A new day, a new quantum computing record broken. In new research, physicists from Stanford were able to entangle two electrons that were located two kilometers (1.2 miles) from each other.
Usually, entangled particles are created together and then separated, but in this case, the electrons were entangled using two messenger photons that carried the properties of each electron in a phenomenon called quantum correlation. The two photons are then sent down an optical fiber and are forced to interact in the middle. The combination of quantum correlation and photon interaction made the electrons entangled.
In very simplistic terms, the two electrons are like spinning tops. If the two tops are entangled when you make one rotate clockwise, the second one will start rotating clockwise as well. In the experiment, the photons are created in such a way that they are correlated to the electron's spin; when the photons interfere, the spin of the two electrons becomes the same.
"Electron spin is the basic unit of a quantum computer," Leo Yu, lead author of the research, said in a statement. "This work can pave the way for future quantum networks that can send highly secure data around the world.”
To make the long-distance entanglement possible, the team had to make sure the photons moving through the optical fiber didn't lose their quantum correlation. To guarantee this didn’t happen, the photons were given a time stamp – this gave the team a reference to know which photon was correlated to which electron.
Keeping the photons correlated was only half the battle. The researchers also had to make sure the two photons would interact and produce the “two-photon interference.” Photons don’t normally interact, so the scientists forced the interference by using a “quantum down-converter” that matched the wavelengths (i.e. colors) of the two photons. When photons have the same wavelength, they can be "added" together, and by doing so, the electrons are linked.
Entanglement is one of the cornerstones of quantum computing. Being able to produce long-distance entanglement pairs could allow for communication that cannot be hacked or spied upon. This work has jumped another hurdle in the road to a working quantum network.
The paper is published in Nature Communications.
