Quantum seismology

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E. G. Brow, W. Donnelly, A. Kempf, R. B. Mann, E. Martín-Martínez, and N. C. Menicucci
New Journal of Physics 16, 105020 (2014)

Entanglement farming is a protocol that involves successively sending pairs of “particle detectors” (such as atoms, ions, molecules, etc) transversely through an optical cavity. As pair after pair traverses the cavity, the field approaches a fixed-point state, where every pair of atoms emerges from the cavity in the same state, which is generically entangled. The fixed point is generally stable to small changes in the parameters.

In their work, Brow and co-workers show that this robustness breaks down dramatically when the frequency at which atoms traverse the cavity is at resonance with a multiple of the cavity’s fundamental frequency. They use this effect to propose a quantum mechanical method of detecting weak vibrational disturbances. Taking advantage of an extremely precise resonance effect, it is possible to find a regime where the fixed- point state is highly sensitive to perturbations, even harmonic vibrations with frequencies several orders of magnitude below the cavityʼs natural frequency. This sensitivity may be useful for high precision metrology.