Measurement of anapole moment of atomic cesium via two-pathway coherent control

An anapole moment of the nucleus arises from the weak nucleon-nucleon interaction due to neutral current in the nucleus. Only one measurement of an anapole moment has been successful so far; the Boulder group’s measurement nearly two decades ago. That moment was much larger than expected, and is not in agreement with other models of nuclear interactions. While the Boulder group derived the anapole moment by comparing two optical PNC transitions, namely 6S1/2 F= 3->7S1/2F = 4 and 6S1/2 F = 4 -> 7S1/2F = 3, our approach is the direct excitation of the ground state hyperfine PNC transition 6S1/2 F= 3->6S1/2 F= 3-4 with microwave fields and Raman lasers.

The two-pathway coherent control, pioneered by D. S. Elliott and demonstrated only recently, involves interference of two transitions by varying the relative phase between the transitions. The excitation rate varies sinusoidally, and if one transition is much strong and the other is weak, the weak amplitude can be derived from the small amplitude modulation in the signal. Our lab has already showcased the effectiveness of the technique by measuring the magnetic dipole moment in the 6S→7S transition. We will employ this technique in both the weak charge and anapole moment measurements; for the 6S→7S measurements, two-photon (strong) and one-photon; for the ground hyperfine state measurements, the Raman lasers (strong) and rf field.