arXiv:1505.02470v1 [quant-ph] 11 May 2015 1 Coherent Quantum Control of S 2 ↔ S 1 Internal Conversion in Pyrazine via S 0 → S 2 /S 1 Weak Field Excitation Timur Grinev [1] Department Of Chemistry, Chemical Physics Theory Group, and Center for Quantum Information and Quantum Control, University of Toronto, Toronto, Ontario M5S 3H6, Canada Moshe Shapiro Department of Chemistry and Department of Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada, and Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel Paul Brumer Department Of Chemistry, Chemical Physics Theory Group, and Center for Quantum Information and Quantum Control, University of Toronto, Toronto, Ontario M5S 3H6, Canada Abstract Coherent control of internal conversion (IC) between the first (S 1 ) and second (S 2 ) singlet excited electronic states in pyrazine, where the S 2 state is populated from the ground singlet electronic state S 0 by weak field excitation, is examined. Control is implemented by shaping the laser which excites S 2 . Excitation and IC are considered simultaneously, using the recently introduced resonance-based control approach. Highly successful control is achieved by optimizing both the amplitude and phase profiles of the laser spectrum. The dependence of control on the properties of resonances in S 2 is demonstrated. I. INTRODUCTION Coherent quantum control [2, 3] has been extensively studied for a wide variety of systems and proven to be a useful approach to controlling properties of atomic and molecular systems. For example, in bound systems it has been used to suppress spontaneous emission from a manifold of states [4], and to control radiationless transitions in collinear carbonyl sulfide OCS [5] and in pyrazine C 4 H 4 N 2 [6–8]. Christopher et al. examined [6, 8] radiationless transitions in pyrazine from the S 2 to the S 1 electronic state and controlled the process by optimizing the superposition states belonging to S 2 . The problem was first studied [6] using a simplified four-mode model for the pyrazine vibrational motion [9]. The optimization technique used showed the possibility of performing active phase control of S 2 ↔ S 1 interconversion, and that this control is directly related to the presence of overlapping resonances [10, 11] in the S 2 manifold. Subsequently [7, 8], the full 24-dimensional vibrational motion of pyrazine [12] was considered, and the dynamical problem solved using an efficient L¨owdin-Feshbach QP-