Intuitive and counter-intuitive multiphoton adiabatic rapid pasasage

In coherent population transfer via a sequence of adiabatic rapid passages through overlapping single-photon resonances, the oscillating dipole remains phase-locked to the field as the frequency of the radiation field is chirped [1]. The process is intuitive, and the atomic frequency follows that of the chirped radiation field [1]. Efficient counter-intuitive population transfer can also occur in which the atomic frequency changes in the direction opposite the change in the radiation frequency [2,3]. In such cases the sequence of single-photon transitions of the intuitive transfer is replaced by a single multiphoton transition, enormously reducing the range of the chirp required to effect the population transfer. Such multi-photon adiabatic rapid passage occurs in both an intuitive and a counter-intuitive manner. We present results of such population transfers among the Rydberg states of atomic Li around $n=70\sim90$ using a frequency chirped microwave pulse. This work has been supported by the NSF. [1] H. Maeda, D.V.L. Norum, and T.F. Gallagher, Science {\bf 307}, 1757 (2005). [2]N.V. Vitanov {\it et al.}, Annu. Rev. Phys. Chem. {\bf 52},763 (2001); N.V. Vitanov {\it et al.}, Adv. At. Mol. Opt. Phys. {\bf 46}, 57 (2001).[3] B. Broers, H.B. van Linden van den Heuvell, and L. D. Noordam, Phys. Rev. Lett. {\bf 69}, 2062 (1992).