# Quantum algorithm for calculating molecular vibronic spectra

## TL;DR

This paper introduces a quantum algorithm for calculating molecular vibronic spectra, effectively handling anharmonicity and preserving state information, which are challenging for classical methods, with potential applications in material design.

## Contribution

The authors develop a quantum algorithm that naturally includes vibrational anharmonicity and maintains state information post-measurement, advancing quantum spectral calculations in chemistry.

## Key findings

- Numerical analysis of truncation errors in harmonic approximation for triatomic molecules.
- Application of the algorithm to anharmonic spectra of sulfur dioxide.
- Potential for future material design and broader spectral calculations.

## Abstract

We present a quantum algorithm for calculating the vibronic spectrum of a molecule, a useful but classically hard problem in chemistry. We show several advantages over previous quantum approaches: vibrational anharmonicity is naturally included; after measurement, some state information is preserved for further analysis; and there are potential error-related benefits. Considering four triatomic molecules, we numerically study truncation errors in the harmonic approximation. Further, in order to highlight the fact that our quantum algorithm's primary advantage over classical algorithms is in simulating anharmonic spectra, we consider the anharmonic vibronic spectrum of sulfur dioxide. In the future, our approach could aid in the design of materials with specific light-harvesting and energy transfer properties, and the general strategy is applicable to other spectral calculations in chemistry and condensed matter physics.