Gravitational redshift measurement with two-photon interference of frequency-entangled pairs

Abstract

In recent years there has been a growing interest in probing the interplay between quantum mechanics and general relativity with delocalized quantum superpositions where the two components of the superposition experience different relativistic effects. Notably, atom interferometry experiments in Stanford's 10-m atomic fountain have measured the effect of a non-vanishing proper-time difference due to spacetime curvature on the interference signal. However, these experiments can be alternatively described in terms of non-relativistic quantum mechanics and Newtonian gravity. In contrast, quantum interference experiments with relativistic particles such as photons, which require a quantum field theory (QFT) treatment, offer the possibility of exploring a regime where both quantum mechanics and general relativity play an essential role. In this talk I will focus on gravitational-redshift measurements relying on two-photon interference of frequency-entangled pairs. Such interferometry experiments, which have no classical analog, can be realized with optical links to low-Earth-orbit spacecrafts employing quantum states of light, and will allow directly testing, for the first time, aspects of QFT in curved spacetime.