A multichannel portable SERF atomic magnetometer for biomagnetic measurement

We present a portable four-channel atomic magnetometer array operating in the spin exchange relaxation-free regime. Each channel was operated with a baseline sensitivity of 5--10 fT$/{\sqrt{\textmd{Hz}}}$, at or near the expected Johnson noise limit of the mu-metal shielding. The magnetometer array has several design features intended to maximize its suitability for fetal magnetocardiography, such as a compact modular design, fiber coupled lasers, and magnetometer channel spacing adjustable from 5--10cm. We present adult magnetocardiogram using this array in a magnetically shielded room. We also show the acquisition and analysis of phantom fetal signals with a peak QRS amplitude of $\sim$1pt, using an advanced nonlinear denoising algorithm.