Deterministic Squeezed States with Collective Measurements and Feedback

We demonstrate the creation of entangled, spin-squeezed states using a collective, or joint, measurement and real-time feedback. The pseudospin state of an ensemble of N=5×10^{4} laser-cooled ^{87}Rb atoms is deterministically driven to a specified population state with angular resolution that is a...

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Bibliographic Details
Published in:Physical review letters 2016-03, Vol.116 (9), p.093602-093602, Article 093602
Main Authors: Cox, Kevin C, Greve, Graham P, Weiner, Joshua M, Thompson, James K
Format: Article
Language:English
Subjects:
Angular resolution
Evolution
Feedback
Laser cooling
Noise levels
Real time
Variance
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Summary:We demonstrate the creation of entangled, spin-squeezed states using a collective, or joint, measurement and real-time feedback. The pseudospin state of an ensemble of N=5×10^{4} laser-cooled ^{87}Rb atoms is deterministically driven to a specified population state with angular resolution that is a factor of 5.5(8) [7.4(6) dB] in variance below the standard quantum limit for unentangled atoms-comparable to the best enhancements using only unitary evolution. Without feedback, conditioning on the outcome of the joint premeasurement, we directly observe up to 59(8) times [17.7(6) dB] improvement in quantum phase variance relative to the standard quantum limit for N=4×10^{5}  atoms. This is one of the largest reported entanglement enhancements to date in any system.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.116.093602