New twists in searches for exotic fields with spin-dependent sensors

Nature has provided many hints that our best current theoretical models of the universe are missing important constituents. These undiscovered constituents could include exotic ultralight bosons such as axions. Many well-motivated theories predict that such fields interact with the intrinsic spins of ordinary particles, producing extremely feeble torques that might be detected with sensitive spin-based quantum sensors.

Some of the most distinctive (and possibly largest) signals may originate from astrophysical sources. The Global Network of Optical Magnetometers for Exotic Physics Searches (GNOME) is a worldwide array of time-synchronized, magnetically shielded spin sensors designed to identify correlated signals from exotic fields of astrophysical origin. GNOME is now being upgraded from atomic magnetometers to noble-gas comagnetometers, which suppress magnetic-field noise and significantly improve sensitivity to exotic interactions with nuclear spins.

The newest search targets for GNOME are signals from black hole scalar sirens. If ultralight spin-0 bosonic fields exist, spinning black holes can grow surrounding clouds of these scalars via superradiance. If the scalars interact with one another, the black holes can continually emit scalar waves. Summed over the expected hundreds of millions of isolated black holes in the Milky Way, these sources could produce a persistent signal up to two orders of magnitude larger than conservative expectations for bosonic fields created in the early universe. Detecting a black hole scalar siren signal would simultaneously reveal the existence of exotic scalar fields and illuminate the otherwise hidden population of isolated black holes in our galaxy.

Finally, our research group is developing a novel type of spin-dependent sensor: a levitated ferromagnetic gyroscope (LFG). This mesoscopic object combines strongly correlated spins, mechanical isolation, and controllable quantum dynamics, offering a promising route toward even more sensitive measurements of exotic spin-dependent interactions.

Speaker: Derek Jackson Kimball, CSU East Bay