The first system for reshaping the time-varying profiles of individual photons has been created by Olivier Morin and colleagues at the Max-Planck-Institute for Quantum Optics in Garching, Germany. The team manipulated a single trapped atom to emit and absorb photons with the desired shapes by fine-tuning the properties of a pulsed laser beam. Their demonstration could bring about important advances towards efficient exchange of quantum information.

A photon is a quantum of light that can be described as a packet of waves that travel through space. A photon’s wavefunction is spread out over time and the specific nature of that distribution is the photon’s temporal shape or mode.

Photons are used to exchange quantum information and the ability to control the temporal shape of photons could be used to boost the performance of quantum networks. However, the reliable creation of photons with specific temporal shapes is difficult and this has hampered developments of quantum communications networks, particularly those with many transmitters and receivers.

Rubidium atom

Now Morin’s team has tackled this problem by coming up with a way of reshaping the temporal modes of single photons before they reached a receiver. Their scheme involves trapping a single atom of rubidium within an optical cavity and having the atom interact with individual information-carrying photons prior to the photons hitting a receiver. A pulsed laser beam causes that atom to absorb a photon with one temporal shape and then emit a photon with a different temporal shape that is compatible with the receiver.

Using this technique, Morin and colleagues were able to change the temporal width of an individual photon from 0.5 ms to 0.5 µs – shrinking the width by a factor of one thousand. They were also able to change the width back to 0.5 ms. This makes their set-up the first-ever demonstration of the complete, flexible and accurate control of time-dependent wavefunctions of single photons, over several orders of magnitude.

Morin and colleagues say that their technique could become an important tool for creating distributed quantum information systems in the future. The researchers envisage applications including all-optical quantum communications systems. In the most imaginative scenarios, photon-reshaping devices could even become crucial components of nonlocal quantum clouds, which would support the rapid exchange of quantum information.

The research is described in Physical Review Letters.