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    A sapphire Schrödinger’s cat shows that quantum effects can scale up

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    In keeping with the grand tradition of tubby cats, a newly created quantum “cat” is particularly massive — at least for the quantum realm.

    Scientists put a jiggling piece of sapphire crystal in what’s known as a “cat state,” in which an object exists in two different states simultaneously. It’s a situation reminiscent of physicists’ favorite imaginary feline, Schrödinger’s cat, known for being alive and dead at the same time.

    The new sapphire cat is a relatively hefty 16 micrograms, physicists report in the April 21 Science. That’s close to half the mass of an eyelash, and more than 100 trillion times the mass of cat states previously created with molecules. “We’ve reached a new regime where quantum mechanics apparently does work,” says physicist Yiwen Chu of ETH Zurich.

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    In a quantum parable dreamt up in the 1930s by physicist Erwin Schrödinger, a cat is trapped in a box and, due to quantum effects, winds up alive and dead at the same time (SN: 5/26/16). This paradoxical scenario doesn’t happen in the real world. While quantum particles are capable of existing in two distinct states simultaneously — what’s called a superposition — those effects wash out for cat-sized stuff.

    Quantum effects are typically confined to atoms, molecules and the like. The everyday world visible to human eyes doesn’t exhibit quantum properties. Scientists can coax certain tiny objects to display quantum features (SN: 4/25/18). But scientists don’t fully understand the border between the quantum and nonquantum realms.

    “We really have only just begun to understand that intermediate regime,” says Benjamin Sussman of the University of Ottawa, who was not involved with the new study. “It’s of really profound interest to see how these quantum systems scale and how they behave.”

    Cat states are a special variety of quantum behavior that come close to re-creating Schrödinger’s idea. They are superpositions of two states that are distinct according to the classical physics that describes the everyday world— like an alive or dead cat — rather than two states that exist only in the quantum domain, such as the energy levels of an atom.

    In the new experiment, the researchers jiggled a portion of a sapphire crystal in such a way that its atoms moved in two directions at once. That’s a distinction that “captures the spirit” of Schrödinger’s cat, Chu says.

    The jiggling was confined within a sliver of the crystal consisting of 100 million billion atoms. That’s large enough that, if extracted from the rest of the crystal, it would be visible to the naked eye, Chu says.

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    Still, the oscillations of the atoms were tiny, about a millionth of a billionth of a millimeter — not exactly the scale of everyday objects. Other demonstrations of cat states have demonstrated much larger spatial separation, despite being made up of fewer atoms.

    In future work, Sussman says he’d like to see the researchers scale up not only the mass, but also the size of the oscillations. “That’s going to be really hard but will be really interesting.” More

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      Imagine if a ripped leather jacket could repair itself instead of needing to be replaced.

      This could one day be a reality, if the jacket is fashioned from fungus, researchers report April 11 in Advanced Functional Materials. The team made a self-healing leather from mushrooms’ threadlike structures called mycelium, building on past iterations of the material to allow it to fix itself.

      Mycelium leather is already an emerging product, but it’s produced in a way that extinguishes fungal growth. Elise Elsacker and colleagues speculated that if the production conditions were tweaked, the mycelium could retain its ability to regrow if damaged.

      That novel approach could offer inspiration to other researchers trying to get into the mycelium leather market, says Valeria La Saponara, a mechanical and aerospace engineer at the University of California, Davis.

      Elsacker, a bioengineer now at the Vrije Universiteit Brussel, and her colleagues first grew mycelium in a soup rich in proteins, carbohydrates and other nutrients. A skin formed on the surface of the liquid, which the scientists scooped off, cleaned and dried to make a thin, somewhat fragile leather material. They used temperatures and chemicals mild enough to form the leather but leave parts of the fungus functional. Left dormant were chlamydospores, little nodules on the mycelium that can spring back to life and grow more mycelium when conditions are prime.

      After punching holes in the leather, the researchers doused the area in the same broth used to grow it to revive the chlamydospores. The mycelium eventually regrew over the punctures. Once healed, the hole-punched areas were just as strong as undamaged areas — however, the repairs were visible from one side of the leather.

      Chlamydospores are little nodules on fungi’s threadlike mycelium that can spring back to life. They’re dormant in the punctured leather (left). With the right nutrients, the chlamydospores reanimated and the leather healed itself (middle), but the tiny patches are still slightly visible in the repaired leather (right).E. Elsacker et al/Advanced Functional Materials, 2023

      The technique could potentially go beyond a proof-of-concept and into commercialization in the next decade, says study coauthor Martyn Dade-Robertson, codirector of the Hub for Biotechnology in the Built Environment in Newcastle upon Tyne. But first, the team will need to make the leather stronger and determine how to control the chlamydospores’ growth. Otherwise, he says, someone could “walk out in the rain, and then all of a sudden find that [their] jacket is growing, or perhaps [has] mushrooms popping out of it.”  More

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      Here’s why some Renaissance artists egged their oil paintings

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      Art historians often wish that Renaissance painters could shell out secrets of the craft. Now, scientists may have cracked one using chemistry and physics.

      Around the turn of the 15th century in Italy, oil-based paints replaced egg-based tempera paints as the dominant medium. During this transition, artists including Leonardo da Vinci and Sandro Botticelli also experimented with paints made from oil and egg (SN: 4/30/14). But it has been unclear how adding egg to oil paints may have affected the artwork.  

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      “Usually, when we think about art, not everybody thinks about the science which is behind it,” says chemical engineer Ophélie Ranquet of the Karlsruhe Institute of Technology in Germany.

      In the lab, Ranquet and colleagues whipped up two oil-egg recipes to compare with plain oil paint. One mixture contained fresh egg yolk mixed into oil paint, and had a similar consistency to mayonnaise. For the other blend, the scientists ground pigment into the yolk, dried it and mixed it with oil — a process the old masters might have used, according to the scant historical records that exist today. Each medium was subjected to a battery of tests that analyzed its mass, moisture, oxidation, heat capacity, drying time and more.

      In both concoctions, the yolk’s proteins, phospholipids and antioxidants helped slow paint oxidation, which can cause paint to turn yellow over time, the team reports March 28 in Nature Communications. 

      In the mayolike blend, the yolk created sturdy links between pigment particles, resulting in stiffer paint. Such consistency would have been ideal for techniques like impasto, a raised, thick style that adds texture to art. Egg additions also could have reduced wrinkling by creating a firmer paint consistency. Wrinkling sometimes happens with oil paints when the top layer dries faster than the paint underneath, and the dried film buckles over looser, still-wet paint.

      The hybrid mediums have some less than eggs-ellent qualities, though. For instance, the eggy oil paint can take longer to dry. If paints were too yolky, Renaissance artists would have had to wait a long time to add the next layer, Ranquet says.

      “The more we understand how artists select and manipulate their materials, the more we can appreciate what they’re doing, the creative process and the final product,” says Ken Sutherland, director of scientific research at the Art Institute of Chicago, who was not involved with the work.

      Research on historical art mediums can not only aid art preservation efforts, Sutherland says, but also help people gain a deeper understanding of the artworks themselves. More

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      These transparent fish turn rainbow with white light. Now, we know why

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      The ghost catfish transforms from glassy to glam when white light passes through its mostly transparent body. Now, scientists know why.

      The fish’s iridescence comes from light bending as it travels through microscopic striped structures in the animal’s muscles, researchers report March 13 in the Proceedings of the National Academy of Sciences.

      Many fishes with iridescent flair have tiny crystals in their skin or scales that reflect light (SN: 4/6/21). But the ghost catfish (Kryptopterus vitreolus) and other transparent aquatic species, like eel larvae and icefishes, lack such structures to explain their luster.

      The ghost catfish’s see-through body caught the eye of physicist Qibin Zhao when he was in an aquarium store. The roughly 5-centimeter-long freshwater fish is a popular ornamental species. “I was standing in front of the tank and staring at the fish,” says Zhao, of Shanghai Jiao Tong University. “And then I saw the iridescence.”

      To investigate the fish’s colorful properties, Zhao and colleagues first examined the fish under different lighting conditions. The researchers determined its iridescence arose from light passing through the fish rather than reflecting off it. By using a white light laser to illuminate the animal’s muscles and skin separately, the team found that the muscles generated the multicolored sheen.

      [embedded content]
      When backlit with a white light, the mostly transparent ghost catfish becomes iridescent. Microscopic striped structures in the fish’s muscles diffract the light, separating it into different wavelengths. These structures change in length as the fish swims, causing the rainbow colors to flicker.  

      The researchers then characterized the muscles’ properties by analyzing how X-rays scatter when traveling through the tissue and by looking at it with an electron microscope. The team identified sarcomeres — regularly spaced, banded structures, each roughly 2 micrometers long, that run along the length of muscle fibers — as the source of the iridescence.

      The sarcomeres’ repeating bands, comprised of proteins that overlap by varying amounts, bend white light in a way that separates and enhances its different wavelengths. The collective diffraction of light produces an array of colors. When the fish contracts and relaxes its muscles to swim, the sarcomeres slightly change in length, causing a shifting rainbow effect.

      Banded structures called sarcomeres (seen in this electron microscope image) make up the threads bundled together in muscle fibers of a ghost catfish. Each sarcomere (one highlighted) consists of two adjacent “tiles” of interlocking myosin filaments and actin filaments, threadlike protein structures responsible for muscle contraction. White light passing through the repeated sarcomeres gets separated into different wavelengths, giving the fish their iridescence.X. Fan et al/PNAS 2023

      The purpose of the ghost catfish’s iridescence is a little unclear, says Heok Hee Ng, an independent ichthyologist in Singapore who was not involved in the new study. Ghost catfish live in murky water and seldom rely on sight, he says. But the iridescence might help them visually coordinate movements when traveling in schools, or it could help them blend in with shimmering water to hide from land predators, like some birds, he adds.

      Regardless of function, Ng is excited to see scientists exploring the ghost catfish’s unusual characteristics.

      “Fishes actually have quite a number of these interesting structures that serve them in many ways,” he says. “And a lot of these structures are very poorly studied.” More

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      Google’s quantum computer reached an error-correcting milestone

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      To shrink error rates in quantum computers, sometimes more is better. More qubits, that is.

      The quantum bits, or qubits, that make up a quantum computer are prone to mistakes that could render a calculation useless if not corrected. To reduce that error rate, scientists aim to build a computer that can correct its own errors. Such a machine would combine the powers of multiple fallible qubits into one improved qubit, called a “logical qubit,” that can be used to make calculations (SN: 6/22/20).  

      Scientists now have demonstrated a key milestone in quantum error correction. Scaling up the number of qubits in a logical qubit can make it less error-prone, researchers at Google report February 22 in Nature.

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      Future quantum computers could solve problems impossible for even the most powerful traditional computers (SN: 6/29/17). To build those mighty quantum machines, researchers agree that they’ll need to use error correction to dramatically shrink error rates. While scientists have previously demonstrated that they can detect and correct simple errors in small-scale quantum computers, error correction is still in its early stages (SN: 10/4/21).

      The new advance doesn’t mean researchers are ready to build a fully error-corrected quantum computer, “however, it does demonstrate that it is indeed possible, that error correction fundamentally works,” physicist Julian Kelly of Google Quantum AI said in a news briefing February 21.

      Quantum computers like Google’s require a dilution refrigerator (pictured) that can cool the quantum processor (which is installed at the bottom of the refrigerator) to frigid temperatures.Google Quantum AI

      Logical qubits store information redundantly in multiple physical qubits. That redundancy allows a quantum computer to check if any mistakes have cropped up and fix them on the fly. Ideally, the larger the logical qubit, the smaller the error rate should be. But if the original qubits are too faulty, adding in more of them will cause more problems than it solves.

      Using Google’s Sycamore quantum chip, the researchers studied two different sizes of logical qubits, one consisting of 17 qubits and the other of 49 qubits. After making steady improvements to the performance of the original physical qubits that make up the device, the researchers tallied up the errors that still slipped through. The larger logical qubit had a lower error rate, about 2.9 percent per round of error correction, compared to the smaller logical qubit’s rate of about 3.0 percent, the researchers found.

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      That small improvement suggests scientists are finally tiptoeing into the regime where error correction can begin to squelch errors by scaling up. “It’s a major goal to achieve,” says physicist Andreas Wallraff of ETH Zurich, who was not involved with the research.

      However, the result is only on the cusp of showing that error correction improves as scientists scale up. A computer simulation of the quantum computer’s performance suggests that, if the logical qubit’s size were increased even more, its error rate would actually get worse. Additional improvement to the original faulty qubits will be needed to enable scientists to really capitalize on the benefits of error correction.

      Still, milestones in quantum computation are so difficult to achieve that they’re treated like pole jumping, Wallraff says. You just aim to barely clear the bar. More

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      Physicists stored data in quantum holograms made of twisted light

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      Particles of twisted light that have been entangled using quantum mechanics offer a new approach to dense and secure data storage.

      Holograms that produce 3-D images and serve as security features on credit cards are usually made with patterns laid down with beams of laser light. In recent years, physicists have found ways to create holograms with entangled photons instead. Now there is, literally, a new twist to the technology.

      Entangled photons that travel in corkscrew paths have resulted in holograms that offer the possibility of dense and ultrasecure data encryption, researchers report in a study to appear in Physical Review Letters.

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      Light can move in a variety of ways, including the up-and-down and side-to-side patterns of polarized light. But when it carries a type of rotation known as orbital angular momentum, it can also propagate in spirals that resemble twisted rotini pasta.

      Like any other photons, the twisted versions can be entangled so that they essentially act as one entity. Something that affects one of an entangled photon pair instantly affects the other, even if they are very far apart.

      In previous experiments, researchers have sent data through the air in entangled pairs of twisted photons (SN: 8/5/15). The approach should allow high-speed data transmission because light can come with different amounts of twist, with each twist serving as a different channel of communication.

      Now the same approach has been applied to record data in holograms. Instead of transmitting information on multiple, twisted light channels, photon pairs with different amounts of twist create distinct sets of data in a single hologram. The more orbital angular momentum states involved, each with different amounts of twist, the more data researchers can pack into a hologram.

      In addition to cramming more data into holograms, increasing the variety of twists used to record the data boosts security. Anyone who wants to read the information out needs to know, or guess, how the light that recorded it was twisted.

      For a hologram relying on two types of twist, says physicist Xiangdong Zhang of the Beijing Institute of Technology, you would have to pick the right combination of the twists from about 80 possibilities to decode the data. Bumping that up to combinations of seven distinct twists leads to millions of possibilities. That, Zhang says, “should be enough to ensure our quantum holographic encryption system has enough security level.”

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      The researchers demonstrated their technique by encoding words and letters in holograms and reading the data back out again with twisted light. Although the researchers produced images from the holographic data, says physicist Hugo Defienne of the Paris Institute of Nanosciences, the storage itself should not be confused with holographic images.

      Defienne, who was not involved with the new research, says that other quantum holography schemes, such as his efforts with polarized photons, produce direct images of objects including microscopic structures.

      “[Their] idea there is very different . . . from our approach in this sense,” Defrienne says. “They’re using holography to store information,” rather than creating the familiar 3-D images that most people associate with holograms.

      The twisted light data storage that Zhang and his colleagues demonstrated is slow, requiring nearly 20 minutes to decode an image of the acronym “BIT,” for the Beijing Institute of Technology where the experiments were performed. And the security that the researchers have demonstrated is still relatively low because they included only up to six forms of twisted light in their experiments.

      Zhang is confident that both limitations can be overcome with technical improvements. “We think that our technology has potential application in quantum information encryption,” he says, “especially quantum image encryption.” More

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      These shape-shifting devices melt and re-form thanks to magnetic fields

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      Shape-shifting liquid metal robots might not be limited to science fiction anymore.

      Miniature machines can switch from solid to liquid and back again to squeeze into tight spaces and perform tasks like soldering a circuit board, researchers report January 25 in Matter.

      This phase-shifting property, which can be controlled remotely with a magnetic field, is thanks to the metal gallium. Researchers embedded the metal with magnetic particles to direct the metal’s movements with magnets. This new material could help scientists develop soft, flexible robots that can shimmy through narrow passages and be guided externally.  

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      Scientists have been developing magnetically controlled soft robots for years. Most existing materials for these bots are made of either stretchy but solid materials, which can’t pass through the narrowest of spaces, or magnetic liquids, which are fluid but unable to carry heavy objects (SN: 7/18/19).

      In the new study, researchers blended both approaches after finding inspiration from nature (SN: 3/3/21). Sea cucumbers, for instance, “can very rapidly and reversibly change their stiffness,” says mechanical engineer Carmel Majidi of Carnegie Mellon University in Pittsburgh. “The challenge for us as engineers is to mimic that in the soft materials systems.”

      So the team turned to gallium, a metal that melts at about 30° Celsius — slightly above room temperature. Rather than connecting a heater to a chunk of the metal to change its state, the researchers expose it to a rapidly changing magnetic field to liquefy it. The alternating magnetic field generates electricity within the gallium, causing it to heat up and melt. The material resolidifies when left to cool to room temperature.

      Since magnetic particles are sprinkled throughout the gallium, a permanent magnet can drag it around. In solid form, a magnet can move the material at a speed of about 1.5 meters per second. The upgraded gallium can also carry about 10,000 times its weight.

      External magnets can still manipulate the liquid form, making it stretch, split and merge. But controlling the fluid’s movement is more challenging, because the particles in the gallium can freely rotate and have unaligned magnetic poles as a result of melting. Because of their various orientations, the particles move in different directions in response to a magnet.

      Majidi and colleagues tested their strategy in tiny machines that performed different tasks. In a demonstration straight out of the movie Terminator 2, a toy person escaped a jail cell by melting through the bars and resolidifying in its original form using a mold placed just outside the bars.

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      On the more practical side, one machine removed a small ball from a model human stomach by melting slightly to wrap itself around the foreign object before exiting the organ. But gallium on its own would turn to goo inside a real human body, since the metal is a liquid at body temperature, about 37° C. A few more metals, such as bismuth and tin, would be added to the gallium in biomedical applications to raise the material’s melting point, the authors say. In another demonstration, the material liquefied and rehardened to solder a circuit board.

      [embedded content]
      With the help of variable and permanent magnets, researchers turned chunks of gallium into shape-shifting devices. In the first clip, a toy figure escapes its jail cell by liquefying, gliding through the bars and resolidifying using a mold placed just outside the bars. In the second clip, one device removes a ball from a model human stomach by melting slightly to wrap itself around the foreign object and exiting the organ.

      Although this phase-shifting material is a big step in the field, questions remain about its biomedical applications, says biomedical engineer Amir Jafari of the University of North Texas in Denton, who was not involved in the work. One big challenge, he says, is precisely controlling magnetic forces inside the human body that are generated from an external device.

      “It’s a compelling tool,” says robotics engineer Nicholas Bira of Harvard University, who was also not involved in the study. But, he adds, scientists who study soft robotics are constantly creating new materials.

      “The true innovation to come lies in combining these different innovative materials.” More

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      Want a ‘Shrinky Dinks’ approach to nano-sized devices? Try hydrogels

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      High-tech shrink art may be the key to making tiny electronics, 3-D nanostructures or even holograms for hiding secret messages.

      A new approach to making tiny structures relies on shrinking them down after building them, rather than making them small to begin with, researchers report in the Dec. 23 Science.

      The key is spongelike hydrogel materials that expand or contract in response to surrounding chemicals (SN: 1/20/10). By inscribing patterns in hydrogels with a laser and then shrinking the gels down to about one-thirteenth their original size, the researchers created patterns with details as small as 25 billionths of a meter across.

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      At that level of precision, the researchers could create letters small enough to easily write this entire article along the circumference of a typical human hair.

      Biological scientist Yongxin Zhao and colleagues deposited a variety of materials in the patterns to create nanoscopic images of Chinese zodiac animals. By shrinking the hydrogels after laser etching, several of the images ended up roughly the size of a red blood cell. They included a monkey made of silver, a gold-silver alloy pig, a titanium dioxide snake, an iron oxide dog and a rabbit made of luminescent nanoparticles.

      These two dragons, each roughly 40 micrometers long, were made by depositing cadmium selenide quantum dots onto a laser-etched hydrogel. The red stripes on the left dragon are each just 200 nanometers thick.The Chinese University of Hong Kong, Carnegie Mellon University

      Because the hydrogels can be repeatedly shrunk and expanded with chemical baths, the researchers were also able to create holograms in layers inside a chunk of hydrogel to encode secret information. Shrinking a hydrogel hologram makes it unreadable. “If you want to read it, you have to expand the sample,” says Zhao, of Carnegie Mellon University in Pittsburgh. “But you need to expand it to exactly the same extent” as the original. In effect, knowing how much to expand the hydrogel serves as a key to unlock the information hidden inside.  

      But the most exciting aspect of the research, Zhao says, is the wide range of materials that researchers can use on such minute scales. “We will be able to combine different types of materials together and make truly functional nanodevices.” More