Ion Entanglement for Fundamental Tests and Precision Measurements
Abstract
We discuss experiments which utilize a system of two entangled and trapped ^9Be^+ ions (equivalent to two entangled spin-1/2 particles). In one experiment, we measured correlations that violate a form of Bell's inequality. Our measured value of the Bell's signal, B = 2.25± 0.03, agrees with a quantum mechanical prediction and exceeds the maximum value of 2 allowed by local realistic theories of nature. This is the first violation of Bell's inequalities in an experiment with massive particles obtained with a complete set of measurements. In addition, the high detection efficiency of our apparatus eliminated the "detection loophole" for the first time. In further experiments, we used entanglement to increase the precision of measurements of phase or rotation angle. For "spin-squeezed" and maximally entangled states we observed a reduction in uncertainty of angular momentum observables beyond the quantum mechanical limits set for unentangled states. As an application, we demonstrated an increase in frequency measurement precision in a Ramsey spectroscopy experiment. With improvements, this may be important for the construction of more accurate atomic clocks.
- Publication:
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APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts
- Pub Date:
- May 2001
- Bibcode:
- 2001APS..DMP.V1002R