Single-molecule optomechanics in “picocavities”

TLDR

Trapping light with noble metal nanostructures overcomes the diffraction limit, confining light to volumes around 30 cubic nanometers. This work establishes a foundation for nanoscale nonlinear quantum optics at the single‑molecule level. Atomic features in the plasmonic gap are dynamically formed and disassembled by laser irradiation, and while unstable at room temperature, they can be stabilized at cryogenic temperatures to allow prolonged probing of single‑atom cavities. Individual atomic features in the plasmonic gap can localize light to sub‑1‑nm volumes, creating picocavities that enable atomic‑scale optical experiments and provide a 10^6‑fold enhancement of optomechanical coupling to individual molecular bond vibrations.

Abstract

Trapping light with noble metal nanostructures overcomes the diffraction limit and can confine light to volumes typically on the order of 30 cubic nanometers. We found that individual atomic features inside the gap of a plasmonic nanoassembly can localize light to volumes well below 1 cubic nanometer ("picocavities"), enabling optical experiments on the atomic scale. These atomic features are dynamically formed and disassembled by laser irradiation. Although unstable at room temperature, picocavities can be stabilized at cryogenic temperatures, allowing single atomic cavities to be probed for many minutes. Unlike traditional optomechanical resonators, such extreme optical confinement yields a factor of 106 enhancement of optomechanical coupling between the picocavity field and vibrations of individual molecular bonds. This work sets the basis for developing nanoscale nonlinear quantum optics on the single-molecule level.