Quantum entanglement occurs when two separate entities become strongly linked in a way that cannot be explained by classical physics; it is a powerful resource in quantum communication protocols and advanced technologies that aim to exploit the enhanced capabilities of quantum systems. To date, entanglement has generally been limited to microscopic quantum units such as pairs or multiples of single ions, atoms, photons, and so on. Kotler et al. and Mercier de Lépinay et al. demonstrate the ability to extend quantum entanglement to massive macroscopic systems (see the Perspective by Lau and Clerk). Entanglement of two mechanical oscillators on such a large length and mass scale is expected to find widespread use in both applications and fundamental physics to probe the boundary between the classical and quantum worlds.

Science, this issue p. 622, p. 625; see also p. 570

Quantum entanglement of mechanical systems emerges when distinct objects move with such a high degree of correlation that they can no longer be described separately. Although quantum mechanics presumably applies to objects of all sizes, directly observing entanglement becomes challenging as masses increase, requiring measurement and control with a vanishingly small error. Here, using pulsed electromechanics, we deterministically entangle two mechanical drumheads with masses of 70 picograms. Through nearly quantum-limited measurements of the position and momentum quadratures of both drums, we perform quantum state tomography and thereby directly observe entanglement. Such entangled macroscopic systems are poised to serve in fundamental tests of quantum mechanics, enable sensing beyond the standard quantum limit, and function as long-lived nodes of future quantum networks.

Particle physics is a field of extremes. Scales always have 10^{really big number} associated. Some results from the Large Hadron Collider Beauty (LHCb) experiment have recently been reported that are statistically significant, and they may have profound implications for the Standard Model, but it might also just be a numbers anomaly, and we won’t get to find out for a while. Let’s dive into the basics of quantum particles, in case your elementary school education is a little rusty.

A new discovery led by Princeton University could upend our understanding of how electrons behave under extreme conditions in quantum materials. The finding provides experimental evidence that this familiar building block of matter behaves as if it is made of two particles: one particle that gives the electron its negative charge and another that supplies its magnet-like property, known as spin.

“We think this is the first hard evidence of spin-charge separation,” said Nai Phuan Ong, Princeton’s Eugene Higgins Professor of Physics and senior author on the paper published this week in the journal Nature Physics.

The experimental results fulfill a prediction made decades ago to explain one of the most mind-bending states of matter, the quantum spin liquid. In all materials, the spin of an electron can point either up or down. In the familiar magnet, all of the spins uniformly point in one direction throughout the sample when the temperature drops below a critical temperature.

An international research team led by the University of Cologne has succeeded for the first time in connecting several atomically precise nanoribbons made of graphene, a modification of carbon, to form complex structures. The scientists have synthesized and spectroscopically characterized nanoribbon heterojunctions. They then were able to integrate the heterojunctions into an electronic component. In this way, they have created a novel sensor that is highly sensitive to atoms and molecules. The results of their research have been published under the title Tunneling current modulation in atomically precise graphene nanoribbon heterojunctions’ in Nature Communications. The work was carried out in close cooperation between the Institute for Experimental Physics with the Department of Chemistry at the University of Cologne, as well as with research groups from Montreal, Novosibirsk, Hiroshima, and Berkeley. It was funded by the German Research Foundation (DFG) and the European Research Council (ERC).

The heterojunctions of graphene nanoribbons are just one nanometer—one millionth of a millimeter—wide. Graphene consists of only a single layer of carbon atoms and is considered the thinnest material in the world. In 2010, researchers in Manchester succeeded in making single-atom layers of graphene for the first time, for which they won the Nobel Prize. The graphene nanoribbon heterojunctions used to make the sensor are each seven and fourteen carbon atoms wide and about 50 nanometres long. What makes them special is that their edges are free of defects. This is why they are called atomically precise nanoribbons, explained Dr. Boris Senkovskiy from the Institute for Experimental Physics. The researchers connected several of these nanoribbon heterojunctions at their short ends, thus creating more complex heterostructures that act as tunneling barriers.

The heterostructures were investigated using angle-resolved photoemission, optical spectroscopy, and scanning tunneling microscopy. In the next step, the generated heterostructures were integrated into an electronic device. The electric current flowing through the nanoribbon heterostructure is governed by the quantum mechanical tunneling effect. This means that under certain conditions, electrons can overcome existing energy barriers in atoms by ‘tunneling,’ so that a current then flows even though the barrier is greater than the available energy of the electron.