For the very first time, scientists at Stanford University have successfully managed to send messages, using photons, between two electrons present almost 2 km (or 1.2 miles) apart. According to the team, being able to send a pair of “entangled” particles over long distances is indeed a major feat, especially since it could lead to the development of near-unhackable quantum communication networks; something that governments, military and banks are tirelessly looking for.
Described by Albert Enstein as “spooky action”, quantum entanglement refers to a physical phenomenon, in which two or more particles are inextricably connected irrespective of the distance separating them. For instance, in case of entangled electrons, when one of the electrons is spun in a particular direction, the other electron in the pair behaves in much the same way, even if it is located at the opposite end of the universe. The Stanford team explains the phenomenon in the following way:
It’s as if you spun a quarter in New York clockwise, an entangled second coin in Los Angeles would start to spin clockwise. And likewise, if you spun that quarter counter-clockwise, the second coin would shift its spin as well.
In the past, scientists have been able to use quantum entanglement, in order to transmit messages over long distances. To be able to carry such information, however, the entangled electrons first need to be brought together, before being taken apart. This poses a major problem, especially when trying to set up communication networks between thousands of electrons. In the new research, recently published in the Nature Communications journal, the scientists have managed to send messages between electrons that have never actually met.
To that end, the researchers adopted an incredibly innovative technique known as quantum correlation, in which a pair of photons is correlated with the electrons. As a result, the entangled photons act as messengers of the electrons’ spin. Previously, a team of Stanford scientists have been able to send messages, using entangled photons, through fiber optic cables several feet in length. Transmitting information over long distances has, until now, proved difficult because photons are known to change their orientation (i.e. polarization) while travelling through optical fibers. When that happens, the message that the photon was carrying also gets lost. Leo Yu, a postdoctoral scholar at Stanford and the study’s leader, said:
Electron spin is the basic unit of a quantum computer. This work can pave the way for future quantum networks that can send highly secure data around the world.
As part of the current research, the team has managed to send messages over a distance of 2 km (around 1.2 miles), using correlated photons. By creating a time-stamp, the researchers were able to correlate the photon’s arrival time with the spin of the electron. To transmit information, the scientists first established a correlation between two photons and two electrons, with each of the pairs situated at either end of a 2 km-long optical fiber. When sent through the cable, the two photons were made to meet in the middle at a “beam splitter” and interact, thus conveying the message in the process. The team explained:
Photons do not normally interact, just two flashlights beams passing through one another, so the researchers had to mediate this interaction called the ‘two-photon interference’.
Photons possessing different characteristics usually do not interact with each other. Consequently, the scientists had to pass the photons through a contraption called “quantum down-converter”, which in turn matched their wavelengths. The device also shifted the photons to a wavelength that allowed them to travel farther inside the fiber optic cables, thus ensuring better interaction. Speaking about the project, Yu said:
Quantum supercomputers promise to be exponentially faster and more powerful than traditional computers, and can communicate with immunity to hacking or spying. With this work, the team has brought the quantum networks one step closer to reality.
Via: Stanford University