Category: Physics

Over the past decades, physicists and engineers have been trying to develop various technologies that leverage quantum mechanical effects, including quantum microscopes. These are microscopy tools that can be used to study the properties of quantum particles and quantum states in depth.

Researchers at Silicon Quantum Computing (SQC)/UNSW Sydney and the University of Melbourne recently created a new solid-state quantum microscope that could be used to control and examine the wave functions of atomic qubits in silicon. This microscope, introduced in a paper published in Nature Electronics, was created combining two different techniques, known as ion implantation and atomic precision lithography.

“Qubit device operations often rely on shifting and overlapping the qubit wave functions, which relate to the spatial distribution of the electrons at play, so a comprehensive knowledge of the latter provides a unique insight into building quantum circuits efficiently,” Benoit Voisin and Sven Rogge, two researchers who carried out the study, told Phys.org.

“Spatial information about the wave functions is typically not possible during qubit device measurements as these are based on fixed charge sensing of the whole quantum state. Direct access to the full spatial extent of the quantum state can however be accessed using a scanning tunneling microscope (STM), which we have developed to place atoms in silicon with atomic precision. In this paper we have combined the local control of the wave function used for device operation directly within the microscope.”

The lab at SQC/UNSW Sydney had been previously manufacturing qubit devices and developing scanning tunneling microscopes to image qubit wave functions in parallel, using individual phosphorus atoms embedded in silicon. In their new paper, Voisin, Rogge and their colleagues tried to merge these two different research efforts into a single platform. More specifically, they set out to realize a quantum microscope that could simultaneously map out and control atomic qubits with local electrodes in a single device.

“A quantum microscope is a tool where arrays of atoms can be engineered with atomic precision, and where each atom, or qubit, can be locally controlled and measured,” Voisin and Rogge said. “Comparable microscopes exist in the cold atom community where laser technology is used in a vacuum. Our solid-state version of a quantum microscope very much resembles a transistor, with local electrodes defining the source and gate sides, and the STM tip acting as a drain which can move with picometer resolution from qubit to qubit and scan their wave function.”

The new quantum microscope created by the researchers was created by combining two different techniques. More specifically, they used atomic precision lithography to introduce dopant atoms and more conventional ion implantation techniques to create the electrodes for their device. This unique approach to fabricate quantum microscopes was pioneered at UNSW.

“The qubits are defined using the atomic precision manufacturing technique, by incorporating a few phosphorus atoms in small patches of desorbed hydrogen at the silicon surface, close to the source electrode, Voisin and Rogge explained. “Contrary to typical STM experiments performed on conductive substrates, here our microscope operates on insulating silicon, and we had to design a light-assisted protocol to first stabilize the STM tip before being able to map out the qubit wave functions.”

The researchers’ microscope essentially utilizes the STM tip as a movable electrode, which can have valuable advantages. Most notably, this approach simplifies the collection of large qubit array measurements, without requiring the use of an increasing number of fixed sensors, but instead measuring entire arrays using a single STM tip.

“The ability to map out the qubit wave functions directly during device operation gives us invaluable and predictive insights on how to optimize the device design as we scale, such as distance and orientation between the qubits,” Voisin and Rogge said. “As a consequence, with regard to the manufacturing of complete circuits using the atomic qubits we engineer at our SQC/UNSW lab, our quantum microscope will help speed up manufacturing cycles for better device performance.”

Atomic precision lithography and ion implantation are two distinct processes typically realized in entirely different laboratory conditions. The integration of these two techniques to create a single device was thus a remarkable achievement for the team.

The recent study by Voisin, Rogge and their colleagues could bring a new wave of innovation in the field of STM and quantum microscopy, as it introduces a new approach for fabricating quantum microscopes. In the future, their proposed approach could be applied to microscopes based on other solid-state systems, such as molecules and magnetic atoms.

The SQC lab at UNSW is now exploring two key research directions. Firstly, they are trying to reach beyond the local electrostatic control demonstrated in their recent paper, by performing microwave coherent operations on the qubits inside their microscope.

“To do this, we need sub-100mK temperatures and finite magnetic fields, and we are currently commissioning a new equipment that will provide these capabilities,” Voisin and Rogge added. “The second application we are exploring is to create and probe new correlated states of matter that are challenging to simulate with classical computation techniques or achieve with other experimental platforms such as cold atoms.

“We will fabricate large arrays of qubits strongly coupled to each other, in a regime where topological and superconducting states are expected to emerge. This is a very exciting area where our combination of precision manufacturing and ability to see wave functions directly will open new horizons in our atomic understanding of the world.”

More information: B. Voisin et al, A solid-state quantum microscope for wavefunction control of an atom-based quantum dot device in silicon, Nature Electronics (2023). DOI: 10.1038/s41928-023-00979-z

Journal information: Nature Electronics 

© 2023 Science X Network

Metamaterials are a type of artificial material which, as the prefix “meta”—meaning in Greek “after” or “beyond”—indicates, demonstrate electromagnetic properties and other characteristics not found in nature.

As a result of these characteristics, including negative refraction and perfect lensing and cloaking, which arise from the lattice design composition of these substances rather than the materials that actually comprise them, metamaterials have become a hot research topic.

In particular, materials scientists are actively hunting for metamaterials that are “perfect absorbers” of electromagnetic radiation with controllable resonance characteristics that lead to their wide usage in applications as varied as solar cells, thermal radiation imaging, sensing technology, and even stealth technology.

In a new paper in The European Physical Journal D, Shahzad Anwar, a researcher at the Department of Physics, Islamia College Peshawar, Pakistan, and his colleagues document the proposed design of a triple-band perfect metamaterial absorber. The new metamaterial could have applications in sensors, filters, and in stealth technology.

“The aim of this work is to achieve a multiband metamaterial absorber and to improve the sensing performance of the multiple band absorbers for their potential applications in optical filters and sensing devices,” the authors write. “The novelty of our work has two major aspects. Firstly, it simplifies the design structure of multiband metamaterial absorbers in the terahertz region. Secondly, it enhances the sensing performance of multiband metamaterial absorbers, which is highly beneficial in improving the design [of] sensing devices.”

The team’s proposed design consists of a gold metallic array, a metallic layer, and a dielectric spacer between the two. Testing by the team demonstrated that the metamaterial perfect absorber has three resonant modes at frequencies 1.655 THz, 1.985 THz, and 2.86 THz, in which an average absorption rate close to 95% was achieved.

The authors also found that by varying the structural parameters of their proposed material, the frequencies of its resonant modes can be tuned.

“These results show that high-order resonance response is much greater in terms of sensing performance than that of the fundamental mode resonance,” they added. “In other words, these studies provide us with a new way to design high-sensitivity sensors.”

More information: Shahzad Anwar et al, Triple-band terahertz metamaterial absorber with enhanced sensing capabilities, The European Physical Journal D (2023). DOI: 10.1140/epjd/s10053-023-00658-w

Journal information: European Physical Journal D 

Provided by Springer 

Predicting the numerical value of the magnetic moment of the muon is one of the most challenging calculations in high-energy physics. Some physicists spend the bulk of their careers improving the calculation to greater precision.

Why do physicists care about the magnetic properties of this particle? Because information from every particle and force is encoded in the numerical value of the muon‘s magnetic moment. If we can both measure and predict this number to ultra-high precision, we can test whether the Standard Model of Elementary Particles is complete.

Muons are identical to electrons, except they are about 200 times more massive, are not stable, and disintegrate into electrons and neutrinos after a short time. At the simplest level, theory predicts that the muon’s magnetic moment, typically represented by the letter g, should equal 2. Any deviation from 2 can be attributed to quantum contributions from the muon’s interaction with other—known and unknown—particles and forces. Hence scientists are focused on predicting and measuring g-2.

Several measurements of muon g-2 already exist. Scientists working on the Muon g-2 experiment at the U.S. Department of Energy’s Fermi National Accelerator Laboratory expect to announce later this year the result of the most precise measurement ever made of the muon’s magnetic moment.

Simultaneously, a large number of scientists are working on improving the Standard Model prediction of the value of muon g-2. Several parts feed into this calculation, related to the electromagnetic force, the weak nuclear force and the strong nuclear force.

The contribution from electromagnetic particles like photons and electrons is considered the most precise calculation in the world. The contribution from weakly interacting particles like neutrinos, W and Z bosons, and the Higgs boson is also well known. The most challenging part of the muon g-2 prediction stems from the contribution from strongly interacting particles like quarks and gluons; the equations governing their contribution are very complex.

Even though the contributions from quarks and gluons are so complex, they are calculable, in principle, and several different approaches have been developed. One of these approaches evaluates the contributions by using experimental data related to the strongly interacting nuclear force. When electrons and positrons collide, they annihilate and can produce particles made of quarks and gluons like pions. Measuring how often pions are produced in these collisions is exactly the data needed to predict the strong nuclear contribution to muon g-2.

For several decades, experiments at electron-positron colliders around the world have measured the contributions from quarks and gluons, including experiments in the US, Italy, Russia, China, and Japan. Results from all these experiments were compiled by a collaboration of experimental and theoretical physicists known as the Muon g-2 Theory Initiative. In 2020, this group announced the best Standard Model prediction for muon g-2 available at that time.

Ten months later, the Muon g-2 collaboration at Fermilab unveiled the result of their first measurement. The comparison of the two indicated a large discrepancy between the experimental result and the Standard Model prediction. In other words, the comparison of the measurement with the Standard Model provided strong evidence that the Standard Model is not complete and muons could be interacting with yet undiscovered particles or forces.

A second approach uses supercomputers to compute the complex equations for the quark and gluon interactions with a numerical approach called lattice gauge theory. While this is a well-tested method to compute the effects of the strong force, computing power has only recently become available to perform the calculations for muon g-2 to the required precision. As a result, lattice calculations published prior to 2021 were not sufficiently precise to test the Standard Model. However, a calculation published by one group of scientists in 2021, the Budapest-Marseille-Wuppertal collaboration, produced a huge surprise. Their prediction using lattice gauge theory was far from the prediction using electron-positron data.

In the last few months, the landscape of predictions for the strong force contribution to muon g-2 has only become more complex. A new round of electron-positron data has come out from the SND and CMD3 collaborations. These are two experiments taking data at the VEPP-2000 electron-positron collider in Novosibirsk, Russia. A result from the SND collaboration agrees with the previous electron-positron data, while a result from the CMD3 collaboration disagrees with the previous data.

What is going on? While there is no simple answer, there are concerted efforts by all the communities involved to better quantify the Standard Model prediction. The Lattice Gauge Theory community is working around the clock towards testing and scrutinizing the BMW collaboration’s prediction in independent lattice calculations with improved precision using different methods. The electron-positron collider community is working to identify possible reasons for the differences between the CMD3 result and all previous measurements. More importantly, the community is in the process of repeating these experimental measurements using much larger data sets. Scientists are also introducing new independent techniques to understand the strong-force contribution, such as a new experiment proposed at CERN called MUonE.

What does this mean for muon g-2? The Fermilab Muon g-2 collaboration will release its next result, based on data taken in 2019 and 2020, later this year. Because of the large amount of additional data that is going into the new analysis, the Muon g-2 collaboration expects its result to be twice as precise as the first result from their experiment. But the current uncertainty in the predicted value makes it hard to use the new result to strengthen our previous indication that the Standard Model is incomplete and there are new particles and forces affecting muon g-2.

What is next? The Fermilab Muon g-2 experiment concluded data taking this spring. It will still take a couple of years to analyze the entire data set, and the experiment expects to release its final result in 2025. At the same time, the Muon g-2 Theory Initiative is working to shore up the predicted value using new data and new lattice calculations that should also be available before 2025. It will be a very exciting showdown. In the meantime, the high-energy physics community is eagerly anticipating the announcement of the world’s best measurement from the Fermilab Muon g-2 experiment later this year.

Provided by Fermi National Accelerator Laboratory 

Imagine shrinking light down to the size of a tiny water molecule, unlocking a world of quantum possibilities. This has been a long-held dream in the realms of light science and technology. Recent advancements have brought us closer to achieving this incredible feat, as researchers from Zhejiang University have made groundbreaking progress in confining light to subnanometer scales.

Traditionally, there have been two approaches to localize light beyond its typical diffraction limit: dielectric confinement and plasmonic confinement. However, challenges such as precision fabrication and optical loss have hindered the confinement of optical fields to sub-10 nanometer (nm) or even 1-nm levels. But now, a new waveguiding scheme reported in Advanced Photonics promises to unlock the potential of subnanometer optical fields.

Picture this: Light travels from a regular optical fiber, embarking on a transformative journey through a fiber taper, and finds its destination in a coupled-nanowire-pair (CNP). Within the CNP, the light morphs into a remarkable nano-slit mode, generating a confined optical field that can be as tiny as a mere fraction of a nanometer (approximately 0.3 nm). With an astonishing efficiency of up to 95% and a high peak-to-background ratio, this novel approach offers a whole new world of possibilities.

The new waveguiding scheme extends its reach into the mid-infrared spectral range, pushing the boundaries of the nano-universe even further. Optical confinement can now reach an astonishing scale of approximately 0.2 nm (λ/20000), offering even more opportunities for exploration and discovery.

Professor Limin Tong of the Zhejiang University Nanophotonics Group notes, “Unlike previous methods, the waveguiding scheme presents itself as a linear optical system, bringing a host of advantages. It enables broadband and ultrafast pulsed operation and allows for the combination of multiple sub-nanometer optical fields. The ability to engineer spatial, spectral, and temporal sequences within a single output opens up endless possibilities.”

This video summary includes an animated demonstration from the authors.

The potential applications of such breakthroughs are awe-inspiring. An optical field so localized that it can interact with individual molecules or atoms holds promise for advancements in light-matter interactions, super-resolution nanoscopy, atom/molecule manipulation, and ultrasensitive detection. We stand at the precipice of a new era of discovery, where the tiniest realms of existence are within our grasp.

More information: Liu Yang et al, Generating a sub-nanometer-confined optical field in a nanoslit waveguiding mode, Advanced Photonics (2023). DOI: 10.1117/1.AP.5.4.046003

Provided by SPIE 

Experts from CERN, DESY, IBM Quantum and others have published a white paper identifying activities in particle physics that could benefit from the application of quantum-computing technologies

Last week, researchers published an important white paper identifying activities in particle physics where burgeoning quantum-computing technologies could be applied. The paper, authored by experts from CERN, DESY, IBM Quantum and over 30 other organizations, is now available as a preprint on arXiv.

With quantum-computing technologies rapidly improving, the paper sets out where they could be applied within particle physics in order to help tackle computing challenges related not only to the Large Hadron Collider’s ambitious upgrade program, but also to other colliders and low-energy experiments worldwide.

The paper was produced by a working group set up at the first-of-its-kind “QT4HEP” conference, held at CERN last November. Over the last eight months, the 46 members of this working group have worked hard to identify areas where quantum-computing technologies could provide a significant boon.

The areas identified relate to both theoretical and experimental particle physics. The paper then maps these areas to “problem formulations” in quantum computing. This is an important step in ensuring that the particle physics community is well positioned to benefit from the massive potential of breakthrough new quantum computers when they come online.

“Quantum computing is very promising, but not every problem in particle physics is suited to this mode of computing,” says Alberto Di Meglio, head of the CERN Quantum Technology Initiative (CERN QTI) and one of the paper’s lead authors, alongside DESY’s Karl Jansen and IBM Quantum’s Ivano Tavernelli. “It’s important to ensure that we are ready and that we can accurately identify the areas where these technologies have the potential to be most useful for our community.”

As far as theoretical particle physics is concerned, the authors have identified promising areas related to evolution of the quantum states, lattice-gauge theory, neutrino oscillations and quantum field theories in general. The applications considered include quantum dynamics, hybrid quantum/classical algorithms for static problems in lattice gauge theory, optimization and classification.

On the experimental side, the authors have identified areas related to jet and track reconstruction, extraction of rare signals, for-and-beyond Standard Model problems, parton showers and experiment simulation. These are then mapped to classification, regression, optimization and generation problems.

Members of the working group behind this paper will now begin the process of selecting specific use cases from the activities listed in the paper to be taken forward through CERN’s and DESY’s participation in the IBM Quantum Network, and through collaboration with IBM Quantum, under its “100×100 Challenge.” IBM Quantum is long-standing collaborator of CERN QTI and the Center for Quantum Technologies and Applications (CQTA) at DESY.

IBM’s 100×100 Challenge will see the company provide a tool capable of calculating unbiased observables of circuits with 100 qubits and depth-100 gate operations in 2024. This will offer an important testbed for taking forward promising selected use cases from both particle physics and other research fields.

More information: Alberto Di Meglio et al, Quantum Computing for High-Energy Physics: State of the Art and Challenges. Summary of the QC4HEP Working Group, arXiv (2023). DOI: 10.48550/arxiv.2307.03236

Journal information: arXiv 

Provided by CERN 

Researchers from the Center of Theoretical Physics of Complex Systems within the Institute for Basic Science (PCS-IBS) made an important discovery that describes the relationship between synchronization and thermodynamics in quantum systems.

The question of how order arises from disorder has captivated humanity for centuries. One fascinating example of such emergence is synchronization, where multiple oscillators initialized randomly could end up oscillating in harmony. Synchronization exists in our everyday lives—for example, the sound of clapping hands or the simultaneous flashing of fireflies.

Remarkably, scientists have discovered many instances of synchronization in diverse natural and artificial phenomena, including in very small systems governed by quantum mechanics.

At the same time, the study of synchronization must also consider the second law of thermodynamics which only allows the total disorder of the universe to increase. This means that for a spontaneous emergence of order-like synchronization to occur, there has to be a cost of increasing disorder somewhere else (e.g., a wasteful heat in the surrounding environment). Yet, despite these intriguing connections, the precise relationship between synchronization and thermodynamics remains a mystery.

To unravel the underlying connection between synchronization and thermodynamics in the quantum regime, PCS-IBS researchers investigated a novel quantum thermal machine that exhibits synchronization. This machine is capable of acting as a quantum heat engine or as a quantum refrigerator. The study is published in the journal Physical Review Letters.

As a heat engine, it transforms heat flow from hot to cold baths to amplify the intensity of laser light. Conversely, as a refrigerator, it uses energy from laser light to maintain the temperature of the cold bath. Importantly, this machine is able to undergo synchronization simultaneously while performing its task due to its continuous interaction with the laser.

Curiously, the researchers found that as they scaled up the machine, multiple synchronizing actors started to arise within the machine. The synchronization behavior of the machine was not solely influenced by its interaction with lasers but also by the interplay between its various components.

These distinct synchronization actors could both cooperate and compete, much like two individuals jumping on a trampoline—for example, let’s call them Jack and Jill. Cooperation arises when both Jack and Jill adjust their jumping rhythm in harmony, reaching their highest and lowest points simultaneously. Conversely, competition occurs when Jack attempts to match Jill’s rhythm while Jill deliberately does the opposite, such as aiming to be at the lowest point when Jack reaches his highest.

According to the corresponding author, Dr. Juzar Thingna, “This is the first example in which synchronizing quantum systems are shown to cooperate and compete, opening a path to a richer synchronization landscape like quantum chimeras.”

Intriguingly, the cooperation and competition between different synchronization mechanisms are intimately related to the thermodynamic functionality of the machine. Cooperation manifests in the case of the refrigerator, i.e., they have a preference for a system that synchronizes in harmony, like a peaceful orchestra. On the other hand, competition arises in the case of heat engines, as their components thrive in the middle of a crazy party and use all the chaos to perform at their best.

These findings are important because not only do they shed light on the fundamental relation between synchronization and thermodynamics, but they also give us new ideas for designing quantum technologies and relate the abstract notion of synchronization to the performance of quantum devices.

In other words, improving our understanding of how synchronization works in quantum machines, will allow us to make better devices that work coherently together. This could lead to more efficient and powerful quantum machines that will one day ignite the quantum revolution.

More information: Taufiq Murtadho et al, Cooperation and Competition in Synchronous Open Quantum Systems, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.131.030401

Journal information: Physical Review Letters 

Provided by Institute for Basic Science 

Self-sustained levitation of millimeter-sized droplets was recently discovered by researchers at Tyumen State University, in Russia, during an experiment to select combinations of immiscible liquids, which don’t form homogeneous mixtures.

Researchers Natalia Ivanova and Denis Klyuev noticed something amazing happen: Droplets of butyl alcohol, after being detached from the syringe needle, levitated above the surface of the layer of another liquid without collapsing onto it for a long period of time.

In the article, “Self-sustaining levitation of droplets above a liquid pool,” published in Applied Physics Letters, they report achieving self-sustaining and long-term levitation of millimeter-sized droplets of several different liquids—without any external forces is authored by Natalia Ivanova and Denis Klyuev.

What was it like to see the droplets levitate? “It was amazing,” said Ivanova. “The phenomenon of noncoalescence of droplets with an underlying liquid is well known. But under natural conditions, a droplet levitates above a liquid pool only an instant—milliseconds, at most. We witnessed a droplet continue to levitate for tens of minutes.”

To get the droplets to levitate, they use solutocapillary convection within a pool of silicone liquid. Solutocapilllary convection occurs when a surface tension gradient is formed by nonuniform distribution of vapor molecules from the droplet at the pool surface.

“Sometimes interesting and miraculous phenomena lie right in front of us and we don’t notice them,” said Ivanova. “By focusing on a certain task, we begin to think ‘tunnel-like’ to some extent and stop noticing alternative approaches to problem solving.”

Typically, to keep the droplets levitating for a long time—from seconds to a long-term period—it’s necessary to continuously generate excess pressure inside an ultrathin gap between a droplet and the surface of underlying liquid. This can be achieved via different methods, such as using vibrations so a droplet acts as if it’s jumping or by creating air flows within the gap under the droplet.

“The latter includes rolling the droplet over the liquid surface, or actively evaporating one of them by, for example, taking advantage of the Leidenfrost effect,” said Klyuev. “There are also magnetic or acoustic levitation methods, but they all have one thing in common: we either do external work on the system or initially create nonequilibrium conditions so that long-term levitation of the droplet can be provided only during their existence.”

Further exploring the effects of various external conditions on self-sustained droplet levitation will reveal whether it can be harnessed and adapted for microbiology and biochemistry applications.

Ivanova and Klyuev believe the effect of long-term self-sustained droplet levitation can be helpful to develop scientific tools to explore the diversity and activity of microorganisms and to improve the understanding of heat and mass transfer within a vapor film.

“Since the topic of droplet levitation is quite popular, we expect solutocapillary convection levitation will be considered by other researchers—since the problem is quite interesting from the point of view of modeling microscale transport,” said Ivanova. “We will also continue our work to establish the influence of external factors on this system.”

More information: Self-sustaining levitation of droplets above a liquid pool, Applied Physics Letters (2023). DOI: 10.1063/5.0152920

Journal information: Applied Physics Letters 

Provided by American Institute of Physics 

A team led by Prof. Guo Guoping and Prof. Cao Gang from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), collaborating with Sigmund Kohler from Materials Science Institute of Madrid, have developed a response theory applicable to strongly coupled and multiqubit systems. Their study was published in Physical Review Letters.

Semiconductor quantum dots (QD) strongly coupled to microwave photons are key for investigating light-matter interactions. In previous studies, the team used a high-impedance super-conducting resonant cavity to implement the strong coupling of the QD–cavity hybrid system. Based on this strong coupling, the team further studied the circuit quantum electrodynamics (cQED) of the periodically driven, strongly coupled hybrid system.

In this study, the researchers first prepared a composite device with a high-impedance resonant cavity integrated with two double quantum dots (DQD). By probing the microwave response signal of the DQD-cavity hybrid system under periodic driving, they found that the existing theory for dispersive cavity readout fails due to the enhancement of the coupling strength.

Therefore, the researchers developed a new response theory that treats the cavity as a part of the driven system. Using this theory, they successfully simulated and interpreted the signals in the experiment and further investigated the case of two-DQD-cavity hybrid system under periodic driving.

This study furthers our understanding of periodically driven QD–cavity hybrid systems. In addition, the theoretical approach developed is not only applicable to hybrid systems with different coupling strength but also can be extended to multiqubit systems.

More information: Si-Si Gu et al, Probing Two Driven Double Quantum Dots Strongly Coupled to a Cavity, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.233602

Journal information: Physical Review Letters 

Provided by Chinese Academy of Sciences 

Physicists worldwide are trying to detect dark matter (DM) particles and their interactions with visible matter using various strategies and detectors. As these particles do not emit, reflect or absorb light, they have so far proved to be very difficult to observe, particularly using common experimental methods.

Researchers at TRIUMF, University of Minnesota, University of California Berkeley and Stanford University recently proposed a new approach that could help to detect these mysterious particles, unexplained by the standard model. This approach, introduced in a paper published in Physical Review Letters, aims to detect signals hinting at the annihilation of dark matter to visible matter inside large neutrino detectors.

“Earth-bound DM (DM particles that are being trapped in the Earth via collisions with Earth’s constituents) that interacts sufficiently strongly with the ordinary baryonic matter can have a tantalizingly large density, almost 15 orders of magnitude larger than the Galactic DM density (~ 0.3 GeV/cm³),” Anupam Ray, one of the researchers who carried out the study, told Phys.org.

“Now the big question was: how to detect such DM particles which are quite abundant in the Earth-volume? Since their kinetic energy is tiny (~ 0.03 eV), their detection in the traditional direct detection experiments is almost impossible as these experiments are not sensitive to such a low energy deposition. So, we were thinking of novel ways to detect such DM particles.”

Instead of searching for signals hinting at the scattering of DM particles, as most direct detection efforts have done so far, Ray and his colleagues suggested looking at their annihilation signals. These are signals that occur when DM are annihilated, or in other words when they collide with other particles and are obliterated, releasing energy in the process.

In contrast with scattering signals, annihilation signals are not limited to tiny amounts of kinetic energy, thus they could potentially be easier to look for and detect. As Earth-bound DM particles are theorized to be abundant, the researchers suggested looking for them by searching for signals hinting at their annihilation inside large-volume neutrino detectors, such as Super-Kamiokande. This is a large-scale Cherenkov detector located under Mount Ikeno in Japan, which is being used to study neutrinos originating from the sun, supernovae, the atmosphere and other sources.

“Earth-bound DMs that interact strongly with ordinary baryonic matter are copiously present inside any large volume neutrino detectors, such as Super-Kamiokande,” Ray explained. “If they annihilate inside the Super-Kamiokande fiducial volume, it could induce observable signatures. Super-K can easily search these annihilation products, and from these searches, one could provide unprecedented sensitivity to DM parameters. It is important to stress that, even if these strongly interacting Earth-bound DM particles make up a very fraction of the whole DM density (there is no reason to believe that DM is made up of a single species), our proposed method can provide world-leading sensitivity to the DM parameters.”

The recent work by this team of researchers introduces a new method that could help to probe Earth-bound strongly interacting DM particles, which are theorized to be highly abundant and yet have so far been very difficult to observe. Even if these specific particles only make up a tiny fraction of the present-day DM density, this new method could work remarkably well and could thus contribute to the ongoing search for DM.

“We now want to explore the neutrino signatures from strongly interacting Earth-bound DM,” Ray added. “In this study, we are not sensitive to a relatively heavy DM mass (say DM mass of 10 GeV or more). Because, as the DM gets heavier, they concentrate towards the center of the Earth, and as a consequence, their number density inside Super-Kamiokande volume significantly depleted, resulting in a negligible signal. However, by using the neutrino signal, we are hopeful to probe the heavy DM parameter space.”

More information: David McKeen et al, Dark Matter Annihilation inside Large-Volume Neutrino Detectors, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.131.011005

Journal information: Physical Review Letters 

© 2023 Science X Network

by Max Planck Society

Simple molecular liquids such as water or glycerol are of great importance for technical applications, in biology or even for understanding properties in the liquid state. Researchers at the Max Planck Institut für Struktur und Dynamik der Materie (MPSD) have now succeeded in observing liquid glycerol in a completely unexpected rubbery state.

In their article published in Proceedings of the National Academy of Sciences, the researchers report how they created rapidly expanding bubbles on the surface of the liquid in vacuum using a pulsed laser. However, the thin, micrometers-thick liquid envelope of the bubble did not behave like a viscous liquid dissipating deformation energy as expected, but like the elastic envelope of a rubber toy balloon, which can store and release elastic energy.

It is the first time an elasticity dominating the flow behavior in a Newtonian liquid like glycerol has been observed. Its existence is difficult to reconcile with common ideas about the interactions in liquid glycerol and motivates the search for more comprehensive descriptions. Surprisingly, the elasticity persists over such long timescales of several microseconds that it could be important for very rapid engineering applications such as micrometer-confined flows under high pressure. Yet, the question remains unsettled whether this behavior is a specific property of liquid glycerol, or rather a phenomenon that occurs in many molecular liquids under similar conditions but has not been observed so far.

The team proposes that the high straining rate and the confined thickness of the shell causes the individual molecules to form groups that are displaced in a correlated and collective manner. This change would stabilize the elastic state over a longer time than would be possible in glycerol’s equilibrium state, where the single molecules are subject to fast diffusion. “We want to reach a better understanding of this unusual state,” says lead author and doctoral student Meghanad Kayanattil, “because it could tell us a lot about collective excitations in disordered systems.”

The existence of such a rubber-like state in liquid glycerol raises the question: Are similar effects possible in other liquid substances? In particular the creation of elastic bubbles in water would be a major achievement because it is the most important and well-studied liquid with implications for multiple scientific fields. However, the glycerol bubbles only formed in a vacuum environment, as shown by the MPSD team. This poses some challenges for similar experiments involving water, because it begins to boil below the vapor pressure of 32 mbar—well above the pressure at which the experiments need to take place.

The research was carried out by members of the Institute’s Scientific Support Unit Ultrafast Beams and guest scientist Zhipeng Huang from the University of Duisburg-Essen. An innovative scientific approach and the right choice of parameters led to the discovery of this novel elastic behavior. “Our experiment invites us to rethink the correlations and the differences between liquids and solids,” says principal investigator Sascha Epp.

“As a next step, we aim to investigate the molecular interaction and structure of the transient bubble shell and whether this effect can also be created in a range of other liquids whose molecular interactions are different from glycerol.”

More information: Meghanad Kayanattil et al, Rubber-like elasticity in laser-driven free surface flow of a Newtonian fluid, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2301956120

Journal information: Proceedings of the National Academy of Sciences 

Provided by Max Planck Society