Extension of the Local Approach to excited states of molecules

Han Jie Guo, Claire E. Dickerson, Ashley Jiwon Shin +5 more

Quantum information processors based on trapped atoms utilize laser-induced optical cycling transitions for state preparation and measurement. These transitions consist of an electronic excitation from the ground to an excited state and a decay back to the initial ground state, associated with a photon emission. While this technique has been used primarily with atoms, it has also recently been shown to work for some divalent metal hydroxides (e.g. SrOH) and alkoxides (e.g. SrOCH3). This extension to molecules is possible because these molecules feature nearly isolated, atomic-like ground and first-excited electronic states centered on the radical metal atom. We theoretically investigate the extension of this idea to a larger scale by growing the alkyl group, R, beyond the initial methyl group, CH3, while preserving the isolated and highly vertical character of the electronic excitation on the radical metal atom, M. Theory suggests that in the limit as the size of the ligand carbon chain increases, it can be considered a functionalized diamond (or cubic boron nitride) surface. Several requirements must be observed for the cycling centers to function when bound to the surface. First, the surface must have a significant band gap that fully encapsulates both the ground and excited states of the cycling center. Second, while the surface lattice imposes strict limits on the achievable spacing between the SrO- groups, at high coverage, SrO- centers can interact, and show geometric changes and/or electronic state mixing. We show that the coverage of the diamond surface with SrO- cycling centers needs to be significantly sub-monolayer for the functionality of the cycling center to be preserved. Having the lattice-imposed spatial control of SrO- placements will allow nanometer-scale proximity between qubits and will eliminate the need for atom traps for localized cycling emitters. Our results also imply that a functionalization could be done on a scanning microscope tip for local quantum sensing or on photonic structures for optically-mediated quantum information processing.

Baldassare Di Bartolo

Tim Wogan

Oskar Weser, Ali Alavi, Giovanni Li Manni

In this paper we propose an improved excitation generation algorithm for the full configuration interaction quantum monte carlo (FCIQMC) method, which is particularly effective in systems described by localized orbitals. The method is an extension of the precomputed heat-bath (PCHB) strategy of Holmes et al., with more effective sampling of double excitations and a novel approach for non-uniform sampling of single excitations. We demonstrate the effectiveness of the algorithm for a chain of 30 hydrogen atoms with atom-localized orbitals, a stack of benzene molecules, an Fe-porphyrin model complex, whereby we show an overall efficiency gain by a factor of two to four, as measured by variance reduction per wall-clock time.

Oskar Weser, Ali Alavi, Giovanni Li Manni

In this paper we propose an improved excitation generation algorithm for the full configuration interaction quantum monte carlo (FCIQMC) method, which is particularly effective in systems described by localized orbitals. The method is an extension of the precomputed heat-bath (PCHB) strategy of Holmes et al., with more effective sampling of double excitations and a novel approach for non-uniform sampling of single excitations. We demonstrate the effectiveness of the algorithm for a chain of 30 hydrogen atoms with atom-localized orbitals, a stack of benzene molecules, an Fe-porphyrin model complex, whereby we show an overall efficiency gain by a factor of two to four, as measured by variance reduction per wall-clock time.