Discovering the magic in superconductivity’s ‘magic angle’

Left: Marc Bockrath, professor of physics. Center: Jeanie Lau, professor of physics. Right: Mohit Randeria, professor of physics.
Photo Credit: Photos courtesy of Ohio State University

Researchers have produced new evidence of how graphene, when twisted to a precise angle, can become a superconductor, moving electricity with no loss of energy.

In a study published today (Feb. 15, 2023) in the journal Nature, the team led by physicists at The Ohio State University reported on the key role that quantum geometry plays in allowing this twisted graphene to become a superconductor.

Graphene is a single layer of carbon atoms, the lead that is found in a pencil.

In 2018, scientists at the Massachusetts Institute of Technology discovered that, under the right conditions, graphene could become a superconductor if one piece of graphene were laid on top of another piece and the layers were twisted to a specific angle – 1.08 degrees – creating twisted bilayer graphene.

Ever since, scientists have been studying this twisted bilayer graphene and trying to figure out how this “magic angle” works, said Marc Bockrath, professor of physics at Ohio State and co-author of the Nature paper.

Engineers discover a new way to control atomic nuclei as “qubits”

Diagram illustrates the way two laser beams of slightly different wavelengths can affect the electric fields surrounding an atomic nucleus, pushing against this field in a way that nudges the spin of the nucleus in a particular direction, as indicated by the arrow.
Illustration Credit: Courtesy of the researchers | MIT
Creative Commons

In principle, quantum-based devices such as computers and sensors could vastly outperform conventional digital technologies for carrying out many complex tasks. But developing such devices in practice has been a challenging problem despite great investments by tech companies as well as academic and government labs.

Today’s biggest quantum computers still only have a few hundred “qubits,” the quantum equivalents of digital bits.

Now, researchers at MIT have proposed a new approach to making qubits and controlling them to read and write data. The method, which is theoretical at this stage, is based on measuring and controlling the spins of atomic nuclei, using beams of light from two lasers of slightly different colors. The findings are described in a paper published Tuesday in the journal Physical Review X, written by MIT doctoral student Haowei Xu, professors Ju Li and Paola Cappellaro, and four others.

Nuclear spins have long been recognized as potential building blocks for quantum-based information processing and communications systems, and so have photons, the elementary particles that are discreet packets, or “quanta,” of electromagnetic radiation. But coaxing these two quantum objects to work together was difficult because atomic nuclei and photons barely interact, and their natural frequencies differ by six to nine orders of magnitude.

Securing supply chains with quantum computing

Sandia National Laboratories scientists Alicia Magann, right, Kenneth Rudinger, top left, Mohan Sarovar, bottom left, and Matthew Grace, not pictured, developed Feedback-based Algorithm for Quantum Optimization, or FALQON, as a new framework for programming quantum computers, an emerging technology that could become a powerful tool for global security.
Photo Credit: Robin Blume-Kohout

The Russo-Ukrainian conflict and the COVID-19 pandemic have shown how vulnerable global supply chains can be. International events can disrupt manufacturing, delay shipping, induce panic buying and send energy costs soaring.

New research in quantum computing at Sandia National Laboratories is moving science closer to being able to overcome supply-chain challenges and restore global security during future periods of unrest.

“Reconfiguring the supply chain on short notice is an exceptionally difficult optimization problem, which restricts the agility of global trade,” said Alicia Magann, a Truman Fellow at Sandia. She has led the development of a new way to design programs on quantum computers, which she and her team think could be especially useful for solving these kinds of massive optimization problems someday in the future when quantum technology becomes more mature.

When the light is neither "on" nor "off" in the nanoworld

Illustration of the slit-shaped nanostructure in gold with quantum state highlighted.
Illustration Credit: Daniel Fersch / Universität Würzburg

Scientists at the Universities of Würzburg and Bielefeld detect the quantum properties of collective optical-electronic oscillations on the nanoscale. The results could contribute to the development of novel computer chips.

Whether the light in our living spaces is on or off can be regulated in everyday life simply by reaching for the light switch. However, when the space for the light is shrunk to a few nanometers, quantum mechanical effects dominate, and it is unclear whether there is light in it or not. Both can even be the case at the same time, as scientists from the Julius-Maximilians-Universität Würzburg (JMU) and the University of Bielefeld show in the journal “Nature Physics.”

“Detecting these exotic states of quantum physics on the size scales of electrical transistors could help in the development of optical quantum technologies of future computer chips,” explains Würzburg professor Bert Hecht. The nanostructures studied were produced in his group.

The 'flip-flop' qubit: realization of a new quantum bit in silicon controlled by electric signals

Dr Tim Botzem, Professor Andrea Morello and Dr Rostyslav Savytskyy in the quantum computing lab at UNSW Sydney.
Photo Credit: Richard Freeman/UNSW

UNSW Sydney research demonstrates a new type of quantum bit in silicon, called ‘flip-flop’ qubit, which can facilitate the construction of a large-scale quantum computer.

A team led by Professor Andrea Morello has just demonstrated the operation of a new type of quantum bit, called ‘flip-flop’ qubit, which combines the exquisite quantum properties of single atoms, with easy controllability using electric signals, just as those used in ordinary computer chips.

A deliberate target: electrical control of a single-atom quantum bit

“Sometimes new qubits, or new modes of operations, are discovered by lucky accident. But this one was completely by design,” says Prof. Morello. “Our group has had excellent qubits for a decade, but we wanted something that could be controlled electrically, for maximum ease of operation. So, we had to invent something completely new.”

Scientists boost quantum signals while reducing noise

This superconducting parametric amplifier can achieve quantum squeezing over much broader bandwidths than other designs, which could lead to faster and more accurate quantum measurements.
 Image Credit: Courtesy of the researchers

A certain amount of noise is inherent in any quantum system. For instance, when researchers want to read information from a quantum computer, which harnesses quantum mechanical phenomena to solve certain problems too complex for classical computers, the same quantum mechanics also imparts a minimum level of unavoidable error that limits the accuracy of the measurements.

Scientists can effectively get around this limitation by using “parametric” amplification to “squeeze” the noise –– a quantum phenomenon that decreases the noise affecting one variable while increasing the noise that affects its conjugate partner. While the total amount of noise remains the same, it is effectively redistributed. Researchers can then make more accurate measurements by looking only at the lower-noise variable.

A team of researchers from MIT and elsewhere has now developed a new superconducting parametric amplifier that operates with the gain of previous narrowband squeezers while achieving quantum squeezing over much larger bandwidths. Their work is the first to demonstrate squeezing over a broad frequency bandwidth of up to 1.75 gigahertz while maintaining a high degree of squeezing (selective noise reduction). In comparison, previous microwave parametric amplifiers generally achieved bandwidths of only 100 megahertz or less.

Researchers devise a new path toward ‘quantum light’

Photo Credit: Scientific Frontline stock image

The researchers, from the University of Cambridge, along with colleagues from the US, Israel and Austria, developed a theory describing a new state of light, which has controllable quantum properties over a broad range of frequencies, up as high as X-ray frequencies. Their results are reported in the journal Nature Physics.

The world we observe around us can be described according to the laws of classical physics, but once we observe things at an atomic scale, the strange world of quantum physics takes over. Imagine a basketball: observing it with the naked eye, the basketball behaves according to the laws of classical physics. But the atoms that make up the basketball behave according to quantum physics instead.

“Light is no exception: from sunlight to radio waves, it can mostly be described using classical physics,” said lead author Dr Andrea Pizzi, who carried out the research while based at Cambridge’s Cavendish Laboratory. “But at the micro and nanoscale so-called quantum fluctuations start playing a role and classical physics cannot account for them.”

Researchers take a step toward novel quantum simulators

A scanning electron microscope image of the "two-island" device, which researchers hope will pave the way toward a quantum simulator. 
Image Credit: Winston Pouse/Stanford University

Some of the most exciting topics in modern physics, such as high-temperature superconductors and some proposals for quantum computers, come down to the exotic things that happen when these systems hover between two quantum states.

Unfortunately, understanding what's happening at those points, known as quantum critical points, has proved challenging. The math is frequently too hard to solve, and today's computers are not always up to the task of simulating what happens, especially in systems with any appreciable number of atoms involved.

Now, researchers at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory and their colleagues have taken a step toward building an alternative approach, known as a quantum simulator. Although the new device, for now, only simulates the interactions between two quantum objects, the researchers argue in a paper published in Nature Physics that it could be scaled up relatively easily. If so, researchers could use it to simulate more complicated systems and begin answering some of the most tantalizing questions in physics. 

New method to control electron spin paves the way for efficient quantum computers

Researchers at the University of Rochester developed a new method for manipulating information in quantum systems by controlling the spin of electrons in silicon quantum dots. Electrons in silicon experience a phenomenon called spin-valley coupling between their spin (up and down arrows) and valley states (blue and red orbitals). When researchers apply a voltage (blue glow) to electrons in silicon, they harness the spin-valley coupling effect and can manipulate the spin and valley states, controlling the electron spin.
Illustration Credit: Michael Osadciw / University of Rochester

The method, developed by Rochester scientists, overcomes the limitations of electron spin resonance.

Quantum science has the potential to revolutionize modern technology with more efficient computers, communication, and sensing devices. Challenges remain in achieving these technological goals, however, including how to precisely manipulate information in quantum systems.

In a paper published in Nature Physics, a group of researchers from the University of Rochester, including John Nichol, an associate professor of physics, outlines a new method for controlling electron spin in silicon quantum dots—tiny, nanoscale semiconductors with remarkable properties—as a way to manipulate information in a quantum system.

“The results of the study provide a promising new mechanism for coherent control of qubits based on electron spin in semiconductor quantum dots, which could pave the way for the development of a practical silicon-based quantum computer,” Nichol says.

The coupling of two quantum dots was successful for the first time

Arne Ludwig was responsible for the design and manufacture of the semiconductor structures for the experiment.
Photo Credit: RUB, Kramer

This means a big step towards the technical applicability of quantum technology, for example for arithmetic operations.

A tiny change means a big breakthrough in quantum physics: an international research team from Bochum and Copenhagen has managed to couple two quantum dots in one nanochip. After exciting a quantum point using a laser, a signal is sent out, the origin of which can no longer be related to one of the quantum points, as if both had each sent half of the signal in the form of a single photon. "At first that sounds like a little success, but this signal entanglement, which sits on a single photon, is more than the sum of its parts," says Dr. Arne Ludwig from the Chair of Solid-State Physics at the Ruhr University Bochum. “It represents a big step towards the usability of quantum technology for computer operations. "Together with researchers from the Niels Bohr Institute at the University of Copenhagen, the Bochum team published the results in the journal Science from 27. Published January 2023.

Researchers combine classical and quantum optics for super-resolution imaging

A conceptual rendering of the super-resolution experiment, which will be enabled by a grant from the Chan Zuckerberg Initiative.
Illustration Credit: Courtesy of Colorado State University

The ability to see invisible structures in our bodies, like the inner workings of cells, or the aggregation of proteins, depends on the quality of one’s microscope. Ever since the first optical microscopes were invented in the 17th century, scientists have pushed for new ways to see things more clearly, at smaller scales and deeper depths.   

Randy Bartels, professor in the Department of Electrical Engineering at Colorado State University, is one of those scientists. He and a team of researchers at CSU and Colorado School of Mines are on a quest to invent some of the world’s most powerful light microscopes – ones that can resolve large swaths of biological material in unimaginable detail.   

The name of the game is super–resolution microscopy, which is any optical imaging technique that can resolve things smaller than half the wavelength of light. The discipline was the subject of the 2014 Nobel Prize in Chemistry, and Bartels and others are in a race to keep circumventing that diffraction limit to illuminate biologically important structures inside the body.  

A Quan­tum Video Reel

Using all of images from the video reel, the team could then estimate the quantum states of the atom.
Image Credit: University of Innsbruck

When it comes to creating ever more intriguing quantum systems, a constant need is finding new ways to observe them in a wide range of physical scenarios.  JILA Fellow Cindy Regal and JILA and NIST Fellow Ana Maria Rey have teamed up with Oriol Romero-Isart from the University of Innsbruck and IQOQI to show that a trapped particle in the form of an atom readily reveals its full quantum state with quite simple ingredients, opening up opportunities for studies of the quantum state of ever larger particles.

In the quantum realm an atom does not behave as point particle, instead it behaves more as a wave.  Its properties (e.g., its position and velocity) are described in terms of what is referred to as the wavefunction of the atom. One way to learn about the wavefunction of a particle is to let the atom fly and then capture its location with a camera. 

And with the right tricks, pictures can be taken of the particle’s quantum state from many vantage points, resulting in what is known as quantum tomography (‘tomo’ being Greek for slice or section, and ‘graphy’ meaning describing or recording).  In the work published in Nature Physics, the authors used a rubidium atom placed carefully in a specific state of its motion in a tightly focused laser beam, known as an optical tweezer.  And they were able to observe it from many vantage points by letting it evolve in the optical tweezer in time.  Like a ball rolling in a bowl, at different times the velocity and location of the particle interchange, and by snapping pictures at the right time during a video reel of the ball, many vantages of the particle’s state can be revealed.

Quantum researchers strike the right chord with silicides

The silicide research team. In the front from left to right: Mark Hersam, Michael Bedzyk, James Ronidnelli and Xiezeng Lu. Back: Carlos Torres and Dominic Goronzy.
Photo Credit: SQMS Center

Just as the sound of a guitar depends on its strings and the materials used for its body, the performance of a quantum computer depends on the composition of its building blocks. Arguably the most critical components are the devices that encode information in quantum computers.

One such device is the transmon qubit — a patterned chip made of metallic niobium layers on top of a substrate, such as silicon. Between the two materials resides an ultrathin layer that contains both niobium and silicon. The compounds of this layer are known as silicides (NbxSiy). Their impact on the performance of transmon qubits has not been well understood — until now.

Silicides form when elemental niobium is deposited onto silicon during the fabrication process of a transmon qubit. They need to be well understood to make devices that reliably and efficiently store quantum information for as long as possible.

Researchers at the Superconducting Quantum Materials and Systems Center, hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory, have discovered how silicides impact the performance of transmon qubits. Their research has been published in APS Physical Review Materials.

Artifacts, Begone! NIST Improves Its Flagship Device for Measuring Mass

For the first time, scientists have integrated a quantum resistance standard directly into mass measurements made with the one-of-a-kind NIST-4 Kibble balance. Using the quantum standard in this way increases the accuracy of the measurements. This animation shows how the new quantum resistance standard, called QHARS, works. The QHARS device uses a sheet of graphene (a single layer of carbon atoms) attached to superconducting electrical contacts. When cooled to low temperature and placed in a strong magnetic field, electrons in the graphene begin moving in closed loops, a phenomenon known as the quantum Hall effect. This behavior results in the graphene having a specific resistance, providing an absolute reference for measuring current in the NIST-4 Kibble balance. 
Video Credit: Sean Kelley/NIST

In a brightly lit subterranean lab at the National Institute of Standards and Technology (NIST) sits a room-sized electromechanical machine called the NIST-4 Kibble balance.

The instrument can already measure the mass of objects of roughly 1 kilogram, about as heavy as a quart of milk, as accurately as any device in the world. But now, NIST researchers have further improved their Kibble balance’s performance by adding to it a custom-built device that provides an exact definition of electrical resistance. The device is called the quantum Hall array resistance standard (QHARS), and it consists of a set of several smaller devices that use a quirk of quantum physics to generate extremely precise amounts of electrical resistance. The researchers describe their work in a Nature Communications paper.

By detecting tiny flashes of heat, scientist pave way for more stable quantum computers

Measuring the heat of a phase slip in a Josephson junction is a significant step forward for quantum thermodynamics toward better quantum technologies.
Photo Credit: Kuan Yen Tan/Aalto University

An international collaboration between quantum scientists resulted in a new way to measure heat dissipation in superconducting quantum circuits – crucial building blocks for quantum technologies such as computers. The discovery represents a step forward for experimental quantum thermodynamics, the field investigating the interaction of the quantum world and heat, and paves the way for improved quantum devices.

As heat sets limits for traditional computing, so it does for quantum computers. Detecting and controlling the heat dissipation of quantum computers is central for developing better and more stable machines. Researchers at Aalto, the Universitét Grenoble Alpes and University of Konstanz worked together to test a theory about heat dissipation in a so-called phase slip in a quantum device. The result was a reliable and efficient way to measure dissipation that could be scaled to cover a range of quantum applications. The discovery was recently published in Nature Physics.

Controlling quantum states in individual molecules with two-dimensional ferroelectrics

Researchers used electricity to control the internal states of molecules.
Illustration Credit: Jose Lado/Aalto University

Researchers demonstrated how to control the quantum states of individual molecules with an electrically controllable substrate.

Controlling the internal states of quantum systems is one of the biggest challenges in quantum materials. At the deepest level, single molecules can display different quantum states, even while possessing the same number of electrons. These states are associated with different electron configurations, which can lead to dramatically different properties.

The capability of controlling the electronic configuration of single molecules could lead to major developments in both fundamental science and technology. On the one hand, controlling the internal states of molecules may allow for the development of new artificial materials with exotic properties. On the other hand, it might also make possible the ultimate miniaturization of classical computer memories, with the two configurations could make it possible to encode a 0 and a 1 in a classical memory unit at the molecular level. However, controlling the internal states of molecules still remains a challenge, and realistic, scalable strategies for overcoming it have not been proposed.

New quantum computing architecture could be used to connect large-scale devices

This image shows a module composed of superconducting qubits that can be used to directionally emit microwave photons.
Illustration Credit: Massachusetts Institute of Technology / Courtesy of the researchers

Quantum computers hold the promise of performing certain tasks that are intractable even on the world’s most powerful supercomputers. In the future, scientists anticipate using quantum computing to emulate materials systems, simulate quantum chemistry, and optimize hard tasks, with impacts potentially spanning finance to pharmaceuticals.

However, realizing this promise requires resilient and extensible hardware. One challenge in building a large-scale quantum computer is that researchers must find an effective way to interconnect quantum information nodes — smaller-scale processing nodes separated across a computer chip. Because quantum computers are fundamentally different from classical computers, conventional techniques used to communicate electronic information do not directly translate to quantum devices. However, one requirement is certain: Whether via a classical or a quantum interconnect, the carried information must be transmitted and received.

To this end, MIT researchers have developed a quantum computing architecture that will enable extensible, high-fidelity communication between superconducting quantum processors. In work published today in Nature Physics, MIT researchers demonstrate step one, the deterministic emission of single photons — information carriers — in a user-specified direction. Their method ensures quantum information flows in the correct direction more than 96 percent of the time.

Chip Circuit for Light Could Be Applied to Quantum Computations

Future versions of the new photonic circuits will feature low-loss waveguides—the channels through which the single photons travel--some 3 meters long but tightly coiled to fit on a chip. The long waveguides will allow researchers to more precisely choose the time intervals (Δt) when photons exit different channels to rendezvous at a particular location.
Illustration Credit: NIST

The ability to transmit and manipulate the smallest unit of light, the photon, with minimal loss, plays a pivotal role in optical communications as well as designs for quantum computers that would use light rather than electric charges to store and carry information.

Now, researchers at the National Institute of Standards and Technology (NIST) and their colleagues have connected on a single microchip quantum dots — artificial atoms that generate individual photons rapidly and on-demand when illuminated by a laser — with miniature circuits that can guide the light without significant loss of intensity.

To create the ultra-low-loss circuits, the researchers fabricated silicon- nitride waveguides—the channels through which the photons traveled—and buried them in silicon dioxide. The channels were wide but shallow, a geometry that reduced the likelihood that photons would scatter out of the waveguides. Encapsulating the waveguides in silicon dioxide also helped to reduce scattering.

More stable states for quantum computers

The properties of gralmonium qubits are dominated by a tiny constriction of only 20 nanometers, which acts like a magnifying glass for microscopic material defects.
Illustration Credit: Dennis Rieger, KIT

Quantum computers are considered the computers of the future. A and O are quantum bits (qubits), the smallest computing unit of quantum computers. Since they not only have two states, but also states in between, qubits process more information in less time. Maintaining such a condition longer is difficult, however, and depends in particular on the material properties. A KIT research team has now produced qubits that are 100 times more sensitive to material defects - a crucial step to eradicate them. The team published the results in the journal Nature Materials.

Quantum computers can process large amounts of data faster because they perform many calculation steps in parallel. The information carrier of the quantum computer is the qubit. With qubits there is not only the information "0" and "1", but also values in between. The difficulty at the moment, however, is to produce qubits that are small enough and can be switched quickly enough to perform quantum calculations. Superconducting circuits are a promising option here. Superconductors are materials that have no electrical resistance at extremely low temperatures and therefore conduct electrical current without loss. This is crucial to maintain the quantum state of the qubits and to connect them efficiently.

Particles of Light May Create Fluid Flow, Data-Theory Comparison Suggests

Brookhaven Lab theorist Bjoern Schenke's hydrodynamic calculations match up with data from collisions of photons with atomic nuclei at the Large Hadron Collider's ATLAS detector, suggesting those collisions create a fluid of "strongly interacting" particles.
Photo Credit: Brookhaven National Laboratory

A new computational analysis by theorists at the U.S. Department of Energy’s Brookhaven National Laboratory and Wayne State University supports the idea that photons (a.k.a. particles of light) colliding with heavy ions can create a fluid of “strongly interacting” particles. In a paper just published in Physical Review Letters, they show that calculations describing such a system match up with data collected by the ATLAS detector at Europe’s Large Hadron Collider (LHC).

As the paper explains, the calculations are based on the hydrodynamic particle flow seen in head-on collisions of various types of ions at both the LHC and the Relativistic Heavy Ion Collider (RHIC), a DOE Office of Science user facility for nuclear physics research at Brookhaven Lab. With only modest changes, these calculations also describe flow patterns seen in near-miss collisions, where photons that form a cloud around the speeding ions collide with the ions in the opposite beam.

“The upshot is that, using the same framework we use to describe lead-lead and proton-lead collisions, we can describe the data of these ultra-peripheral collisions where we have a photon colliding with a lead nucleus,” said Brookhaven Lab theorist Bjoern Schenke, a coauthor of the paper. “That tells you there’s a possibility that, in these photon-ion collisions, we create a small dense strongly interacting medium that is well described by hydrodynamics—just like in the larger systems.”