Modeling singlet fission on a quantum computer

TL;DR

This paper demonstrates the use of quantum computing to model singlet fission in a simple H4 molecule, employing strategies to reduce computational costs and achieve results aligning with theoretical energy requirements.

Contribution

It introduces practical quantum computing strategies for modeling singlet fission, including qubit tapering, measurement optimization, and parallel execution on real hardware.

Findings

Results meet energetic criteria for singlet fission

Quantum results agree with exact transition energies

Outperform classical computational methods

Abstract

We present a use case of practical utility of quantum computing by employing a quantum computer in the investigation of the linear H$_4$ molecule as a simple model to comply with the requirements of singlet fission. We leverage a series of independent strategies to bring down the overall cost of the quantum computations, namely 1) tapering off qubits in order to reduce the size of the relevant Hilbert space; 2) measurement optimization via rotations to eigenbases shared by groups of qubit-wise commuting (QWC) Pauli strings; 3) parallel execution of multiple state preparation + measurement operations, implementing quantum circuits onto all 20 qubits available in the Quantinuum H1-1 quantum hardware. We report results that satisfy the energetic prerequisites of singlet fission and which are in excellent agreement with the exact transition energies (for the chosen one-particle basis), and much superior to classical methods deemed computationally tractable for singlet fission candidates