Atomic dance gives rise to a magnet

Tong Lin (from left), Hanyu Zhu and Jiaming Luo at EQUAL lab.
Photo Credit: Jeff Fitlow/Rice University

Quantum materials hold the key to a future of lightning-speed, energy-efficient information systems. The problem with tapping their transformative potential is that, in solids, the vast number of atoms often drowns out the exotic quantum properties electrons carry.

Rice University researchers in the lab of quantum materials scientist Hanyu Zhu found that when they move in circles, atoms can also work wonders: When the atomic lattice in a rare-earth crystal becomes animated with a corkscrew-shaped vibration known as a chiral phonon, the crystal is transformed into a magnet.

According to a study published in Science, exposing cerium fluoride to ultrafast pulses of light sends its atoms into a dance that momentarily enlists the spins of electrons, causing them to align with the atomic rotation. This alignment would otherwise require a powerful magnetic field to activate, since cerium fluoride is naturally paramagnetic with randomly oriented spins even at zero temperature.

Spinaron: A Rugby in a Ball Pit. New Quantum Effect Demonstrated for the First Time

The cobalt atom (red) has a magnetic moment (“spin,” blue arrow ), which is constantly reoriented (from spin-up to spin-down) by an external magnetic field. As a result, the magnetic atom excites the electrons of the copper surface (gray), causing them to oscillate (creating ripples). This revelation by the Würzburg-Dresden Cluster of Excellence ct.qmat was made possible thanks to the physicists’ inclusion of an iron tip (yellow) on their scanning tunneling microscope.
Illustration Credit: © Juba Bouaziz/Ulrich Puhlfürst

For the first time, experimental physicists from the Würzburg-Dresden Cluster of Excellence ct.qmat have demonstrated a new quantum effect aptly named the “spinaron.” In a meticulously controlled environment and using an advanced set of instruments, they managed to prove the unusual state a cobalt atom assumes on a copper surface. This revelation challenges the long-held Kondo effect – a theoretical concept developed in the 1960s, and which has been considered the standard model for the interaction of magnetic materials with metals since the 1980s. These groundbreaking findings were published today in the esteemed journal Nature Physics.

Ultra-Cold & Ultra-Strong: Pushing Boundaries in the Lab

Extreme conditions prevail in the Würzburg laboratory of experimental physicists Professor Matthias Bode and Dr. Artem Odobesko. Affiliated with the Cluster of Excellence ct.qmat, a collaboration between JMU Würzburg and TU Dresden, these visionaries are setting new milestones in quantum research. Their latest endeavor is unveiling the spinaron effect. They strategically placed individual cobalt atoms onto a copper surface, brought the temperature down to 1.4 Kelvin (–271.75° Celsius), and then subjected them to a powerful external magnetic field. “The magnet we use costs half a million euros. It’s not something that’s widely available,” explains Bode. Their subsequent analysis yielded unexpected revelations.

Researchers probe molten rock to crack Earth’s deepest secrets

Deep inside rocky planets like Earth, the behavior of iron can greatly affect the properties of molten rock materials: properties that influenced how Earth formed and evolved. Scientists used powerful lasers and ultrafast X-rays to recreate the extreme conditions in these molten rock materials, called silicate melts, and measure properties of iron. 
Illustration Credit: Greg Stewart/SLAC National Accelerator Laboratory

Deep inside rocky planets like Earth, the behavior of iron can greatly affect the properties of molten rock materials: properties that influenced how Earth formed and evolved. 

In fact, the evolution of our entire planet may be driven by the microscopic quantum state of these iron atoms. One special feature of iron is its “spin state,” which is a quantum property of the electrons in each iron atom that drives their magnetic behavior and reactivity in chemical reactions. Changes in the spin state can influence whether iron prefers to be in the molten rock or in solid form and how well the molten rock conducts electricity.

Until now, it’s been challenging to recreate the extreme conditions in these molten rock materials, called silicate melts, to measure the spin state of iron. Using powerful lasers and ultrafast X-rays, an international team of researchers at the Department of Energy’s SLAC National Accelerator Laboratory, Stanford University, Universite ́ Grenoble Alpes, Laboratoire pour l’Utilisation des Lasers Intenses (LULI), and Arizona State University overcame this challenge. They showed that at extremely high pressures and temperatures, the iron in silicate melts mostly has a low-spin state, meaning its electrons stay closer to the center and pair up in their energy levels, making the iron less magnetic and more stable.

A miniature magnetic resonance imager made of diamond

Prof. Dominik Bucher uses defects in diamond (NV-centers) as quantum sensors for NMR spectroscopy on the nano- to microscale. His research group works at the unique interface between quantum sensing and (bio) chemistry with interdisciplinary approaches from applied quantum physics, chemical synthesis and biophysics. The over goal is to perform NMR spectroscopy on smallest length-scales - from nano- and surface science to microfluidics and single-cell biology.
Photo Credit: Andreas Heddergott / TUM

The development of tumors begins with minuscule changes within the body's cells; ion diffusion at the smallest scales is decisive in the performance of batteries. Until now the resolution of conventional imaging methods has not been high enough to represent these processes in detail. A research team led by the Technical University of Munich (TUM) has developed diamond quantum sensors which can be used to improve resolution in magnetic imaging.

Nuclear magnetic resonance (NMR) is an important imaging method in research which can be used to visualize tissue and structures without damaging them. The technique is better known from the medical field as Magnetic Resonance Imaging (MRI), where the patient is moved into the bore of a large magnet on a table. The MRI device creates a very strong magnetic field which interacts with the tiny magnetic fields of the hydrogen nuclei in the body. Since the hydrogen atoms are distributed in a particular way amongst different types of tissues, it becomes possible to differentiate organs, joints, muscles and blood vessels.

Simulations of ‘backwards time travel’ can improve scientific experiments

Image Credit: Scientific Frontline stock graphic

If gamblers, investors and quantum experimentalists could bend the arrow of time, their advantage would be significantly higher, leading to significantly better outcomes. 

Researchers at the University of Cambridge have shown that by manipulating entanglement – a feature of quantum theory that causes particles to be intrinsically linked – they can simulate what could happen if one could travel backwards in time. So that gamblers, investors and quantum experimentalists could, in some cases, retroactively change their past actions and improve their outcomes in the present.

Whether particles can travel backwards in time is a controversial topic among physicists, even though scientists have previously simulated models of how such spacetime loops could behave if they did exist. By connecting their new theory to quantum metrology, which uses quantum theory to make highly sensitive measurements, the Cambridge team has shown that entanglement can solve problems that otherwise seem impossible. The study appears in the journal Physical Review Letters.

“Imagine that you want to send a gift to someone: you need to send it on day one to make sure it arrives on day three,” said lead author David Arvidsson-Shukur, from the Hitachi Cambridge Laboratory. “However, you only receive that person’s wish list on day two. So, in this chronology-respecting scenario, it’s impossible for you to know in advance what they will want as a gift and to make sure you send the right one.

A New Way to Erase Quantum Computer Errors

While errors are normally hard to spot in quantum devices, researchers have shown that, with careful control, some errors can cause atoms to glow. Researchers used this capability to execute a quantum simulation using an array of atoms and a laser beam, as shown in this simplified artist's concept. The experiment showed that they could discard the glowing, erroneous atoms and make the quantum simulation run more efficiently.
Illustration Credit: Caltech/Lance Hayashida

Quantum computers of the future hold promise in solving all sorts of problems. For example, they could lead to more sustainable materials, new medicines, and even crack the hardest problems in fundamental physics. But compared to classical computers in use today, rudimentary quantum computers are more prone to errors. Wouldn't it be nice if researchers could just take out a special quantum eraser and get rid of the mistakes?

Reporting in the journal Nature, a group of researchers led by Caltech is among the first to demonstrate a type of quantum eraser. The physicists show that they can pinpoint and correct mistakes in quantum computing systems known as "erasure" errors.

"It's normally very hard to detect errors in quantum computers, because just the act of looking for errors causes more to occur," says Adam Shaw, co-lead author of the new study and a graduate student in the laboratory of Manuel Endres, a professor of physics at Caltech. "But we show that with some careful control, we can precisely locate and erase certain errors without consequence, which is where the name erasure comes from."

Exploring Parameter Shift for Quantum Fisher Information

Image Credit: Scientific Frontline stock image

Quantum computing uses quantum mechanics to process and store information in a way that is different from classical computers. While classical computers rely on bits like tiny switches that can be either 0 or 1, quantum computers use quantum bits (qubits). Qubits are unique because they can be in a mixture of 0 and 1 simultaneously - a state referred to as superposition. This unique property enables quantum computers to solve specific problems significantly faster than classical ones.

In a recent publication in EPJ Quantum Technology, Le Bin Ho from Tohoku University's Frontier Institute for Interdisciplinary Sciences has developed a technique called "Time-dependent Stochastic Parameter Shift" in the realm of quantum computing and quantum machine learning. This breakthrough method revolutionizes the estimation of gradients or derivatives of functions, a crucial step in many computational tasks.

Typically, computing derivatives requires dissecting the function and calculating the rate of change over a small interval. But even classical computers cannot keep dividing indefinitely. In contrast, quantum computers can accomplish this task without having to discrete the function. This feature is achievable because quantum computers operate in a realm known as "quantum space," characterized by periodicity, and no need for endless subdivisions.

Optimizing Continuous-Variable Functions with Quantum Annealing

Quantum annealing (QA) can be competitive to classical algorithms in optimizing continuous-variable functions when running on appropriate hardware, show researchers from Tokyo Tech. By comparing the performance of QA running on a D-Wave quantum computer to that of state-of-the-art classical algorithms, they find that a sufficient suppression of thermal noise can enable QA to significantly outperform classical algorithms.

Quantum annealing (QA) is a cutting-edge algorithm that leverages the unique properties of quantum computing to tackle complex combinatorial optimization problems (a class of mathematical problems dealing with discrete-variable functions). Quantum computers use the rules of quantum physics to solve such problems potentially faster than classical computers. In essence, they can explore multiple solutions to a problem simultaneously, giving them a significant speed advantage for certain tasks over classical computers. In particular, QA harnesses the phenomenon of "quantum tunneling," where particles can "tunnel" through energy barriers without the requisite energy to cross over them, to find solutions for combinatorial optimization problems.

Up until now, QA has almost exclusively been used to solve discrete-variable functions (functions that have discrete-valued variables). The potential of QA for optimizing continuous-variable functions has remained largely unexplored.

Topological Insulator Catalysts for High-Yield Room-Temperature Synthesis of Organoureas

The unique quantum properties of bismuth selenide make it a promising catalyst for the synthesis of organic ureas, as demonstrated by scientists at Tokyo Tech. Thanks to its topological surface states, the proposed catalyst exhibits remarkably high catalytic activity and durability when used for the synthesis of various urea derivatives, which are widely utilized as nitrogen fertilizers.

Synthetic fertilizers, one the most important developments in modern agriculture, have enabled many countries to secure a stable food supply. Among them, organic ureas (or organoureas) have become prominent sources of nitrogen for crops. Since these compounds do not dissolve immediately in water, but instead are slowly decomposed by soil microorganisms, they provide a stable and controlled supply of nitrogen, which is crucial for plant growth and function.

However, traditional methods to synthesize organoureas are environmentally harmful due to their use of toxic substances, such as phosgene. Although alternative synthesis strategies have been demonstrated, these either rely on expensive and scarce noble metals or employ catalysts that cannot be reused easily.

Photosynthesis, Key to Life on Earth, Starts with a Single Photon

A cutting-edge experiment has revealed the quantum dynamics of one of nature’s most crucial processes
Illustration Credit: Jenny Nuss/Berkeley Lab

Using a complex cast of metal-studded pigments, proteins, enzymes, and co-enzymes, photosynthetic organisms can convert the energy in light into the chemical energy for life. And now, thanks to a study published today in Nature, we know that this organic chemical reaction is sensitive to the smallest quantity of light possible – a single photon.

The discovery solidifies our current understanding of photosynthesis and will help answer questions about how life works on the smallest of scales, where quantum physics and biology meet.

“A huge amount of work, theoretically and experimentally, has been done around the world trying to understand what happens after a photon is absorbed. But we realized that nobody was talking about the first step. That was still a question that needed to be answered in detail,” said co-lead author Graham Fleming, a senior faculty scientist in the Biosciences Area at Lawrence Berkeley National Laboratory (Berkeley Lab) and professor of chemistry at UC Berkeley.

In their study, Fleming, co-lead author Birgitta Whaley, a senior faculty scientist in the Energy Sciences Area at Berkeley Lab, and their research groups showed that a single photon can indeed initiate the first step of photosynthesis in photosynthetic purple bacteria. Because all photosynthetic organisms use similar processes and share an evolutionary ancestor, the team is confident that photosynthesis in plants and algae works the same way. “Nature invented a very clever trick,” Fleming said.

Curved spacetime in a quantum simulator

   In the background: the gravitational lens effect, an example of an effect explained by relativity. With quantum particles, analogous effects can be studied.
Image Credit: NASA / TU Wien

New techniques can answer questions that were previously inaccessible experimentally - including questions about the relationship between quantum mechanics and relativity.

The theory of relativity works well when you want to explain cosmic-scale phenomena - such as the gravitational waves created when black holes collide. Quantum theory works well when describing particle-scale phenomena - such as the behavior of individual electrons in an atom. But combining the two in a completely satisfactory way has yet to be achieved. The search for a "quantum theory of gravity" is considered one of the significant unsolved tasks of science.

This is partly because the mathematics in this field is highly complicated. At the same time, it is tough to perform suitable experiments:  One would have to create situations in which phenomena of both the relativity theory play an important role, for example, a spacetime curved by heavy masses, and at the same time, quantum effects become visible, for example the dual particle and wave nature of light.

Ultralow temperature terahertz microscope capabilities enable better quantum technology

Terahertz microscope with cryogenic insert.
Image Credit: Courtesy of Ames National Laboratory

A team of scientists from the Department of Energy’s Ames National Laboratory have developed a way to collect terahertz imaging data on materials under extreme magnetic and cryogenic conditions. They accomplished their work with a new scanning probe microscope. 

This microscope was recently developed at Ames Lab. The team used the ultralow temperature terahertz microscope to take measurements on superconductors and topological semimetals. These materials were exposed to high magnetic fields and temperatures below liquid helium (below 4.2 Kelvins or -452 degrees Fahrenheit).

According to Jigang Wang, a scientist at Ames Lab, professor of Physics and Astronomy at Iowa State University, and the team leader, the team has been improving their terahertz microscope since it was first completed in 2019. “We have improved the resolution in terms of the space, time and energy,” said Wang. “We have also simultaneously improved operation to very low temperatures and high magnetic fields.”

Study reveals new ways for exotic quasiparticles to “relax”

By sandwiching bits of perovskite between two mirrors and stimulating them with laser beams, researchers were able to directly control the spin state of quasiparticles known as exciton-polariton pairs, which are hybrids of light and matter.
Illustration Credit: Courtesy of the researchers
(CC BY-NC-ND 3.0)

New findings from a team of researchers at MIT and elsewhere could help pave the way for new kinds of devices that efficiently bridge the gap between matter and light. These might include computer chips that eliminate inefficiencies inherent in today’s versions, and qubits, the basic building blocks for quantum computers, that could operate at room temperature instead of the ultracold conditions needed by most such devices.

The new work, based on sandwiching tiny flakes of a material called perovskite in between two precisely spaced reflective surfaces, is detailed in the journal Nature Communications, in a paper by MIT recent graduate Madeleine Laitz PhD ’22, postdoc Dane deQuilettes, MIT professors Vladimir Bulovic, Moungi Bawendi and Keith Nelson, and seven others.

By creating these perovskite sandwiches and stimulating them with laser beams, the researchers were able to directly control the momentum of certain “quasiparticles” within the system. Known as exciton-polariton pairs, these quasiparticles are hybrids of light and matter. Being able to control this property could ultimately make it possible to read and write data to devices based on this phenomenon.

With new experimental method, researchers probe spin structure in 2D materials for first time

In the study, researchers describe what they believe to be the first measurement showing direct interaction between electrons spinning in a 2D material and photons coming from microwave radiation.
 Graphic Credit: Jia Li, an assistant professor of physics at Brown.

For two decades, physicists have tried to directly manipulate the spin of electrons in 2D materials like graphene. Doing so could spark key advances in the burgeoning world of 2D electronics, a field where super-fast, small and flexible electronic devices carry out computations based on quantum mechanics.

Standing in the way is that the typical way in which scientists measure the spin of electrons — an essential behavior that gives everything in the physical universe its structure — usually doesn’t work in 2D materials. This makes it incredibly difficult to fully understand the materials and propel forward technological advances based on them. But a team of scientists led by Brown University researchers believe they now have a way around this longstanding challenge. They describe their solution in a new study published in Nature Physics.

In the study, the team — which also include scientists from the Center for Integrated Nanotechnologies at Sandia National Laboratories, and the University of Innsbruck — describe what they believe to be the first measurement showing direct interaction between electrons spinning in a 2D material and photons coming from microwave radiation. Called a coupling, the absorption of microwave photons by electrons establishes a novel experimental technique for directly studying the properties of how electrons spin in these 2D quantum materials — one that could serve as a foundation for developing computational and communicational technologies based on those materials, according to the researchers.

Jellybeans – a sweet solution for overcrowded circuitry in quantum computer chips

Engineers show that a jellybean-shaped quantum dot creates more breathing space in a microchip packed with qubits.

The silicon microchips of future quantum computers will be packed with millions, if not billions of qubits – the basic units of quantum information – to solve the greatest problems facing humanity. And with millions of qubits needing millions of wires in the microchip circuitry, it was always going to get cramped in there.

But now engineers at UNSW Sydney have made an important step towards solving a long-standing problem about giving their qubits more breathing space -- and it all revolves around jellybeans.

Not the kind we rely on for a sugar hit to get us past the 3pm slump. But jellybean quantum dots –elongated areas between qubit pairs that create more space for wiring without interrupting the way the paired qubits interact with each other.

As lead author Associate Professor Arne Laucht explains, the jellybean quantum dot is not a new concept in quantum computing, and has been discussed as a solution to some of the many pathways towards building the world’s first working quantum computer.

Entangled quantum circuits

Par­tial sec­tion of the 30-​meter-long quantum con­nec­tion between two su­per­con­duct­ing cir­cuits. The va­cuum tube (center) con­tains a mi­crowave wave­guide that is cooled to around –273°C and con­nects the two quantum cir­cuits.
Pho­to Credit: ETH Zurich / Daniel Wink­ler

A group of researchers led by Andreas Wallraff, Professor of Solid State Physics at ETH Zurich, has performed a loophole-free Bell test to disprove the concept of “local causality” formulated by Albert Einstein in response to quantum mechanics. By showing that quantum mechanical objects that are far apart can be much more strongly correlated with each other than is possible in conventional systems, the researchers have provided further confirmation for quantum mechanics. What’s special about this experiment is that the researchers were able for the first time to perform it using superconducting circuits, which are considered to be promising candidates for building powerful quantum computers.

Quantum Entanglement of Photons Doubles Microscope Resolution

Using a "spooky" phenomenon of quantum physics, Caltech researchers have discovered a way to double the resolution of light microscopes.
Photo Credit: Lance Hayashida/Caltech

In a paper appearing in the journal Nature Communications, a team led by Lihong Wang, Bren Professor of Medical Engineering and Electrical Engineering, shows the achievement of a leap forward in microscopy through what is known as quantum entanglement. Quantum entanglement is a phenomenon in which two particles are linked such that the state of one particle is tied to the state of the other particle regardless of whether the particles are anywhere near each other. Albert Einstein famously referred to quantum entanglement as "spooky action at a distance" because it could not be explained by his relativity theory.

According to quantum theory, any type of particle can be entangled. In the case of Wang's new microscopy technique, dubbed quantum microscopy by coincidence (QMC), the entangled particles are photons. Collectively, two entangled photons are known as a biphoton, and, importantly for Wang's microscopy, they behave in some ways as a single particle that has double the momentum of a single photon.

Since quantum mechanics says that all particles are also waves, and that the wavelength of a wave is inversely related to the momentum of the particle, particles with larger momenta have smaller wavelengths. So, because a biphoton has double the momentum of a photon, its wavelength is half that of the individual photons.

Beyond Moore’s Law: Innovations in solid-state physics include ultra-thin ‘two-dimensional’ materials and more

From left to right: Kaustav Banerjee and Arnab Pal
Photo Credit: Lilli McKinney

In the ceaseless pursuit of energy-efficient computing, new devices designed at UC Santa Barbara show promise for enhancements in information processing and data storage.

Researchers in the lab of Kaustav Banerjee, a professor of electrical and computer engineering, have published a new paper describing several of these devices, “Quantum-engineered devices based on 2D materials for next-generation information processing and storage,” in the journal Advanced Materials. Arnab Pal, who recently received his doctorate, is the lead author.

Each device is intended to address challenges associated with conventional computing in a new way. All four operate at very low voltages and are characterized as being low leakage, as opposed to the conventional metal-oxide semiconductor field-effect transistors (MOSFETs) found in smartphones that drain power even when turned off. But because they are based on processing steps similar to those used to make MOSFETs, the new devices could be produced at scale using existing industry-standard manufacturing processes for semiconductors.

The most promising of the two information-processing devices, according to Banerjee, is the spin-based field-effect transistor, or spin-FET, which takes advantage of the magnetic moment — or spin — of the electrons that power the device. In this case, the materials belong to the transition metal dichalcogenide group of compounds, which are based on transition metals. 

Paradoxical quantum phenomenon measured for the first time

Photo Credit: © Thomas Schweigler, TU Wien

How do quantum particles share information? A peculiar conjecture about quantum information has been experimentally confirmed at the TU Wien.

Some things are related, others are not. Suppose you randomly select a person from a crowd who is significantly taller than the average. In that case, there is a good chance that they will also weigh more than the average. Statistically, one quantity also contains some information about the other.

Quantum physics allows for even stronger links between different quantities: different particles or parts of an extensive quantum system can "share" a certain amount of information. There are curious theoretical predictions about this: surprisingly, the measure of this "mutual information" does not depend on the size of the system but only on its surface. This surprising result has been confirmed experimentally at the TU Wien and published in "Nature Physics". Theoretical input to the experiment and its interpretation came from the Max-Planck-Institut für Quantenoptik in Garching, FU Berlin, ETH Zürich and New York University.

Scientists Create a Longer-Lasting Exciton that May Open New Possibilities in Quantum Information Science

Alessandra Lanzara at Berkeley Lab.
Photo Credit: Mark Joseph Hanson

In a new study, scientists have observed long-lived excitons in a topological material, opening intriguing new research directions for optoelectronics and quantum computing. 

Excitons are charge-neutral quasiparticles created when light is absorbed by a semiconductor. Consisting of an excited electron coupled to a lower-energy electron vacancy or hole, an exciton is typically short-lived, surviving only until the electron and hole recombine, which limits its usefulness in applications. 

“If we want to make progress in quantum computing and create more sustainable electronics, we need longer exciton lifetimes and new ways of transferring information that don’t rely on the charge of electrons,” said Alessandra Lanzara, who led the study. Lanzara is a senior faculty scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and a UC Berkeley physics professor. “Here we’re leveraging topological material properties to make an exciton that is long lived and very robust to disorder.” 

In a topological insulator, electrons can only move on the surface. By creating an exciton in such a material, the researchers hoped to achieve a state in which an electron trapped on the surface was coupled to a hole that remained confined in the bulk. Such a state would be spatially indirect – extending from the surface into the bulk – and could retain the special spin properties inherent to topological surface states.