A quantum memory node is a tiny diamond with a defect that can store and emit single photons. But its light has a wavelength of 637 nanometers, the same red as a ruby, and is almost completely absorbed after just a few meters of standard optical fiber. For long-distance communication, you need a 'translator' that repaints the photon into the infrared telecom range, where glass is nearly transparent.
Scientists assembled a compact frequency converter right in the fiber. Inside is a periodically poled lithium niobate crystal that acts like a grating: the incoming photon 'slides' along it and exits at 1588 nanometers, suitable for transmission over hundreds of kilometers. The device, about the size of a matchbox, converts roughly one in eleven photons, and pump noise is suppressed to 154 counts per second — quieter than a whisper in an empty room.
Such a converter is key to the quantum internet. The authors calculated that even after 100 kilometers of fiber, the entanglement between the nitrogen-vacancy spin in the diamond and the transmitted photon would persist with an accuracy above 52 percent. This means quantum repeaters can be built from off-the-shelf fiber components, without laying new lines.
Light at 637 nanometers is the same red we see in rubies, while 1588 nanometers is invisible to the eye and lies in the near-infrared, where optical fiber is most transparent.
In 'Star Trek', subspace is used for long-range communication, but here it's just a change in photon color, yet the effect is the same: information arrives without loss.