Laser Probing of Alkali Rydberg-Rydberg Transitions with a Phase-Modulated Optical Lattice

This talk discusses a new method of optically manipulating alkali Rydberg electrons using the intensity gradient of a phase-modulated optical lattice. A cold sample of ⁸⁵Rb is trapped within a 1064-nm optical lattice and excited to a Rydberg-nS_1/2 state. The time-independent ponderomotive A² interaction of the light field exerts a conservative force on the center-of-mass coordinate of the Rydberg atom at the lattice periodicity while the time-dependent A² interaction from the phase-modulation at the q-th subharmonic of a Rydberg-Rydberg transition changes the internal state of the atom. Only atoms spatially located within the ∼10 μm beam waist of the optical lattice are addressed. Prohibitive selection rules of the orbital-angular-momentum are avoided in this method; i.e., any change in l is permitted under resonant driving of the transition in first-order perturbation theory. Furthermore, the magnitude of modulation order q is independent from the ponderomotive electronic matrix element. Experimental evidence of this optical manipulation is provided by lattice phase-modulation spectroscopy of the 46S_1/2 →46P_1/2 and 48S_1/2→49S_1/2 transitions.