Knowledge Bank

A molecule in a state of total angular momentum $F$ has a familiar $2F+1$ degeneracy. In the presence of a pure magnetic field, this $2F+1$ degeneracy is completely lifted with each magnetic sub-level $MF$ acquiring its own energy. In the presence of an electric field, quantum states with non-zero magnetic quantum numbers $|MF|$ remain doubly degenerate. This fact is well established by Stark spectroscopy and is a consequence of time-reversal symmetry. In 1950, Purcell and Ramsey pointed out that time-reversal symmetry could be broken by the existence of an electric dipole moment of the electron. Over the last 60 years, the interest in such a symmetry breaking dipole moment has increased, in part because it may explain the matter-antimatter asymmetry of the Universe, and in part because it could help to differentiate between competing fundamental models of Physics. If large enough, such a dipole moment could lead to an observable lifting of the degeneracy between $+MF$ and $-MF$ states of a molecule in a pure electric field. We report on progress toward searching for an electric dipole moment by an optical quantum beat experiment utilizing the $X1 2\Pi 1/2$ state of PbF molecule.