Adaptive noise reduction techniques used in devices that pass light from a laser through a quantum medium such as a rubidium vapor cell. A CPT frequency standard that employs the techniques has a first channel in which the laser light passes through the quantum medium and to a photodetector to produce a first signal and a second channel in which the light passes to a second photodetector without passing through the quantum medium to produce a second signal. The first and second signals are processed in a signal processor to produce an enhanced output signal in which the noise has been reduced. The signal processor implements noise predictor and noise remover. In a preferred embodiment, the noise predictor employs a FIR filter in which the coefficients are set in response to feedback from the enhanced output signal.