Researches prove viability of quantum internet

4 February 2013
By Edward Gent
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The atom’s quantum information is written onto the polarization state of the photon (Credit: Harald Ritsch)

The atom’s quantum information is written onto the polarization state of the photon (Credit: Harald Ritsch)

The quantum internet has moved a step closer after a research team transferred the quantum information stored in an atom onto a particle of light.

Many scientists believe the future of computing is in quantum computers as they are able to carry out certain computational tasks much faster than conventional computers and promising technologies their construction, such as single atoms, confined in so-called ion traps and manipulated with lasers, have been tested in the laboratory.

But designing interfaces to transfer information from one quantum computer to another has proved difficult as the laws of quantum mechanics don’t allow quantum information to be simply copied.

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

Now, for the first time, quantum information has been directly transferred from an atom in an ion trap onto a single photon. Such information could then be sent over optical fiber to a distant atom.

The work is reported in the current issue of Nature Photonics by a research team led by Tracy Northup and Rainer Blatt of the University of Innsbruck’s Institute for Experimental Physics.

To achieve the result the team first trap a single calcium ion in an ion trap and position it between two highly reflective mirrors.

“We use a laser to write the desired quantum information onto the electronic states of the atom,” explains Phd student Andreas 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.

Phd studetn Bernardo Casabone said: “The two mirrors steer the photon in a specific direction, effectively guiding it into an optical fibre.

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

Support for this research was provided by the Austrian Science Funds and by the European Union.

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