Gravitational Quantum Optics
Over the last 100 years theorists have attempted to unify quantum theory with gravitational physics by extrapolating known physics in a coherent way. Dimensional arguments suggest that quantum gravity must dominate close to the Planck scale, which is still far beyond current experimental and technological capabilities. However, there remains the distinct possibility that quantum gravity phenomena already become observable at scales that are just becoming accessible. Quantum entangled systems subjected to high and low accelerations is one such regime where new physical phenomena might be expected to arise. Also, experimental investigations involving hyper- or microgravity can cause unexpected changes to physical phenomena. Exposing genuine quantum systems, such as entangled photons, to such extreme conditions can aid in the understanding of that system, and lead to a deeper understanding of the physical processes themselves.
We have performed an experiment that demonstrates the extent to which state-of-the-art quantum hardware can be exposed to such harsh operational conditions and was intended to stimulate research on theories beyond the current paradigm which can be tested with the kind of experiments presented here. Our experimental platform represents a first test-bed that can readily be upgraded for measurements with higher precision, and higher-dimensional degrees of freedom, such as energy-time entanglement. We also envisage bringing such a system very close to zero-g conditions for several tens of seconds and reaching hyper-gravity environments of up to 150 g for many hours of operation.
 M. Fink, A. Rodriguez-Aramendia, J. Handsteiner, A. Ziarkash, F. Steinlechner, T. Scheidl, I. Fuentes, J. Pienaar, T. C. Ralph, and R. Ursin, Nat Comm. 8, 1 (2017).
 Siddarth Koduru Joshi, Jacques Pienaar, Timothy C. Ralph, Luigi Cacciapuoti, Will McCutcheon, John Rarity, Dirk Giggenbach, Vadim Makarov, Ivette Fuentes, Thomas Scheidl, Erik Beckert, Mohamed Bourennane, David Edward Bruschi, Adan Cabello, Jose Capmany, José A. Carrasco, Alberto Carrasco-Casado, Eleni Diamanti, Miloslav Duusek, Dominique Elser, Angelo Gulinatti, Robert H. Hadfield, Thomas Jennewein, Rainer Kaltenbaek, Michael A. Krainak, Hoi-Kwong Lo, Christoph Marquardt, Gerard Milburn, Momtchil Peev, Andreas Poppe, Valerio Pruneri, Renato Renner, Christophe Salomon, Johannes Skaar, Nikolaos Solomos, Mario Stipčević, Juan P. Torres, Morio Toyoshima, Paolo Villoresi, Ian Walmsley, Gregor Weihs, Harald Weinfurter, Anton Zeilinger, Marek Żukowski, Rupert Ursin, arXiv:1703.08036 [quant-ph] (2017), submitted
 D. E. Bruschi, A. Datta, R. Ursin, T. C. Ralph, and I. Fuentes, Phys Rev D 90, 124001 (2014).