Linear Stark Shift in Dressed Atoms as a Signal to Measure a Nuclear Anapole Moment with a Cold-Atom Fountain or Interferometer

Abstract

We demonstrate theoretically the existence of a linear dc Stark shift of the individual substates of an alkali atom in its ground state, dressed by a circularly polarized laser field. It arises from the electroweak nuclear anapole moment violating P but not T. It is characterized by the pseudoscalar xi k wedge E x B involving the photon angular momentum and static electric and magnetic fields. We derive the relevant left-right asymmetry with its complete signature in a field configuration selected for a precision measurement with cold-atom beams. The 3, 3 --> 4, 3 Cs transition frequency shift amounts to 7 microHz for a laser power of approximately 1 kW at 877 nm, E=100 kV/cm and B approximately > 0.5 G.