Modern radio-optical methods in quantum magnetometry

This paper is an extension of a part of the talk delivered under the more general title “Narrow spectral lines in fundamental metrology: state-of-the-art, prospects and problems” at the oral presentation of the 90th anniversary “Usp. Fiz. Nauk” issue. The talk reviewed the past development and current status of the metrology of length, frequency/time and magnetic field. The measurement of these quantities currently relies on the high stability of energies of standard transitions between metastable atomic states. Because of journal space restrictions, all metrology topics other than the title one were omitted in the present review.