In described examples, a physics cell includes: a laser source configured to emit light towards an atomic chamber containing an atomic gas; a photodetector configured to receive emissions from the atomic chamber; and a field coil for generating a magnetic field in the atomic chamber. An electronics circuit includes: a controller circuit coupled to the photodetector output and having control outputs to a digital to analog converter circuit; the digital to analog converter circuit having a coil current output to adjust the magnetic field, a modulation control output to control a modulation of the light, and having an output to control a voltage controlled oscillator; and a radio-frequency output circuit having a voltage controlled oscillator coupled to the output of the digital to analog converter circuit outputting a radio frequency signal to the laser source in the physics cell.