Researchers demonstrate control over the Josephson diode effect in a device that connects two superconducting materials with a topological insulator.
Category: computing
Put a nanodiamond under intense pressure and it becomes flexible
Diamond is among the hardest naturally occurring substances on Earth, but if you shrink it down to the nanoscale, it is surprisingly elastic. And that could be useful for a host of applications such as quantum computing. In a paper published in the journal Physical Review X, Chongxin Shan at Zhengzhou University in China and colleagues studied diamonds as small as four nanometers across to see how they respond to pressure.
Scientists already know that nanodiamonds, which are thousands of times smaller than a grain of sand, can survive being stretched or squeezed in ways that destroy a regular diamond. But nobody knew how.
So the team placed individual nanodiamonds (ranging from 4 to 13 nanometers across) inside a transmission electron microscope between two diamond indenters and compressed them. These were connected to a sensor that measured how strongly each nanodiamond resisted being squeezed while a high-resolution camera imaged diamond atoms as they moved. The researchers backed up their observations with computer simulations.
Laser bursts flip nanoscale magnetic vortices at blistering speeds, opening a path to brain-like spintronics
Spintronics are devices that operate leveraging the spin, an intrinsic form of angular momentum, of electrons. The ability to switch magnetic states is central to the functioning of these devices, as it ultimately allows them to represent binary digits (i.e., “0” and “1”) when processing or storing information.
Some of these devices rely on magnetic vortices, nanoscale whirlpool-like patterns of magnetization that influence the alignment of spins. These vortices possess a property known as helicity, which is essentially the direction in which they rotate.
Reliably switching the helicity of magnetic vortices could open new possibilities for both neuromorphic computing systems, devices that mimic the brain’s neural organization, and multi-state memories. So far, however, this has proved challenging, mainly because it requires a synchronized wave-like rotation of spins without disrupting the geometric structure of vortices.
Pressure-tuned quantum spin liquid-like behavior observed in material Y-kapellasite
A quantum spin liquid is a phase of matter in which the magnetic moments in a material do not align or freeze, even at temperatures close to absolute zero (i.e., at 0 K). The experimental realization of this highly dynamic state could have important implications for the development of quantum computers and other technologies that operate leveraging quantum mechanical effects.
Previous studies have collected evidence that a quantum spin liquid phase emerges in various materials, including herbertsmithite, α-RuCl3, and EtMe3Sb[Pd(dmit)2]2. However, so far none of these materials have been conclusively confirmed to host this state.
Researchers at University Paris-Saclay-CNRS, University of Stuttgart and other institutes in Europe gathered evidence of quantum spin liquid-like behavior in a recently discovered material called Y-kapellasite. Their paper, published in Physical Review Letters, shows that this material is a promising experimental platform for studying exotic states of matter, particularly those driven by quantum magnetism.
ATLAS acts as a cosmic-ray laboratory with first measurement of proton–oxygen collisions
Tens of kilometers above Earth’s surface, high-energy particles from outer space constantly strike the atmosphere, creating showers of energetic secondary particles that rain down from the sky. Approximately one of these particles passes through your head every second, but the “cosmic rays” that produce them are still not fully understood. In a recent paper posted to the arXiv preprint server, the ATLAS Collaboration describes how its first measurement of proton–oxygen collisions at the LHC could help us learn more about them.
Cosmic rays were discovered over a century ago by physicist Victor Hess in experiments conducted aboard hot-air balloons. Today, astrophysicists use detectors on the ground to image cosmic-ray showers and computer simulations of the showers to understand that data.
However, these simulations depend on properties of the strong force—one of the fundamental forces of the universe—which is difficult to accurately model. Current simulations disagree with one another, making it difficult for astrophysicists to interpret their measurements of cosmic rays.
Universal Quantum Computing as a Markov Chain
Let’s say you have a probabilistic computer with a single bit of memory. Some algorithms on the computer will stochastically flip the single bit of memory such that its new value will be uniformly distributed with a 50% chance of being 0 and a 50% chance of being 1. Other programs will place it into a degenerate distribution, meaning it either has 100% chance of being 0 every time you run the program, or other programs will produce 1 100% of the time.
A magician tells you to run one of the programs in one of the two categories of your choosing and then copy the computer’s memory state onto a thumb drive and hand it to him. You pick one, run the program, copy the bit of the memory to your thumb drive, then hand it to the magician. The magician then does something with the thumb drive you cannot see, then looks up at you and tell you exactly what category the program you ran to produce that bit came from.
Curious, you repeat this many times over: you run a program from one of the two categories (degenerate or uniform), copy the bit value produced from the algorithm, and then hand the thumb drive to the magician. Each and every time he always correctly guesses which category of program was ran to produce it.
A long-sought quantum computing milestone arrives as fermionic atom gates top 99% accuracy
Two independent research teams have each demonstrated collisional quantum gates using fermionic atoms: a long-sought milestone in quantum computing where logic operations are performed through the direct physical overlap of atoms, rather than forcing them into fragile, highly excited states.
The studies have been published simultaneously in Nature: the first led by Petar Bojović at the Max Planck Institute for Quantum Optics in Garching, Germany, and the second by Yann Kiefer and colleagues at ETH Zurich, Switzerland.
Two paths to scalable quantum computing: Optical links between fridges and higher-temperature qubits
Superconducting qubits—bits of quantum information—have been widely considered a promising technology for moving quantum computing forward. But there’s still much work to be done before they can be brought out of a near absolute zero temperature environment. The lab of Professor Hong Tang has recently published two studies that advance the technology.
To solve practical problems, quantum processors need a lot of qubits—up to thousands to millions. Such a large number of qubits requires significantly complex wiring and a way to store them at a temperature colder than deep space. This is complicated by the physical size of the cryogenic devices, known as dilution refrigerators, that maintain qubits at a temperature just above absolute zero. In a study published in Nature Photonics, Tang’s research team has found a way around this obstacle.
A flexible and cost-effective solution is to build a quantum network by connecting qubits inside separate refrigerators. Connecting qubits with standard coaxial cables, however, wouldn’t work if those cables were kept in a room temperature environment. And storing them all in one very cold room would be near impossible. Even under an optimistic assumption of 1,000 qubits per refrigerator, scaling to 1 million qubits would require linking 1,000 refrigerators—an arrangement that is physically impractical within a single room.
Why ultrashort laser pulses could make low-power electron sources far more practical
A new theoretical study finds shorter laser pulses achieve higher quantum efficiency for photoemission from a solid surface without increasing power or intensity. Using light to knock electrons loose from a surface—known as photoemission—may soon be achievable more easily in smaller labs with smaller lasers. Shortening the length of a laser pulse can increase the emitted electrons by several orders of magnitude without increasing the laser intensity or power, according to a University of Michigan Engineering study.
The study is published in Physical Review Research.
Efficient, low-power photoemission could make particle acceleration and high-resolution imaging techniques to visualize cells and atoms more accessible. It could also help researchers develop lightwave electronics, which use light to move charge carriers, for ultrafast computing.
Each protein in the epigenome produces a different pattern of gene expression, study finds
A new study finds the proteins responsible for controlling which genes are expressed in a genome do more than simply turn a gene on or off. Essentially, each type of protein that interacts with a gene produces different behaviors—a finding with ramifications for everything from biomedical therapeutics to biological computing. A paper on the study, “Epigenome Regulators Imbue a Single Eukaryotic Promoter with Diverse Gene Expression Dynamics,” is published in the journal iScience.
At issue are “epigenome regulators.” Every organism’s genome is made up of DNA. But that DNA is bound up with many different proteins into very compact structures. The proteins that are bound to the DNA are called the epigenome, and they control which parts of the DNA get expressed. Your blood cells, nerve cells, and skin cells all have the same DNA, but perform very different functions. That’s because different parts of the DNA sequence are being expressed in each cell—and that is largely controlled by which proteins are bound to different parts of the DNA in each cell.
“We already knew that the proteins in the epigenome control the way DNA is expressed,” says Albert Keung, corresponding author of the study and an associate professor of chemical and biomolecular engineering at North Carolina State University. “Our goal here was to look at a single gene and quantify the full range of ways that the gene could be expressed by different proteins.” Keung is the Goodnight Distinguished Scholar in Innovation in Biotechnology and Biomolecular Engineering and director of biotechnology programs in NC State’s Integrative Sciences Initiative.