Spontaneous emission, in which an excited electron lowers its energy by emitting a photon, is a fundamental process in light-matter interactions. In principle, the electron can relax from the excited state to any unoccupied lower energy level. In practice, however, most of these transitions are too slow and so are effectively forbidden. Rivera et al. show theoretically that the plasmonic excitations associated with two-dimensional materials can be used to enhance and control the light-matter interaction. Transitions that were once considered forbidden can thus be accessed, opening up the entire spectrum of an optical emitter.
The diversity of light-matter interactions accessible to a system is limited by the small size of an atom relative to the wavelength of the light it emits, as well as by the small value of the fine-structure constant. We developed a general theory of light-matter interactions with two-dimensional systems supporting plasmons. These plasmons effectively make the fine-structure constant larger and bridge the size gap between atom and light. This theory reveals that conventionally forbidden light-matter interactions--such as extremely high-order multipolar transitions, two-plasmon spontaneous emission, and singlet-triplet phosphorescence processes--can occur on very short time scales comparable to those of conventionally fast transitions. Our findings may lead to new platforms for spectroscopy, sensing, and broadband light generation, a potential testing ground for quantum electrodynamics (QED) in the ultrastrong coupling regime, and the ability to take advantage of the full electronic spectrum of an emitter.
Vibrational energy transfer (VET) between solute molecules is generally unfavorable in liquids because of weak intermolecular forces. Xiang et al. measured the two-dimensional infrared spectrum of a molecular mixture, W(CO)6 and W(13CO)6, with saturated concentrations in a binary solvent embedded in an optical microcavity. This experiment showed that the VET between the asymmetric stretch vibrations of two solute molecules is enhanced via polaritonic intermediate states formed by a strong coupling with the cavity mode. The efficiency is modulated by the cavity lifetime, which provides an opportunity to control the VET process in the liquid phase. This could lead to various practical implementations.
The maker of an ultra-efficient light-powered AI chip, Lightmatter recently announced that it will be investing $11 million in the production of the industry's first chip to take advantage of the unique properties of light for enabling fast and efficient inference and training engines. Recently Stan Reiss from Matrix and Santo Politi from Spark have joined the company's board of directors.