Scientists were able to get two quantum memories entangled over 50 km (31 miles) of fiber optic cables– over 40 times the past record– bringing the idea of faster and super-secure quantum internet more possible.
Quantum communication depends on quantum entanglement, where two particles become inseparably linked and reliant on each other despite being separated.
Meanwhile, quantum memory is the quantum equivalent of classical computing memory– the capability to store quantum data and keep it for later.
Quantum networks would need to span around the globe in order to be most functional. In the new study, researchers entangled two quantum memories using particles of light that were plied across a longer distance than ever before.
"The main significance of this paper lies in extending the entangling distance in [optical] fiber between quantum memories to the city scale," said lead researcher Jian-Wei Pan of the University of Science and Technology of China (USTC), whose paper was published in Nature journal.
The entangled quantum memories, although physically situated near one another, needed photons to detour either 22 or 50 km (14 to 31 miles) through optical fibers to generate the entanglement.
The quantum memories were first entangled with photons, and then after traveling for kilometers, the photons were made to hinder one another and then measured.
As a result, the interaction caused two memories to become entangled, indicating that quantum memories can go the distance.
According to study co-author Dr. Xiao Hui Bao also from USTC, "the main technology advance lies in developing an efficient atom-photon entanglement source that is suitable for low-loss transmission in fibers."
The team's output is an "absolutely formidable achievement," according to Australian National University physicist Ben Buchler. "The level of complexity and the things that they've done to make this work are just absolutely mind-boggling."
"Entanglement of two quantum memories via fibres over dozens of kilometres" – Yu, Y. et al – Nature – DOI: 10.1038/s41586-020-1976-7
A quantum internet that connects remote quantum processors should enable a number of revolutionary applications such as distributed quantum computing. Its realization will rely on entanglement of remote quantum memories over long distances. Despite enormous progress, at present the maximal physical separation achieved between two nodes is 1.3 kilometres, and challenges for longer distances remain. Here we demonstrate entanglement of two atomic ensembles in one laboratory via photon transmission through city-scale optical fibres. The atomic ensembles function as quantum memories that store quantum states. We use cavity enhancement to efficiently create atom–photon entanglement and we use quantum frequency conversion to shift the atomic wavelength to telecommunications wavelengths. We realize entanglement over 22 kilometres of field-deployed fibres via two-photon interference and entanglement over 50 kilometres of coiled fibres via single-photon interference. Our experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the atomic quantum network, paving the way towards establishing atomic entanglement over many nodes and over much longer distances.
Featured image credit: geralt/Pixabay
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