Gravitationally induced phase shift on a single photon

FWF Standalone Project P 30817


Project Abstract

Quantum mechanics and general relativity are two fundamentally different theories and have both been tested independently with very high precision. Quantum mechanics allows for describing nature at very small scales whereas general relativity gives access to descriptions at very large scales. But even after a century of research, the interplay of those two very different theories has never been tested experimentally. The ongoing search for a unified framework, capable of combining all known forces of nature, suffers from this lack of experimental guidance. This project aims to explore the interface between quantum mechanics and general relativity by performing high-precision experiments at the level of single quanta of light, the photons. Such quantum systems allow one to examine the influence of gravity on interference effects. For this purpose, a high-precision interferometer whose paths are subject to different gravitational potentials will be used. If the mass-energy equivalence principle holds, the photon’s energy must provide its gravitational mass. Then a relative phase shift between the different paths of the interferometer located at different potentials can be detected. This kind of experiments would therefore directly probe the gravitational mass-energy equivalence principle of relativity. The import insights of this experiment will influence the design of even more sensitive interferometers that allow for a genuine experimental verification of the interplay between quantum mechanics and general relativity in a table-top experiment. According to general relativity, clocks at different heights within the gravitational field of the Earth are not ticking at the same rate. If this time difference is comparable to the ‘length’ of the photon inside the interferometer, then each path leads to a different arrival time. This results in a drop in the interferometric visibility, which shows up in addition to the relative phase shift.