Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 27; pp. 10960 - 10965
• Main Authors: Appel, J, Windpassinger, P.J, Oblak, D, Hoff, U.B, Kjærgaard, N, Polzik, E.S
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 07-07-2009; National Acad Sciences
• Subjects: Atoms; Fringe; Information science; Interferometers; Measurement; Noise measurement; Noise reduction; Photons; Physical Sciences; Precision; Quantum decoherence; Quantum entanglement; Signal noise; Spectroscopy; Spectrum analysis; Weights & measures
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0901550106

Squeezing of quantum fluctuations by means of entanglement is a well-recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between 2-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for [greater, similar] 10⁵ cold caesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A 2-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared with a single-color QND measurement.