Entering the quantum Internet at the speed of light

Posted by Thomas Anderson

A team of Innsbruck University physicists have managed to directly transfer the quantum information stored in an atom onto a particle of light - theoretically allowing data to be sent over optical fiber to a distant atom.

"Thanks to the strange laws of quantum mechanics, quantum computers would be able to carry out certain computational tasks much faster than conventional computers," explained Andreas Stute and Bernardo Casabone, both PhD students at the University of Innsbruck’s Institute for Experimental Physics.

"Among the most promising technologies for the construction of a quantum-computer are systems of single atoms, confined in so-called ion traps and manipulated with lasers. In the laboratory, these systems have already been used to test key building blocks of a future quantum computer."

Although Stute and Casabone confirm they can conduct successful quantum computations with atoms, the team, led by Rainer Blatt and Tracy Northup, is still missing viable interfaces with which quantum information can be transferred over optical channels from one computer to another.

Indeed, what makes the construction of these interfaces especially challenging is that the laws of quantum mechanics don’t allow quantum information to be simply copied.

Instead, a future quantum internet – that is, a network of quantum computers linked by optical channels – would have to transfer quantum information onto individual particles of light, known as photons. These photons would then be transported over an optical-fiber link to a distant computing site.

Nevertheless, quantum information - for the very first time - has been directly transferred from an atom in an ion trap onto a single photon.

"We use a laser to write the desired quantum information onto the electronic states of the atom," said Stute.

"The atom is then excited with a second laser, and as a result, it emits a photon. At this moment, we write the atom’s quantum information onto the polarization state of the photon, thus mapping it onto the light particle."

The photon is stored between the mirrors until it eventually flies out through one mirror, which is less reflective than the other.

"The two mirrors steer the photon in a specific direction, effectively guiding it into an optical fiber," Casabone added.

"The quantum information stored in the photon could thus be conveyed over the optical fiber to a distant quantum computer, where the same technique could be applied in reverse to write it back onto an atom."