Effects of gravitational time dilation on multi-photon interference.

The unification of quantum mechanics and general relativity remains elusive due to the lack of experimental signatures. To explore the parameter regimes where both theories are relevant, growing attention is being paid to investigating the general relativistic effects on low-energy quantum systems. Such research offers valuable insights into the connection between the two pillars of modern physics. Entanglement and gravitational time dilation capture key aspects of quantum mechanics and general relativity, respectively. Thus, the dynamical evolution of entangled systems in curved space unambiguously reflects the interplay between quantum mechanics and general relativity. Specifically, we investigate the interference visibility reduction of entangled N00N states and quadrature entanglement in gravitational fields. The interference visibility reduction induced by gravitational time dilation differs significantly between N00N states and quadrature entanglement, owing to their distinct gravitational phase encoding mechanisms. For N00N states, the gravitational phase is encoded as a relative phase between the H and V polarization modes, and the visibility reduction is enhanced by a factor of N compared to the single-photon case, rendering them highly sensitive to observing the gravitational effect. In contrast, quadrature entanglement encodes the gravitational phase across its full Gaussian spectrum, leading to vanishing interference visibility in large-scale interferometers spanning from geostationary orbit to ground level.