Controlling Light with a Single Photon via Electron Avalanches

Light is the gold standard for high-speed communication and computing due to its low power consumption and rapid propagation. However, a major hurdle has been the weak optical nonlinearity of standard materials, making it difficult to control light with light at ultra-low intensities. A new study surmounts this by demonstrating all-optical modulation of the refractive index in silicon using just single photons.

The key mechanism involves an 'electron avalanche' process. When a single photon strikes the material, it triggers a cascade of electrons, drastically altering the material's optical properties. This method yields a nonlinear refractive index orders of magnitude higher than the best-known nonlinear optical materials. Crucially, this allows for gigahertz-frequency optical switching on chips at room temperature. This breakthrough could revolutionise on-chip photonic and quantum devices, enabling the precise control of light without the need for high-intensity lasers.