Harvard researchers have succeeded in creating quantum switches that can be turned on and off using a single photon, a technological achievement that could pave the way for creating highly secure quantum networks.
Built from single atoms, the first-of-their-kind switches could one day be networked via fiber-optic cables to form the backbone of a “quantum Internet” that allows for perfectly secure communications, said Professor of Physics Mikhail Lukin, who, together with Professor Vladan Vuletic of MIT, led a team consisting of graduate students Jeff Thompson and Lee Liu and postdoctoral fellows Tobias Tiecke and Nathalie de Leon to construct the new system. Their research is detailed in a recently published paper in the journal Nature.
“From a technical standpoint, it’s a remarkable accomplishment,” Lukin said of the advance. “Conceptually, the idea is very simple: Push the conventional light switch to its ultimate limit. What we’ve done here is to use a single atom as a switch that, depending on its state, can open or close the flow of photons … and it can be turned on and off using a single photon.”
Though the switches could be used to build a quantum computer, Lukin said it’s unlikely the technology will show up in the average desktop computer. Where it will be used, he said, is in creating fiber-optical networks that use quantum cryptography, a method for encrypting communications using the laws of quantum mechanics to allow for perfectly secure information exchanges. Such systems make it impossible to intercept and read messages sent over a network, because the very act of measuring a quantum object changes it, leaving behind telltale signs of the spying.
“It’s unlikely everyone would need this type of technology,” he said. “But there are some realistic applications that could someday have transformative impact on our society. At present, we are limited to using quantum cryptography over relatively short distances — tens of kilometers. Based on the new advance, we may eventually be able to extend the range of quantum cryptography to thousands of kilometers.”
Importantly, Tiecke said, their system is highly scalable, and could one day allow for the fabrication of thousands of such switches in a single device.