Nuclear Spin Oscillator Based on 3He to Search for Exotic Spin Coupling

We describe an experimental investigation of a nuclear spin oscillator based on 3He nuclei as a possible detector to search for exotic spin couplings. A magnetically shielded vapor cell comprising an alkali atom mixture (95% potassium and 5% rubidium) and 3He gas is polarized via laser light resonant with the D1 transition in rubidium in the presence of a dc magnetic field. The potassium atoms and 3He nuclei are polarized via spin-exchange collisions with the polarized rubidium atoms. The nuclear spins are tipped with a magnetic field applied perpendicular to the dc magnetic field. The resulting Larmor precession of the 3He nuclear spins is monitored via Faraday rotation of laser light near resonant with the D1 transition in potassium. The Faraday rotation signal is filtered, amplified, and used to apply a magnetic field in a direction perpendicular to the dc magnetic field, resulting in a self-sustained oscillation of the nuclear spins at a frequency that is directly proportional to the dc magnetic field. We demonstrate a sensitivity to exotic spin couplings that is ≈5 times higher than the alkali atom magnetometers that have been used in the Global Network of Optical Magnetometers to Search for Exotic Physics collaboration.