Few-photon coherent nonlinear optics with a single molecule

TL;DR

This paper demonstrates coherent nonlinear spectroscopy of a single molecule using continuous-wave illumination, showing efficient photon-molecule coupling and potential for quantum information applications.

Contribution

It presents the first observation of nonlinear optical effects at the single-molecule level under continuous-wave excitation, highlighting organic molecules' potential for quantum technologies.

Findings

Efficient photon-molecule coupling achieved in a tight focus.

Laser beam switching with fewer than ten pump photons.

Potential for organic molecules in quantum information processing.

Abstract

The pioneering experiments of linear spectroscopy were performed using flames in the 1800s, but nonlinear optical measurements had to wait until lasers became available in the twentieth century. Because the nonlinear cross section of materials is very small, usually macroscopic bulk samples and pulsed lasers are used. Numerous efforts have explored coherent nonlinear signal generation from individual nanoparticles or small atomic ensembles with millions of atoms. Experiments on a single semiconductor quantum dot have also been reported, albeit with a very small yield. Here, we report on coherent nonlinear spectroscopy of a single molecule under continuous-wave single-pass illumination, where efficient photon-molecule coupling in a tight focus allows switching of a laser beam by less than a handful of pump photons nearly resonant with the sharp molecular transition. Aside from their fundamental importance, our results emphasize the potential of organic molecules for applications such as quantum information processing, which require strong nonlinearities.