Researchers Reveal New Method For Entangling Photons
November 3, 2012

Researchers Reveal New Method For Entangling Photons

April Flowers for - Your Universe Online

A research team led by the University of Vienna has developed a new method for entangling single photons that gyrate in opposite directions. This is the first step towards entangling and twisting even macroscopic, spatially separated objects in two different directions, according to the team. The findings of this study have been published in the journal Science.

Quantum physics is the theory of lightweight objects such as atoms or photons, or exceptionally small units such as very small quantum numbers. Entanglement is one of the most fascinating phenomena found in quantum physics because entangled quanta of light behave as if able to influence each other even when they are spatially separated. Scientists have been trying to discover if entanglement is limited to tiny objects or very small quantum numbers since the early days of quantum physics.

The team, which included members from UV's Vienna Center for Quantum Science and Technology (VCQ) and the Institute for Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences, has taken the first steps towards testing quantum mechanical entanglement with rotating photons.

For example, think of two quantum mechanical figure skaters. One would have the uncanny ability to pirouette both clockwise and counter clockwise simultaneously. The direction of her rotations would be correlated with the movements of the second, entangled, skater — even if the two were in separate rinks on different continents. The faster they twirl, the larger the quantum number of their rotation direction. This is called the angular momentum.

"In our experiment, we entangled the largest quantum numbers of any kind of particle ever measured," declares Anton Zeilinger in a press release.

For about 20 years it has been common knowledge, at least theoretically, that there is no upper limit for the angular momentum of photons. Due to physical restrictions, previous experiments have been limited to very weak angular momentum and small quantum numbers. It is theoretically possible to create entanglement regardless of the strength of the angular momentum or the scale of its quantum number with this new experiment in Vienna.

"Only our limited technical means stop us from creating entanglement with twisted photons that could be sensed even with bare hands," states Robert Fickler.

Theoretically, though, the research team has demonstrated that it is possible to twirl the entangled ice dancers in both directions simultaneously. In practical terms, a number of major problems need to be overcome before such an experiment can be realized with macroscopic objects.

The research team also addresses the possible applications of their findings, as well as the fundamental issue of the limits of macroscopic entanglement. Created photons could be used for very precise angular measurements already at low intensities of light, for example. This would be a particular advantage when investigating light sensitive materials, for example with some biological substances.

Fickler goes on to explain in the release, "The special features of entanglement provide the fantastic possibility to perform such measurements from arbitrary distances and without any contact whatsoever with the measured object, or even at a point in time that lies in the future!"