What would happen if only photons existed?

21.11.2014 13:28

Physicists transfer information from a photon to an atom

Thorsten Mohr Press office of the Saarland University
University of Saarland

A working group of Saarbrücken physicists has succeeded in demonstrating the transfer of information from a single photon to a single atom. The method is based on the controlled quantum mechanical superposition of light absorption events, which the researchers at the “Quantum Photonics” chair of Professor Jürgen Eschner recently developed (http://idw-online.de/de/news602341). A single light quantum (a photon) transfers its polarization state to a single atom; the atom, in turn, signals successful transmission with another emitted light particle. The results have now been published in Nature Communications.

In the quantum world, light consists of the smallest, no longer divisible units, the light quanta or photons. However, a single photon can still carry information in the form of its polarization, i.e. its direction of oscillation. There are basically two opposite polarization states, horizontal and vertical. In addition, however, all superimpositions of these states are allowed, so an infinite number of polarizations are possible overall. Individual photons are therefore very suitable carriers for the transmission of quantum information. The disadvantage: the light particles are, however, quite volatile. In order to store your information, it has to be transferred to another quantum mechanical system, such as a single atom. Unfortunately, when individual atoms and photons are brought together, such a conversion is very unlikely to happen. Jürgen Eschner's researchers have now presented a procedure that nevertheless allows this storage with great reliability.

The physicists work with a single atom, which is held freely floating in space with electric fields (in a so-called "Paul trap"). The atom absorbs a single photon from a laser beam, which carries information in the form of its polarization. After absorption, the atomic state is determined, i.e. the information that the atom contains. The researchers found that the information from the photon was stored in the atom with a very low error rate: each polarization is converted into a corresponding state of the atom.

“What is special about the experiment is that the atom signals that it has been successfully stored by emitting a photon, so we can differentiate between successful and unsuccessful attempts,” comments Christoph Kurz, who was responsible for this experiment, on the result. Although only a fraction of the individual attempts are successful, the stored information is reliably available in the atom, for example to be further processed with laser pulses and read out again later.

Jürgen Eschner adds: “The overlay in which the quantum information is located is only preserved if the emitted photon reveals the storage that has taken place, but not the stored polarization. Our trick is therefore to ensure that the atom always sends out the same signal for all different polarizations of the photon. In this way, all overlays are also reliably saved. "

Building blocks like this atom-photon interface will be of great importance in the future when information technology is miniaturized down to the scale of individual particles (atoms for storing, photons for sending information) and the quantum mechanical properties of these particles are to be exploited. One expects special computing power and particularly secure information transmission from this.

The article "Experimental protocol for high-fidelity heralded photon-to-atom quantum state transfer" was published in Nature communications on November 21, 2014 (DOI: 10.1038 / ncomms6527)

Additional Information:
Prof. Dr. Jürgen Eschner
Tel .: (0681) 30258016
Email: [email protected]

Christoph Kurz
Tel .: (0681) 30270378
Email: [email protected]

Additional Information:


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Information technology, physics / astronomy
Research results, scientific publications