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    Two real-world tests of quantum memories bring a quantum internet closer to reality

    In the quest to build a quantum internet, scientists are putting their memories to the test. Quantum memories, that is.

    Quantum memories are devices that store fragile information in the realm of the very small. They’re an essential component for scientists’ vision of quantum networks that could allow new types of communication, from ultra-secure messaging to linking up far-flung quantum computers (SN: 6/28/23). Such memories would help scientists establish quantum connections, or entanglement, throughout a network (SN: 2/12/20). More

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    The neutrino’s quantum fuzziness is beginning to come into focus

    Neutrinos are known for funny business. Now scientists have set a new limit on a quantum trait responsible for the subatomic particles’ quirkiness: uncertainty.

    The lightweight particles morph from one variety of neutrino to another as they travel, a strange phenomenon called neutrino oscillation (SN: 10/6/15). That ability rests on quantum uncertainty, a sort of fuzziness intrinsic to the properties of quantum objects, such as their location or momentum. But despite the importance of quantum uncertainty, the uncertainty in the neutrino’s position has never been directly measured.  More

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    Artificial intelligence helped scientists create a new type of battery 

    In the hunt for new materials, scientists have traditionally relied on tinkering in the lab, guided by intuition, with a hefty serving of trial and error.

    But now a new battery material has been discovered by combining two computing superpowers: artificial intelligence and supercomputing. It’s a discovery that highlights the potential for using computers to help scientists discover materials suited to specific needs, from batteries to carbon capture technologies to catalysts. 

    Calculations winnowed down more than 32 million candidate materials to just 23 promising options, researchers from Microsoft and Pacific Northwest National Laboratory, or PNNL, report in a paper submitted January 8 to arXiv.org. The team then synthesized and tested one of those materials and created a working battery prototype. More

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    A maverick physicist is building a case for scrapping quantum gravity

    A rift runs deep through the heart of physics. The general theory of relativity, which describes gravity, clashes with quantum physics. In an effort to seal that physics fissure, untold numbers of physicists have spent their careers working to build a theory of quantum gravity.

    But one physicist is championing a radically different path. Jonathan Oppenheim thinks that gravity might be fundamentally classical, meaning it isn’t quantum at all. It’s an unconventional idea, to say the least.

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    “When we started, maybe 99 percent of our colleagues thought we were crackpots and that’s now down to maybe 70 percent,” quips Oppenheim, of University College London.

    All known forces except gravity are formulated in terms of quantum physics. The prevailing view is that gravity will need to assimilate with its quantum colleagues. But gravity is different, Oppenheim argues. While other forces evolve within a landscape of spacetime, gravity is the warping of spacetime itself. So, Oppenheim says, “it is pretty unclear that it should have a quantum nature, in my view.”

    Physicists have devised several “no-go” theorems that seemingly forbid a classical theory of gravity. Such theorems highlight inconsistencies, apparently fatal to the idea, that arise when classical gravity is applied to quantum particles. But it’s possible to get around those prohibitions by adding some randomness to the way that spacetime bends in response to quantum particles, Oppenheim reports December 4 in Physical Review X.

    Consider the famous double-slit experiment of quantum physics (SN: 5/3/19). Particles are sent toward a detector, separated by a barrier with two slits in it. When those particles arrive at the detector, they create a stripy pattern called an interference pattern. That pattern arises because, in quantum physics, the particle isn’t constrained to pass through one slit or the other. Instead, it can exist in a superposition, taking a quantum combination of both possible routes. If a scientist makes a measurement to determine which slit the particle passed through, that pattern disappears.

    When particles, in this case particles of light called photons, are sent toward a barrier with two slits in it, the particles produce an interference pattern (stripes) due to quantum effects.Dorling Kindersley/Getty Images

    If a standard classical picture of gravity were correct, it would be possible to measure the gravitational field of that particle so precisely that you could determine which slit the particle went through. This possibility would destroy the interference pattern, even without actually doing the measurement. Because scientists do observe interference patterns in the lab, that’s a big blow for a standard classical theory of gravity.

    But the randomness baked into Oppenheim’s theory means that, instead of a particle having a determined gravitational field, the field fluctuates. That means, unlike for the standard version of classical gravity, it’s not possible to determine which slit a particle went through by precisely measuring its gravitational field. Particles can pass through the slits in a superposition, and the interference pattern is saved, restoring the possibility gravity could be classical.

    Experiments can test this theory by searching for evidence of those random gravitational fluctuations, Oppenheim and colleagues report December 4 in Nature Communications. “Essentially, you very precisely measure the response of a mass to a gravitational field,” says study coauthor Zach Weller-Davies, who completed the work at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.

    This is not the first time scientists have proposed a way to make classical gravity comport with quantum physics. But Oppenheim has been “leading a renaissance,” says physicist Vivishek Sudhir of MIT. Sudhir hopes to test the theory with another type of experiment, measuring the correlations between the motions of two masses that interact gravitationally, he and a colleague report September 16 at arXiv.org.

    However, the theory has features some physicists might find unsatisfying. For example, the randomness involved means that the theory is not reversible: Unlike other theories, there’s no way to start from the endpoint of an interaction and trace its steps backward.

    Still, even some quantum gravity believers think that the work has merit.

    “The reason why this work is interesting for me is not really because I would believe that gravity is classical,” says Flaminia Giacomini of ETH Zurich. The result, she says, is interesting regardless of whether gravity is found to be classical or quantum. That’s because, in order for an experiment to confidently proclaim that gravity is quantum, scientists need to understand the possibilities for classical gravity. “Only in that way will we be able to prove in a strong way that gravity is not compatible with a classical description.” More

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    Salty sweat helps one desert plant stay hydrated

    Sweat keeps some animals cool in scorching heat. Salty secretions also serve one desert shrub a refreshing sip of water. 

    The Athel tamarisk uses a special selection of salts excreted from its leaves to pull water from the air, researchers report October 30 in the Proceedings of the National Academy of Sciences. This study provides new insights into the clever chemical strategies that plants have evolved to survive in harsh environments.

    The Athel tamarisk (Tamarix aphylla) thrives in the arid, salt-rich soils of coastal flats across the Middle East. That’s because the tamarisk is a halophyte, a type of plant that secretes excess salt in concentrated droplets from glands in its leaves. The moisture from these briny excretions dissipates in the heat of the day, leaving the tamarisk encrusted in white crystals that shake off in the wind.

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    While driving through the hot, humid deserts of the United Arab Emirates, materials scientist Marieh Al-Handawi of New York University Abu Dhabi noticed water condensing on these crystals. There are lots of plants with leaf structures adapted to attract liquid water from fog. But Al-Handawi, who looks to nature for strategies to tackle water scarcity, suspected that the chemical composition of the excreted salts might have something to do with the dew.

    To investigate, Al-Handawi and her team recorded time-lapse videos of Athel tamarisk plants in their natural habitat. These recordings showed that salt crystals that form from daytime excretions swell with water at night. Back in the lab, the researchers found that at 35° Celsius and 80 percent relative humidity, a naturally encrusted branch collected 15 milligrams of water on its leaves after two hours, while a washed branch yielded only about one-tenth as much.

    “This result was conclusive to us,” Al-Handawi says, “because it proved salts are the main contributor to the water harvesting, and it’s not the surface of the plant.” What’s more, the researchers observed dew form on the crystals down to just 50 percent relative humidity. 

    When the scientists scrutinized the mineral makeup of the tamarisk’s saline sprinkles, they found more than 10 different types of salt all crystallized together. These crystals are made mostly of sodium chloride and gypsum. Yet the researchers also spotted traces of a secret ingredient: lithium sulfate. This mineral is exceptionally good at taking in water and at much lower humidity than either sodium chloride or gypsum. While sodium chloride and gypsum bring in the largest volumes of water, the addition of lithium sulfate to the mineral mélange, the researchers say, helps explain how the tamarisk collects water even at low humidity.

    “This paper provides a new level of detailed understanding of how some desert plants can both excrete salt and use it to take up water from the air into leaves,” says plant physiologist and ecologist Lawren Sack of UCLA, who was not involved in the study.

    He is excited to see the chemical complexity of the salts involved. Desert plants have evolved intricate chemical strategies to squeeze every last drop of water from the environment, he says, and most of those systems await discovery.

    Al-Handawi agrees, noting that the salt recipe may differ across regions and seasons. It makes her hopeful, she says, that there are other exciting water-harvesting materials waiting to be found in the desert. More

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    The development of quantum dots wins the 2023 Nobel prize in chemistry

    Work on tiny dots that light up TV screens and help doctors see the blood vessels that feed tumors has earned three scientists the 2023 Nobel Prize in chemistry.  

    Chemist Moungi Bawendi, chemist Louis Brus and physicist Alexei Ekimov split the prize for the discovery and synthesis of quantum dots, the Royal Swedish Academy of Sciences announced October 4.

    Chemist Moungi Bawendi (left), chemist Louis Brus (middle) and physicist Alexei Ekimov (right) have split the 2023 Nobel Prize in chemistry for “the discovery and development of quantum dots, nanoparticles so tiny that their size determines their properties.”MIT, Columbia University, Nexdot

    “Quantum dots are a new class of materials, different from molecules,” said Heiner Linke, a member of the Nobel committee. Just adjusting the size of these nanoparticles, roughly a few billionths of a meter across, can change their properties — optical, electric, magnetic, even melting points — thanks to quantum mechanics (SN: 6/29/15). 

    That’s also true of color. “If you want to make different colors with molecules, you would choose a new molecule, a new set of atoms” arranged in a different structure, Linke said. But quantum dots of different colors have the exact same arrangement of atoms. The only difference is particle size.

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    When quantum dots are irradiated by light, electrons within get energized, eventually releasing that energy as fluorescent light. The smaller the dots are, the more they compress the wave function of an electron, increasing its energy so that the dot appears blue. Larger dots appear red. 

    Dots of the same size made from different materials may also emit slightly different wavelengths of light, says Jean-Marc Pecourt, a chemist at CAS, a division of the American Chemical Society. Quantum dots are usually made from semiconductor materials, such as graphene, selenite or metal sulfides, Pecourt says. So by adjusting materials or the size of quantum dots, chemists can alter their properties for a wide variety of uses.

    The idea that the size of these nanoparticles could alter their properties was predicted nearly a century ago, but at the time it seemed impossible to reproduce that effect in the real world. To do that, researchers would need a perfectly crystalline material, and would need to control the size of the nanomaterial very precisely, sculpting it atom layer by atom layer.  

    Then, in the early 1980s, Ekimov and Brus independently showed that it could be done. Ekimov, now at Nanocrystals Technology, Inc., in Briarcliff Manor, N.Y., demonstrated this in glass, adding copper chloride to produce tiny crystals and revealing that the color of the glass was linked to the size of those crystals. Brus, of Columbia University, made a similar discovery, but in a different context: He demonstrated the link between size and color for nanoparticles floating freely in a solution and in gaseous compounds (SN: 10/3/92). 

    Those discoveries triggered intense interest in how to harness these little dots for a variety of applications. But manufacturing them would require being able to control the size of the particles to precise specifications. 

    A decade later, Bawendi, of MIT, developed a method to precisely control the speed of the crystals’ growth in a solution, figuring out how to stop them right when they reach a desired size. He did this by first injecting chemical reagents into the solution that instantaneously formed the tiny crystals and then promptly adjusting the temperature of the solution, halting their growth. 

    “I’m deeply honored and surprised and shocked by the announcement this morning,” Bawendi said October 4 during an MIT news conference. “I’m especially honored to share this with Lou Brus, who was my postdoctoral mentor [from] whom I learned so much. I tried to emulate his scholarship and his mentoring style as a professor myself when I came to MIT.” 

    Bawendi started working on quantum dots after he met Brus at Nokia Bell Labs, headquartered in Murray Hill, N.J. The researchers needed high quality quantum dots to study the physics of the nanoparticles, Bawendi said. “It wasn’t because I wanted to make the best quantum dots possible for application, it was because we needed to make the best possible quantum dots to study them.” It took years of trial and error to work out the method, he said.

    By making it possible to manufacture quantum dots, Bawendi’s method opened up a world of possible uses for the nanoparticles. Quantum dots make it possible to very precisely change the color of LED lights and dramatically improve their efficiency. Dots that glow with fluorescent light, injected into the body and attached to immune cells that swarm to cancerous tissues, can help surgeons distinguish even hard-to-see tumors (SN: 8/3/04). The ability to be tuned to absorb different wavelengths of light could also allow the manufacture of customized solar cells that are highly efficient in different light conditions. The dots might also be used to build quantum computers, Pecourt says (SN: 2/14/18). 

    Biomedical engineer and chemist Warren Chan says the prize is well deserved. “They’re the ones who built the foundation,” says Chan, of the University of Toronto. “I’m really happy that the field is getting credit for really changing the world, not just in quantum dots, but in a lot of different areas.” 

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    One of the first applications came in the late 1990s when Chan and colleagues used quantum dots to tag cells in the lab, he says. “The surface modifications that were used for integrating quantum dots for applications were then also adapted for other types of nanoparticles.”

    The Nobel committee looks not only at past contributions, but also the effect a discovery may have on the future, Chan says. The ability to tune nanoparticles by changing their size or surface properties could open a wide variety of possibilities that have not yet been explored. Chan and colleagues are now using quantum dots to detect infectious diseases, including HIV, influenza and hepatitis B.

    “I was absolutely thrilled to see this,” says Judith Giordan, president of the American Chemical Society. “We have three people recognized who brought this technology from a dream, a hope, a theoretical construct … all the way through synthesis and manufacture.”

    Earlier this week, the development of mRNA vaccines — widely speculated as a candidate for the 2023 chemistry Nobel Prize — received the Nobel in medicine or physiology instead (SN: 10/2/23). 

    “Sometimes chemistry gets a bad rap,” Giordan says. “But here are two magnificent examples of how chemistry has solved problems in the world.”

    The three winners will share the prize of 11 million Swedish kronor, or about $1 million. More

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    Chemists turned plastic waste into tiny bars of soap

    Luis Melecio-Zambrano is the summer 2023 science writing intern at Science News. They are finishing their master’s degree in science communication from the University of California, Santa Cruz, where they have reported on issues of environmental justice and agriculture. More

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    Tear-resistant rubbery materials could pave the way for tougher tires

    A new material design could reduce pollution where the rubber meets the road.

    Strategically adding weak points along microscopic chains called polymers actually makes them harder to tear, researchers report in the June 23 Science. Because polymers are used in car tires, the findings could help reduce plastic pollution as tires wear down over time.

    When tires scrape against the road, they drop tiny particles of rubber and plastic polymers, which pollute waterways and contaminate the air (SN: 11/12/18). Every year, tires release an estimated 6 million metric tons of these microplastics into the environment. Stronger polymers that break apart less easily could limit the amount of particles shed annually. More