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      One of nature’s key constants is much larger in a quantum material

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      A crucial number that rules the universe goes big in a strange quantum material.

      The fine-structure constant is about 10 times its normal value in a type of material called quantum spin ice, physicists calculate in the Sept. 10 Physical Review Letters. The new calculation hints that quantum spin ice could give a glimpse at physics within an alternate universe where the constant is much larger.

      With an influence that permeates physics and chemistry, the fine-structure constant sets the strength of interactions between electrically charged particles. Its value, about 1/137, consternates physicists because they can’t explain why it has that value, even though it is necessary for the complex chemistry that is the basis of life (SN: 11/2/16).

      If the fine-structure constant throughout the cosmos were as large as the one in quantum spin ices, “the periodic table would only have 10 elements,” says theoretical physicist Christopher Laumann of Boston University. “And it probably would be hard to make people; there wouldn’t be enough richness to chemistry.”

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      Quantum spin ices are a class of substances in which particles can’t agree. The materials are made up of particles with spin, a quantum version of angular momentum, which makes them magnetic. In a normal material, particles would come to a consensus below a certain temperature, with the magnetic poles lining up in either the same direction or in alternating directions. But in quantum spin ices, the particles are arranged in such a way that the magnetic poles, or equivalently the spins, can’t agree even at a temperature of absolute zero (SN: 2/13/11).

      The impasse occurs because of the materials’ geometry: The particles are located at the corners of an array of pyramids that are connected at the corners. Conflicts between multiple sets of neighbors mean that the closest these particles can get to harmony is arranging themselves so that two spins face out from each pyramid, and two face in.

      In quantum spin ices, particles (black dots) are located at the corners of an array of pyramids (red). Normally, the spins of the particles (green arrows) arrange so that two are pointing into the pyramid and two out. If that rule is broken, as illustrated, quasiparticles called spinons (orange and blue) form.S.D. Pace et al/PRL 2021

      This uneasy truce can give rise to disturbances that behave like particles within the material, or quasiparticles (SN: 10/3/14). Flip particles’ spins around and you can get what are called spinons, quasiparticles that can move through the material and interact with other spinons in a manner akin to electrons and other charged particles found in the world outside the material. The material re-creates the theory of quantum electrodynamics, the piece of particles physics’ standard model that hashes out how electrically charged particles do their thing. But the specifics, including the fine-structure constant, don’t necessarily match those in the wider universe.

      So Laumann and colleagues set out to calculate the fine-structure constant in quantum spin ices for the first time. The team pegged the number at about 1/10, instead of 1/137. What’s more, the researchers found that they could change the value of the fine-structure constant by tweaking the properties of the theoretical material. That could help scientists study the effects of altering the fine-structure constant — a test that’s well out of reach in our own universe, where the fine-structure constant is fixed.

      Unfortunately, scientists haven’t yet found a material that definitively qualifies as quantum spin ice. But one much-studied prospect is a group of minerals called pyrochlores, which have magnetic ions, or electrically charged atoms, arranged in the appropriate pyramid configuration. Scientists might also be able to study the materials using a quantum computer or another quantum device designed to simulate quantum spin ices (SN: 6/29/17).

      If scientists succeed in creating quantum spin ice, the materials could reveal how quantum electrodynamics and the standard model would work in a universe with a much larger fine-structure constant. “That would be the hope,” says condensed matter theorist Shivaji Sondhi of the University of Oxford, who was not involved with the research. “It’s interesting to be able to make a fake standard model … and ask what would happen.” More

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      New ‘vortex beams’ of atoms and molecules are the first of their kind

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      Like soft serve ice cream, beams of atoms and molecules now come with a swirl.

      Scientists already knew how to dish up spiraling beams of light or electrons, known as vortex beams (SN: 1/14/11). Now, the first vortex beams of atoms and molecules are on the menu, researchers report in the Sept. 3 Science.

      Vortex beams made of light or electrons have shown promise for making special types of microscope images and for transmitting information using quantum physics (SN: 8/5/15). But vortex beams of larger particles such as atoms or molecules are so new that the possible applications aren’t yet clear, says physicist Sonja Franke-Arnold of the University of Glasgow in Scotland, who was not involved with the research. “It’s maybe too early to really know what we can do with it.”

      In quantum physics, particles are described by a wave function, a wavelike pattern that allows scientists to calculate the probability of finding a particle in a particular place (SN: 6/8/11). But vortex beams’ waves don’t slosh up and down like ripples on water. Instead, the beams’ particles have wave functions that move in a corkscrewing motion as a beam travels through space. That means the beam carries a rotational oomph known as orbital angular momentum. “This is something really very strange, very nonintuitive,” says physicist Edvardas Narevicius of the Weizmann Institute of Science in Rehovot, Israel.

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      Narevicius and colleagues created the new beams by passing helium atoms through a grid of specially shaped slit patterns, each just 600 nanometers wide. The team detected a hallmark of vortex beams: a row of doughnut-shaped rings imprinted on a detector by the atoms, in which each doughnut corresponds to a beam with a different orbital angular momentum.

      Another set of doughnuts revealed the presence of vortex beams of helium excimers, molecules created when a helium atom in an excited, or energized, state pairs up with another helium atom.

      A pattern of rings reveals the presence of vortex beams of atoms and molecules. Each doughnut shape corresponds to a beam of helium atoms with a different angular momentum. Two hard-to-see circles from helium molecules sit in between the center dot and the first two doughnuts left and right of the center.A. Luski et al/Science 2021

      A pattern of rings reveals the presence of vortex beams of atoms and molecules. Each doughnut shape corresponds to a beam of helium atoms with a different angular momentum. Two hard-to-see circles from helium molecules sit in between the center dot and the first two doughnuts left and right of the center.A. Luski et al/Science 2021

      Next, scientists might investigate what happens when vortex beams of molecules or atoms collide with light, electrons or other atoms or molecules. Such collisions are well-understood for normal particle beams, but not for those with orbital angular momentum. Similar vortex beams made with protons might also serve as a method for probing the subatomic particle’s mysterious innards (SN: 4/18/17).

      In physics, “most important things are achieved when we are revisiting known phenomena with a fresh perspective,” says physicist Ivan Madan of EPFL, the Swiss Federal Institute of Technology in Lausanne, who was not involved with the research. “And, for sure, this experiment allows us to do that.” More

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      These weird, thin ice crystals are springy and bendy

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      Try to bend an icicle and it’ll snap in two. With its tendency to crack into shards, ice’s reputation for being stiff and brittle seems well-established. But thin, pristine threads of ice are bendy and elastic, scientists report in the July 9 Science.

      To create the flexible ice, Peizhen Xu of Zhejiang University in Hangzhou, China and colleagues used a needle with an electric voltage applied to it, which attracted water vapor within a chilled chamber. The resulting ice whiskers were a few micrometers in diameter or less, a fraction of the width of a typical human hair.

      Usually, ice contains defects: tiny cracks, pores or misaligned sections of crystal. But the specially grown ice threads consisted of near-perfect ice crystals with atypical properties. When manipulated at temperatures of –70° Celsius and –150° C, the ice could be curved into a partial circle with a radius of tens of micrometers. When the bending force was released, the fibers sprang back to their original shape.

      [embedded content]
      Researchers bent a tiny fiber of ice (thin white line) into a loop, showing that the usually brittle material can be flexible under certain conditions.

      Bending the fibers compresses the ice on its inside edge. The new measurements indicate that the compression induces the ice to take on a different structure. That’s to be expected for ice, which is known to morph into a variety of phases depending on pressure and temperature (SN: 1/11/09). The discovery could give researchers a new way to study ice’s properties when squeezed.

      Thin ice strands form naturally in snowflakes. Unlike the ice in the experiment, snowflakes don’t consist of single, flawless ice crystals. But small sections of the flakes could be single crystals, the researchers say, suggesting that tiny bits of snowflakes could also bend. More

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      A proposed ‘quantum compass’ for songbirds just got more plausible

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      Scientists could be a step closer to understanding how some birds might exploit quantum physics to navigate.

      Researchers suspect that some songbirds use a “quantum compass” that senses the Earth’s magnetic field, helping them tell north from south during their annual migrations (SN: 4/3/18). New measurements support the idea that a protein in birds’ eyes called cryptochrome 4, or CRY4, could serve as a magnetic sensor. That protein’s magnetic sensitivity is thought to rely on quantum mechanics, the math that describes physical processes on the scale of atoms and electrons (SN: 6/27/16). If the idea is shown to be correct, it would be a step forward for biophysicists who want to understand how and when quantum principles can become important in various biological processes.

      In laboratory experiments, the type of CRY4 in retinas of European robins (Erithacus rubecula) responded to magnetic fields, researchers report in the June 24 Nature. That’s a crucial property for it to serve as a compass. “This is the first paper that actually shows that birds’ cryptochrome 4 is magnetically sensitive,” says sensory biologist Rachel Muheim of Lund University in Sweden, who was not involved with the research.

      Scientists think that the magnetic sensing abilities of CRY4 are initiated when blue light hits the protein. That light sets off a series of reactions that shuttle around an electron, resulting in two unpaired electrons in different parts of the protein. Those lone electrons behave like tiny magnets, thanks to a quantum property of the electrons called spin.

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      The two electrons’ magnets can point either parallel to one another or in opposite directions. But quantum physics dictates that the electrons do not settle on either arrangement. Rather they exist in a limbo called a quantum superposition, which describes only the probability of finding the electrons in either configuration.

      Magnetic fields change those probabilities. That, in turn, affects how likely the protein is to form an altered version instead of returning to its original state. Birds may be able to determine their orientation in a magnetic field based on how much of the altered protein is produced, although that process is not yet understood. “How does the bird perceive this? We don’t know,” says chemist Peter Hore of the University of Oxford, a coauthor of the new study.

      The idea that cryptochromes play a role in birds’ internal compasses has been around for decades, but “no one could confirm this experimentally,” says Jingjing Xu of the University of Oldenburg in Germany. So in the new study, Xu, Hore and colleagues observed what happened when the isolated proteins were hit with blue laser light. After the laser pulse, the researchers measured how much light the sample absorbed. For robin CRY4, the addition of a magnetic field changed the amount of absorbance, a sign that the magnetic field was affecting how much of the altered form of the protein was produced.

      When the researchers performed the same test on CRY4 found in nonmigratory chickens and pigeons, the magnetic field had little effect. The stronger response to the magnetic field in CRY4 from a migratory bird “could suggest that maybe there is really something special about the cryptochromes of migratory birds that use this for a compass,” says biophysicist Thorsten Ritz of the University of California, Irvine.

      But laboratory tests with chickens and pigeons have shown that those birds can sense magnetic fields, Ritz and Muheim both note. It’s not clear whether the higher sensitivity of robin CRY4 in laboratory tests is a result of evolutionary pressure for migratory birds to have a better magnetic sensor.

      One factor making interpretation of the results more difficult is that experiments on isolated proteins don’t match the conditions in birds’ eyes. For example, Xu says, scientists think the proteins may be aligned in one direction within the retina. To further illuminate the process, the researchers hope to perform future studies on actual retinas, to get a literal bird’s-eye view. More

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      Physicists used LIGO’s mirrors to approach a quantum limit

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      Quantum mechanics usually applies to very small objects: atoms, electrons and the like. But physicists have now brought the equivalent of a 10-kilogram object to the edge of the quantum realm.

      Scientists with the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, reduced vibrations in a combination of the facility’s mirrors to nearly the lowest level allowed by quantum mechanics, they report in the June 18 Science.

      The researchers quelled differences between the jiggling of LIGO’s four 40-kilogram mirrors, putting them in near-perfect sync. When the mirrors are combined in this way, they behave effectively like a single, 10-kilogram object.

      LIGO is designed to measure gravitational waves, using laser light that bounces between sets of mirrors in the detector’s two long arms (SN: 2/11/16). But physicist Vivishek Sudhir of MIT and colleagues instead used the laser light to monitor the mirrors’ movements to extreme precision and apply electric fields to resist the motion. “It’s almost like a noise-canceling headphone,” says Sudhir. But instead of measuring nearby sounds and canceling out that noise, the technique cancels out motion.

      The researchers reduced the mirrors’ relative motions to about 10.8 phonons, or quantum units of vibration, close to the zero-phonon quantum limit.

      The study’s purpose is not to better understand gravitational waves, but to get closer to revealing secrets of quantum mechanics. Scientists are still trying to understand why large objects don’t typically follow the laws of quantum mechanics. Such objects lose their quantum properties, or decohere. Studying quantum states of more massive objects could help scientists pin down how decoherence happens.

      Previous studies have observed much smaller objects in quantum states. In 2020, physicist Markus Aspelmeyer of the University of Vienna and colleagues brought vibrations of a nanoparticle to the quantum limit (SN: 1/30/20). LIGO’s mirrors are “a fantastic system to study decoherence effects on super-massive objects in the quantum regime,” says Aspelmeyer. More

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      The teeth of ‘wandering meatloaf’ contain a rare mineral found only in rocks

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      The hard, magnetic teeth of a leathery red-brown mollusk nicknamed “the wandering meatloaf” possess a rare mineral previously seen only in rocks. The mineral may help the mollusk — the giant Pacific chiton (Cryptochiton stelleri) — meld its soft flesh to the hard teeth it uses for grazing on rocky coastlines, researchers report online May 31 in Proceedings of the National Academy of Sciences.

      C. stelleri is the world’s largest chiton, reaching up to roughly 35 centimeters long. It is equipped with several dozen rows of teeth on a slender, flexible, tonguelike appendage called a radula that it uses to scrape algae off rocks. Those teeth are covered in magnetite, the hardest, stiffest known biomineral to date: It’s as much as three times as hard as human enamel and mollusk shells.

      C. stelleri uses its radula, a tonguelike structure (pictured) studded with hard magnetic teeth (dark objects), to graze on rocks. This composite image shows the radula’s stages of development, from earliest (left) to latest (right).Northwestern University

      Materials scientist Derk Joester and colleagues analyzed these teeth using high-energy X-rays from the Advanced Photon Source at Argonne National Laboratory in Lemont, Ill. They discovered that the interface between the teeth and flesh contained nanoparticles of santabarbaraite, an iron-loaded mineral never seen before in a living organism’s body.

      These nanoparticles help the underpinnings of the teeth vary in hardness and stiffness by at least a factor of two over distances of just several hundred micrometers — a few times the average width of a human hair. Such variations let these structures bridge the hard and soft parts of the mollusk’s body. Now that santabarbaraite has been found in one organism, the researchers suggest looking for it in insect cuticles and bacteria that sense magnetic fields.

      The teeth on C. stelleri’s tonguelike organ, seen in closeup in this scanning electron microscope image, help the mollusk scrape algae off of rocks.Northwestern University

      Using nanoparticles of a mineral similar to santabarbaraite, the scientists also 3-D printed strong, light materials with a range of hardness and stiffness. These composites might find use in soft robotics, including marrying soft and hard parts in bots that can squirm past obstacles that conventional robots cannot given their rigid parts, says Joester, of Northwestern University in Evanston, Ill. More

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      A newfound quasicrystal formed in the first atomic bomb test

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      In an instant, the bomb obliterated everything.

      The tower it sat on and the copper wires strung around it: vaporized. The desert sand below: melted.

      In the aftermath of the first test of an atomic bomb, in July 1945, all this debris fused together, leaving the ground of the New Mexico test site coated with a glassy substance now called trinitite. High temperatures and pressures helped forge an unusual structure within one piece of trinitite, in a grain of the material just 10 micrometers across — a bit longer than a red blood cell.

      That grain contains a rare form of matter called a quasicrystal, born the moment the nuclear age began, scientists report May 17 in Proceedings of the National Academy of Sciences.

      Normal crystals are made of atoms locked in a lattice that repeats in a regular pattern. Quasicrystals have a structure that is orderly like a normal crystal but that doesn’t repeat. This means quasicrystals can have properties that are forbidden for normal crystals. First discovered in the lab in 1980s, quasicrystals also appear in nature in meteorites (SN: 12/8/16).

      Penrose tilings (one shown) are an example of a structure that is ordered but does not repeat. Quasicrystals are a three-dimensional version of this idea.Inductiveload/Wikimedia Commons

      The newly discovered quasicrystal from the New Mexico test site is the oldest one known that was made by humans.

      Trinitite takes its moniker from the nuclear test, named Trinity, in which the material was created in abundance (SN: 4/8/21). “You can still buy lots of it on eBay,” says geophysicist Terry Wallace, a coauthor of the study and emeritus director of Los Alamos National Laboratory in New Mexico.

      But, he notes, the trinitite the team studied was a rarer variety, called red trinitite. Most trinitite has a greenish tinge, but red trinitite contains copper, remnants of the wires that stretched from the ground to the bomb. Quasicrystals tend to be found in materials that have experienced a violent impact and usually involve metals. Red trinitite fit both criteria.

      But first the team had to find some.

      “I was asking around for months looking for red trinitite,” says theoretical physicist Paul Steinhardt of Princeton University. But Steinhardt, who is known for trekking to Siberia to seek out quasicrystals, wasn’t deterred (SN: 2/19/19). Eventually he and his colleagues got some from an expert in trinitite who began collaborating with the team. Then, the painstaking work started, “looking through every little microscopic speck” of the trinitite sample, says Steinhardt. Finally, the researchers extracted the tiny grain. By scattering X-rays through it, the researchers revealed that the material had a type of symmetry found only in quasicrystals.

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      The new quasicrystal, formed of silicon, copper, calcium and iron, is “brand new to science,” says mineralogist Chi Ma of Caltech, who was not involved with the study. “It’s a quite cool and exciting discovery,” he says.

      Future searches for quasicrystals could examine other materials that experienced a punishing blow, such as impact craters or fulgurites, fused structures formed when lightning strikes soil (SN: 3/16/21).

      The study shows that artifacts from the birth of the atomic age are still of scientific interest, says materials scientist Miriam Hiebert of the University of Maryland in College Park, who has analyzed materials from other pivotal moments in nuclear history (SN: 5/1/19). “Historic objects and materials are not just curiosities in collectors’ cabinets but can be of real scientific value,” she says. More

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      Morphing noodles start flat but bend into curly pasta shapes as they’re cooked

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      This pasta is no limp noodle.

      When imprinted with carefully designed arrangements of grooves, flat pasta morphs as it cooks, forming tubes, spirals and other shapes traditional for the starchy sustenance. The technique could allow for pasta that takes up less space, Lining Yao and colleagues report May 5 in Science Advances.

      Pasta aficionados “are very picky about the shapes of pasta and how they pair with different sauces,” says Yao, who studies the design of smart materials at Carnegie Mellon University in Pittsburgh. But those shapes come at a cost of excess packaging and inefficient shipping: For some varieties of curly pasta, more than 60 percent of the packaging space is used to hold air, the researchers calculated.

      Yao and colleagues stamped a series of grooves onto one side of each noodle. As the pasta absorbed water during cooking, the liquid couldn’t penetrate as fully on the grooved side, causing it to swell less than the smooth side of the pasta. That asymmetric swelling bent the previously flat noodle into a curve. By changing the arrangement of the grooves, the researchers controlled the final shape. Computer simulations of swelling pasta replicated the shapes seen in the experiments.

      [embedded content]
      Flat pasta (top) with the right pattern of grooves imprinted on it curls into traditional pasta shapes when boiled. Computer simulations of the pasta (bottom) show the same behavior.

      The technique isn’t limited to pasta: Another series of experiments, performed with silicone rubber in a solvent, produced similar results. But whereas the pasta held its curved shape, the silicone rubber eventually absorbed enough solvent to flatten out again. The gluey nature of cooked pasta helps lock in the twists by fusing neighboring grooves together, the researchers determined. Removing the silicone from the solvent caused the silicone to bend in the opposite direction. This reversible bending process could be harnessed for other purposes, such as a grabber for robot hands, Yao says.

      The pasta makes particularly good camping food, Yao says. A member of her team brought it along on a recent hiking trip. The pasta slips easily into a cramped pack but cooks into a satisfying shape. More