Giant Leaps for Quantum Networks

For decades, large-scale quantum communication has been little more than a pipe dream. But scientists have recently overcome a number of hurdles to bring quantum networks closer to reality than ever before.

Quantum communication relies on a property called “entanglement” in which two photons transfer information between each other instantaneously, even over large distances. Although it’s not completely understood, entanglement has been demonstrated between particles separated by over 1,200 kilometers. In addition to speed, entangled photons create an unhackable system of data transmittal because any attempt to eavesdrop or intercept information would decouple the particles. This hampers long-distance communication, prompting researchers to place repeaters at set distances along the path, but this introduced other issues.

The first is that repeaters can only handle limited amounts of data. To address this, one team has developed a way to create a ready supply of entangled photons to handle as much data as needed. The second major problem is that repeaters cannot store large amounts of information. However, using a glass jar of Cesium vapor and lasers, another team has successfully demonstrated the ability to store and retrieve information at room temperature. This process also extends the lifespan of the entangled particles so that repeaters are only needed every 50 kilometers rather than every 10 kilometers.

Finally, previous methods have been limited to the use of only two nodes at a time, which is not practical for a large-scale network. But it has now been demonstrated that a single photon can be entangled with multiple photons by splitting the signal into several different wavelengths, making it possible to connect several users at once.