RUI: Search for a spin-gravity coupling using laser-addressed atomic gyroscopes

California State University, East Bay Foundation, Inc., Hayward CA

Investigators

Abstract

This award supports an experiment to search for a new long-range coupling between nuclear spins and the mass of the Earth. Depending on interpretation, the experiment would improve present experimental limits by as much as two orders of magnitude or more. The presence of such an interaction would imply the existence of a gravitational dipole moment (GDM) of an elementary particle --- which can be envisioned semiclassically as a small separation between the position of the center of inertial mass and the center of gravitational mass. Detection of a GDM would be evidence that gravity violated parity and time-reversal symmetries to a small degree, as well as being a breakdown of the equivalence principle which underlies the theory of general relativity. The experiment would also set new experimental limits on hypothetical scalar and vector components of gravitational fields, and new limits on the existence of certain classes of massless or nearly massless axion-like pseudoscalar particles. This new experimental search is motivated by recently developed techniques in the field of atomic magnetometry enabling significant improvement in sensitivity to atomic spin precession. The experiment will use nonlinear optical rotation of near-resonant laser light to measure the spin-precession frequency of alkali atoms in the presence of a magnetic field and use differences between the frequencies for the two different ground state hyperfine levels to search for a signal proportional only to anomalous interactions. This work will fundamentally advance our knowledge of the gravitational force by testing how well gravity respects parity and time-reversal symmetries, and by probing the limits of the equivalence principle. Tremendous efforts at the theoretical level are being undertaken to integrate our understanding of gravity into the framework of quantum field theory, and this work offers a unique opportunity to gain new experimental insight into the symmetry properties of gravity. Furthermore, new techniques for precision measurement of the precession of spin-polarized atoms will be developed, advancing the technology driving the next generation of ultra-sensitive atomic magnetometers and gyroscopes. This research program forms the basis for an integrative approach to hands- on education in experimental physics at California State University, East Bay. New curricula for the advanced laboratory course will be developed to provide a natural connection to the ongoing research, and undergraduate students will be directly involved in the research program. An active research program at this institution will especially benefit a diverse student population, since two-thirds of our students are women and over seventy percent are underrepresented minorities.