Developments in chip scale atomic magnetometers

Microfabrication techniques developed at NIST have led to the demonstration [1] of a chip-scale atomic magnetometer (CSAM) with a sensitivity of 5 pT/Hz$^{1/2}$, using $M_x$ modulation in a 2x1x1 mm $^{87}$Rb vapor cell. An alternative to the $M_x$ technique is Bell-Bloom modulation of the optical pumping light [2]. This is advantageous in a CSAM since it allows for a simpler device, and it eliminates a source of heading error due to possible misalignment of the light beam relative to the $M_x$ rf coils. We have demonstrated that Bell-Bloom modulation gives comparable magnetometer performance compared to $M_x$ in a millimeter scale vapor cell. We have also achieved 70 fT/Hz$^{1/2}$ sensitivity in a microfabricated vapor cell by operating near zero magnetic field in the SERF regime [3]. The addition of high permeability flux concentrators near the vapor cell amplifies the applied field by a factor of 10 to 100 depending on the geometry. This can potentially push the sensitivity close to the femtotesla level, comparable to low-$T_c$ SQUID sensors, but in a non-cryogenic, simple, low-power device. \\[1ex] [1] P.D.D. Schwindt {\it et al.}, App. Phys. Lett., {\bf 90}, 081102 (2007). \newline [2] W.E. Bell and A.L. Bloom, Phys. Rev. Lett., {\bf 6}, 280 (1961). \newline [3] V. Shah, {\it et al.}, Nature Photonics, {\bf 1}, 649 (2007).