Controlling Photons for Use in Quantum Computing

Feb 13, 2007 feature

“Quantum information science makes use of the quantum nature of particles to perform computation,” Gerhard Rempe explains to “One approach is to use single particles of light – photons – as the basis of the computer, storing information in a property of the light such as its polarization. To do this, you need a source able to produce photons under full control.”

Rempe, a Director at Germany’s Max Planck Institute for Quantum Optics, and a team of fellow scientists believe they have solved the problem of producing and controlling photons by using an optical cavity.

Rempe and his colleagues, Doctors Wilk, Webster and Specht at the Max Planck Institute, and Doctor Kuhn at the University of Oxford, have completed an experiment in which they were able to control the direction of a photon emitted from an atom, and its polarization. “This represents a great single-photon source that we can control,” Rempe says. The team details the results of the ground breaking experiment in a paper that appears in Physical Review Letters with the title, “Polarization-Controlled Single Photons.”

In the experiment, laser pulses were used to make a single atom emit photons in a stream. “Typically, if you excite an atom and it emits a photon, you can’t control the direction it is emitted in,” Rempe explains. He describes, in an email, an optical cavity, consisting of a pair of mirrors facing each other. These mirrors are separated by a distance of only 1 mm, and used to set the direction of the emitted photons. “The cavity influences the atom so that photons it produces are likely to be emitted in a direction perpendicular to the surface of the mirrors,” Rempe says. “Once emitted, a photon bounces between the mirrors thousands of times before passing through one of them to escape into the laboratory in a known direction.”

Rempe admits that the generation of single photons inside an optical cavity has been demonstrated before. But this new experiment adds another layer to the work done before. Rempe’s group takes the control demonstrated in prior optical cavity experiments one step further by being able to determine the polarization of the photons produced. A magnetic field is applied to the atom, allowing different polarizations to be produced, depending on the frequency of the laser pulses used. So, not only can the direction of the photons be controlled, but it is now also possible to completely control all the photon’s degrees of freedom.

This, Rempe says, is only a first step towards using quantum processes for computing and communicating. He hopes that his team’s work can lead to additional advances in quantum information processing. “We should be able to extend our scheme to produce photons that are entangled with the internal state of the atom,” says Rempe. “This would be a first step towards creating a quantum network which would allow quantum information to be transferred between different laboratories.” He emphasizes that this new process “opens more possibilities in quantum information processing.”

By Miranda Marquit, Copyright 2007
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of

Explore further: New filter could advance terahertz data transmission

add to favorites email to friend print save as pdf

Related Stories

A transistor-like amplifier for single photons

Jul 29, 2014

Data transmission over long distances usually utilizes optical techniques via glass fibres – this ensures high speed transmission combined with low power dissipation of the signal. For quite some years ...

A quantum logic gate between light and matter

Apr 10, 2014

Scientists at Max Planck Institute of Quantum Optics, Garching, Germany, successfully process quantum information with a system comprising an optical photon and a trapped atom.

Seeing a photon without absorbing it

Nov 14, 2013

Light is of fundamental importance. It allows us to see the world around us and record pictures of our environment. It enables communication over long distances through optical fibers. All current methods ...

A 'Sisyphus' method for cooling trapped molecules

Nov 14, 2012

(—The investigation of ultracold molecules is of great interest for a number of problems. It could lead to a better understanding of chemical reactions in astrophysics. Ensembles of ultracold molecules ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

Top-precision optical atomic clock starts ticking

Feb 26, 2015

A state-of-the-art optical atomic clock, collaboratively developed by scientists from the University of Warsaw, Jagiellonian University, and Nicolaus Copernicus University, is now "ticking away" at the National ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.