Excitation of the coherence of an optically orientable atomic ensemble by a pulsed magnetic field
It is shown that a perturbation of an optically oriented ensemble of atoms by a nonadiabatically applied external magnetic field makes the density matrix of the ground state generally nondiagonal. The appearance of nonzero nondiagonal elements of the density matrix (i.e., the appearance of coherence) between different Zeeman states is manifested not only by the appearance of transverse components of the magnetization but also by the excitation of nonequilibrium higher-order multipole moments. In particular, if the initial state is oriented, a transverse magnetic field pulse produces an oriented nonequilibrium state. A discussion is given of the possibility of optical detection of nonequilibrium states produced in this way and of their relaxation.