When we observe the interference of two counter-propagating waves surrounding a closed area, we observe a phase shift induced by the rotation of the frame of the experiment. The instrument is then called a gyrometer. This well-known effect is called the Sagnac effect, from the French physicist who sought to highlight it as early as 1913, to test the laws of combination of the speeds of light. The Sagnac effect is a relativistic effect, somewhat analogous to Langevin’s twin paradox, but where the acceleration comes from the rotation of the frame. Also the Sagnac effect played a key role in establishing the theory of relativity and prompted the development of precision optical interferometers.
Sensitivity to rotation gives rise to numerous applications for the navigation of devices such as submarines, planes, rockets... When the Sagnac gyroscopes are sufficiently precise, the study of the spectra of the Earth’s rotation provides information on earthquakes and variations in the gravity field that disturb the rotation of the Earth.
Also the fundamental importance of the Sagnac effect motivated the realization of experiments aiming to test its validity for waves other than optical. Absolute and precision measurements remain a major challenge.
The Atomic Interferometry and Inertial Sensors team at SYRTE has just published in the journal Science Advances a precise and accurate test of the Sagnac effect by matter waves. A matter wave is the wave equivalent of particles, here Cesium atoms cooled by laser. In the SYRTE gyrometer, the atoms are launched in such a way that their trajectories form a figure 8 and contains a geometric surface of 11 cm2 and two axes of sensitive measurements. The team was able to measure the Earth’s rotation-induced phase shift and find agreement with the theoretical prediction at an accuracy level of 25 parts per million.
Beyond the importance for fundamental physics, our work opens up practical applications in seismology and geodesy.
Reference
Gautier, R., Guessoum, M., Sidorenkov, L.A., Bouton, Q., Landragin, A. Geiger, R. : 2022, Accurate measurement of the Sagnac effect for matter waves, Science Advances, 8, 23 www.science.org