Observer dependence of photon bunching: The influence of the relativistic redshift on Hong-Ou-Mandel interference

Time-delayed single quantum repeater node for global quantum communications with a single satellite

“…Additionally, utilizing more recent finite key calculations that specifically address space-based QKD scenarios can potentially increase calculated secret key lengths by approximately ∼10%. Finally, ULL QMs in orbit may also serve as useful probes to investigate the intersection of quantum physics and general relativity [51] and enable human-assisted Bell tests across Earth-Moon distances [11,52,53].…”

Introduction to gravitational redshift of quantum photons propagating in curved spacetime

“…A recent trend of work has initiated the study of the effects of gravity on the propagation of photons between different users located at different heights in the gravitational potential of the Earth [43,44,57,105,58,138,59]. The core idea is to model photons and excitations of a quantum field in (weakly) curved spacetime.…”

“…The physical principles described here set themselves apart from many experiments that have been proposed and already performed, since we would not use massive particles [154], but photons (which are modelled as massless excitations of a quantum field). Photons can be engineered to propagate (i.e., "free fall") between two users at different heights in the gravitational potential of the Earth or another planet, and the shift that is induced can be measured using interferometric setups [61,138]. The degree of control over photons and the high precisions that modern photonics have reached very high levels and this would enable the possiblity to test the universality of the gravitational redshift as a function, for example, of the initial (quantum) state of the photon, of the motion of photons (i.e., of the parameters of the trajectory), and of the polarization.…”

Gravitational Redshift Induces Quantum Interference

“…Photons can propagate (i.e., "free fall") between two users at different height in the gravitational potential, and the shift can be measured using interferometric setups. [30,46] Given the high degree of control over photons and the high precisions allowed by photonics, it would be possible to test the universality of the gravitational redshift against, for example, the initial (quantum) state of the photon, the different motion of photons (i.e., varying the trajectory), and the polarization. Since gravitational redshift is to be expected on first principles as a direct consequence of the EEP applied to two accelerated objects that exchange electromagnetic pulses, [37] we conclude that this avenue is yet another dimension that can be explored with the mechanism described here.…”