Quantum computation of π → π* and n → π* excited states of aromatic heterocycles

Abstract

The computation of excited electronic states is an important application for quantum computers. In this work, we simulate the excited state spectra of four aromatic heterocycles on IBM superconducting quantum computers, focussing on active spaces of $\pi \to {\pi }^{\ast }$ and $n\to {\pi }^{\ast }$ excitations. We approximate the ground state with the entanglement forging method, a qubit reduction technique that maps a spatial orbital to a single qubit, rather than two qubits. We then determine excited states using the quantum subspace expansion method. We showcase these algorithms on quantum hardware using up to 8 qubits and employing readout and gate error mitigation techniques. Our results demonstrate a successful application of quantum computing in the simulation of active-space electronic wavefunctions of substituted aromatic heterocycles, and outline challenges to be overcome in elucidating the optical properties of organic molecules with hybrid quantum-classical algorithms.

GRAPHICAL ABSTRACT

Keywords:

• Quantum computation
• electronic excited states
• aromatic heterocycles

Acknowledgments

We gratefully acknowledge Jake Lishman, Doug McClure, Paul Nation, Pedro Rivero-Ramirez, Matt Riedemann, and Jessie Yu for generous help and guidance in carrying out simulation on quantum hardware.

Disclosure statement

No potential conflict of interest was reported by the author(s).