# Quantum Computation of Electronic Transitions using a Variational Quantum Eigensolver

## TL;DR

This paper introduces MC-VQE, an extension of VQE, enabling efficient quantum computation of molecular electronic transition energies and oscillator strengths, demonstrated through simulation of a photosynthetic complex's absorption spectrum.

## Contribution

The paper presents a novel multistate, contracted VQE algorithm that efficiently computes multiple excited states and transition properties of molecules on quantum computers.

## Key findings

- Successfully simulated absorption spectrum of a complex light-harvesting system.
- Demonstrated the ability to compute transition energies and oscillator strengths.
- Extended VQE to handle multiple states simultaneously.

## Abstract

We develop an extension of the variational quantum eigensolver (VQE) algorithm - multistate, contracted VQE (MC-VQE) - that allows for the efficient computation of the transition energies between the ground state and several low-lying excited states of a molecule, as well as the oscillator strengths associated with these transitions. We numerically simulate MC-VQE by computing the absorption spectrum of an ab initio exciton model of an 18-chromophore light-harvesting complex from purple photosynthetic bacteria.