Scientists entangle quantum memories over 50 km (31 miles), bringing super-secure quantum internet closer to reality


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.

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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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One Comment

  1. According to current mainstream physics, quantum entanglement is the process where seemingly pairs or groups of counter-intuitive matter instantly affects each other, for example, the measurement of one particle on Earth instantly affecting another particle at the opposite end of the universe. This is absolutely true, but at the same time it is not proof to the validity of quantum mechanics. Instead, it is proof to the continuity of magnetic fields throughout the Universe. If you subject an electron to a magnetic field, you affect its spin. And if that electron is entangled with another, then any time electron A changes its spin, electron B will react as well, even though it was never subjected to the magnetic field. In physical reality this makes a perfect sense, since magnetic fields are permanently present in the building blocks of matter.
    Quantum mystics came up with plenty of quantum magic, like virtual particles, quantum entanglement, renormalization, borrowing energy from the vacuum and so many others. These mystic notions are attempts to explain – and only superficially- observations on subatomic and cosmological scales that Newtonian physics can’t explain them. Anything human mind would imagine can be proven to be physically possible in quantum theory. The probability for any physical event is not zero. Because, based on its logic, events in nature are intrinsically probabilistic, not perfectly deterministic. Therefore, any physical phenomenal is possible even with the absurdly tiny probabilities. The probabilities that you can fly to Mars by only flapping your arms or putting the Sun in your pocket are not zero. So do not be surprised when you hear about Multiverse (or Meta-Universe), Parallel Universes or our Universe will become black hole and so many other dark myths and colorful fantasies. Quantum theory is the worst thing that happened to physics. It has become the ideal refuge for the creators of physics myths The theory should not be called quantum mechanics or quantum physics, but quantum mysticism, because it is based on metaphysical beliefs. Physics has been turned into mysticism, by using probability and infinity instead of using Causality- relationship between causes and effects-which is the most fundamental principle to all nature science, especially physics. However, the so-called Q. Entanglement is not proof to the validity of quantum mechanics. It is a misinterpreted physical effect. The misinterpretation of physical phenomena is a fundamental feature of quantum theory, because, it is not a causal theory. Theoreticians are referring to Heisenberg Uncertainty Principle (HUP). But, from a physics viewpoint, HUP itself is wrong. So many physicists who called themselves experts on quantum theory do not know the origin of HUP. This principle is based on a theorem in mathematical analysis (independent of physics). Namely, it came from the Hilbert space notion, of the Square-Integrable function. The theorem says that for any two complementary variables, there is a non-zero lower bound for the product of their standard deviations. In other words, the two variables cannot be measured concurrently with infinite accuracy. So it is clear that HUP is extracted from a theoretical mathematics, not from experimental findings or any physical observations. This principle which is in the heart of quantum theory must not be considered as a physics postulate or even as a mathematical physics notion, but rather as a metaphysics notion. More important, HUP violates the conservation law of energy. So, quantum theory does not only break causality, but also violates conservation laws of physics which our current technologies are based on. Thus, I am not surprised that recent pioneering experiments have found HUP to be incorrect. Scientists cast doubt on renowned uncertainty principle http://phys.org/news/2012-09-scientists-renowned-uncertainty-principle.html

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