Photon-Powered PCs Proposed

A new theory uses nonlinear optics to create the photon transistors necessary to drive future quantum computers.

Incredibly fast supercomputers that can solve extremely complicated tasks have long been a dream for researchers, but there are some serious obstacles to achieving that goal. One of them is the transistors, which are the systems that process the signals. Today the signal used is an electric current, but a quantum computer uses an optical signal. Today we can send information via an optic cable and each bit comprises millions of photons. In quantum optics, each bit is just one photon, the smallest component of light.

Two photons are sent through a nanowire toward an atom, where they collide, allowing one photon (red) to transfer its information to the other.(Image courtesy Anders Søndberg Sørensen, University of Copenhagen)

"To work, the photons have to meet and 'talk,' and the photons very rarely interact together," said Anders Søndberg Sørensen, a quantum physicist and associate professor at the University of Copenhagen's Niels Bohr Institute. Researchers from the institute and from Harvard University developed the new theory.

Light doesn't function like in the movie "Star Wars," where people can fight with swords of light, he said. Instead, when two rays of light meet and cross, linear optics ensures that the rays go right through each other.

Sørensen wants to use nonlinear optics, which would allow the photons to collide and affect each other, but which is very difficult to accomplish. Photons are so small that one could never be directed to hit another unless they can be precisely controlled -- and that is the foundation of Sørensen's theory.

Instead of shooting two photons at each other from different directions and trying to get them to hit each other, Sørensen said he wants to use an atom as an intermediary. According to the laws of physics, the atom can only absorb one photon. But if you direct two photons toward the atom they will collide on the atom, which is what Sørensen said he wants to happen. However, the atom is very small and difficult to hit, meaning the photons have to be focused very precisely.

In a previous experiment, researchers discovered that microwaves could be focused on an atom via a superconducting nanowire, so they proposed that the same could happen with visible light. In Sørensen's theoretical model, which is a step toward building a phototransistor for a quantum computer, the atom is brought close to the nanowire. Two photons are sent toward the atom and when they hit it an interaction occurs between them, with one imparting information to the other. The information is sent in bits as either ones or zeros, and the order of digits produces the message. The photon has now received its message and the signal continues on its way.

The research was recently published in the journal Nature Physics.

For more information, visit: www.ku.dk/english/