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Category: particle physics – Page 290

A sheet of magic-angle twisted bilayer graphene can host novel topological phases of matter, a study has revealed.

Magic-angle twisted , first discovered in 2018, is made from two sheets of graphene (a form of carbon consisting of a single layer of atoms in a honeycomb-like lattice pattern), layered atop one another, with one sheet twisted at precisely 1.05 degrees with respect to the other. The resulting bilayer has unusual electronic properties: for example, it can be made into an insulator or a superconductor depending on how many electrons are added.

The discovery launched a new field of research into magic-angle twisted graphene, known as “twistronics.” At Caltech, Stevan Nadj-Perge, assistant professor of applied physics and , has been among the researchers leading the charge: in 2019, he and his colleagues directly imaged the electronic properties of magic-angle twisted graphene at atomic-length scales; and in 2020, they demonstrated that superconductivity in twisted can exist away from the magic angle when coupled to a two-dimensional semiconductor.

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Electrons inhabit a strange and topsy-turvy world. These infinitesimally small particles have never ceased to amaze and mystify despite the more than a century that scientists have studied them. Now, in an even more amazing twist, physicists have discovered that, under certain conditions, interacting electrons can create what are called ‘topological quantum states.’ This finding, which was recently published in the journal Nature, has implications for many technological fields of study, especially information technology.

Topological states of matter are particularly intriguing classes of quantum phenomena. Their study combines quantum physics with topology, which is the branch of theoretical mathematics that studies geometric properties that can be deformed but not intrinsically changed. Topological quantum states first came to the public’s attention in 2016 when three scientists—Princeton’s Duncan Haldane, who is Princeton’s Thomas D. Jones Professor of Mathematical Physics and Sherman Fairchild University Professor of Physics, together with David Thouless and Michael Kosterlitz—were awarded the Nobel Prize for their work in uncovering the role of topology in electronic materials.

“The last decade has seen quite a lot of excitement about new topological quantum states of electrons,” said Ali Yazdani, the Class of 1909 Professor of Physics at Princeton and the senior author of the study. “Most of what we have uncovered in the last decade has been focused on how electrons get these topological properties, without thinking about them interacting with one another.”

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In Einstein’s theory of general relativity, gravity arises when a massive object distorts the fabric of spacetime the way a ball sinks into a piece of stretched cloth. Solving Einstein’s equations by using quantities that apply across all space and time coordinates could enable physicists to eventually find their “white whale”: a quantum theory of gravity.

In a new article in The European Physical Journal H 0, Donald Salisbury from Austin College in Sherman, USA, explains how Peter Bergmann and Arthur Komar first proposed a way to get one step closer to this goal by using Hamilton-Jacobi techniques. These arose in the study of particle motion in order to obtain the complete set of solutions from a single function of particle position and constants of the motion.

Three of the four —strong, weak, and electromagnetic—hold under both the ordinary world of our everyday experience, modeled by , and the spooky world of quantum physics. Problems arise, though, when trying to apply to the fourth force, gravity, to the quantum world. In the 1960s and 1970s, Peter Bergmann of Syracuse University, New York and his associates recognized that in order to someday reconcile Einstein’s of with the quantum world, they needed to find quantities for determining events in space and time that applied across all frames of reference. They succeeded in doing this by using the Hamilton-Jacobi techniques.

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A team of researchers from Nanjing University of Posts and Telecommunications and the Chinese Academy of Sciences in China and Nanyang Technological University and the Agency for Science Technology and Research in Singapore developed an artificial neuron that is able to communicate using the neurotransmitter dopamine. They published their creation and expected uses for it in the journal Nature Electronics.

As the researchers note, most machine-brain interfaces rely on as a communications medium, and those signals are generally one-way. Electrical signals generated by the brain are read and interpreted; signals are not sent to the brain. In this new effort, the researchers have taken a step toward making a that can communicate in both directions, and it is not based on electrical signals. Instead, it is chemically mediated.

The work involved building an artificial neuron that could both detect the presence of dopamine and also produce dopamine as a response mechanism. The neuron is made of graphene (a single sheet of carbon atoms) and a carbon nanotube electrode (a single sheet of carbon atoms rolled up into a tube). They then added a sensor capable of detecting the presence of dopamine and a device called a memristor that is capable of releasing dopamine using a heat-activated hydrogel, attached to another part of their artificial neuron.

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A new method for shaping matter into complex shapes, with the use of ‘twisted’ light, has been demonstrated in research at the University of Strathclyde.

When are cooled to temperatures close to absolute zero (−273 degrees C), they stop behaving like particles and start to behave like waves.

Atoms in this condition, which are known as Bose–Einstein condensates (BECs), are useful for purposes such as realization of atom lasers, slow light, quantum simulations for understanding the complex behavior of materials like superconductors and superfluids, and the precision measurement technique of atom interferometry.

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If we could harness fusion to generate electricity, it would be one of the most efficient and least polluting sources of energy possible.

A major breakthrough in nuclear fusion has been confirmed a year after it was achieved at a laboratory in California.

Researchers at Lawrence Livermore National Laboratory’s (LLNL’s) National Ignition Facility (NIF) recorded the first case of ignition on August 8, 2021, the results of which have now been published in three peer-reviewed papers.

Nuclear fusion is the process that powers the Sun and other stars: heavy hydrogen atoms collide with enough force that they fuse together to form a helium atom, releasing large amounts of energy as a by-product. Once the hydrogen plasma “ignites”, the fusion reaction becomes self-sustaining, with the fusions themselves producing enough power to maintain the temperature without external heating.

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A research team succeeded in executing the world’s fastest two-qubit gate (a fundamental arithmetic element essential for quantum computing) using a completely new method of manipulating, with an ultrafast laser, micrometer-spaced atoms cooled to absolute zero temperature. For the past two decade.

“ data-gt-translate-attributes=’[{“attribute”:” data-cmtooltip”, “format”:” html”}]’quantum computing ) using a completely new method of manipulating, with an ultrafast laser, micrometer-spaced atoms cooled to absolute zero.

Absolute zero is the theoretical lowest temperature on the thermodynamic temperature scale. At this temperature, all atoms of an object are at rest and the object does not emit or absorb energy. The internationally agreed-upon value for this temperature is −273.15 °C (−459.67 °F; 0.00 K).

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Astronomers have long sought the launch sites for some of the highest-energy protons in our galaxy. Now a study using 12 years of data from NASA’s Fermi Gamma-ray Space Telescope confirms that one supernova remnant is just such a place.

Fermi has shown that the of exploded stars boost particles to speeds comparable to that of light. Called , these particles mostly take the form of protons, but can include atomic nuclei and electrons. Because they all carry an electric charge, their paths become scrambled as they whisk through our galaxy’s magnetic field. Since we can no longer tell which direction they originated from, this masks their birthplace. But when these particles collide with interstellar gas near the supernova remnant, they produce a telltale glow in gamma rays—the highest-energy light there is.

“Theorists think the highest-energy cosmic ray protons in the Milky Way reach a million billion electron volts, or PeV energies,” said Ke Fang, an assistant professor of physics at the University of Wisconsin, Madison. “The precise nature of their sources, which we call PeVatrons, has been difficult to pin down.”

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