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Mission impossible? Stopping light for tiny fractions of a second

A team of scientists can halt individual photons and release them at the push of a button. Their technique could be used for various applications like bug-proof communication.

Fundamental Research

Being able to stop light and harness its incredible speed could be the key to developing super-powerful quantum computers, connecting them to high-speed, high-capacity quantum networks, as well as developing more precise sensors and bug-proof communication. But can you stop light, the fastest thing in the universe? Supported by the EU-funded LIMQUET project, a team of scientists has stopped light for tiny fractions of a second and released it at the push of a button. The scientists could even halt individual light particles, or photons, “which are used in quantum technology as information carriers”, as noted in a news item on the website of LIMQUET project partner Technical University of Darmstadt (TU Darmstadt). They see light as an intriguing candidate for quantum computing because it can rapidly transfer data between two points along optical fibre networks. With photons interacting weakly with the outside environment, information that is being transmitted is kept intact. However, to harness the potential of light, scientists need to make photons interact strongly with each other, which they don’t naturally do. The news item states: “In future quantum computers, photons will for example have to transfer their information to atoms and vice versa. To [t]his end too, the interaction between the two types of particles must be intensified, which the photons stopped by the group from the TU Darmstadt could make possible.” As explained in the same news item, the researchers utilise “a special glass fibre with a hollow channel in the centre with a diameter of less than ten thousandths of a millimetre. The fibre has a porous structure round the core that keeps light at bay. This causes a laser beam to concentrate in the centre of the hollow channel. Its cross-section narrows to around one thousandth of a millimetre.” The news item adds that the team uses “the light beam as a kind of trap for atoms. They introduce atoms of rubidium into the hollow fibre, which concentrate in the centre of the laser beam due to electromagnetic forces. The researchers then send the photons they want to stop into the channel.” The photon comes to a complete stop by two extra laser beams “that are guided into the hollow fibre on both sides.”

Quantum information processing

The researchers have recently published their findings in the journal ‘Optics Express’. They state: “An experimental platform operating at the level of individual quanta and providing strong light-matter coupling is a key requirement for quantum information processing. In our work, we show that hollow-core photonic bandgap fibers filled with laser-cooled atoms might serve as such a platform, despite their typical complicated birefringence properties. To this end, we present a detailed theoretical and experimental study to identify a fiber with suitable properties to achieve operation at the single-photon level.” The ongoing LIMQUET (Light-Matter Interfaces for Quantum Enhanced Technology) project trains high-level young researchers within a network that consists of academic and industrial partners from Bulgaria, France, Germany, Switzerland and the United Kingdom. It focuses on “the development of innovative techniques to interface light and matter at the quantum level using atoms, nanostructures and photons, with applications in optics and quantum information processing,” as noted on the project website. For more information, please see: LIMQUET project website

Keywords

LIMQUET, quantum computing, photon, quantum information processing, optics

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