# Complete elimination of nonlinear light-matter interactions with broadband ultrafast laser pulses

## TL;DR

This paper presents a theoretical method to completely eliminate nonlinear light-matter interactions using optimized broadband ultrafast laser pulses, enabling pure single-photon absorption in quantum systems.

## Contribution

It introduces a novel multi-objective optimization algorithm to design spectral phases that suppress nonlinear effects, achieving linear response and maximizing single-photon absorption.

## Key findings

- Linear response achieved across all transition probabilities
- Nonlinear optical responses can be fully suppressed
- Enhanced control over quantum light-matter interactions

## Abstract

The absorption of a single photon that excites a quantum system from a low to a high energy level is an elementary process of light-matter interaction, and a route towards realizing pure single-photon absorption has both fundamental and practical implications in quantum technology. Due to nonlinear optical effects, however, the probability of pure single-photon absorption is usually very low, which is particularly pertinent in the case of strong ultrafast laser pulses with broad bandwidth. Here we demonstrate theoretically a counterintuitive coherent single-photon absorption scheme by eliminating nonlinear interactions of ultrafast laser pulses with quantum systems. That is, a completely linear response of the system with respect to the spectral energy density of the incident light at the transition frequency can be obtained for all transition probabilities between 0 and 100% in a multi-level quantum systems. To that end, a new multi-objective optimization algorithm is developed to find an optimal spectral phase of an ultrafast laser pulse, which is capable of eliminating all possible nonlinear optical responses while maximizing the probability of single-photon absorption between quantum states. This work not only deepens our understanding of light-matter interactions, but also offers a new way to study photophysical and photochemical processes in the "absence" of nonlinear optical effects.