title: Flat-response spin-exchange relaxation free atomic magnetometer under negative feedback.
abstract: We demonstrate that the use of negative feedback extends the detection bandwidth of an atomic magnetometer in a spin-exchange relaxation free (SERF) regime. A flat-frequency response from zero to 190 Hz was achieved, which is nearly a three-fold enhancement while maintaining sensitivity, 3 fT/Hz1/2 at 100 Hz. With the extension of the bandwidth, the linear correlation between measured signals and a magne-tocardiographic field synthesized for comparison was increased from 0.21 to 0.74. This result supports the feasibility of measuring weak biomagnetic signals containing multiple frequency components using a SERF atomic magnetometer under negative feedback.
authors.forename: Hyun Joon
authors.initials: HJ
authors.lastname: Lee
authors.forename: Jeong Hyun
authors.initials: JH
authors.lastname: Shim
authors.forename: Han Seb
authors.initials: HS
authors.lastname: Moon
authors.forename: Kiwoong
authors.initials: K
authors.lastname: Kim