing,
measurements, and communications. This has stimulated the research in different
areas of physics to engineer and manipulate fragile many-particle entangled
states. Progress has been particularly rapid for atoms. Thanks to the large and
tunable nonlinearities and the well developed techniques for trapping,
controlling and counting, many groundbreaking experiments have demonstrated the
generation of entangled states of trapped ions, cold and ultracold gases of
neutral atoms. Moreover, atoms can couple strongly to external forces and light
fields, which makes them ideal for ultra-precise sensing and time keeping. All
these factors call for generating non-classical atomic states designed for
phase estimation in atomic clocks and atom interferometers, exploiting
many-body entanglement to increase the sensitivity of precision measurements.
The goal of this article is to review and illustrate the theory and the
experiments with atomic ensembles that have demonstrated many-particle
entanglement and quantum-enhanced metrology.Comment: 76 pages, 40 figures, 1 table, 603 references. Some figures bitmapped
at 300 dpi to reduce file siz