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Quantum Control of Nuclear Motion at a Metal Surface

The possibility of quantum control of surface photochemical reactions is demonstrated for the system of Cs/Cu(111). Coherent nuclear wave packet motion is induced by resonant dipole excitation with 3.08 eV light from an occupied surface state intrinsic to the Cu(111) surface to an unoccupied Cs antibonding 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 ∼25 fs. This makes it possible to control the position and momentum of the excited state wave packet through the phase of the excitation field. Quantum control is demonstrated for excitation with phase-related <20 fs pulse pairs or single chirped laser pulses. The phase dependence of two-photon photoemission spectra demonstrates the control of desorptive motion of Cs atoms.