Dual-axis pi-pulse SERF magnetometer for biomedical applications

We present a new two-axis vector SERF magnetometer with suppressed technical 1/f noise on both sensitive axes. It reaches a probe sensitivity of 2\,fT$\times$Hz$^{-1/2}$ ($\hat{x}$) and 8\,fT$\times$Hz$^{-1/2}$ ($\hat{y}$) at 10\,mHz, outperforming the DC SERF magnetometer in the same setup (27\,fT$\times$Hz$^{-1/2}$). The lowest probe noise of 0.7\,fT$\times$Hz$^{-1/2}$ ($\hat{x}$) and 1.5\,fT$\times$Hz$^{-1/2}$ ($\hat{y}$) is reached at 10\,Hz, comparable to the DC SERF probe noise at the same frequency (0.3\,fT$\times$Hz$^{-1/2}$). The magnetometer operates by applying a superposition of a DC offset field and a $\pi$-pulse comb while remaining in the SERF regime. The resulting alkali precession signals for $B_x$ and $B_y$ fields are orthogonal to each other and synchronous to the pulse repetition rate.