Quantum simulators: When nature reveals its natural laws

Photo Credit: © Oliver Diekmann/TU Wien

Quantum simulators are a completely new tool for research: quantum physics is studied by other kinds of quantum physics. Research teams from Innsbruck and Vienna are developing a new method that will allow this new technology to be reliably verified.

Quantum physics is a very diverse field: it describes particle collisions shortly after the Big Bang as well as electrons in solid materials or atoms far out in space. But not all quantum objects are equally easy to study. For some – such as the early universe – direct experiments are not possible at all. However, in many cases quantum simulators can be used instead: One quantum system (for example, a cloud of ultracold atoms) is studied in order to learn something about another system that looks physically very different, but still follows the same laws, i.e. adheres to the same mathematical equations.

It is often difficult to find out which equations determine a particular quantum system. Normally, one first has to make theoretical assumptions and then conduct experiments to check whether these assumptions prove correct. Strikingly, researchers at the University of Innsbruck, opens an external URL in a new window, the Institute of Quantum Optics and Quantum Information, opens an external URL in a new window (IQOQI) and TU Wien (Vienna) have now jointly achieved an important step in this field: they have developed a method that allows them to read directly from the experiment which physical theory effectively describes the behavior of the quantum system. This now allows for a new kind of quality control: it is possible to directly check whether the quantum simulator actually does what it is supposed to simulate. This should enable quantitative statements to be made about quantum systems that cannot be investigated directly.

Chemical reactions can scramble quantum information as well as black holes

Rice University theorist Peter Wolynes and collaborators at the University of Illinois Urbana-Champaign have shown that molecules can be as formidable at scrambling quantum information as black holes.
Image Credit: Courtesy of Martin Gruebele; DeepAI was used in image production

If you were to throw a message in a bottle into a black hole, all of the information in it, down to the quantum level, would become completely scrambled. Because in black holes this scrambling happens as quickly and thoroughly as quantum mechanics allows, they are generally considered nature’s ultimate information scramblers.

New research from Rice University theorist Peter Wolynes and collaborators at the University of Illinois Urbana-Champaign, however, shows that molecules can be as formidable at scrambling quantum information as black holes. Combining mathematical tools from black hole physics and chemical physics, they have shown that quantum information scrambling takes place in chemical reactions and can nearly reach the same quantum mechanical limit as it does in black holes. The work is published online in the Proceedings of the National Academy of Sciences.

“This study addresses a long-standing problem in chemical physics, which has to do with the question of how fast quantum information gets scrambled in molecules,” Wolynes said. “When people think about a reaction where two molecules come together, they think the atoms only perform a single motion where a bond is made or a bond is broken.

“It’s ultimately about predicting everything” – theory could be a map to hunted quantum materials

Photo Credit: Vendi Jukic Buca

A breakthrough in theoretical physics is an important step towards predicting the behavior of the fundamental matter of which our world is built. It can be used to calculate systems of enormous quantities of quantum particles, a feat thought impossible before. The University of Copenhagen research may prove of great importance for the design of quantum computers and could even be a map to superconductors that function at room-temperature.

On the fringes of theoretical physics, Berislav Buca investigates the nearly impossible by way of "exotic" mathematics. His latest theory is no exception. By making it possible to calculate the dynamics, i.e., movements and interactions, of systems with enormous quantities of quantum particles, it has delivered something that had been written off in physics. An impossibility made possible.

The unexpected presence of a white cat adorns the illustrations of Buca's research. Pulci the cat is his eye-catching muse. Arrows through the cat's body illustrate the quantum mechanical origin of the playful cat's movements – and this is precisely the relationship that Buca is trying to understand by making it possible to calculate the dynamics of the very smallest particles.

The breakthrough has reinvigorated an old and fundamental scientific question: Theoretically, if all behavior in the universe can be calculated by way of the laws of physics, can we then predict everything by calculating its smallest particles? 

Kapitza-Dirac effect used to show temporal evolution of electron waves

Time dependent interference fringes from the ultrafast Kapitza Dirac Effect. An electron wave packet is exposed to two counterpropagating ultrashort laser pulses. The time span from back to front is 10 pico seconds.
Illustration Credit: © Goethe University Frankfurt

One of the most fundamental interactions in physics is that of electrons and light. In an experiment at Goethe University Frankfurt, scientists have now managed to observe what is known as the Kapitza-Dirac effect for the first time in full temporal resolution. This effect was first postulated over 90 years ago, but only now are its finest details coming to light. 

It was one of the biggest surprises in the history of science: In the early days of quantum physics around 100 years ago, scholars discovered that the particles which make up our matter always behave like waves. Just as light can scatter at a double slit and produce scattering patterns, electrons can also display interference effects. In 1933, the two theorists Piotr Kapitza and Paul Dirac proved that an electron beam is even diffracted from a standing light wave (due to the particles' properties) and that interference effects as a result of the wave properties are to be expected. 

A German-Chinese team led by Professor Reinhard Dörner from Goethe University Frankfurt has succeeded in using this Kapitza-Dirac effect to visualize even the temporal evolution of the electron waves, known as the electrons' quantum mechanical phase. The researchers have now presented their results in the journal Science. 

Magnetic Avalanche Triggered by Quantum Effects

Christopher Simon holds a crystal of lithium holmium yttrium fluoride.
Photo Credit: Lance Hayashida/Caltech

Iron screws and other so-called ferromagnetic materials are made up of atoms with electrons that act like little magnets. Normally, the orientations of the magnets are aligned within one region of the material but are not aligned from one region to the next. Think of groups of tourists in Times Square pointing to different billboards all around them. But when a magnetic field is applied, the orientations of the magnets, or spins, in the different regions line up and the material becomes fully magnetized. This would be like the packs of tourists all turning to point at the same sign.

The process of spins lining up, however, does not happen all at once. Rather, when the magnetic field is applied, different regions, or so-called domains, influence others nearby, and the changes spread across the material in a clumpy fashion. Scientists often compare this effect to an avalanche of snow, where one small lump of snow starts falling, pushing on other nearby lumps, until the entire mountainside of snow is tumbling down in the same direction.

A new type of cooling for quantum simulators

Tiantian Zhang and Maximilian Prüfer discussing measurements in the quantum lab
Photo Credit: Courtesy of Technische Universität Wien

Quantum experiments always have to deal with the same problem, regardless of whether they involve quantum computers, quantum teleportation or new types of quantum sensors: quantum effects break down very easily. They are extremely sensitive to external disturbances - for example, to fluctuations caused simply by the surrounding temperature. It is therefore important to be able to cool down quantum experiments as effectively as possible.

At TU Wien (Vienna), it has now been shown that this type of cooling can be achieved in an interesting new way: A Bose-Einstein condensate is split into two parts, neither abruptly nor particularly slowly, but with a very specific temporal dynamic that ensures that random fluctuations are prevented as perfectly as possible. In this way, the relevant temperature in the already extremely cold Bose-Einstein condensate can be significantly reduced. This is important for quantum simulators, which are used at TU Wien to gain insights into quantum effects that could not be investigated using previous methods.

Scientists propose a new way to search for dark matter

(Left) The new dark matter detection proposal looks for frequent interactions between nuclei in a detector and low-energy dark matter that may be present in and around Earth. (Right) A conventional direct detection experiment looks for occasional recoils from dark matter scattering.
Image Credit: Anirban Das, Noah Kurinsky and Rebecca Leane

Ever since its discovery, dark matter has remained invisible to scientists, despite the launch of multiple ultra-sensitive particle detector experiments around the world over several decades. 

Now, physicists at the Department of Energy’s (DOE) SLAC National Accelerator Laboratory are proposing a new way to look for dark matter using quantum devices, which might be naturally tuned to detect what researchers call thermalized dark matter.

Most dark matter experiments hunt for galactic dark matter, which rockets into Earth directly from space, but another kind might have been hanging around Earth for years, said SLAC physicist Rebecca Leane, who was an author on the new study. 

“Dark matter goes into the Earth, bounces around a lot, and eventually just gets trapped by the gravitational field of the Earth,” Leane said, bringing it into an equilibrium scientists refer to as thermalized. Over time, this thermalized dark matter builds up to a higher density than the few loose, galactic particles, meaning that it could be more likely to hit a detector. Unfortunately, thermalized dark matter moves much more slowly than galactic dark matter, meaning it would impart far less energy than galactic dark matter – likely too little for traditional detectors to see.

Satellites for quantum communications

Tobias Vogl investigates single photon sources in 2D materials in an experimental setup
Photo Credit: Jens Meyer / University of Jena

Through steady advances in the development of quantum computers and their ever-improving performance, it will be possible in the future to crack our current encryption processes. To address this challenge, researchers at the Technical University of Munich (TUM) are participating in an international research consortium to develop encryption methods that will apply physical laws to prevent the interception of messages. To safeguard communications over long distances, the QUICK³ space mission will deploy satellites.

How can it be ensured that data transmitted through the internet can be read only by the intended recipient? At present our data are encrypted with mathematical methods that rely on the idea that the factorization of large numbers is a difficult task. With the increasing power of quantum computers, however, these mathematical codes will probably no longer be secure in the future.

Umbrella for Atoms: The First Protective Layer for 2d Quantum Materials

Amalgamation of experimental images. At the top, a scanning tunneling microscopy image displays the graphene’s honeycomb lattice (the protective layer). In the center, electron microscopy shows a top view of the material indenene as a triangular lattice. Below it is a side view of the silicon carbide substrate. It can be seen that both the indenene and the graphene consist of a single atomic layer.
Image Credit: © Jonas Erhardt/Christoph Maeder

As silicon-based computer chips approach their physical limitations in the quest for faster and smaller designs, the search for alternative materials that remain functional at atomic scales is one of science's biggest challenges. In a groundbreaking development, researchers at the Würzburg-Dresden Cluster of Excellence ct.qmat have engineered a protective film that shields quantum semiconductor layers just one atom thick from environmental influences without compromising their revolutionary quantum properties. This puts the application of these delicate atomic layers in ultrathin electronic components within realistic reach. The findings have just been published in Nature Communications.

2D Quantum Materials Instead of Silicon

The race to create increasingly faster and more powerful computer chips continues as transistors, their fundamental components, shrink to ever smaller and more compact sizes. In a few years, these transistors will measure just a few atoms across – by which point, the miniaturization of the silicon technology currently used will have reached its physical limits. Consequently, the quest for alternative materials with entirely new properties is crucial for future technological advancements.

New quantum entangled material could pave way for ultrathin quantum technologies

Artistic illustration depicts heavy-fermion Kondo matter in a monolayer material.
Illustration Credit: Adolfo Fumega/Aalto University

Researchers reveal the microscopic nature of the quantum entangled state of a new monolayer van der Waals material

Two-dimensional quantum materials provide a unique platform for new quantum technologies, because they offer the flexibility of combining different monolayers featuring radically distinct quantum states. Different two-dimensional materials can provide building blocks with features like superconductivity, magnetism, and topological matter. But so far, creating a monolayer of heavy-fermion Kondo matter – a state of matter dominated by quantum entanglement – has eluded scientists. Now, researchers at Aalto University have shown that it’s theoretically possible for heavy-fermion Kondo matter to appear in a monolayer material, and they’ve described the microscopic interactions that produces its unconventional behavior. These findings were published in Nano Letters.

“Heavy-fermion materials are promising candidates to discover unconventional topological superconductivity, a potential building block for quantum computers robust to noise,” says Adolfo Fumega, the first author of the paper and a post-doctoral researcher at Aalto University.

These materials can feature two phases: one analogous to a conventional magnet, and one where the state of the system is dominated by quantum entanglement, known as the heavy-fermion Kondo state. At the transition between the magnetic phase and the heavy-fermion state, macroscopic quantum fluctuations appear, leading to exotic states of matter including unconventional superconducting phases.

Out of the desert, a quantum powerhouse rises

Postdoctoral researcher Caitlin McCowan inspects pieces of silicon at the atomic level. She uses a scanning tunneling microscope to spot imperfections as part of a quantum research project at Sandia National Laboratories.
Photo Credit: Craig Fritz

They knew it was an ambitious goal. But by the time they announced it in 2022, Sandia National Laboratories and The University of New Mexico — two of the state’s largest research institutions — had been working out their strategy for more than a year.

Their goal: transform the state into a global powerhouse in the emerging quantum technology market. Success would mean the arrival of tech companies and startups, jobs and investments — an economic resurgence for the southwestern state.

The plan is picking up steam.

In January, Sandia and UNM created the Quantum New Mexico Institute, a cooperatively run research center headquartered at the university. This marks a major milestone in the comprehensive strategy to advance research, court businesses and train a quantum-ready workforce.

“Our vision is to make New Mexico a destination for quantum companies and scientists across the world,” said Setso Metodi, institute co-director and Sandia manager of quantum computer science.

Resurrecting niobium for quantum science

The Josephson junction is the information-processing heart of the superconducting qubit. Pictured here is the niobium Josephson junction engineered by David Schuster of Stanford University and his team. Their junction design has resurrected niobium as a viable option as a core qubit material.
Image Credit: Alexander Anferov/the University of Chicago’s Pritzker Nanofabrication Facility.

For years, niobium was considered an underperformer when it came to superconducting qubits. Now scientists supported by Q-NEXT have found a way to engineer a high-performing niobium-based qubit and so take advantage of niobium’s superior qualities.

When it comes to quantum technology, niobium is making a comeback.

For the past 15 years, niobium has been sitting on the bench after experiencing a few mediocre at-bats as a core qubit material.

Qubits are the fundamental components of quantum devices. One qubit type relies on superconductivity to process information.

Touted for its superior qualities as a superconductor, niobium was always a promising candidate for quantum technologies. But scientists found niobium difficult to engineer as a core qubit component, and so it was relegated to the second string on Team Superconducting Qubit.

Now, a group led by Stanford University’s David Schuster has demonstrated a way to create niobium-based qubits that rival the state-of-the-art for their class.

Fundamental Equation for Superconducting Quantum Bits Revised

Cryogenic microwave setup used for quantum device measurements.
Photo Credit: Qinu GmbH

Quantum bits can be described more precisely with the help of newly 

Physicists from Forschungszentrum Jülich and the Karlsruhe Institute of Technology have uncovered that Josephson tunnel junctions – the fundamental building blocks of superconducting quantum computers – are more complex than previously thought. Just like overtones in a musical instrument, harmonics are superimposed on the fundamental mode. As a consequence, corrections may lead to quantum bits that are 2 to 7 times more stable. The researchers support their findings with experimental evidence from multiple laboratories across the globe, including the University of Cologne, Ecole Normale Supérieure in Paris, and IBM Quantum in New York.

It all started in 2019, when Dr. Dennis Willsch and Dennis Rieger – two PhD students from FZJ and KIT at the time and joint first authors of the paper – were having a hard time understanding their experiments using the standard model for Josephson tunnel junctions. This model had won Brian Josephson the Nobel Prize in Physics in 1973. Excited to get to the bottom of this, the team led by Professor Ioan Pop scrutinized further data from the Ecole Normale Supérieure in Paris and a 27-qubit device at IBM Quantum in New York, as well as data from previously published experiments. Independently, researchers from the University of Cologne were observing similar deviations of their data from the standard model.

Electronic pathways may enhance collective atomic vibrations’ magnetism

Andrey Baydin (left) and Fuyang Tay
Photo Credit: Gustavo Raskosky/Rice University

Materials with enhanced thermal conductivity are critical for the development of advanced devices to support applications in communications, clean energy and aerospace. But in order to engineer materials with this property, scientists need to understand how phonons, or quantum units of the vibration of atoms, behave in a particular substance.

“Phonons are quite important for studying new materials because they govern several material properties such as thermal conductivity and carrier properties,” said Fuyang Tay, a graduate student in applied physics working with the Rice Advanced Magnet with Broadband Optics (RAMBO), a tabletop spectrometer in Junichiro Kono’s laboratory at Rice University. “For example, it is widely accepted that superconductivity arises from electron–phonon interactions.

“Recently, there has been growing interest in the magnetic moment carried by phonon modes that show circular motion, also known as chiral phonons. But the mechanisms that can lead to a large phonon magnetic moment are not well understood.”

Now an international team of researchers led by Felix Hernandez from Brazil’s Universidade de São Paulo and Rice assistant research professor Andrey Baydin has published a study detailing the intricate connections between the magnetic properties of these quantum whirling dervishes and a material’s underlying topology of the electronic band structure, which determines the range of energy levels that electrons have within it.

Quantum batteries break causality

Charging quantum batteries in indefinite causal order.
In the classical world, if you tried to charge a battery using two chargers, you would have to do so in sequence, limiting the available options to just two possible orders. However, leveraging the novel quantum effect called ICO opens the possibility to charge quantum batteries in a distinctively unconventional way. Here, multiple chargers arranged in different orders can exist simultaneously, forming a quantum superposition.
Illustration Credit: ©2023 Chen et al.
CC BY-ND 4.0 DEED

Batteries that exploit quantum phenomena to gain, distribute and store power promise to surpass the abilities and usefulness of conventional chemical batteries in certain low-power applications. For the first time, researchers including those from the University of Tokyo take advantage of an unintuitive quantum process that disregards the conventional notion of causality to improve the performance of so-called quantum batteries, bringing this future technology a little closer to reality.

When you hear the word “quantum,” the physics governing the subatomic world, developments in quantum computers tend to steal the headlines, but there are other upcoming quantum technologies worth paying attention to. One such item is the quantum battery which, though initially puzzling in name, holds unexplored potential for sustainable energy solutions and possible integration into future electric vehicles. Nevertheless, these new devices are poised to find use in various portable and low-power applications, especially when opportunities to recharge are scarce.

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.