Pushing the limits of atom interferometry...The system we want to realize is a Mach-Zender spatial interferometer operating with trapped Bose-Einstein condensates (BECs). Phase diffusion caused by interatomic collisions are suppressed implementing BECs with tunable interactions in ultra-stable optical potentials. Entangled states can be used to improve the sensitivity of the sensor beyond the standard quantum limit to ideally reach the ultimate, Heisenberg, limit set by quantum mechanics. Our project aims at developing a sensor with unprecedented spatial resolution able to compete with, and eventually overcome, state-of-the-art interferometers with cold (non condensed) atomic waves.

Differential interferometry works also with quantum entangled states

Differential interferometry (DI) with two coupled sensors is a most powerful approach for precision measurements in the presence of strong phase noise. However, DI has been studied and implemented only with classical resources. Here we generalize the theory of differential interferometry to the case of entangled probe states. We demonstrate that, for perfectly correlated interferometers and in the presence of arbitrary large phase noise, sub-shot noise sensitivities — up to the Heisenberg limit — are still possible with a special class of entangled states in the ideal lossless scenario.

M. Landini et al.,
Phase-noise protection in quantum-enhanced differential interferometry
New J. Phys. 16, 113074 (2014)

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