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. 

A quasiparticle that can transfer heat under electrical control

Because thermal conductivity in this class of materials can be changed with application of an external electric field at room temperature, they hold promise for use in heat switches for everyday applications, like collection of solar power.
Photo Credit: American Public Power Association

Scientists have found the secret behind a property of solid materials known as ferroelectrics, showing that quasiparticles moving in wave-like patterns among vibrating atoms carry enough heat to turn the material into a thermal switch when an electrical field is applied externally.

A key finding of the study is that this control of thermal conductivity is attributable to the structure of the material rather than any random collisions among atoms. Specifically, the researchers describe quasiparticles called ferrons whose polarization changes as they “wiggle” in between vibrating atoms – and it’s that ordered wiggling and polarization, receptive to the externally applied electrical field, that dictates the material’s ability to transfer the heat at a different rate.

“We figured out that this change in position of these atoms, and the change of the nature of the vibrations, must carry heat, and therefore the external field which changes this vibration must affect the thermal conductivity,” said senior author Joseph Heremans, professor of mechanical and aerospace engineering, materials science and engineering, and physics at The Ohio State University. 

A new way to explore proton’s structure with neutrinos yields first results

One of two magnetic focusing horns used in the beamline at Fermilab that produces intense neutrino beams for MINERvA and other neutrino experiments.
Photo Credit: Reidar Hahn, Fermilab

Physicists used MINERvA, a Fermilab neutrino experiment, to measure the proton’s size and structure using a neutrino-scattering technique.

For the first time, particle physicists have been able to precisely measure the proton’s size and structure using neutrinos. With data gathered from thousands of neutrino-hydrogen scattering events collected by MINERvA, a particle physics experiment at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, physicists have found a new lens for exploring protons. The results were published today in the scientific journal Nature.

This measurement is also important for analyzing data from experiments that aim to measure the properties of neutrinos with great precision, including the future Deep Underground Neutrino Experiment, hosted by Fermilab.

“The MINERvA experiment has found a novel way for us to see and understand proton structure, critical both for our understanding of the building blocks of matter and for our ability to interpret results from the flagship DUNE experiment on the horizon,” said Bonnie Fleming, Fermilab deputy director for science and technology.

Solid material that 'upconverts' visible light photons to UV light photons could change how we utilize sunlight

Low-intensity visible blue light or lower energy photons being converted into higher energy UV photons using a solid film formed on a round glass substrate, developed by researchers at Tokyo Tech
 Image Credit: Prof. Yoichi Murakami

Ultraviolet (UV) light has higher energy photons than visible light and, thus, has more applications. Tokyo Tech researchers have now developed a brilliant innovation—a solid-state material that can stably and efficiently upconvert sunlight- intensity visible light photons to UV light photons. This photon upconversion (UC) material can utilize visible light to successfully drive reactions that would conventionally need UV light, broadening the spectrum of utility for the former.

The importance of solar power as a renewable energy resource is increasing. Sunlight contains high-energy UV light with a wavelength shorter than 400 nm, which can be broadly used, for example, for photopolymerization to form a resin and activation of photocatalysts to drive reactions that generate green hydrogen or useful hydrocarbons (fuels, sugars, olefins, etc.). The latter of these is often called "artificial photosynthesis." Photocatalytic reaction by UV light to efficiently kill viruses and bacteria is another important application. Unfortunately, only about 4% of terrestrial sunlight falls within the UV range in the electromagnetic spectrum. This leaves a large portion of sunlight spectrum unexploited for these purposes.

Astronomers reveal new map of dark matter, mass in universe

Victor M. Blanco 4-meter Telescope, left, at the Cerro Tololo Inter-American Observatory in Chile houses the camera used by the Dark Energy Survey.
Image Credit: Dark Energy Survey

For decades, cosmologists have mapped the distribution of mass in the universe, both visible material and the mysterious dark matter, in an effort to improve our understanding of these fundamental building blocks. Astronomer Eric Baxter from the University of Hawaiʻi Institute for Astronomy co-authored new research that traces the mass distribution in the universe in three dimensions. The updated analysis was published in Physical Review D.

Baxter and his University of Chicago collaborators, Chihway Chang and Yuuki Omori, compiled data using two different sky surveying methods. This new analysis shows that there is six times as much dark matter in the universe compared to matter that is visible—a finding that was already well-known. However, the team also found that the matter is not as clumpy as previously expected when compared to the current best model of the universe.

The researchers claim the findings could add to a growing body of evidence that there may be something missing from the existing standard model of the universe.

New type of solar cell is being tested in space

Magnus Borgström Professor, Solid State Physics Lund University
Photo Credit: Lund University

Physics researchers at Lund University in Sweden recently succeeded in constructing small solar radiation-collecting antennas – nanowires – using three different materials that are a better match for the solar spectrum compared with today’s silicon solar cells. As the nanowires are light and require little material per unit of area, they are now to be installed for tests on satellites, which are powered by solar cells and where efficiency, in combination with low weight, is the most important factor. The new solar cells were sent into space a few days ago.

A group of nanoengineering researchers at Lund University working on solar cells made a breakthrough last year when they succeeded in building photovoltaic nanowires with three different band gaps. This, in other words, means that one and the same nanowire consists of three different materials that react to different parts of solar light. The results have been published in Materials Today Energy and subsequently in more detail in Nano Research.

“The big challenge was to get the current to transfer between the materials. It took more than ten years, but it worked in the end,” says Magnus Borgström, professor of solid-state physics, who wrote the articles with the then doctoral student Lukas Hrachowina.

Researchers can ‘see’ crystals perform their dance moves

Wenbin Li (left) and Aditya Mohite.
Photo Credit: Jeff Fitlow/Rice University

Rice University researchers already knew the atoms in perovskites react favorably to light. Now they can see precisely how those atoms move.

A breakthrough in visualization supports their efforts to squeeze every possible drop of utility out of perovskite-based materials, including solar cells, a long-standing project that only recently yielded an advance to make the devices far more durable.

A study published in Nature Physics details the first direct measurement of structural dynamics under light-induced excitation in 2D perovskites. Perovskites are layered materials that have well-ordered crystal lattices. They are highly efficient harvesters of light that are being explored for use as solar cells, photodetectors, photocatalysts, light-emitting diodes, quantum emitters and more.

“The next frontier in light-to-energy conversion devices is harvesting hot carriers,” said Rice University’s Aditya Mohite, a corresponding author of the study. “Studies have shown that hot carriers in perovskite can live up to 10-100 times longer than in classical semiconductors. However, the mechanisms and design principles for the energy transfer and how they interact with the lattice are not understood.”

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.

Astronomers use novel technique to find starspots

Sunspots
Image Credit: HMI / SFLORG/ Via ESO Helioviewer

Astronomers have developed a powerful technique for identifying starspots, according to research presented this month at the 241st meeting of the American Astronomical Society, and published in the journal Monthly Notices of the Royal Astronomical Society

Our sun is at times dotted with sunspots, cool dark regions on the stellar surface generated by strong magnetic fields, which suppress churning motions and impede the free escape of light. "On other stars, these phenomena are called starspots," said Lyra Cao, lead author of the study and a graduate student in astronomy at The Ohio State University. 

“Our study is the first to precisely characterize the spottiness of stars and use it to directly test theories of stellar magnetism,” said Cao. “This technique is so precise and broadly applicable that it can become a powerful new tool in the study of stellar physics.”

Use of the technique will soon allow Cao and her colleagues to release a catalog of starspot and magnetic field measurements for more than 700,000 stars – increasing the number of these measurements available to scientists by three orders of magnitude.

MLU physicists solve mystery of two-dimensional quasicrystal formation from metal oxides

A substructure consisting of rings of different sizes embeds itself seamlessly into a hexagonal structure
 Photo Credit: Dr. Stefan Förster

The structure of two-dimensional titanium oxide breaks up at high temperatures by adding barium; instead of regular hexagons, rings of four, seven and ten atoms are created that order periodically. A team at Martin Luther University Halle-Wittenberg (MLU) made this discovery in collaboration with researchers from the Max Planck Institute (MPI) for Microstructure Physics, the Université Grenoble Alpes and the National Institute of Standards and Technology (Gaithersburg, USA), thereby solving the riddle of two-dimensional quasicrystal formation from metal oxides. Their findings have been published in the renowned journal "Nature Communications".

Hexagons are frequently found in nature. The best-known example is honeycomb, but graphene or various metal oxides, such as titanium oxide, also form this structure. "Hexagons are an ideal pattern for periodic arrangements," explains Dr Stefan Förster, researcher in the Surface and Interface Physics group at MLU’s Institute of Physics. "They fit together so perfectly that there are no gaps." In 2013, this group made an astonishing discovery upon depositing an ultrathin layer containing titanium oxide and barium on a platinum substrate and heating it to around 1,000 degrees centigrade in an ultra-high vacuum. The atoms arranged themselves into triangles, squares and rhombuses that group in even larger symmetrical shapes with twelve edges. A structure with 12-fold rotational symmetry was created, instead of the expected 6-fold periodicity. According to Förster, "Quasicrystals were created that have an aperiodic structure. This structure is made of basic atomic clusters that are highly ordered, even if the systematics behind this ordering is difficult for the observer to discern." The physicists from Halle were the first worldwide to demonstrate the formation of two-dimensional quasicrystals in metal oxides. 

Thermal motions and oscillation modes determine the uptake of bacteria in cells

Photo of a membrane bubble with different oscillation modes in the background and experimental scheme in the foreground. Optical tweezers (laser focus in red) bring a thermally fluctuating particle into contact with a membrane bubble (green) until the particle is invaginated into the membrane and taken up.
Graphic Credit: AG Rohrbach

How and with what effort does a bacterium - or a virus - enter a cell and cause an infection? Researchers from Freiburg have now made an important contribution to answering this question: A team led by physicist Prof. Dr. Alexander Rohrbach and his collaborator Dr. Yareni Ayala was able to show how thermal fluctuations of a model bacterium and membrane oscillation modes of a model cell influence the energy with which the model bacteria dock and enter the membrane. The results have just been published in the journal Nature Communications.

Like a sticky piece of candy on a wobbly balloon

“To understand how a bacterium or virus enters a cell, you can imagine a sticky candy on a floppy, wobbly balloon. When a child shakes the rubber balloon around, the candy sticks even tighter to its surface,” said Rohrbach, a professor of -Bio- and Nano-Photonics at the Department of Microsystems Engineering at the University of Freiburg. In his lab, the laser and bio-physicists set up a similar experiment to study the physics of infection processes. The wobbly balloon corresponds to a giant uni-lamellar vesicle (GUV), which serves as a biological model cell. The membrane vesicle is the size of a tiny grain of sand about 20 micrometers in diameter.

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.

How a 3 cm glass sphere could help scientists understand space weather

UCLA researchers effectively reproduced the type of gravity that exists on or near stars and other planets inside of a glass sphere 3 centimeters in diameter.
Photo Credit: John Koulakis/UCLA 

Solar flares and other types of space weather can wreak havoc with spaceflight and with telecommunications and other types of satellites orbiting the Earth. But, to date, scientists’ ability to research ways to overcome that challenge has been severely limited. That’s because experiments they conduct in laboratories here on Earth are affected by gravity in ways that are so different from conditions in space.

But a new study by UCLA physicists could, at last, help conquer that issue — which could be a big step toward safeguarding humans (and equipment) during space expeditions, and to ensuring the proper functioning of satellites. The paper is published in Physical Review Letters.

The UCLA researchers effectively reproduced the type of gravity that exists on or near stars and other planets inside of a glass sphere measuring 3 centimeters in diameter (about 1.2 inches). To do so, they used sound waves to create a spherical gravitational field and generate plasma convection — a process in which gas cools as it nears the surface of a body and then reheats and rises again as it nears the core — creating a fluid current that in turn generates a magnetic current.

The achievement could help scientists overcome the limiting role of gravity in experiments that are intended to model convection that occurs in stars and other planets.

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.

A new model for dark matter

This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689, containing about 1,000 galaxies and trillions of stars. Dark matter is an invisible form of matter that accounts for most of the universe’s mass. Hubble cannot see the dark matter directly. Astronomers inferred its location by analyzing the effect of gravitational lensing, where light from galaxies behind Abell 1689 is distorted by intervening matter within the cluster. Researchers used the observed positions of 135 lensed images of 42 background galaxies to calculate the location and amount of dark matter in the cluster. They superimposed a map of these inferred dark matter concentrations, tinted blue, on an image of the cluster taken by Hubble’s Advanced Camera for Surveys. If the cluster’s gravity came only from the visible galaxies, the lensing distortions would be much weaker. The map reveals that the densest concentration of dark matter is in the cluster’s core. Abell 1689 resides 2.2 billion light-years from Earth. The image was taken in June 2002.
Image credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology, and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford (Johns Hopkins University)

Dark matter remains one of the greatest mysteries of modern physics. It is clear that it must exist, because without dark matter, for example, the motion of galaxies cannot be explained. But it has never been possible to detect dark matter in an experiment.

Currently, there are many proposals for new experiments: They aim to detect dark matter directly via its scattering from the constituents of the atomic nuclei of a detection medium, i.e., protons and neutrons.

A team of researchers—Robert McGehee and Aaron Pierce of the University of Michigan and Gilly Elor of Johannes Gutenberg University of Mainz in Germany—has now proposed a new candidate for dark matter: HYPER, or “HighlY Interactive ParticlE Relics.”

Removing water, stains, contaminants with hydrogel beads

Snapshots of the hydrogel bead impacting the droplet causing the droplet to lift off the surface.
Photo Credit: Courtesy of University of Hawaiʻi

There may be a more efficient future for water repellent materials and methods thanks to new research from the University of Hawaiʻi at Mānoa College of Engineering. Associate Professor John S. Allen III and an international team of researchers have discovered a method to remove liquid from non-stick surfaces using hydrogel beads, a material similar to gel cap medications.

“Ever want to remove a puddle completely without touching it? How about removing staining coffee off your clothes? Do you know that all the dangerous contaminants are off the surface? All these might be facilitated with low-cost hydrogel beads in the future,” Allen explained.

For a variety of everyday and industrial waterproof/water resistant objects, it is important to reduce the contact time of an impacting water or liquid drop with the surface. Many people are familiar with water repellent coating on buildings and on clothing. Repellants are also used to mitigate icing on a plane, as bouncing droplets are less likely to have time to freeze.

Ripples in the fabric of the universe may reveal the start of time

Numerical simulation of the neutron stars merging to form a black hole, with their accretion disks interacting to produce electromagnetic waves.
Illustration Credit: L. Rezolla (AEI) & M. Koppitz (AEI & Zuse-Institut Berlin

Scientists have advanced in discovering how to use ripples in space-time known as gravitational waves to peer back to the beginning of everything we know. The researchers say they can better understand the state of the cosmos shortly after the Big Bang by learning how these ripples in the fabric of the universe flow through planets and the gas between the galaxies.

“We can’t see the early universe directly, but maybe we can see it indirectly if we look at how gravitational waves from that time have affected matter and radiation that we can observe today,” said Deepen Garg, lead author of a paper reporting the results in the Journal of Cosmology and Astroparticle Physics. Garg is a graduate student in the Princeton Program in Plasma Physics, which is based at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL).

Garg and his advisor Ilya Dodin, who is affiliated with both Princeton University and PPPL, adapted this technique from their research into fusion energy, the process powering the sun and stars that scientists are developing to create electricity on Earth without emitting greenhouse gases or producing long-lived radioactive waste. Fusion scientists calculate how electromagnetic waves move through plasma, the soup of electrons and atomic nuclei that fuels fusion facilities known as tokamaks and stellarators.

Ionic Liquids' Good Vibrations Change Laser Colors with Ease

Shooting a green laser through a tube filled with a particular ionic liquid (right side of photo) can easily convert the green laser light to orange (upper left)—a long-sought color for medical applications. The method can be tailored for different color shifts by choosing different ionic liquids.
Photo Credit: Brookhaven National Laboratory

Lasers are intense beams of colored light. Depending on their color and other properties, they can scan your groceries, cut through metal, eradicate tumors, and even trigger nuclear fusion. But not every laser color is available with the right properties for a specific job. To fix that, scientists have found a variety of ways to convert one color of laser light into another. In a study just published in the journal Physical Review Applied, scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory demonstrate a new color-shifting strategy that’s simple, efficient, and highly customizable.

The new method relies on interactions between the laser and vibrational energy in the chemical bonds of materials called “ionic liquids.” These liquids are made only of positively and negatively charged ions, like ordinary table salt, but they flow like viscous fluids at room temperature. Simply shining a laser through a tube filled with a particular ionic liquid can downshift the laser’s energy and change its color while retaining other important properties of the laser beam.