Atomic hyperfine resonances in a magnetic quadrupole field
  The quantum resonances of an atom possessing a single valence electron which shows hyperfine interaction with the nucleus is investigated in the presence of a three dimensional magnetic quadrupole field. Particular emphasis is put on the study of the interplay of the hyperfine and quadrupole forces. Analyzing the underlying Hamiltonian a variety of symmetries are revealed which give rise to a two-fold degeneracy of the resonance energies. Our numerical approach employs the complex scaling method and a Sturmian basis set. Several regimes and classes of short-lived and long-lived resonances are identified. The energies and decay widths of the resonances are characterized by their electronic and nuclear spin properties. 
Shahpoor Saeidian, Igor Lesanovsky, Peter Schmelcher