Quantum control of nuclear motion at a metal surface

The possibility of quantum control of surface photochemical reactions is de monstrated for the system of Cs/Cu(111). Coherent nuclear wave packet motio n is induced by resonant dipole excitation with 3.08 eV light from an occup ied surface state intrinsic to the Cu(111) surface to an unoccupied Cs anti bonding state for a Cs atom coverage of 0.1 monolayer. Interferometric time -resolved two-photon photoemission measurements show that the polarization induced between the two states decays in similar to 25 fs. This makes it po ssible to control the position and momentum of the excited state wave packe t through the phase of the excitation field. Quantum control is demonstrate d for excitation with phase-related <20 fs pulse pairs or single chirped la ser pulses. The phase dependence of two-photon photoemission spectra demons trates the control of desorptive motion of Cs atoms.