A group of researchers from Pisa, Jyväskylä, San Sebastian and MIT have demonstrated how a heterostructure consisting of superconductors and magnets can be used to create unidirectional current like that found in semiconductor diodes.
These novel superconductor diodes, however, operate at much lower temperatures than their semiconductor counterparts and are therefore useful in quantum technologies.
The current state of affairs, however, is a bit more complicated. While quantum computers have officially gone from theory to fact—a remarkable achievement—none are yet practical.
To realize a useful quantum computer, Google, IBM, Microsoft, Amazon, and others are pouring resources into machines that run on a menagerie of qubits. The most popular approach, favored by Google and IBM, involves tiny loops of superconducting wire. Honeywell and IonQ are pursuing atomic qubits made of trapped ions. Researchers in China are building intricate, Rube-Goldberg-like machines on lab benches to run quantum computations with mirrors and light.
The quantum race is anything but settled, and as outlined in a paper published this week in Nature, there’s a new horse on the track. Instead of superconducting loops, ions, or photons, a team of scientists led by the Department of Energy’s Argonne National Laboratory, made qubits from single electrons.
Computational detective work by U.S. and German physicists has confirmed that cerium zirconium pyrochlore is a 3D quantum spin liquid.
Despite the name, quantum spin liquids are solid materials in which quantum entanglement and the geometric arrangement of atoms frustrate the natural tendency of electrons to magnetically order themselves in relation to one another. The geometric frustration in a quantum spin liquid is so severe that electrons fluctuate between quantum magnetic states no matter how cold they become.
Theoretical physicists routinely work with quantum mechanical models that manifest quantum spin liquids, but finding convincing evidence that they exist in actual physical materials has been a decades-long challenge. While a number of 2D or 3D materials have been proposed as possible quantum spin liquids, Rice University physicist Andriy Nevidomskyy has said there’s no established consensus among physicists that any of them qualify.
Less than a millionth of a billionth of a second long, attosecond X-ray pulses allow researchers to peer deep inside molecules and follow electrons as they zip around and ultimately initiate chemical reactions.
Scientists at the Department of Energy’s SLAC National Accelerator Laboratory devised a method to generate X-ray laser bursts lasting hundreds of attoseconds (or billionths of a billionth of a second) in 2018. This technique, known as X-ray laser-enhanced attosecond pulse generation (XLEAP), enables researchers to investigate how electrons racing about molecules initiate key processes in biology, chemistry, materials science, and other fields.
“Electron motion is an important process by which nature can move energy around,” says SLAC scientist James Cryan. “A charge is created in one part of a molecule and it transfers to another part of the molecule, potentially kicking off a chemical reaction. It’s an important piece of the puzzle when you start to think about photovoltaic devices for artificial photosynthesis, or charge transfer inside a molecule.”
Circa 2015 o.o!
The publication of Green and Schwarz’s paper “was 30 years ago this month,” the string theorist and popular-science author Brian Greene wrote in Smithsonian Magazine in January, “making the moment ripe for taking stock: Is string theory revealing reality’s deep laws? Or, as some detractors have claimed, is it a mathematical mirage that has sidetracked a generation of physicists?” Greene had no answer, expressing doubt that string theory will “confront data” in his lifetime.
Recently, however, some string theorists have started developing a new tactic that gives them hope of someday answering these questions. Lacking traditional tests, they are seeking validation of string theory by a different route. Using a strange mathematical dictionary that translates between laws of gravity and those of quantum mechanics, the researchers have identified properties called “consistency conditions” that they say any theory combining quantum mechanics and gravity must meet. And in certain highly simplified imaginary worlds, they claim to have found evidence that the only consistent theories of “quantum gravity” involve strings.
According to many researchers, the work provides weak but concrete support for the decades-old suspicion that string theory may be the only mathematically consistent theory of quantum gravity capable of reproducing gravity’s known form on the scale of galaxies, stars and planets, as captured by Albert Einstein’s theory of general relativity. And if string theory is the only possible approach, then its proponents say it must be true — with or without physical evidence. String theory, by this account, is “the only game in town.”
Circa 2014 o.o!
When someone mentions “different dimensions,” we tend to think of things like parallel universes – alternate realities that exist parallel to our own, but where things work or happened differently. However, the reality of dimensions and how they play a role in the ordering of our Universe is really quite different from this popular characterization.
To break it down, dimensions are simply the different facets of what we perceive to be reality. We are immediately aware of the three dimensions that surround us on a daily basis – those that define the length, width, and depth of all objects in our universes (the x, y, and z axes, respectively).
Beyond these three visible dimensions, scientists believe that there may be many more. In fact, the theoretical framework of Superstring Theory posits that the universe exists in ten different dimensions. These different aspects are what govern the universe, the fundamental forces of nature, and all the elementary particles contained within.
A theoretical study shows that long-range entanglement can indeed survive at temperatures above absolute zero, if the correct conditions are met.
Quantum computing has been earmarked as the next revolutionary step in computing. However current systems are only practically stable at temperatures close to absolute zero. A new theorem from a Japanese research collaboration provides an understanding of what types of long-range quantum entanglement survive at non-zero temperatures, revealing a fundamental aspect of macroscopic quantum phenomena and guiding the way towards further understanding of quantum systems.
When things get small, right down to the scale of one-thousandth the width of a human hair, the laws of classical physics get replaced by those of quantum physics. The quantum world is weird and wonderful, and there is much about it that scientists have yet to understand. Large-scale or “macroscopic” quantum effects play a key role in extraordinary phenomena such as superconductivity, which is a potential game-changer in future energy transport, as well for the continued development of quantum computers.
The development of experimental platforms that advance the field of quantum science and technology (QIST) comes with a unique set of advantages and challenges common to any emergent technology. Researchers at Stony Brook University, led by Dominik Schneble, PhD, report the formation of matter-wave polaritons in an optical lattice, an experimental discovery that permits studies of a central QIST paradigm through direct quantum simulation using ultracold atoms. The scientists project that their novel quasiparticles, which mimic strongly interacting photons in materials and devices but circumvent some of the inherent challenges, will benefit the further development of QIST platforms that are poised to revolutionize computing and communication technology.
The research findings are detailed in a paper published in the journal Nature Physics.
The study sheds light on fundamental polariton properties and related many-body phenomena, and it opens up novel possibilities for studies of polaritonic quantum matter.
The physics of the microrealm involves two famous and bizarre concepts: The first is that prior to observation, it is impossible to know with certainty the outcome of a measurement on a particle; rather the particle exists in a “superposition” encompassing multiple mutually exclusive states. So a particle can be in two or more places at the same time, and you can only calculate the probability of finding it in a certain location when you look. The second involves “entanglement,” the spooky link that can unite two objects, no matter how far they are separated. Both superposition and entanglement are described mathematically by quantum theory. But many physicists believe that the ultimate theory of reality may lie beyond quantum theory. Now, a team of physicists and mathematicians has discovered a new connection between these two weird properties that does not assume that quantum theory is correct. Their study appears in Physical Review Letters.
“We were really excited to find this new connection that goes beyond quantum theory because the connection will be valid even for more exotic theories that are yet to be discovered,” says Ludovico Lami, a member of the physics think-tank, the Foundational Questions Institute, FQXi, and a physicist at the University of Ulm, in Germany. “This is also important because it is independent of the mathematical formalism of quantum theory and uses only notions with an immediate operational interpretation,” he adds. Lami co-authored the study with Guillaume Aubrun of Claude Bernard University Lyon 1, in France, Carlos Palazuelos, of the Complutense University of Madrid, in Spain, and Martin Plávala, of Siegen University, in Germany.
While quantum theory has proven to be supremely successful since its development a century ago, physicists have struggled to unify it with gravity to create one overarching “theory of everything.” This suggests that quantum theory may not be the final word on describing reality, inspiring physicists to hunt for a more fundamental framework. But any such ultimate theory must still incorporate superposition, entanglement, and the probabilistic nature of reality, since these features have been confirmed time and again in lab tests. The interpretation of these experiments does not depend on quantum theory being correct, notes Lami.
Abstract: Spin-two particles appear in the spectra of both open and closed string theories. We studied a graviton and massive symmetric rank-two tensor in string theory, both of which carry spin two. A graviton is a massless spin-two particle in closed string theory while a symmetric rank-two tensor is a massive particle with spin two in open string theory. Using Polyakov’s string path integral formulation of string scattering amplitudes, we calculated cubic interactions of both spin-two particles explicitly, including $\ap$-corrections (string corrections). We observed that the cubic interactions of the massive spin-two particle differed from those of the graviton. The massive symmetric rank-two tensor in open string theory becomes massless in the high energy limit where $\ap \rightarrow \infty$ and $\ap$-correction terms, containing higher derivatives, dominate: In this limit the local cubic action of the symmetric rank-two tensor of open string theory coincides with that of the graviton in closed string theory.
From: Taejin Lee [view email].