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In the vast majority of superconducting materials, Cooper pairs have what is known as even parity, which essentially means that their wave function does not change when electrons swap spatial coordinates. Conversely, some unconventional superconductors have been found to contain odd-parity Cooper pairs. This quality makes these unconventional materials particularly promising for quantum computing applications.

Past studies have predicted that noncentrosymmetric superconductors, which have a crystal structure with no center of inversion, could exhibit unique and unusual properties. In recent years, noncentrosymmetric superconductors have become a popular topic of research due to the structure of the Cooper pairs contained within them, which have a mixture of odd and even parity.

CaPtAs is a new noncentrosymmetric superconductor discovered by researchers at Zhejiang University. Together with scientists at the Paul Scherrer Institut and other institutes worldwide, these researchers have recently carried out a study investigating unconventional superconductivity in this compound. Their paper, published in Physical Review Letters, offers evidence that in its superconducting state, CaPtAs simultaneously exhibits both nodal superconductivity and broken time-reversal symmetry (TRS).

The Micius satellite has enabled messages with unbreakable encryption to be sent 1,200km.

Researchers at Empa and EPFL have created one of the smallest motors ever made. It’s composed of just 16 atoms, and at that tiny size it seems to function right on the boundary between classical physics and the spooky quantum realm.

Like its macroscopic counterparts, this mini motor is made up of a moving part (the rotor) and a fixed part (the stator). The stator in this case is a cluster of six palladium atoms and six gallium atoms arranged in a rough triangular shape. Meanwhile, the rotor is a four-atom acetylene molecule, which rotates on the surface of the stator. The whole machine measures less than a nanometer wide.

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A research team from Empa and EPFL has developed a molecular motor which consists of only 16 atoms and rotates reliably in one direction. It could allow energy harvesting at the atomic level. The special feature of the motor is that it moves exactly at the boundary between classical motion and quantum tunneling — and has revealed puzzling phenomena to researchers in the quantum realm.

The smallest motor in the world—consisting of just 16 atoms: this was developed by a team of researchers from Empa and EPFL. “This brings us close to the ultimate size limit for molecular motors,” explains Oliver Gröning, head of the Functional Surfaces Research Group at Empa. The motor measures less than one nanometer—in other words it is around 100,000 times smaller than the diameter of a human hair.

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Now, the same researchers have achieved their goal of entanglement-based quantum cryptography using the Micius satellite. The scientists, who detailed their findings online in the 15 June edition of the journal Nature, say they again connected two observatories separated by 1,120 kilometers. But this time, the collection efficiency of the links was improved by up to four-fold, which resulted in data rates of about 0.12 bits per second.

A space-based, virtually unhackable quantum Internet may be one step closer to reality due to satellite experiments that linked ground stations more than 1,000 kilometers apart, a new study finds.

Quantum physics makes a strange effect known as entanglement possible. Essentially, two or more particles such as photons that get linked or “entangled” can influence each other simultaneously no matter how far apart they are.

Continue reading “Quantum Satellite Links Extend More Than 1,000 Kilometers” »

An exotic physical phenomenon known as a Kohn anomaly has been found for the first time in an unexpected type of material by researchers at MIT and elsewhere. They say the finding could provide new insights into certain fundamental processes that help determine why metals and other materials display the complex electronic properties that underlie much of today’s technology.

The way electrons interact with phonons—which are essentially vibrations passing through a crystalline material —determines the physical processes that take place inside many electronic devices. These interactions affect the way metals resist electric current, the temperature at which some materials suddenly become superconductors, and the very low temperature requirements for quantum computers, among many other processes.

But electron-phonon interactions have been difficult to study in detail because they are generally very weak. The new study has found a new, stronger kind of unusual electron-phonon interaction: The researchers induced a Kohn anomaly, which was previously thought to exist only in metals, in an exotic material called a topological Weyl semimetal. The finding could help shed light on important aspects of the complex interplay between electrons and phonons, they say.

Quantum key distribution (QKD)^1,2,3 is a theoretically secure way of sharing secret keys between remote users. It has been demonstrated in a laboratory over a coiled optical fibre up to 404 kilometres long^4,5,6,7. In the field, point-to-point QKD has been achieved from a satellite to a ground station up to 1,200 kilometres away^8,9,10. However, real-world QKD-based cryptography targets physically separated users on the Earth, for which the maximum distance has been about 100 kilometres^11,12. The use of trusted relays can extend these distances from across a typical metropolitan area^13,14,15,16 to intercity¹⁷ and even intercontinental distances¹⁸. However, relays pose security risks, which can be avoided by using entanglement-based QKD, which has inherent source-independent security^19,20. Long-distance entanglement distribution can be realized using quantum repeaters²¹, but the related technology is still immature for practical implementations²². The obvious alternative for extending the range of quantum communication without compromising its security is satellite-based QKD, but so far satellite-based entanglement distribution has not been efficient²³ enough to support QKD. Here we demonstrate entanglement-based QKD between two ground stations separated by 1,120 kilometres at a finite secret-key rate of 0.12 bits per second, without the need for trusted relays. Entangled photon pairs were distributed via two bidirectional downlinks from the Micius satellite to two ground observatories in Delingha and Nanshan in China. The development of a high-efficiency telescope and follow-up optics crucially improved the link efficiency. The generated keys are secure for realistic devices, because our ground receivers were carefully designed to guarantee fair sampling and immunity to all known side channels^24,25. Our method not only increases the secure distance on the ground tenfold but also increases the practical security of QKD to an unprecedented level.

To create large quantum networks, researchers will first need to develop efficient quantum repeaters. A key component of these repeaters are quantum memories, which are the quantum-mechanical equivalents of more conventional computer memories, such as random-access memories (RAM).

Ideally, a quantum memory should be able to retain information for substantial periods of time, store true quantum states, read out data efficiently and operate at low-loss telecommunication wavelengths. While research teams have made great progress in the development of quantum memories, no solution proposed so far has been able to meet all of these requirements simultaneously.

With this in mind, researchers at Delft University of Technology (TU Delft) set out to develop a new mechanical quantum memory with sufficiently long storage times, a high readout efficiency, and the ability to operate at telecom wavelengths. The memory they devised, presented in a paper published in Nature Physics, could ultimately enable the practical implementation of mechanical systems with quantum effects developed in their previous works.