Synchronously Pumped Noble-Gas NMR Oscillator

A noble-gas atom that is polarized by spin-exchange with optically pumped alkali atoms can be made to coherently oscillate by driving the NMR resonance with an oscillating field that is phase-locked to the transverse component of the detected oscillation. Using the alkali atoms as the magnetometer for the NMR detection allows an extremely high signal-to-noise ratio for detection of magnetic fields, rotations, etc. Such oscillators have been developed previously by various laboratories, as described in a recent review [1]. In AMO physics there has been a sustained interest in searches for violations of fundamental symmetries. As technologies develop, they are continually applied to ever more sensitive tests of the fundamental symmetries of nature. Perhaps most visible of these tests are those for permanent electric dipole moments, with recent results for the electron [2] and nuclear edms [3] coming out, and a large number of new efforts using a variety of technologies[4–6]. Another extremely visible area of study has been searches for time-variation of fundamental constants [7]. A third class of experiments include searches for violations of Lorentz Invariance [8, 9] and for anomalous forces from axions [10, 11]. An important approach to symmetry tests has been the use of hyperpolarized noble gases, that is, noble-gas nuclei polarized to tens of percent polarization (millions of times in excess of thermal polarizations). Noble-gases are of particular interest due to the relative insensitivity of their precession frequencies to their chemical environment, and their ability to have coherence times of 100s to 1000s of seconds and storage times of many hours. In particular, spin-exchange optical pumping of a variety of noble-gas isotopes has been used in a variety of ways for fundamental symmetry tests. This was pioneered in the early ’80s by Fortson’s group, placing an early upper limit on the edm of 129-Xe [12]. Further developments came in the ’90s with the invention of the dual noble-gas maser by Chupp and Walsworth [13, 14], and more recently the self-compensated alkali-noble gas comagnetometer of Romalis [15], which recently published a frequency sensitivity of 18 pHz[16]. Noble gas NMR has also been extensively, but quietly, developed for gyroscopes in industrial laboratories such as Litton (now Northrop-Grumman), with recent work at Northrop-Grumman [17] and at NIST[18]. These developments were recently reviewed by E. Donley [1]. Northrop-Grumman uses a 129-Xe/131-Xe comagnetometer system to highly suppress magnetic field fluctuations while allowing high SNR readout of the NMR by the alkali atoms that also polarize the nuclei by spinexchange. GIVE PERFORMANCE SUMMARY The approach to precision measurements with hyperpolarized noble gases can be understood by the fundamental equation for the noble-gas resonance frequency for isotope i: