Selecting Excited States

Giampaolo Co’

Ya-Zhou Chen, Shuo Wang

Abstract We have theoretically investigated the population transfer and the selective excitation of vibrational states of the target state in a three-state Na 2 molecule using the chirped adiabatic passage. The population transfer among electronic states is studied. Compared with the single negative chirped pulse, complete population transfer can be achieved by using a positive chirped pulse. The effects of laser parameters on vibrational population distribution are discussed, and the selective excitation of vibrational states can be achieved by adjusting the central frequency. Finally, we give the method of selective excitation of specific vibrational states.

Peter Fulde

Hisaki Oka

We theoretically investigate strongly enhanced vibrational-mode-selective two-step excitation by ultrabroadband frequency-entangled photons. A diatomic molecule having three sets of vibronic states is used to evaluate the excitation efficiency of the two-step excitation. We show that the photon entanglement has little influence on the populations of intermediate vibrational modes of intermediate states but selectively increases the population of a single vibrational mode of excited states, resonant with the total energy of the entangled photons. For an ultrashort pulse close to a monocycle with high degree of entanglement, the population of the vibrational mode is enhanced 2500 times more than by uncorrelated photons, and the selectivity nearly reaches unity. Our results indicate that the two-step excitation with ultrabroadband frequency-entangled photons can achieve highly selective and strongly enhanced excitation of a single vibrational mode.

Ernest Pastor

Nicole M. Braunscheidel, Vibin Abraham, Nicholas J. Mayhall

6098], we introduced a new approach for accurately approximating full CI ground states in large electronic active-spaces called Tensor Product Selected CI (TPSCI). In TPSCI, a large orbital active space is first partitioned into disjoint sets (clusters) for which the exact, local many-body eigenstates are obtained. Tensor products of these locally correlated many-body states are taken as the basis for the full, global Hilbert space. By folding correlation into the basis states themselves, the low-energy eigenstates become increasingly sparse, creating a more compact selected CI expansion. While we demonstrated that this approach can improve accuracy for a variety of systems, there is even greater potential for applications to excited states, particularly those which have some excited-state character. In this paper, we report on the accuracy of TPSCI for excited states, including a far more efficient implementation in the Julia programming language. In traditional SCI methods that use a Slater determinant basis, accurate excitation energies are obtained only after a linear extrapolation and at a large computational cost. We find that TPSCI with perturbative corrections provides accurate excitation energies for several excited states of various polycyclic aromatic hydrocarbons with respect to the extrapolated result (i.e., near exact result). Further, we use TPSCI to report highly accurate estimates of the lowest 31 eigenstates for a tetracene tetramer system with an active space of 40 electrons in 40 orbitals, giving direct access to the initial bright states and the resulting 18 doubly excited (biexcitonic) states.