Entangling Two Photons Serving Two Distinct Purposes. Diligent efforts at the U.S. National Institute of Standards and Technology have produced entangled photons of two different wavelengths. The image below and the following explanation sum up this creative device.
By carefully engineering the geometry of a micrometer-scale, ring-shaped resonator, researchers at NIST produced pairs of entangled photons (particles of light) that have two very different colors or wavelengths. Light from a pump laser (purple regions in the resonator) generates one photon in each pair at a visible-light wavelength (red patches in and around resonator); the other photon has a wavelength in the telecommunications (near-infrared) part of the spectrum (blue patches). From the perspective of quantum communication, these pairings combine the best of both worlds in an optical circuit: The visible-light partner can interact with trapped atoms, ions, or other systems that serve as quantum versions of computer memory, while the telecommunications wavelength member of each couple is free to propagate over long distances through an optical fiber network. (Credit: S. Kelley/NIST)