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    This stick-on ultrasound patch could let you watch your own heart beat

    Picture a smartwatch that doesn’t just show your heart rate, but a real-time image of your heart as it beats in your chest. Researchers may have taken the first step down that road by creating a wearable ultrasound patch — think of a Band-Aid with sonar — that provides a flexible way to see deep inside the body. 

    Ultrasound, which maps tissues and fluids by recording how sound waves bounce off them, can help doctors examine organs for damage, diagnose cancer or even track bacteria (SN: 1/3/18). But most ultrasound machines aren’t portable, and the wearable ones either struggle to spot details or can be used for only short periods. 

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    The new patch can work for up to 48 hours straight — even while the user is doing something active, like exercising. And the miniature device sees just as well as a more unwieldy hospital machine, researchers report in the July 29 Science. 

    “This is just the beginning,” says Xuanhe Zhao, a mechanical engineer at MIT. His team plans to make the patch wireless and able to interface with a user’s phone, which could then show the ultrasound signals as 3-D images. 

    The medical possibilities range wide. Stick a patch over a person’s heart, and the frequent images it takes could help predict heart attacks and blood clots potentially months before disaster hits, explains Aparna Singh, a biomedical engineer at Columbia University. Placed on a COVID-19 patient, the patch — which is only about the size of a quarter — could be an easy way to catch lung problems as they develop.

    “This also has a huge potential to be available for developing countries,” where limited access to hospitals can make monitoring patients difficult, Singh says. The patch costs about $100 to make. One of the researchers’ next steps will be to try to make the device cheaper. More

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    Quantum entanglement makes quantum communication even more secure

    Stealthy communication just got more secure, thanks to quantum entanglement.

    Quantum physics provides a way to share secret information that’s mathematically proven to be safe from the prying eyes of spies. But until now, demonstrations of the technique, called quantum key distribution, rested on an assumption: The devices used to create and measure quantum particles have to be known to be flawless. Hidden defects could allow a stealthy snoop to penetrate the security unnoticed.

    Now, three teams of researchers have demonstrated the ability to perform secure quantum communication without prior confirmation that the devices are foolproof. Called device-independent quantum key distribution, the method is based on quantum entanglement, a mysterious relationship between particles that links their properties even when separated over long distances.

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    In everyday communication, such as the transmission of credit card numbers over the internet, a secret code, or key, is used to garble the information, so that it can be read only by someone else with the key. But there’s a quandary: How can a distant sender and receiver share that key with one another while ensuring that no one else has intercepted it along the way?

    Quantum physics provides a way to share keys by transmitting a series of quantum particles, such as particles of light called photons, and performing measurements on them. By comparing notes, the users can be sure that no one else has intercepted the key. Those secret keys, once established, can then be used to encrypt the sensitive intel (SN: 12/13/17). By comparison, standard internet security rests on a relatively shaky foundation of math problems that are difficult for today’s computers to solve, which could be vulnerable to new technology, namely quantum computers (SN: 6/29/17).

    But quantum communication typically has a catch. “There cannot be any glitch that is unforeseen,” says quantum physicist Valerio Scarani of the National University of Singapore. For example, he says, imagine that your device is supposed to emit one photon but unknown to you, it emits two photons. Any such flaws would mean that the mathematical proof of security no longer holds up. A hacker could sniff out your secret key, even though the transmission seems secure.

    Device-independent quantum key distribution can rule out such flaws. The method builds off of a quantum technique known as a Bell test, which involves measurements of entangled particles. Such tests can prove that quantum mechanics really does have “spooky” properties, namely nonlocality, the idea that measurements of one particle can be correlated with those of a distant particle. In 2015, researchers performed the first “loophole-free” Bell tests, which certified beyond a doubt that quantum physics’ counterintuitive nature is real (SN: 12/15/15).

    “The Bell test basically acts as a guarantee,” says Jean-Daniel Bancal of CEA Saclay in France. A faulty device would fail the test, so “we can infer that the device is working properly.”

    In their study, Bancal and colleagues used entangled, electrically charged strontium atoms separated by about two meters. Measurements of those ions certified that their devices were behaving properly, and the researchers generated a secret key, the team reports in the July 28 Nature.

    Typically, quantum communication is meant for long-distance dispatches. (To share a secret with someone two meters away, it would be easier to simply walk across the room.) So Scarani and colleagues studied entangled rubidium atoms 400 meters apart. The setup had what it took to produce a secret key, the researchers report in the same issue of Nature. But the team didn’t follow the process all the way through: The extra distance meant that producing a key would have taken months.

    In the third study, published in the July 29 Physical Review Letters, researchers wrangled entangled photons rather than atoms or ions. Physicist Wen-Zhao Liu of the University of Science and Technology of China in Hefei and colleagues also demonstrated the capability to generate keys, at distances up to 220 meters. This is particularly challenging to do with photons, Liu says, because photons are often lost in the process of transmission and detection.

    Loophole-free Bell tests are already no easy feat, and these techniques are even more challenging, says physicist Krister Shalm of the National Institute of Standards and Technology in Boulder, Colo. “The requirements for this experiment are so absurdly high that it’s just an impressive achievement to be able to demonstrate some of these capabilities,” says Shalm, who wrote a perspective in the same issue of Nature.

    That means that the technique won’t see practical use anytime soon, says physicist Nicolas Gisin of the University of Geneva, who was not involved with the research.

    Still, device-independent quantum key distribution is “a totally fascinating idea,” Gisin says. Bell tests were designed to answer a philosophical question about the nature of reality — whether quantum physics really is as weird as it seems. “To see that this now becomes a tool that enables something else,” he says, “this is the beauty.” More

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    Quantum physics exponentially improves some types of machine learning

    Machine learning can get a boost from quantum physics.

    On certain types of machine learning tasks, quantum computers have an exponential advantage over standard computation, scientists report in the June 10 Science. The researchers proved that, according to quantum math, the advantage applies when using machine learning to understand quantum systems. And the team showed that the advantage holds up in real-world tests.

    “People are very excited about the potential of using quantum technology to improve our learning ability,” says theoretical physicist and computer scientist Hsin-Yuan Huang of Caltech. But it wasn’t entirely clear if machine learning could benefit from quantum physics in practice.

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    In certain machine learning tasks, scientists attempt to glean information about a quantum system — say a molecule or a group of particles — by performing repeated experiments, and analyzing data from those experiments to learn about the system.

    Huang and colleagues studied several such tasks. In one, scientists aim to discern properties of the quantum system, such as the position and momentum of particles within. Quantum data from multiple experiments could be input into a quantum computer’s memory, and the computer would process the data jointly to learn the quantum system’s characteristics.

    The researchers proved theoretically that doing the same characterization with standard, or classical, techniques would require exponentially more experiments in order to learn the same information. Unlike a classical computer, a quantum computer can exploit entanglement — ethereal quantum linkages — to better analyze the results of multiple experiments.

    But the new work goes beyond just the theoretical. “It’s crucial to understand if this is realistic, if this is something we could see in the lab or if this is just theoretical,” says Dorit Aharonov of Hebrew University in Jerusalem, who was not involved with the research.

    So the researchers tested machine learning tasks with Google’s quantum computer, Sycamore (SN: 10/23/19). Rather than measuring a real quantum system, the team used simulated quantum data, and analyzed it using either quantum or classical techniques.

    Quantum machine learning won out there, too, even though Google’s quantum computer is noisy, meaning errors can slip into calculations. Eventually, scientists plan to build quantum computers that can correct their own errors (SN: 6/22/20). But for now, even without that error correction, quantum machine learning prevailed. More

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    Experiments hint at why bird nests are so sturdy

    To build its nest, a bird won’t go for any old twig. Somehow, birds pick and choose material that will create a cozy, sturdy nest.

    “That’s just totally mystifying to me,” says physicist Hunter King of the University of Akron in Ohio. Birds seem to have a sense for how the properties of an individual stick will translate to the characteristics of the nest. That relationship “is something we don’t know the first thing about predicting,” King says.

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    A bird’s nest is a special version of a granular material: a substance, such as sand, made up of many smaller objects (SN: 4/30/19). King and colleagues combined laboratory experiments and computer simulations to better understand the quirks of nestlike granular materials, the researchers report in a study to appear in Physical Review Letters.

    In the experiments, a piston repeatedly compressed 460 bamboo rods scattered inside a cylinder. The computer simulations let researchers analyze the points where sticks touched, which is key to understanding the material, the team says.

    The more force the piston applied to the pile, the stiffer the pile became, meaning it resisted further deformation. As the piston bore down, sticks slid against one another, and the contact points between them rearranged. That stiffened the pile by allowing additional contact points to form between sticks, which prevented them from flexing further, the simulations showed.

    Changes in the pile’s stiffness seemed to lag behind the piston’s motion, a phenomenon called hysteresis. That effect caused the pile to be stiffer when the piston pushed in than when the material bounced back as the piston retracted. Simulations suggest that the hysteresis arose because the initial friction between sticks needed to be overcome before the contact points started to rearrange.

    Beyond bird nests, this research could be applied to other materials made of disordered arrangements of long fibers, such as felt. With a better understanding of the physical qualities of such materials, engineers could use them to create new structures designed to protect not only bird eggs, but other cargo that humans consider precious. More

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    This fabric can hear your heartbeat

    Someday our clothing may eavesdrop on the soundtrack of our lives, capturing the noises around and inside us.

    A new fiber acts as a microphone — picking up speech, rustling leaves and chirping birds — and turns those acoustic signals into electrical ones. Woven into a fabric, the material can even hear handclaps and faint sounds, such as its wearer’s heartbeat, researchers report March 16 in Nature. Such fabrics could provide a comfortable, nonintrusive — even fashionable — way to monitor body functions or aid with hearing.

    Acoustic fabrics have existed for perhaps hundreds of years, but they’re used to dampen sound, says Wei Yan, a materials scientist at Nanyang Technological University in Singapore. Fabric as a microphone is “totally a different concept,” says Yan, who worked on the fabric while at MIT.

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    Yan and his colleagues were inspired by the human eardrum. Sound waves cause vibrations in the eardrum, which are converted to electrical signals by the cochlea. “It turns out that this eardrum is made of fibers,” says Yoel Fink, a materials scientist at MIT. In the eardrum’s inner layers, collagen fibers radiate from the center, while others form concentric rings. The crisscrossing fibers play a role in hearing and look similar to the fabrics people weave, Fink says.

    Analogous to what’s happening in an eardrum, sound vibrates fabric at the nanoscale. In the new fabric, cotton fibers and others of a somewhat stiff material called Twaron efficiently convert incoming sound to vibrations. Woven together with these threads is a single fiber that contains a blend of piezoelectric materials, which produce a voltage when pressed or bent (SN: 8/22/17). The buckling and bending of the piezoelectric-containing fiber create electrical signals that can be sent through a tiny circuit board to a device that reads and records the voltage.

    The fabric microphone is sensitive to a range of noise levels, from a quiet library to heavy traffic, the team reports, although it is continuing to investigate what signal processing is needed to detangle target sounds from ambient noise. Integrated into clothing, this sound-sensing fabric feels like regular fabric, Yan says. And it continued to work as a microphone after washing it 10 times.

    Woven into fabric, a specialized fiber (pictured, center) creates electrical signals when bent or buckled, turning the entire material into a microphone.Fink Lab/MIT, Elizabeth Meiklejohn/RISD, Greg Hren

    Piezoelectric materials have “huge potential” for applications from observing the function of bodies to monitoring the integrity of aircraft materials, says Vijay Thakur, a materials scientist at Scotland’s Rural College in Edinburgh who was not part of this work. They’ve even been proposed for energy generation, but, he says, many uses have been limited by the tiny voltages they produce (SN: 10/1/15). The way the fibers are made in this fabric — sandwiching a blend of piezoelectric materials between other components, including a flexible, stretchy outer material — concentrates the energy from the vibrations into the piezoelectric layer, enhancing the signal it produces.

    As a proof of concept, the team incorporated the fabric into a shirt, which could hear its wearer’s heart like a stethoscope does. Used this way, the fabric microphone could listen for murmurs and may someday be able to provide information similar to an echocardiogram, an ultrasound of the heart, Thakur says. If it proves effective as a monitoring and diagnostic tool, placing such microphones into clothing may someday make it easier for doctors to track heart conditions in young children, who have trouble keeping still, he says.

    The team also anticipates that fabric microphones could aid hearing and communication. Another shirt the team created had two piezoelectric fibers spaced apart on the shirt’s back. Based on when each fiber picked up the sound, this shirt can be used to detect the direction a clap came from. And when hooked up to a power source, the fabric microphones can project sound as a speaker.

    “For the past 20 years, we’ve been trying to introduce a new way of thinking about fabrics,” Fink says. Beyond providing beauty and warmth, fabrics may help solve technological problems. And perhaps, Fink says, they can beautify technology too.  More

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    A new gravity sensor used atoms’ weird quantum behavior to peer underground

    The best way to find buried treasure may be with a quantum gravity sensor.

    In these devices, free-falling atoms reveal subtle variations in Earth’s gravitational pull at different places. Those variations reflect differences in the density of material beneath the sensor — effectively letting the instrument peer underground. In a new experiment, one of these machines teased out the tiny gravitational signature of an underground tunnel, researchers report in the Feb. 24 Nature.

    “Instruments like this would find many, many applications,” says Nicola Poli, an experimental physicist at the University of Florence, who coauthored a commentary on the study in the same issue of Nature.

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    Poli imagines using quantum gravity sensors to monitor groundwater or magma beneath volcanoes, or to help archaeologists uncover hidden tombs or other artifacts without having to dig them up (SN: 11/2/17). These devices could also help farmers check soil quality or help engineers inspect potential construction sites for unstable ground.

    “There are many tools to measure gravity,” says Xuejian Wu, an atomic physicist at Rutgers University in Newark, N.J., who wasn’t involved in the study. Some devices measure how far gravity pulls down a mass hanging from a spring. Other tools use lasers to clock how fast an object tumbles down a vacuum chamber. But free-falling atoms, like those in quantum gravity sensors, are the most pristine, reliable test masses out there, Wu says. As a result, quantum sensors promise to be more accurate and stable in the long run than other gravity probes.

    Inside a quantum gravity sensor, a cloud of supercooled atoms is dropped down a chute. A pulse of light then splits each of the falling atoms into a superposition state — a quantum limbo where each atom exists in two places at once (SN: 11/7/19). Due to their slightly different positions in Earth’s gravitational field, the two versions of each atom feel a different downward tug as they fall. Another light pulse then recombines the split atoms.

    Thanks to the atoms’ wave-particle duality — a strange rule of quantum physics that says atoms can act like waves — the reunited atoms interfere with each other (SN: 1/13/22). That is, as the atom waves overlap, their crests and troughs can reinforce or cancel each other out, creating an interference pattern. That pattern reflects the slightly different downward pulls that the split versions of each atom felt as they fell — revealing the gravity field at the atom cloud’s location.

    Extremely precise measurements made by such atom-based devices have helped test Einstein’s theory of gravity (SN: 10/28/20) and measure fundamental constants, such as Newton’s gravitational constant (SN: 4/12/18). But atom-based gravity sensors are highly sensitive to vibrations from seismic activity, traffic and other sources.

    “Even very, very small vibrations create enough noise that you have to measure for a long time” at any location to weed out background tremors, says Michael Holynski, a physicist at the University of Birmingham in England. That has made quantum gravity sensing impractical for many uses outside the lab.  

    Holynski’s team solved that problem by building a gravity sensor with not one but two falling clouds of rubidium atoms. With one cloud suspended a meter above the other, the instrument could gauge the strength of gravity at two different heights in a single location. Comparing those measurements allowed the researchers to cancel out the effects of background noise.

    Holynski and colleagues tested whether their sensor — a 2-meter-tall chute on wheels tethered to a rolling cart of equipment — could detect an underground passageway on the University of Birmingham campus. The 2-by-2-meter concrete tunnel lay beneath a road between two multistory buildings. The quantum sensor measured the local gravitational field every 0.5 meters along an 8.5-meter line that crossed over the tunnel. Those readouts matched the predictions of a computer simulation, which had estimated the gravitational signal of the tunnel based on its structure and other factors that could influence the local gravitational field, such as nearby buildings.

    Based on the machine’s sensitivity in this experiment, it could probably provide a reliable gravity measurement at each location in less than two minutes, the researchers estimate. That’s about one-tenth the time needed for other types of gravity sensors.

    The team has since built a downsized version of the gravity sensor used in the tunnel-detecting experiment. The new machine weighs about 15 kilograms, compared with the 300-kilogram beast used for the tunnel test. Other upgrades could also boost the gravity sensor’s speed.

    In the future, engineer Nicole Metje envisions building a quantum gravity sensor that could be pushed from place to place like a lawn mower. But portability isn’t the only challenge for making these tools more user-friendly, says Metje, a coauthor on the study who is also at the University of Birmingham. “At the moment, we still need someone with a physics degree to operate the sensor.”

    So hopeful beachcombers may be waiting a long time to trade in their metal detectors for quantum gravity sensors. More

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    Core memory weavers and Navajo women made the Apollo missions possible

    The historic Apollo moon missions are often associated with high-visibility test flights, dazzling launches and spectacular feats of engineering. But intricate, challenging handiwork — comparable to weaving — was just as essential to putting men on the moon. Beyond Neil Armstrong, Buzz Aldrin and a handful of other names that we remember were hundreds of thousands of men and women who contributed to Apollo over a decade. Among them: the Navajo women who assembled state-of-the-art integrated circuits for the Apollo Guidance Computer and the women employees of Raytheon who wove the computer’s core memory.

    In 1962, when President John F. Kennedy declared that putting Americans on the moon should be the top priority for NASA, computers were large mainframes; they occupied entire rooms. And so one of the most daunting yet crucial challenges was developing a highly stable, reliable and portable computer to control and navigate the spacecraft.

    NASA chose to use cutting-edge integrated circuits in the Apollo Guidance Computer. These commercial circuits had been introduced only recently. Also known as microchips, they were revolutionizing electronics and computing, contributing to the gradual miniaturization of computers from mainframes to today’s smartphones. NASA sourced the circuits from the original Silicon Valley start-up, Fairchild Semiconductor. Fairchild was also leading the way in the practice known as outsourcing; the company opened a factory in Hong Kong in the early 1960s, which by 1966 employed 5,000 people, compared with Fairchild’s 3,000 California employees.

    At the same time, Fairchild sought low-cost labor within the United States. Lured by tax incentives and the promise of a labor force with almost no other employment options, Fairchild opened a plant in Shiprock, N.M., within the Navajo reservation, in 1965. The Fairchild factory operated until 1975 and employed more than 1,000 individuals at its peak, most of them Navajo women manufacturing integrated circuits.

    It was challenging work. Electrical components had to be placed on tiny chips made of a semiconductor such as silicon and connected by wires in precise locations, creating complex and varying patterns of lines and geometric shapes. The Navajo women’s work “was performed using a microscope and required painstaking attention to detail, excellent eyesight, high standards of quality and intense focus,” writes digital media scholar Lisa Nakamura.

    A brochure commemorating the dedication of Fairchild Semiconductor’s plant in Shiprock, N.M., included this Fairchild 9040 integrated circuit.Courtesy of the Computer History Museum

    In a brochure commemorating the dedication of the Shiprock plant, Fairchild directly compared the assembly of integrated circuits with what the company portrayed as the traditional, feminine, Indigenous craft of rug-weaving. The Shiprock brochure juxtaposed a photo of a microchip with one of a geometric-patterned rug, and another of a woman weaving such a rug. That portrayal, Nakamura argues, reinforced racial and gender stereotypes. The work was dismissed as “women’s work,” depriving the Navajo women of appropriate recognition and commensurate compensation.  Journalists and Fairchild employees also “depict[ed] electronics manufacture as a high-tech version of blanket weaving performed by willing and skillful Indigenous women,” Nakamura notes, yet “the women who performed this labor did so for the same reason that women have performed factory labor for centuries — to survive.”

    Far from the Shiprock desert, outside of Boston, women employees at Raytheon assembled the Apollo Guidance Computer’s core memory with a process that in this case directly mimicked weaving. Again, the moon missions demanded a stable and compact way of storing Apollo’s computing instructions. Core memory used metal wires threaded through tiny doughnut-shaped ferrite rings, or “cores,” to represent 1s and 0s. All of this core memory was woven by hand, with women sitting on opposite sides of a panel passing a wire-threaded needle back and forth to create a particular pattern. (In some cases, a woman worked alone, passing the needle through the panel to herself.)

    Women employees of Raytheon assembled core memory for the Apollo Guidance Computer by threading metal wires through rings. (This unnamed woman was described as a “space age needleworker” in a Raytheon press kit.)Courtesy of the collection of David Meerman Scott, Raytheon public relations

    Apollo engineers referred to this process of building memory as the “LOL,” or “Little Old Ladies,” method. Yet this work was so mission critical that it was tested and inspected multiple times. Mary Lou Rogers, who worked on Apollo, recalled, “[Each component] had to be looked at by three of four people before it was stamped off. We had a group of inspectors come in for the federal government to check our work all the time.”

    The core memory was also known as rope memory, and those who supervised its development were “rope mothers.” We know a great deal about one rope mother — Margaret Hamilton. She has been recognized with the Presidential Medal of Freedom, among other awards, and is now remembered as the woman who oversaw most of the Apollo software. But her efforts were unrecognized by many at the time. Hamilton recalled, “At the beginning, nobody thought software was that big a deal. But then they began to realize how much they were relying on it…. Astronauts‘ lives were at stake. Our software needed to be ultrareliable and it needed to be able to detect an error and recover from it at any time during the mission. And it all had to fit on the hardware.” Yet, little is known about the thousands of others who performed this mission-critical work of weaving integrated circuits and core memory.

    Margaret Hamilton is known for overseeing the development of the Apollo software. Draper Laboratory, restored by Adam Cuerden/Wikimedia Commons

    At the time, Fairchild’s representation of the Navajo women’s work as a feminine craft differentiated it from the high-status and masculine work of engineering. As Nakamura has written, the work “came to be understood as affective labor, or a ‘labor of love.’” Similarly, the work performed at Raytheon was described by Eldon Hall, who led the Apollo Guidance Computer’s hardware design, as “tender loving care.” Journalists and even a Raytheon manager presented this work as requiring no thinking and no skill.

    Recently, the communications scholar Samantha Shorey, engineer Daniela Rosner, technologist Brock Craft and quilt artist Helen Remick firmly overturned the notion that weaving core memory was a “no-brainer” with their Making Core Memory project. In nine workshops, they invited participants to weave core memory “patches” using metal matrices, beads and conductive threads, showcasing the deep focus and meticulous attention to detail required. The patches were then assembled in an electronic quilt that played aloud accounts from 1960s Apollo engineers and Raytheon managers. The Making Core Memory collaboration challenged the dichotomy of masculine, high-status, well-paid science and engineering cognitive labor versus feminine, low-status, low-paid, manual labor.

    A 1975 NASA report that summarized the Apollo missions spoke glowingly of the Apollo computing systems — but mentioned none of the Navajo or Raytheon women. “The performance of the computer was flawless,” the report declared. “Perhaps the most significant accomplishment during Apollo pertaining to guidance, navigation, and control was the demonstration of the versatility and adaptability of the computer software.”

    That computer, and that software, relied on the skilled, technical, embodied expertise and labor of thousands of women, including women of color. They were indubitably women of science, and their untold stories call us to reconsider who does science, and what counts as scientific expertise.  More