New J. Phys http://doi.org/b2tw (2017)
The study of gravitational effects on a single photon is potentially important because it could verify the equivalence between the energy of a single photon and its effective gravitational mass. Unfortunately, given that the gravitational effect is so small such an experiment would require interferometers with arm lengths of a few thousand kilometres in order to be measured. Now, Christopher Hilweg and co-workers from the University of Vienna, Austria and Massachusetts Institute of Technology in the USA have proposed a table-top, fibre-based experimental scheme to tackle the task. The scheme consists of a rotatable three-arm Mach–Zehnder interferometer. To observe a phase shift on the order of 10−5 radians for photons at 1,550 nm, each arm had an optical fibre spool containing 100 km of fibre. The interferometry is performed at rotations about an axis parallel to the arms to measure different gravitational potential differences as well as to calibrate the interferometer in the horizontal position.
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Horiuchi, N. Gravitational phase shift. Nature Photon 11, 208 (2017). https://doi.org/10.1038/nphoton.2017.49