Using 2D materials, researchers have built superconducting qubits that are a fraction of the size of previous qubits, paving the way for smaller quantum supercomputers.

For quantum supercomputers to surpass their classical counterparts in speed and capacity, their qubits—which are superconducting circuits that can exist in an infinite combination of binary states—need to be on the same wavelength. Achieving this, however, has come at the cost of size. Whereas the transistors used in classical computers have been shrunk down to nanometer scales, superconducting qubits these days are still measured in millimeters—one millimeter is one million nanometers. 

Combine qubits together into larger and larger circuit chips, and you end up with, relatively speaking, a big physical footprint, which means quantum supercomputers take up a lot of physical space. These are not yet devices we can carry in our backpacks or wear on our wrists.

To shrink qubits down while maintaining their performance, the field needs a new way to build the capacitors that store the energy that “powers” the qubits. In collaboration with Raytheon BBN Technologies, Wang Fong-Jen Professor James Hone’s lab at Columbia Engineering recently demonstrated a superconducting qubit capacitor built with 2D materials, rendering it a fraction of the size of previous capacitors.

To build qubit chips previously, engineers have had to use planar capacitors, which set the necessary charged plates side by side. Stacking those plates would save space, but the metals used in conventional parallel capacitors interfere with qubit information storage. In the current work, published on November 18 in NanoLetters, Hone’s Ph.D. students Abhinandan Antony and Anjaly Rajendra sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium diselenide. These layers are each just a single atom thick and held together by van der Waals forces, the weak interaction between electrons. The team then combined their capacitors with aluminum circuits to create a chip containing two qubits with an area of 109 square micrometers and just 35 nanometers thick—that’s 1,000 times smaller than chips produced under conventional approaches.

When they cooled their qubit chip down to just above absolute zero, the qubits found the same wavelength. The team also observed key characteristics that showed that the two qubits were becoming entangled and acting as a single unit, a phenomenon known as quantum coherence; that would mean the qubit’s quantum state could be manipulated and read out via electrical pulses, said Hone. The coherence time was short—a little over one microsecond, compared to about 10 microseconds for a conventionally built coplanar capacitor, but this is only a first step in exploring the use of 2D materials in this area, he said.

Separate work published on arXiv in August from researchers at MIT also took advantage of niobium diselenide and boron nitride to build parallel-plate capacitors for qubits. The devices studied by the MIT team showed even longer coherence times—up to 25 microseconds—indicating that there is still room to further improve performance.

From here, Hone and his team will continue refining their fabrication techniques and test other types of 2D materials to increase coherence times, which reflect how long the qubit is storing information. New device designs should be able to shrink things down even further, said Hone, by combining the elements into a single van der Waals stack or by deploying 2D materials for other parts of the circuit.

“We now know that 2D materials may hold the key to making quantum computers possible,” Hone said. “It is still very early days, but findings like these will spur researchers worldwide to consider novel applications of 2D materials. We hope to see a lot more work in this direction going forward.”

A multi-institutional team of astrophysicists headquartered at Boston University, led by BU astrophysicist Merav Opher, has made a breakthrough discovery in our understanding of the cosmic forces that shape the protective bubble surrounding our solar system—a bubble that shelters life on Earth and is known by space researchers as the heliosphere. 

Astrophysicists believe the heliosphere protects the planets within our solar system from powerful radiation emanating from supernovas, the final explosions of dying stars throughout the universe. They believe the heliosphere extends far beyond our solar system, but despite the massive buffer against cosmic radiation that the heliosphere provides Earth’s life-forms, no one knows the shape of the heliosphere—or, for that matter, the size of it. 

“How is this relevant for society? The bubble that surrounds us, produced by the sun, offers protection from galactic cosmic rays, and the shape of it can affect how those rays get into the heliosphere,” says James Drake, an astrophysicist at the University of Maryland who collaborates with Opher. “There are lots of theories but, of course, the way that galactic cosmic rays can get in can be impacted by the structure of the heliosphere—does it have wrinkles and folds and that sort of thing?”

Opher’s team has constructed some of the most compelling supercomputer simulations of the heliosphere, based on models built on observable data and theoretical astrophysics. At BU, in the Center for Space Physics, Opher, a College of Arts & Sciences professor of astronomy, leads a NASA DRIVE (Diversity, Realize, Integrate, Venture, Educate) Science Center that’s supported by $1.3 million in NASA funding. That team, made up of experts Opher recruited from 11 other universities and research institutes, develops predictive models of the heliosphere in an effort the team calls SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics). 

Since BU’S NASA DRIVE Science Center first received funding in 2019, Opher’s SHIELD team has hunted for answers to several puzzling questions: What is the overall structure of the heliosphere? How do its ionized particles evolve and affect heliospheric processes? How does the heliosphere interact and influence the interstellar medium, the matter, and the radiation that exists between stars? And how do cosmic rays get filtered by, or transported through, the heliosphere? 

“SHIELD combines theory, modeling, and observations to build comprehensive models,” Opher says. “All these different components work together to help understand the puzzles of the heliosphere.”

And now a paper published by Opher and collaborators in Astrophysical Journal reveals that neutral hydrogen particles streaming from outside our solar system most likely play a crucial role in the way our heliosphere takes shape.

In their latest study, Opher’s team wanted to understand why heliospheric jets—blooming columns of energy and matter that are similar to other types of cosmic jets found throughout the universe—become unstable. “Why do stars and black holes—and our sun—eject unstable jets?” Opher says. “We see these jets projecting as irregular columns, and [astrophysicists] have been wondering for years why these shapes present instabilities.”

Similarly, SHIELD models predict that the heliosphere, traveling in tandem with our sun and encompassing our solar system, doesn’t appear to be stable. Other models of the heliosphere developed by other astrophysicists tend to depict the heliosphere as having a comet-like shape, with a jet—or a “tail”—streaming behind in its wake. In contrast, Opher’s model suggests the heliosphere is shaped more like a croissant or even a donut.

The reason for that? Neutral hydrogen particles, so-called because they have equal amounts of positive and negative charges that net no charge at all.

“They come streaming through the solar system,” Opher says. Using a computational model like a recipe to test the effect of ‘neutrals’ on the shape of the heliosphere, she “took one ingredient out of the cake—the neutrals—and noticed that the jets coming from the sun, shaping the heliosphere, become super stable. When I put them back in, things start bending, the center axis starts wiggling, and that means that something inside the heliospheric jets is becoming very unstable.”

Instability like that would theoretically cause disturbance in the solar winds and jets emanating from our sun, causing the heliosphere to split its shape—into a croissant-like form. Although astrophysicists haven’t yet developed ways to observe the actual shape of the heliosphere, Opher’s model suggests the presence of neutrals slamming into our solar system would make it impossible for the heliosphere to flow uniformly like a shooting comet. And one thing is for sure—neutrals are pelting their way through space.

Drake, a coauthor on the new study, says Opher’s model “offers the first clear explanation for why the shape of the heliosphere breaks up in the northern and southern areas, which could impact our understanding of how galactic cosmic rays come into Earth and the near-Earth environment.” That could affect the threat that radiation poses to life on Earth and also for astronauts in space or future pioneers attempting to travel to Mars or other planets.

“The universe is not quiet,” Opher says. “Our BU model doesn’t try to cut out the chaos, which has allowed me to pinpoint the cause [of the heliosphere’s instability]…. The neutral hydrogen particles.”

Specifically, the presence of the neutrals colliding with the heliosphere triggers a phenomenon well known by physicists, called the Rayleigh-Taylor instability, which occurs when two materials of different densities collide, with the lighter material pushing against the heavier material. It’s what happens when oil is suspended above the water, and when heavier fluids or materials are suspended above lighter fluids. Gravity plays a role and gives rise to some wildly irregular shapes. In the case of the cosmic jets, the drag between the neutral hydrogen particles and charged ions creates a similar effect as gravity. The “fingers” seen in the famous Horsehead Nebula, for example, are caused by the Rayleigh-Taylor instability. 

“This finding is a breakthrough, it’s set us in a direction of discovering why our model gets its distinct croissant-shaped heliosphere and why other models don’t,” Opher says.

Research published in the journal Anatomical Record finds that humans have more in common with endangered crocodiles than we think—namely, a deviated septum.

Gharials are some of the rarest crocodylians on Earth and members of a group of animals that once roamed the planet with the dinosaurs. Native to India, gharials resemble American alligators and crocodiles, but with bulging eyes and an extremely long and thin snout that allows them to cut through water when hunting prey. In males, this snout houses an even longer nose that ends in an enlarged bulb.

At first glance, these unusual animals appear to have little in common with humans. However, a new study led by Jason Bourke, Ph.D., assistant professor of basic sciences at the College of Osteopathic Medicine at Arkansas State University (NYITCOM-Arkansas), reports that—just like humans—gharials suffer from nasal septal deviation. 

The Cleveland Clinic estimates that up to 80 percent of people have a deviated septum, a condition in which the nasal cartilage is “off-center.” While the condition is mild in most individuals, larger deviations can restrict nasal breathing and require reconstructive surgery.

Bourke and his colleagues are the first to document deviated nasal septa in crocodylians. Using medical imaging technology, they analyzed the heads of multiple gharial specimens, including that of a large female from the Fort Worth Zoo nicknamed “Louise,” which fueled their curiosity.

“This weird nasal septum was an unexpected discovery,” said study co-author Casey Holliday, Ph.D., associate professor of pathology and anatomical sciences at the University of Missouri, who initially scanned the specimen for a separate project on gharial anatomy. “I saw this roller coaster of a septum and wondered what this might mean for respiration.”

Holliday shared Louise’s extreme anatomy with Bourke, a vertebrate paleontologist whose lab specializes in modeling fluid dynamics in animal noses using sophisticated supercomputer software that simulates air movement.

“We know remarkably little about normal gharial anatomy, much less their pathology. I couldn’t pass up such a unique opportunity,” said Bourke, who has also studied nasal airflow and thermoregulation in dinosaurs.

Intrigued, Bourke and the team began collecting samples from other gharial specimens housed in zoos around the country. While some specimens showed minor septal deviations, Louise had the most extreme case.

Like humans who experience severe nasal septum deviation, Louise had to work harder to achieve the same breathing rate as her peers. This produced high shearing stresses along the nasal walls, which may have made the animal more prone to nosebleeds. Despite the physiological challenges produced from this nasal pathology, Louise successfully made it to adulthood and lived to the ripe old age of 50.

“It’s a testament to crocodylian resiliency,” said Bourke. “A human with this pathology would need surgery to fix it, but these critters just keep on going.”

In contrast to humans, the researchers found that gharial septal deviation comes with a unique twist. “When the septum deviates in humans, a part or all of the septum bows into one of the airways,” said Nicole Fontenot, fourth-year NYITCOM student, and study co-author. “In our gharials, the septum is so long that it wiggles back and forth along the snout, creating a wavy pattern.”

While this pathology is not found in other modern crocodylians, in the distant past, many other animals showed similarly stretched-out noses, including crested, duck-billed dinosaurs like Parasaurolophus and strange crocodile-mimicking reptiles known as Champsosaurus. Bourke suspects that at least a few of them would have also suffered from nasal septum deviations. As for why other crocodylians don’t seem to be as prone to these deviated noses, Bourke explains: “Other crocodylians have wider snouts with much thicker nasal septa. Thinning out the snout places a premium on space inside the nose. Gharials’ long and very thin nasal septa probably don’t need much to make them start wobbling.

Next, the researchers will continue their investigation by examining the sound-producing abilities of gharials' unique noses.

Light not only plays a key role as an information carrier for optical computer chips but also in particular for the next generation of quantum supercomputers. Its lossless guidance around sharp corners on tiny chips and the precise control of its interaction with other light are the focus of research worldwide. Scientists at Paderborn University, one of the fourteen public research universities in the state of North Rhine-Westphalia in Germany, have now demonstrated, for the very first time, the spatial confinement of a light wave to a point smaller than the wavelength in a ‘topological photonic crystal’. These are artificial electromagnetic materials that facilitate robust manipulation of light. The state is protected by special properties and is important for use in quantum chips, for example. The findings have now been published in the academic journal “Science Advances.” 

Topological crystals function based on specific structures, the properties of which remain largely unaffected by disturbances and deviations. While in normal photonic crystals the effects needed for light manipulation are fragile and can be affected by defects in the material structure, for example, in topological photonic crystals, they are protected from this. The topological structures allow properties such as unidirectional light propagation and increased robustness for guiding photons, small particles of light – features that are crucial for future light-based technologies.

Photonic crystals influence the propagation of electromagnetic waves with the help of an optical bandgap for photons, which blocks the movement of light in certain directions. Scattering usually occurs – some photons are reflected, while others are reflected away. “With topological light states that span an extended range of photonic crystals, you can prevent this. In normal optical waveguides and fibers, back reflection poses a major problem because it leads to unwanted feedback. Loss during propagation hinders large-scale integration in optical chips, in which photons are responsible for transmitting the information. With the help of topological photonic crystals, novel unidirectional waveguides can be achieved that transmits light without any back reflection, even in the presence of arbitrarily large disorder,” explains Professor Thomas Zentgraf, head of the Ultrafast Nanophotonics research group at Paderborn University. The concept, which has its origins in solid-state physics, has already led to numerous applications, including robust light transmission, topological delay lines, topological lasers, and quantum interference. “It was also recently proven that topological photonic crystals based on a weak topology with a crystal dislocation in the periodic structure also exhibit these special properties and also support what is known as topologically-protected strongly spatially localized light states. When something is topologically protected, any changes in the parameters do not affect the protected properties. Localized light states are extremely useful for non-linear amplification, miniaturization of photonic components, and integration of photonic quantum chips,” adds Zentgraf. In this context, weak topological states are special states for the light that result not only from the topological band structure but also from the formation of the crystal structure.

In a joint experiment, researchers from Paderborn University and RWTH Aachen University used a special near-field optical microscope to demonstrate the existence of such strongly localized light states in topological structures. “We showed that the versatility of weak topology can produce a strongly spatially localized optical field in an intentionally induced structural dislocation,” explains Jinlong Lu, a Ph.D. student in Zentgraf’s group and lead author of the paper. “Our study demonstrates a viable strategy for achieving a topologically-protected, localized zero-dimensional state for light,” adds Zentgraf. With their work, the researchers have proven that near-field microscopy is a valuable tool for characterizing topological structures with nanoscale resolution at optical frequencies.

The findings provide a basis for the use of strongly localized optical light states based on weak topology. Phase-change materials with a tunable refractive index could therefore also be used for the nanostructures used in the experiment to produce robust and active topological photonic elements. “We’re now working on concepts to equip the dislocation centers in the crystal structure with special quantum emitters for single-photon generation,” says Zentgraf, adding: “These could then be used in future optical quantum computers, for which single-photon generation plays an important role.”