Tag: discovery

Metallic hydrogen, once theory, becomes reality

Metallic hydrogen, once theory, becomes reality

Image of diamond anvils compressing molecular hydrogen. At higher pressure the sample converts to atomic hydrogen, as shown on the right. Credit: R. Dias and I.F. Silvera

Nearly a century after it was theorized, Harvard scientists have succeeded in creating the rarest – and potentially one of the most valuable – materials on the planet.

The material – atomic  – was created by Thomas D. Cabot Professor of the Natural Sciences Isaac Silvera and post-doctoral fellow Ranga Dias. In addition to helping scientists answer fundamental questions about the nature of matter, the material is theorized to have a wide range of applications, including as a . The creation of the rare material is described in a January 26 paper published in Science.

“This is the holy grail of high-pressure physics,” Silvera said. “It’s the first-ever sample of metallic hydrogen on Earth, so when you’re looking at it, you’re looking at something that’s never existed before.”

To create it, Silvera and Dias squeezed a tiny hydrogen sample at 495 gigapascal, or more than 71.7 million pounds-per-square inch – greater than the pressure at the center of the Earth. At those extreme pressures, Silvera explained, solid molecular hydrogen -which consists of molecules on the lattice sites of the solid – breaks down, and the tightly bound molecules dissociate to transforms into , which is a metal.

While the work offers an important new window into understanding the general properties of hydrogen, it also offers tantalizing hints at potentially revolutionary new .

“One prediction that’s very important is metallic hydrogen is predicted to be meta-stable,” Silvera said. “That means if you take the pressure off, it will stay metallic, similar to the way diamonds form from graphite under intense heat and pressure, but remains a diamond when that pressure and heat is removed.”

Understanding whether the material is stable is important, Silvera said, because predictions suggest metallic hydrogen could act as a superconductor at room temperatures.

“That would be revolutionary,” he said. “As much as 15 percent of energy is lost to dissipation during transmission, so if you could make wires from this material and use them in the electrical grid, it could change that story.”

Among the holy grails of physics, a room temperature superconductor, Dias said, could radically change our transportation system, making magnetic levitation of high-speed trains possible, as well as making electric cars more efficient and improving the performance of many electronic devices.

The material could also provide major improvements in energy production and storage – because superconductors have zero resistance energy could be stored by maintaining currents in superconducting coils, and then be used when needed.

Metallic hydrogen, once theory, becomes reality
Photos of compressed hydrogen transitioning with increasing pressure from transparent molecular to black molecular to atomic metallic hydrogen. The sketches below show a molecular solid being compressed and then dissociated to atomic hydrogen. Credit: R. Dias and I.F. Silvera

Though it has the potential to transform life on Earth, metallic hydrogen could also play a key role in helping humans explore the far reaches of space, as the most powerful rocket propellant yet discovered.

“It takes a tremendous amount of energy to make metallic hydrogen,” Silvera explained. “And if you convert it back to molecular hydrogen, all that energy is released, so it would make it the most powerful rocket propellant known to man, and could revolutionize rocketry.”

The most powerful fuels in use today are characterized by a “specific impulse” – a measure, in seconds, of how fast a propellant is fired from the back of a rocket – of 450 seconds. The specific impulse for metallic hydrogen, by comparison, is theorized to be 1,700 seconds.

“That would easily allow you to explore the outer planets,” Silvera said. “We would be able to put rockets into orbit with only one stage, versus two, and could send up larger payloads, so it could be very important.”

To create the new material, Silvera and Dias turned to one of the hardest materials on Earth – diamond.

But rather than natural diamond, Silvera and Dias used two small pieces of carefully polished synthetic diamond which were then treated to make them even tougher and then mounted opposite each other in a device known as a .

“Diamonds are polished with diamond powder, and that can gouge out carbon from the surface,” Silvera said. “When we looked at the diamond using atomic force microscopy, we found defects, which could cause it to weaken and break.”

The solution, he said, was to use a reactive ion etching process to shave a tiny layer – just five microns thick, or about one-tenth of a human hair – from the diamond’s surface. The diamonds were then coated with a thin layer of alumina to prevent the hydrogen from diffusing into their crystal structure and embrittling them.

After more than four decades of work on metallic hydrogen, and nearly a century after it was first theorized, seeing the material for the first time, Silvera said, was thrilling.

“It was really exciting,” he said. “Ranga was running the experiment, and we thought we might get there, but when he called me and said, ‘The sample is shining,’ I went running down there, and it was metallic hydrogen.

“I immediately said we have to make the measurements to confirm it, so we rearranged the lab…and that’s what we did,” he said. “It’s a tremendous achievement, and even if it only exists in this diamond anvil cell at high pressure, it’s a very fundamental and transformative discovery.”

Astronomers discover new gas giant exoplanet

Astronomers discover new gas giant alien world

Observed data for event OGLE-2014-BLG-0676/MOA-2014-BLG-175 from the MOA (gray), OGLE (red) and Wise (green) microlensing survey groups along with data from the RoboNET/LCOGT (cyan) and MiNDSTEp (magenta) groups. Also shown is the best-fitting binary lens model light-curve (black line). The epoch when the OGLE collaboration issued an alert for this event is indicated with a black arrow. Data with extremely large errors are omitted. Credit: Nicolas Rattenbury et al., 2016.

Using the gravitational microlensing method, an international team of astronomers has recently detected a new gas giant exoplanet three times more massive than Jupiter. The newly discovered planet received designation OGLE-2014-BLG-0676Lb and is an important addition to the short list of extrasolar worlds detected by the microlensing technique. The discovery was described in a paper published Dec. 12 on arXiv.org.

Unlike other methods of detecting exoplanets, microlensing is most sensitive when it comes to searching for exoworlds that orbit around one to 10 AU away from their host stars. These planets are of special interest for astronomers studying planetary formation theories due to proximity to their parent stars, within the so-called “snow line.” Just beyond this line, the most active planet formation occurs; therefore, understanding the distribution of exoplanets in this region could offer important clues to how planets form.

So far, 47 planets have been discovered by microlensing. Currently, several ground-based observation programs routinely monitor dense stellar fields to search for microlensing events. When a new event is discovered, an alert to the broader scientific community is issued in order to allow follow-up observations. Astronomers are particularly interested in events showing evidence for perturbations that could be due to the presence of a planet, or which are predicted to have a high sensitivity to such perturbations.

OGLE-2014-BLG-0676, discovered in April 2014 by a Polish astronomical project called the Optical Gravitational Lensing Experiment (OGLE), is one of those interesting microlensing events. Recently, a collaboration of researchers consisting of the OGLE group, the Microlensing Observations in Astrophysics (MOA), the Wise Observatory Group and the Microlensing Network for the Detection of Small Terrestrial Exoplanets (MiNDSTEp), has detected an anomalous signal in this event consistent with a planetary lens system.

“The source star passed through the central caustic, with the second caustic crossing being well recorded by the MOA microlensing survey collaboration. Observations at epochs between the unrecorded first caustic crossing and the second caustic crossing were made by the OGLE, Wise and MOA collaborations. (…) All analyses of the light curve data favor a lens system comprising a planetary mass orbiting a host star,” the paper reads.

According to the research, the newly discovered planet has a mass of about 3.1 Jupiter masses and orbits its parent star at a deprojected orbital separation of about 4.4 AU. The host star is approximately 38 percent less massive than our sun and was classified as a K-dwarf. The distance to the  is about 7,200 light years.

Moreover, the team revealed some information about the source star. They revealed that is rather faint and very red, noting that there is a possibility that the source may be blended with a nearby red star, causing an incorrect identification of the source star type.

In conclusion, the scientists emphasize the importance of their discovery, noting that OGLE-2014-BLG-0676Lb could serve as a test bed for planet formation scenarios. “Planet OGLE-2014-BLG-0676Lb can be added to the growing list of planets discovered by microlensing against which planetary formation theories can be tested,” the researchers wrote in the paper.

Quantum computing with single photons getting closer to reality

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One promising approach for scalable quantum computing is to use an all-optical architecture, in which the qubits are represented by photons and manipulated by mirrors and beam splitters. So far, researchers have demonstrated this method, called Linear Optical Quantum Computing, on a very small scale by performing operations using just a few photons. In an attempt to scale up this method to larger numbers of photons, researchers in a new study have developed a way to fully integrate single-photon sources inside optical circuits, creating integrated quantum circuits that may allow for scalable optical quantum computation.

The researchers, Iman Esmaeil Zadeh, Ali W. Elshaari, and coauthors, have published a paper on the integrated quantum circuits in a recent issue ofNano Letters.

As the researchers explain, one of the biggest challenges facing the realization of an efficient Linear Optical Quantum Computing system is integrating several components that are usually incompatible with each other onto a single platform. These components include a single-photon source such as quantum dots; routing devices such as waveguides; devices for manipulating photons such as cavities, filters, and quantum gates; and single-photon detectors.

In the new study, the researchers have experimentally demonstrated a method for embedding single-photon-generating quantum dots inside nanowires that, in turn, are encapsulated in a waveguide. To do this with the high precision required, they used a “nanomanipulator” consisting of a tungsten tip to transfer and align the components. Once inside the waveguide, single photons could be selected and routed to different parts of the optical circuit, where logical operations can eventually be performed.

“We proposed and demonstrated a hybrid solution for integrated quantum optics that exploits the advantages of high-quality single-photon sources with well-developed silicon-based photonics,” Zadeh, at Delft University of Technology in The Netherlands, told Phys.org. “Additionally, this method, unlike previous works, is fully deterministic, i.e., only quantum sources with the selected properties are integrated in photonic circuits.

“The proposed approach can serve as an infrastructure for implementing scalable integrated quantum optical circuits, which has potential for many quantum technologies. Furthermore, this platform provides new tools to physicists for studying strong light-matter interaction at nanoscales and cavity QED [quantum electrodynamics].”

One of the most important performance metrics for Linear Optical Quantum Computing is the coupling efficiency between the single-photon source and photonic channel. A low efficiency indicates photon loss, which reduces the computer’s reliability. The set-up here achieves a coupling efficiency of about 24% (which is already considered good), and the researchers estimate that optimizing the waveguide design and material could improve this to 92%.

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In addition to improving the coupling efficiency, in the future the researchers also plan to demonstrate on-chip entanglement, as well as increase the complexity of the photonic circuits and single-photon detectors.

“Ultimately, the goal is to realize a fully integrated quantum network on-chip,” said Elshaari, at Delft University of Technology and the Royal Institute of Technology (KTH) in Stockholm. “At this moment there are a lot of opportunities, and the field is not well explored, but on-chip tuning of sources and generation of indistinguishable photons are among the challenges to be overcome.”

New state of matter detected in a two-dimensional material

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An international team of researchers have found evidence of a mysterious new state of matter, first predicted 40 years ago, in a real material. This state, known as a quantum spin liquid, causes electrons – thought to be indivisible building blocks of nature – to break into pieces.

The researchers, including physicists from the University of Cambridge, measured the first signatures of these fractional particles, known as Majorana fermions, in a two-dimensional material with a structure similar to graphene. Their experimental results successfully matched with one of the main theoretical models for a quantum spin liquid, known as a Kitaev model. The results are reported in the journal Nature Materials.

Quantum spin liquids are mysterious states of matter which are thought to be hiding in certain magnetic materials, but had not been conclusively sighted in nature.

The observation of one of their most intriguing properties—electron splitting, or fractionalisation—in real materials is a breakthrough. The resulting Majorana fermions may be used as building blocks of quantum computers, which would be far faster than conventional computers and would be able to perform calculations that could not be done otherwise.

“This is a new quantum state of matter, which has been predicted but hasn’t been seen before,” said Dr Johannes Knolle of Cambridge’s Cavendish Laboratory, one of the paper’s co-authors.

In a typical magnetic material, the electrons each behave like tiny bar magnets. And when a material is cooled to a low enough temperature, the ‘magnets’ will order themselves, so that all the north magnetic poles point in the same direction, for example.

But in a material containing a spin liquid state, even if that material is cooled to absolute zero, the bar magnets would not align but form an entangled soup caused by quantum fluctuations.

“Until recently, we didn’t even know what the experimental fingerprints of a quantum spin liquid would look like,” said paper co-author Dr Dmitry Kovrizhin, also from the Theory of Condensed Matter group of the Cavendish Laboratory. “One thing we’ve done in previous work is to ask, if I were performing experiments on a possible quantum spin liquid, what would I observe?”

Knolle and Kovrizhin’s co-authors, led by the Oak Ridge National Laboratory, used neutron scattering techniques to look for experimental evidence of fractionalisation in crystals of ruthenium chloride (RuCl3). The researchers tested the magnetic properties of the RuCl3 crystals by illuminating them with neutrons, and observing the pattern of ripples that the neutrons produced on a screen.

A regular magnet would create distinct sharp spots, but it was a mystery what sort of pattern the Majorana fermions in a quantum spin liquid would make. The theoretical prediction of distinct signatures by Knolle and his collaborators in 2014 match well with what experimentalists observed on the screen, providing for the first time direct evidence of a quantum spin liquid and the fractionalisation of electrons in a two dimensional material.

“This is a new addition to a short list of known quantum states of matter,” said Knolle.

“It’s an important step for our understanding of quantum matter,” said Kovrizhin. “It’s fun to have another new quantum state that we’ve never seen before – it presents us with new possibilities to try new things.”

Scientists find clues to the mystery of what causes lightning

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It’s well-known that lightning is an electric current—a quick, powerful burst of charge that flows within a cloud or between a cloud and the ground. But surprisingly, scientists still don’t fully understand how the initial spark forms that generates such powerful lightning.

In a new paper published in Nature Communications, researchers from Langmuir Laboratory at the New Mexico Institute of Mining and Technology near Socorro, New Mexico, have reported observations of a rare but extremely powerful type of lightning spark, or discharge, called narrow bipolar events. The scientists found that this powerful type of lightning is caused by a newly recognized type of discharge called fast positive breakdown, and the data suggests that this same discharge initiates most or even all of the lightning flashes typically seen in thunderstorms. These sparks travel at speeds that are fast even for lightning—around 10 to 100 million meters per second—and produce very powerful radiofrequency (RF) radiation as high as a few megawatts, making them the strongest natural sources of RF radiation on Earth.

This discovery is surprising, since previous simulations have shown that lightning breakdown appears to be negative, meaning the spark moves upward in the cloud from a negative to a positive region. In positive breakdown, the spark moves downward from a positive to a negative region.

“It is impossible to simulate thunderstorm conditions in a conventional laboratory,” coauthor William Rison at the New Mexico Institute of Mining and Technology told Phys.org. “The sparks in thunderstorms are hundreds of meters to kilometers long, a scale that is orders of magnitude larger than in any laboratory environment. Theorists have been trying to simulate these conditions in computer experiments, and the most plausible results have suggested that the sparks are initiated with relativistic electron avalanches, which is a type of negative breakdown. Our results clearly show that the initiation is with a positive breakdown, not a negative breakdown.”

The results could help scientists better understand how a cloud can generate a current that is powerful enough to cause lightning. Currently, the largest electric fields that have been measured inside thunderstorms are several times weaker than what is needed to break down cloudy air and initiate lightning.

In general, lightning occurs when the positive and negative electric charges in a cloud separate in different parts of the cloud. Charge separation sets the stage for lightning to form either between the negative and positive parts of the cloud (intracloud lightning), or downward to the ground (cloud-to-ground lightning), where it often strikes a tree, telephone pole, or other tall object.

Over the past few decades, researchers have gained a better understanding of how the charges become separated in thunderclouds. Data and simulations show that charge separation occurs when small hail-like particles called “graupel” and ice crystals collide with one another in a cloud. The charges are separated as the heavier graupel particles fall, while the lighter ice crystals are carried upward by updrafts in the turbulent thundercloud. This process is somewhat like how rubbing your feet on carpet separates charges in your body, causing you to produce static electricity when you touch a metal doorknob.

Since the 1990s, one of the leading proposals for lightning formation is that the initial spark comes from relativistic electrons that come from either high-energy cosmic rays or a process called relativistic runaway electron avalanche. However, the new results cast doubt on this idea.

“If relativistic electron showers were the initiating events for lightning flashes, then the motion of the breakdown would be initially upward for intracloud flashes between the mid-level negative and upper positive charges,” Rison explained. “Using a recently developed broadband interferometer to observe the propagation of electrical breakdown in lightning, we found that the propagation direction of narrow bipolar events is downward rather than upward, showing they are caused by downward-developing positive rather than upward-developing negative breakdown.”

Both negative breakdown and positive breakdown can move charges, which can intensify the fields at both ends of the cloud. But the data here shows that all flashes for which the interferometer could determine the motion exhibited an initial breakdown that was fast and positive.

The next step is to investigate how fast positive breakdown develops physically. Fast positive streamers have been observed in sprites, a type of electrical breakdown that occurs in the upper atmosphere where the pressure is several orders of magnitude lower than in thunderclouds. The discharge observed here move at the same fast propagation speeds but at lower altitudes and higher pressures.

“Theorists are now trying to determine how fast positive breakdown works at the higher pressures inside thunderclouds,” Rison said.

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Exceptionally strong and lightweight new metal created

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A team led by researchers from the UCLA Henry Samueli School of Engineering and Applied Science has created a super-strong yet light structural metal with extremely high specific strength and modulus, or stiffness-to-weight ratio. The new metal is composed of magnesium infused with a dense and even dispersal of ceramic silicon carbide nanoparticles. It could be used to make lighter airplanes, spacecraft, and cars, helping to improve fuel efficiency, as well as in mobile electronics and biomedical devices.

To create the super-strong but lightweight metal, the team found a new way to disperse and stabilize nanoparticles in molten metals. They also developed a scalable manufacturing method that could pave the way for more high-performance lightweight metals. The research was published today in Nature.

“It’s been proposed that nanoparticles could really enhance the strength of metals without damaging their plasticity, especially light metals like magnesium, but no groups have been able to disperse ceramic nanoparticles in molten metals until now,” said Xiaochun Li, the principal investigator on the research and Raytheon Chair in Manufacturing Engineering at UCLA. “With an infusion of physics and materials processing, our method paves a new way to enhance the performance of many different kinds of metals by evenly infusing dense nanoparticles to enhance the performance of metals to meet energy and sustainability challenges in today’s society.”

Structural metals are load-bearing metals; they are used in buildings and vehicles. Magnesium, at just two-thirds the density of aluminum, is the lightest structural metal. Silicon carbide is an ultra-hard ceramic commonly used in industrial cutting blades. The researchers’ technique of infusing a large number of silicon carbide particlessmaller than 100 nanometers into magnesium added significant strength, stiffness, plasticity and durability under high temperatures.

The researchers’ new silicon carbide-infused magnesium demonstrated record levels of specific strength—how much weight a material can withstand before breaking—and specific modulus—the material’s stiffness-to-weight ratio. It also showed superior stability at high temperatures.

Ceramic particles have long been considered as a potential way to make metals stronger. However, with microscale ceramic particles, the infusion process results in a loss of plasticity.

Nanoscale particles, by contrast, can enhance strength while maintaining or even improving metals’ plasticity. But nanoscale ceramic particles tend to clump together rather than dispersing evenly, due to the tendency of small particles to attract one other.

To counteract this issue, researchers dispersed the particles into a molten magnesium zinc alloy. The newly discovered nanoparticle dispersion relies on the kinetic energy in the particles’ movement. This stabilizes the particles’ dispersion and prevents clumping.

To further enhance the new metal’s strength, the researchers used a technique called high-pressure torsion to compress it.

“The results we obtained so far are just scratching the surface of the hidden treasure for a new class of metals with revolutionary properties and functionalities,” Li said.

The new metal (more accurately called ametal nanocomposite) is about 14 percent silicon carbide nanoparticles and 86 percent magnesium. The researchers noted that magnesium is an abundant resource and that scaling up its use would not cause environmental damage.

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