Optical fibers may transport quantum information

Ashley N. Rice, ashley.rice@photonics.com

Optical fibers, which transport data around the world, now may be able to carry quantum information, according to new research.

Rainer Blatt and Tracy Northup of the University of Innsbruck have directly transferred the quantum information stored in an atom onto a particle of light – theoretically enabling information to be sent over optical fibers 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. Among the most promising technologies for the construction of such a computer are single atoms confined in so-called ion traps and manipulated with lasers. These systems have already been used in labs to test key building blocks of a future quantum computer.

University of Innsbruck scientists have directly transferred the quantum information stored in an atom onto a particle of light – theoretically enabling information to be sent over optical fibers to a distant atom. The atom’s quantum information is written onto the polarization state of the photon.

“Currently, we can carry out successful quantum computations with atoms,” said doctoral candidate Andreas Stute of the university’s Institute for Experimental Physics. “But we are still missing viable interfaces with which quantum information can be transferred over optical channels from one computer to another.”

Constructing these interfaces is challenging because the laws of quantum mechanics don’t allow quantum information to be simply copied; rather, quantum information would have to be transferred onto individual photons and transported over an optical fiber link to a distant computing site.

In their experiment, the Innsbruck physicists trapped a calcium ion in an ion trap and positioned it between two highly reflective mirrors.

“We use a laser to write the desired quantum information onto the electronic states of the atom,” Stute said. “The atom is then excited with a second laser, and as a result, it emits a photon.” As this happens, the atom’s quantum information is written onto the polarized state of the photon, which is stored between the mirrors until it flies out of the trap and into the optical fiber.

“The two mirrors steer the photon in a specific direction, effectively guiding it into an optical fiber,” said doctoral student Bernardo Casabone, also of the Institute for Experimental Physics.

The researchers believe that quantum information stored in the photon could be sent to a distant quantum computer, where the same technique could be applied in reverse to write it back onto an atom.

The research, supported by the Austrian Science Funds and by the European Union, was published in Nature Photonics (doi: 10.1038/nphoton.2012.358).