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Wednesday, 20 October 2021

Physics Experiment Reveals Formation of a New State of Matter – Breaks Time-Reversal Symmetry


The central principle of superconductivity is that electrons form pairs. But can they also condense into foursomes? Recent findings have suggested they can, and a physicist at KTH Royal Institute of Technology today published the first experimental evidence of this quadrupling effect and the mechanism by which this state of matter occurs.

Reporting today in Nature Physics, Professor Egor Babaev and collaborators presented evidence of fermion quadrupling in a series of experimental measurements on the iron-based material, Ba1−xKxFe2As2. The results follow nearly 20 years after Babaev first predicted this kind of phenomenon, and eight years after he published a paper predicting that it could occur in the material.  

The pairing of electrons enables the quantum state of superconductivity, a zero-resistance state of conductivity which is used in MRI scanners and quantum computing. It occurs within a material as a result of two electrons bonding rather than repelling each other, as they would in a vacuum. The phenomenon was first described in a theory by, Leon Cooper, John Bardeen and John Schrieffer, whose work was awarded the Nobel Prize in 1972.

So-called Cooper pairs are basically “opposites that attract”. Normally two electrons, which are negatively-charged subatomic particles, would strongly repel each other. But at low temperatures in a crystal they become loosely bound in pairs, giving rise to a robust long-range order. Currents of electron pairs no longer scatter from defects and obstacles and a conductor can lose all electrical resistance, becoming a new state of matter: a superconductor. 

Only in recent years has the theoretical idea of four-fermion condensates become broadly accepted. 

For a fermion quadrupling state to occur there has to be something that prevents condensation of pairs and prevents their flow without resistance, while allowing condensation of four-electron composites, Babaev says.

The Bardeen-Cooper-Schrieffer theory didn’t allow for such behavior, so when Babaev’s experimental collaborator at Technische Universtät Dresden, Vadim Grinenko, found in 2018 the first signs of a fermion quadrupling condensate, it challenged years of prevalent scientific agreement.

What followed was three years of experimentation and investigation at labs at multiple institutions in order to validate the finding.

Babaev says that key among the observations made is that fermionic quadruple condensates spontaneously break time-reversal symmetry. In physics time-reversal symmetry is a mathematical operation of replacing the expression for time with its negative in formulas or equations so that they describe an event in which time runs backward or all the motions are reversed.

If one inverts time direction, the fundamental laws of physics still hold. That also holds for typical superconductors: if the arrow of time is reversed, a typical superconductor would still be the same superconducting state.

“However, in the case of a four-fermion condensate that we report, the time reversal puts it in a different state,” he says.

“It will probably take many years of research to fully understand this state," he says. "The experiments open up a number of new questions, revealing a number of other unusual properties associated with its reaction to thermal gradients, magnetic fields and ultrasound that still have to be better understood.”

Reference:

Vadim Grinenko, State with spontaneously broken time-reversal symmetry above the superconducting phase transition, Nature Physics (2021). DOI: 10.1038/s41567-021-01350-9

Scientists develop novel 'shapeshifting' liquid crystal


Physicists at Case Western Reserve University and Tufts University say they've changed the shape of a flat liquid crystal surface without applying any local stimulus—essentially remotely altering its physical appearance without touching it.

That's something that scientists have never done before, the researchers said. In doing so, they defied the gravitational force that ordinarily would cause a level plane to occur where liquid and surrounding air meet.

"This is a groundbreaking accomplishment and could prove to be the starting point for future applications—many which we cannot yet imagine," said Charles Rosenblatt, Ohio Eminent Scholar and professor of physics at Case Western Reserve, who is one of project's lead researchers. "Right now, this work is foundational, but it will be built upon by our team and others and new applications could someday become reality."

Previously, scientists who have similarly transformed the shape of liquid crystal surfaces have done so by using heat, light or some other kind of force applied directly to that otherwise undisturbed surface.

But this team took a new route, managing to change the liquid crystal surface simply by placing a "bumpy" or patterned substrate on the opposite side of a thin film in which the molecules are aligned in parallel. The result: an identically bumpy shape where there "should" be a flat, undisturbed surface.

The research team's findings were recently published in the journal Physical Review Letters and highlighted by the journal's editors for special attention.

Shapeshifting materials?

Future applications could lead to improvements in microchips and even the development of fluid microscopic tools that could perform repairs less invasively, flowing back into their original shape after use.

"Think of what water does when you put your hand into a bucket and take it back out: It returns to its original shape," said Andrew Ferris, a 2020 Case Western Reserve PhD in physics whose dissertation included this work and is now a staff physicist at Sandia National Laboratory in Albuquerque, New Mexico. "We could someday build tools that could do that." 

The scientists at Case Western Reserve and Tufts aren't the only ones pursuing malleable liquid crystal materials with multiple applications.

Scientists elsewhere are "already doing amazing things with liquid crystals," but always in response to a localized stimulus like heat or light, said Timothy Atherton, associate professor of physics at Tufts University and a former postdoctoral scholar and former visiting assistant professor at Case Western Reserve.

Atherton said this new work suggests an even more exotic application, one he acknowledged might even sound a bit far-fetched.

"Think 'Mystique' from X-Men—you know, shapeshifting," he said, referring to the super villain from the Marvel Comics and movies who can change her skin to look like any other person. "By doing what we've done, we've taken the first step toward altering the surface of something—maybe not skin, but other materials—without touching them or heating them."

How they did it

The scientists essentially manipulated what Rosenblatt called "an orientable Newtonian liquid," referring in this case to a nematic liquid crystal that behaves predictably, i.e., linearly, when an outside stimulus is applied. The nematic is a phase that consists of cigar-shaped molecules arranged parallel to each other, but which can flow like water.

To understand the significance, consider that when a glass is filled with water, the surface where the air and water meet is essentially flat. But in this case, the researchers forced the liquid crystal/air interface to change shape merely by exploiting the orientability of the molecules that comprise the liquid crystal.

To do that, the team placed the patterned substrate on the opposite side of a thin (a few hundred nanometers) nematic film. By doing so, they were able to control the alignment of molecules throughout the material. 

The result: the appearance of a predetermined "bumpy" surface where the liquid and air meet—accomplished without any stimulus at the surface and without any control  beyond the patterned "bottom" of the pool far from the surface. That relative change was huge, as much as a 30-70% increase in height from a flat surface.

Rosenblatt said the team will next work on fine-tuning the surface shape by applying an external electric field and varying temperature.

Team members also intend to study another liquid crystal phase called the "smectic phase," in which the molecules not only are oriented, but also form layers—like books on a bookshelf. Preliminary work suggests an even larger effect than the nematic phase, with much finer features, he said.

Reference: 

Andrew J. Ferris et al, Spontaneous Anchoring-Mediated Topography of an Orientable Fluid, Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.126.057803

Tuesday, 19 October 2021

Engineers make critical advance in quantum computer design


Quantum engineers from UNSW Sydney have removed a major obstacle that has stood in the way of quantum computers becoming a reality. They discovered a new technique they say will be capable of controlling millions of spin qubits—the basic units of information in a silicon quantum processor.

Until now, quantum computer engineers and scientists have worked with a proof-of-concept model of quantum processors by demonstrating the control of only a handful of qubits.

But with their latest research, published recently in Science Advances, the team have found what they consider "the missing jigsaw piece" in the quantum computer architecture that should enable the control of the millions of qubits needed for extraordinarily complex calculations.

Dr. Jarryd Pla, a faculty member in UNSW's School of Electrical Engineering and Telecommunications says his research team wanted to crack the problem that had stumped quantum computer scientists for decades—how to control not just a few but millions of qubits without taking up valuable space with more wiring, which uses more electricity and generates more heat.

"Up until this point, controlling electron spin qubits relied on us delivering microwave magnetic fields by putting a current through a wire right beside the qubit," Dr. Pla says.

"This poses some real challenges if we want to scale up to the millions of qubits that a quantum computer will need to solve globally significant problems, such as the design of new vaccines.

"First off, the magnetic fields drop off really quickly with distance, so we can only control those qubits closest to the wire. That means we would need to add more and more wires as we brought in more and more qubits, which would take up a lot of real estate on the chip."

And since the chip must operate at freezing cold temperatures, below -270°C, Dr. Pla says introducing more wires would generate way too much heat in the chip, interfering with the reliability of the qubits.

"So we come back to only being able to control a few qubits with this wire technique," Dr. Pla says.

Lightbulb moment

The solution to this problem involved a complete reimagining of the silicon chip structure.

Rather than having thousands of control wires on the same thumbnail-sized silicon chip that also needs to contain millions of qubits, the team looked at the feasibility of generating a magnetic field from above the chip that could manipulate all of the qubits simultaneously.

This idea of controlling all qubits simultaneously was first posited by quantum computing scientists back in the 1990s, but so far, nobody had worked out a practical way to do this, until now.

"First we removed the wire next to the qubits and then came up with a novel way to deliver microwave-frequency magnetic control fields across the entire system. So in principle, we could deliver control fields to up to four million qubits," says Dr. Pla.

Dr. Pla and the team introduced a new component directly above the silicon chip—a crystal prism called a dielectric resonator. When microwaves are directed into the resonator, it focuses the wavelength of the microwaves down to a much smaller size.

"The dielectric resonator shrinks the wavelength down below one millimeter, so we now have a very efficient conversion of microwave power into the magnetic field that controls the spins of all the qubits.

"There are two key innovations here. The first is that we don't have to put in a lot of power to get a strong driving field for the qubits, which crucially means we don't generate much heat. The second is that the field is very uniform across the chip, so that millions of qubits all experience the same level of control."

Quantum team-up

Although Dr. Pla and his team had developed the prototype resonator technology, they didn't have the silicon qubits to test it on. So he spoke with his engineering colleague at UNSW, Scientia Professor Andrew Dzurak, whose team had over the past decade demonstrated the first and the most accurate quantum logic using the same silicon manufacturing technology used to make conventional computer chips.

"I was completely blown away when Jarryd came to me with his new idea," Prof. Dzurak says, "and we immediately got down to work to see how we could integrate it with the qubit chips that my team has developed.

"We put two of our best Ph.D. students on the project, Ensar Vahapoglu from my team, and James Slack-Smith from Jarryd's.

"We were overjoyed when the experiment proved successful. This problem of how to control millions of qubits had been worrying me for a long time, since it was a major roadblock to building a full-scale quantum computer."

Once only dreamt about in the 1980s, quantum computers using thousands of qubits to solve problems of commercial significance may now be less than a decade away. Beyond that, they are expected to bring new firepower to solving global challenges and developing new technologies because of their ability to model extraordinarily complex systems.

Climate change, drug and vaccine design, code decryption and artificial intelligence all stand to benefit from quantum computing technology.

Looking ahead

Next up, the team plans to use this new technology to simplify the design of near-term silicon quantum processors.

"Removing the on-chip control wire frees up space for additional qubits and all of the other electronics required to build a quantum processor. It makes the task of going to the next step of producing devices with some tens of qubits much simpler," says Prof. Dzurak.

"While there are engineering challenges to resolve before processors with a million qubits can be made, we are excited by the fact that we now have a way to control them," says Dr. Pla.

Reference: 

Single-electron spin resonance in a nanoelectronic device using a global field, Science Advances (2021). DOI: 10.1126/sciadv.abg9158

NASA Selects Gamma-ray Telescope to Chart Milky Way Evolution


NASA has selected a new space telescope proposal that will study the recent history of star birth, star death, and the formation of chemical elements in the Milky Way. The gamma-ray telescope, called the Compton Spectrometer and Imager (COSI), is expected to launch in 2025 as NASA’s latest small astrophysics mission.

NASA’s Astrophysics Explorers Program received 18 telescope proposals in 2019 and selected four for mission concept studies. After detailed review of these studies by a panel of scientists and engineers, NASA selected COSI to continue into development.

“For more than 60 years, NASA has provided opportunities for inventive, smaller-scale missions to fill knowledge gaps where we still seek answers,” said Thomas Zurbuchen, associate administrator for the agency’s Science Mission Directorate in Washington. “COSI will answer questions about the origin of the chemical elements in our own Milky Way galaxy, the very ingredients critical to the formation of Earth itself.”

COSI will study gamma rays from radioactive atoms produced when massive stars exploded to map where chemical elements were formed in the Milky Way. The mission will also probe the mysterious origin of our galaxy’s positrons, also known as antielectrons – subatomic particles that have the same mass as an electron but a positive charge. 

COSI’s principal investigator is John Tomsick at the University of California, Berkeley. The mission will cost approximately $145 million, not including launch costs. NASA will select a launch provider later.

The COSI team spent decades developing their technology through flights on scientific balloons. In 2016, they sent a version of the gamma-ray instrument aboard NASA’s super pressure balloon, which is designed for long flights and heavy lifts.

NASA's Explorers Program is the agency's oldest continuous program. It provides frequent, low-cost access to space using principal investigator-led space research relevant to the astrophysics and heliophysics programs. Since the 1958 launch of Explorer 1, which discovered Earth’s radiation belts, the program has launched more than 90 missions. The Cosmic Background Explorer, another NASA Explorer mission, led to a Nobel Prize in 2006 for its principal investigators.

NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the program for the agency.

Source: Link

Amount of information in visible universe quantified


Researchers have long suspected a connection between information and the physical universe, with various paradoxes and thought experiments used to explore how or why information could be encoded in physical matter. The digital age propelled this field of study, suggesting that solving these research questions could have tangible applications across multiple branches of physics and computing.

In AIP Advances, a University of Portsmouth researcher attempts to shed light on exactly how much of this information is out there and presents a numerical estimate for the amount of encoded information in all the visible matter in the universe—approximately 6 times 10 to the power of 80 bits of information. While not the first estimate of its kind, this study's approach relies on information theory.

"The information capacity of the universe has been a topic of debate for over half a century," said author Melvin M. Vopson. "There have been various attempts to estimate the information content of the universe, but in this paper, I describe a unique approach that additionally postulates how much information could be compressed into a single elementary particle."

To produce the estimate, the author used Shannon's information theory to quantify the amount of information encoded in each elementary particle in the observable universe as 1.509 bits of information. Mathematician Claude Shannon, called the Father of the Digital Age because of his work in information theory, defined this method for quantifying information in 1948.

"It is the first time this approach has been taken in measuring the information content of the universe, and it provides a clear numerical prediction," said Vopson. "Even if not entirely accurate, the numerical prediction offers a potential avenue toward experimental testing."

Recent research sheds light on the ways information and physics interact, such as how information exits a black hole. However, the precise physical significance of information remains elusive, but multiple radical theories contend information is physical and can be measured.

In previous studies, Vopson postulated information is a fifth state of matter alongside solid, liquid, gas, and plasma, and that elusive dark matter could be information. Vopson's study also included derivation of a formula that reproduces accurately the well-known Eddington number, the total number of protons in the observable universe.

While the approach in this study ignored antiparticles and neutrinos and made certain assumptions about information transfer and storage, it offers a unique tool for estimating the information content per elementary particle. Practical experiments can now be used to test and refine these predictions, including research to prove or disprove the hypothesis that information is the fifth state of matter in the universe.

Reference: 

"Estimation of the information contained in the visible matter of the universe" AIP Advances, aip.scitation.org/doi/full/10.1063/5.0064475

Samples from China mission show Moon 'active' more recently than thought


The first lunar rocks brought back to Earth in decades show the Moon was volcanically active more recently than previously thought, Chinese scientists said Tuesday.

A Chinese spacecraft carried lunar rocks and soil to Earth last year—humanity's first mission in four decades to collect samples from the Moon, and a milestone for Beijing's growing space program.

The samples included basalt—a form of cooled lava—from 2.03 billion years ago, scientists found, pushing the last known date of volcanic activity on the moon closer to the present day by as much as 900 million years.

Analysis of the samples "reveals that the Moon's interior was still evolving at around two billion years ago", the Chinese Academy of Sciences (CAS) said in a statement.

Previous moon rocks brought back by US and Soviet missions showed evidence of lunar activity up to 2.8 billion years ago, but left a gap in scientists' knowledge about the more recent history of Earth's natural satellite as they were from older parts of the lunar surface.

The Chang'e-5 mission—named after a mythical moon goddess—collected two kilograms (4.5 pounds) of samples from a previously unexplored area of the moon called Mons Ruemker in the Oceanus Procellarum or "Ocean of Storms".

The area was selected as it was thought by scientists to be more recently formed, based on the lower density of craters from meteors on its surface.

"Altogether those results are extremely exciting, providing amazing science and results on understanding the lunar formation and evolution over time," Audrey Bouvier, a planetology professor at Germany's University of Bayreuth, said in a video message at a Beijing press conference on Tuesday.

The latest findings—published in three papers in the Nature journal on Tuesday—open up new questions for scientists trying to decipher the history of the Moon.

"How did the Moon sustain volcanic activity for so long? The Moon is naturally small and should disperse heat quickly, or so the thinking goes," CAS researcher Li Xianhua, one of the authors of the studies, told reporters.

The Chang'e 5 samples marked a major step for the Chinese space program, which has sent a rover to Mars and landed another craft on the far side of the Moon.

The country, racing to catch up with the United States and Russia, sent three astronauts to its new space station on Saturday, which is expected to become operational by 2022.

References: 

Non-KREEP origin for Chang'E-5 basalts in the Procellarum KREEP Terrane, Nature (2021). DOI: 10.1038/s41586-021-04119-5

Two billion-year-old volcanism on the Moon from Chang'E-5 basalts, Nature (2021). DOI: 10.1038/s41586-021-04100-2

A dry lunar mantle reservoir for young mare basalts of Chang'E-5, Nature (2021). DOI: 10.1038/s41586-021-04107-9

Astronomer's research suggests 'magnetic tunnel' surrounds our solar system


A University of Toronto astronomer's research suggests the solar system is surrounded by a magnetic tunnel that can be seen in radio waves.

Jennifer West, a research associate at the Dunlap Institute for Astronomy & Astrophysics, is making a scientific case that two bright structures seen on opposite sides of the sky—previously considered to be separate—are actually connected and are made of rope-like filaments. The connection forms what looks like a tunnel around our solar system.

The data results of West's research have been published in The Astrophysical Journal.

"If we were to look up in the sky," says West, "we would see this tunnel-like structure in just about every direction we looked—that is, if we had eyes that could see radio light."

Called "the North Polar Spur" and "the Fan Region," astronomers have known about these two structures for decades, West says. But most scientific explanations have focused on them individually. West and her colleagues, by contrast, believe they are the first astronomers to connect them as a unit.

Made up of charged particles and a magnetic field, the structures are shaped like long ropes. They are located about 350 light-years away from us, and are about 1,000 light-years long.

"That's the equivalent distance of traveling between Toronto and Vancouver two trillion times," West says.

West has been thinking about these features on and off for 15 years—ever since she first saw a map of the radio sky. More recently, she built a computer model that calculated what the radio sky would look like from Earth as she varied the shape and location of the long ropes. The model allowed West to "build" the structure around us, and showed her what the sky would look like through our telescopes. It was this new perspective that helped her to match the model to the data.

"A few years ago, one of our co-authors, Tom Landecker, told me about a paper from 1965—from the early days of radio astronomy," West says. "Based on the crude data available at this time, the authors [Mathewson and Milne], speculated that these polarized radio signals could arise from our view of the Local Arm of the galaxy, from inside it.

"That paper inspired me to develop this idea and tie my model to the vastly better data that our telescopes give us today."

West uses the Earth's map as an example. The North pole is on the top and the equator is through the middle—unless you re-draw the map from a different perspective. The same is true for the map of our galaxy. "Most astronomers look at a map with the North pole of the galaxy up and the galactic centre in the middle," West explains. "An important part that inspired this idea was to remake that map with a different point in the middle."

"This is extremely clever work," says Bryan Gaensler, a professor at the Dunlap Institute and an author of the publication. "When Jennifer first pitched this to me, I thought it was too 'out-there' to be a possible explanation. But she was ultimately able to convince me. Now, I'm excited to see how the rest of the astronomy community reacts."

An expert in magnetism in galaxies and the interstellar medium, West looks forward to the more possible discoveries connected to this research.

"Magnetic fields don't exist in isolation," she says. "They all must to connect to each other. So, a next step is to better understand how this local magnetic field connects both to the larger-scale galactic magnetic field, and also to the smaller scale magnetic fields of our sun and Earth."

In the meantime, West agrees that the new "tunnel" model not only brings new insight to the science community, but also a ground-breaking concept for the rest of us.

"I think it's just awesome to imagine that these structures are everywhere whenever we look up into the night sky."

Reference: 

J. L. West et al, A Unified Model for the Fan Region and the North Polar Spur: A bundle of filaments in the Local Galaxy. arXiv:2109.14720v1 [astro-ph.GA], arxiv.org/abs/2109.14720

Monday, 18 October 2021

Analysis puts most general constraints on nonstandard neutrino interactions


For decades, physicists have theorized that the current best theory describing particle physics—the "Standard Model"—was not sufficient to explain the way the universe works. In the search for physics beyond the Standard Model (BSM), elusive particles called neutrinos might point the way.

Neutrinos are sometimes called "ghost particles" because they so rarely interact with matter that they can travel through just about anything. However, while traveling through matter, they may be "slowed down," depending on the neutrino's type (or "flavor"), in what is known as a "matter effect."

In many BSM models, neutrinos have extra interactions with matter due to new and thus far unknown forces of nature. Different neutrino flavors might be affected to varying extents by these interactions, and the strength of the resulting matter effects depends on the density of matter the neutrinos are passing through. If researchers observe matter effects that can be explained as "nonstandard interactions" (NSI), it might point to new physics.

The IceCube Neutrino Observatory, an array of sensors embedded in the South Pole ice, was built to detect and study neutrinos from outer space. But in IceCube's center is a subset of more densely packed sensors called DeepCore; this region is sensitive to lower energy neutrinos formed in Earth's atmosphere that are potentially more strongly affected by nonstandard matter effects. In a paper published today in Physical Review D, the IceCube Collaboration discusses an analysis in which they examined three years of DeepCore data to see whether atmospheric neutrinos have extra interactions with matter. This analysis puts limits on all the parameters used to describe NSI, an improvement upon earlier analyses that were restricted to only the NSI regimes to which IceCube is most sensitive.

Valuable ambassadors for new physics

"Atmospheric neutrinos are a great probe for testing whether neutrinos have NSI because they pass right through Earth, including its center, which has a very high matter density," says Elisa Lohfink, graduate student at the University of Mainz in Germany and a lead on this publication. Changes in matter density directly change the neutrinos' oscillation patterns—the way neutrinos change their flavors, or "oscillate"—and therefore which flavors of neutrinos arrive at the South Pole detector. IceCube DeepCore is sensitive to these matter effects because of the huge number of atmospheric neutrinos it detects every year.

In this analysis, led by University of Mainz graduate student Thomas Ehrhardt, the researchers looked at the oscillation patterns of neutrinos that had arrived at DeepCore from all directions and determined whether they matched the Standard Model expectations or showed effects from any of five effective parameters that measure how much more a neutrino flavor interacts than it would in the Standard Model. The researchers could then constrain the effective NSI parameters by testing how well the oscillation pattern matches different NSI scenarios.

First, Ehrhardt and his collaborators examined one effective parameter at a time, yielding the results shown in the figure above. Fully free NSI were investigated separately. Since the analysis was largely independent from any specific underlying models, the researchers were able to constrain NSI without relying on one model to be correct.

The researchers were able to put limits on each of the five possible NSI parameters individually at a sensitivity that is at least comparable to the world's combined limits, an accomplishment described by Lohfink as "unprecedented." More importantly, the researchers say, is the finding that IceCube can probe models in which they fit all the parameters at once. "To our understanding, there is no other experiment in the world that can do this from a single measurement," says Sebastian Böser, professor at the University of Mainz. "We can put limits on an unprecedented range of models for new physics in the neutrino sector." The result is a major improvement on a previous IceCube analysis that looked at just one parameter.

The researchers hope that the rest of the neutrino community will pick up on the results and incorporate them into the global fits. And Lohfink and her collaborators are already working on a follow-up analysis using a much larger data sample—eight years of data instead of three years—with much better sensitivity. They hope to have an improved limit soon.

"In the long run, the IceCube Upgrade will be a real game changer for this type of analysis," says Böser. "Not only will the Upgrade provide better calibration and reduce the impact of systematic uncertainties, but it will also allow us to resolve the neutrino oscillations much, much better, and therefore let us see potential deviations from the Standard Model much more clearly. I am truly excited about this!"

Reference: 

R. Abbasi et al, All-flavor constraints on nonstandard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data, Physical Review D (2021). DOI: 10.1103/PhysRevD.104.072006