Rb nf quantum defects from millimeter-wave spectroscopy of cold 85Rb Rydberg atoms

Millimeter-wave resonance spectroscopy has been used to measure the (n+2)d(5/2) to nf(5/2,7/2) transition frequencies of cold Rb-85 atoms in a magneto-optical trap. From these intervals we extract substantially improved Rb nf quantum defects, fine structure intervals, and limits for the dipole and quadrupole polarizabilities of Rb+.