Abstract: An apparatus and method for measuring CPT is disclosed. The apparatus includes a quantum absorber that is irradiated by radiation from an electromagnetic radiation source. The quantum absorber includes a material that exhibits CPT. The electromagnetic radiation source generates electromagnetic radiation having first and second CPT-generating frequency components. The first CPT-generating frequency component has a frequency ?L??, and a first CPT component amplitude. The second CPT generating frequency component has a frequency ?L+? and a second CPT component amplitude. The apparatus also includes a detector for generating a detector signal related to the power of electromagnetic radiation that leaves the quantum absorber. The detector signal exhibits an asymmetry as a function of frequency ? in a frequency range about a frequency ?0. The apparatus includes an asymmetry servo loop that alters one of ?L, the first CPT component amplitude, and the second CPT component amplitude to reduce the asymmetry.

Abstract: An apparatus for generating a stabilized frequency signal is disclosed. The apparatus includes a quantum absorber having first, second, and third energy states. The quantum absorber is irradiated by a first radiation source that generates electromagnetic radiation having a frequency, ?L, that induces transitions between the first and third energy states. The quantum absorber is also irradiated by a second radiation source that generates electromagnetic radiation having a frequency, ?M, that induces transitions between the first and second energy states. A detector that generates a detector signal indicative of the level of radiation leaving the quantum absorber in a frequency range including ?L is used by a number of servo loops. One of the servo loops determines the value of ?L that minimizes or maximizes the detector signal and a second servo loop determines an offset signal that reduces the dependence of ?M on the intensity of the first radiation source.