Analog quantum simulation of non-Condon effects in molecular spectroscopy

TL;DR

This paper introduces a linear optical method for simulating non-Condon effects in molecular spectra, enabling the approximation of non-unitary operations beyond the Condon regime with high accuracy.

Contribution

It presents the first implementation of non-Condon effects in analog quantum simulation using linear optics, expanding the capabilities of quantum spectral simulations.

Findings

Successfully simulated vibronic spectra of naphthalene, phenanthrene, and benzene.

Achieved quadratically small truncation errors in non-Condon operation approximations.

Demonstrated the potential for simulating arbitrary non-unitary operations in quantum systems.

Abstract

In this work, we present a linear optical implementation for analog quantum simulation of molecular vibronic spectra, incorporating the non-Condon scattering operation with a quadratically small truncation error. Thus far, analog and digital quantum algorithms for achieving quantum speedup have been suggested only in the Condon regime, which refers to a transition dipole moment that is independent of nuclear coordinates. For analog quantum optical simulation beyond the Condon regime (i.e., non-Condon transitions) the resulting non-unitary scattering operations must be handled appropriately in a linear optical network. In this paper, we consider the first and second-order Herzberg-Teller expansions of the transition dipole moment operator for the non-Condon effect, for implementation on linear optical quantum hardware. We believe the method opens a new way to approximate arbitrary non-unitary operations in analog and digital quantum simulations. We report in-silico simulations of the vibronic spectra for naphthalene, phenanthrene, and benzene to support our findings.