Influence of Earth´s rotation on entangled photon pairs

How does the Earth`s rotation affect the particular features of quantum physics, such as quantum entanglement Einsteins spooky action at the distance? Can we use quantum entanglement to determine the reference frame of a laboratory? These are the questi ons that this research project aims to answer via quantum experiments. So-called Sagnac interferometers are routinely used to precisely measure rotation, e.g. in inertial guidance applications. However, these experiments use conventional laser light without quantum features like quantum entanglement. Recent work in quantum photonics suggests that we now have the sensitivity to measure the change in quantum entanglement induced by Earth`s rotation. By probing non-inertial effects on entanglement at this scale, we set the stage for future experiments probing gravity with light, and reach a new technological regime for quantum entanglement-enhanced measurements.

Utilizing the interference effect between waves following different paths is one of the best methods for extremely precise physical measurements. The most advanced instruments that make use of this potential are optical interferometers. Among other things, they are used for the detection of gravitational waves and the high-precision determination of rotation rates in optical gyroscopes. The latter are based on the Sagnac effect, which makes it possible to measure rotations with an accuracy that is fundamentally limited by quantum mechanical shot noise. In order to fall below this limit, non-classical correlations must be used, which can be found in entangled photon states, among other things. However, these states are susceptible to loss, so that they can usually only be used in small interferometers. In this project, we measured the rotational velocity of the Earth using maximally path-entangled quantum states of light propagating in an optical fiber interferometer with an effective area of 715 square meters. We have shown that the inclusion of an optical switch enables an orientation-independent calibration of our apparatus and thus a way to determine absolute rotation with pure quantum resources. This provides a new experimental way to test the interplay between special relativity and quantum physics. We anticipate that our techniques can be scaled up so that future quantum-enhanced gyroscopes will be sensitive to general relativistic corrections to the Sagnac effect. Measurements of this kind would for the first time enter an experimental realm where gravitational effects based on Einstein's theory and quantum mechanical effects can be observed simultaneously.