Speaker: Thomas Agrenius Gustafsson (KTH Royal Institute of Technology)

Title: Special & general relativity in quantum optics

Abstract: Quantum state descriptions are always relative to a frame of reference. The vacuum state of a quantum field is no exception -- a photodetector on an accelerated trajectory will perceive the electromagnetic vacuum as a thermal gas of photons (the Unruh effect). I will briefly discuss a new approach, based on Wigner functions, to study this phenomenon, and some contributions I recently made to understanding coincidence photodetection within this framework. Next, we will forget the quantum field and discuss matter-wave interferometry in curved spacetime. Here, gravitational time dilation suggests that internal energy superposition states ("clocks") inside particles can provide which-path information in interferometry experiments. I will take this proposal to an extreme limit, and discuss some new perspectives this brings on gravitational interferometry and quantum clocks.