Probing gravity 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 [1, 2]. 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 [3, 4]. 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 [5]. [1] M. Zych et al., Nat. Comm. 2, 505 (2011). [2] A. Roura, Phys. Rev. X 10, 021014 (2020). [3] C. Overstreet et al., Science 375, 226 (2022). [4] A. Roura, Science 375, 142 (2022). [5] M. Mohageg et al., EPJ Quant. Tech. 9, 25 (2022).