Category: Physics

Today, astronomers seek to observe the faintest and most distant objects possible. Extremely Large Telescopes (ELTs), with apertures in the order of several dozen meters, are the next generation facilities to do so. However, building larger telescopes is only one part of the equation. The other part is the capability of detecting the gathered photons in the most efficient way possible.

This is where making all other optical components in astronomical instruments more efficient becomes crucial. One essential component used in modern astronomical science is the diffraction grating. Its role is to spatially spread incoming light into its constituent frequencies, similar to how a glass prism does.

Thanks to a precisely engineered structure that leverages the wave-like nature of photons, diffraction gratings can separate light of different wavelengths with very high resolution. When coupled with a telescope and a spectrometer, gratings allow scientists to analyze the spectral properties of celestial bodies.

Motivated by the somewhat stagnant progress made in grating technology over the past decade, researchers Hanshin Lee of the University of Texas at Austin and Menelaos K. Poutous of the University of North Carolina at Charlotte, focused on a completely different way of fabricating diffraction gratings.

In their paper recently published in the Journal of Astronomical Telescopes, Instruments, and Systems, they report their success on manufacturing proof-of-concept high-efficiency diffraction gratings using reactive ion-plasma etching (RIPLE), a plasma-based manufacturing technology normally used for semiconductors.

Put simply, the RIPLE process used in this study involves “drawing” (using a high-precision electron beam) the desired grating pattern onto a chrome masking layer placed atop a quartz substrate. The grating pattern is then carved directly onto the quartz substrate using chemically reactive plasma; the chrome mask acts as a shield and the plasma only eats away at the exposed regions.

After fine tuning various parameters of the process through theoretical calculations, simulations, and experimental trial and error, the researchers managed to produce first-order diffraction gratings with very precise nano-scale structures. This translated to a near-theoretical unpolarized diffraction efficiency, reaching 94.3% at its peak and staying over 70% across a wavelength range broader than 200 nm.

“This type of performance has been only rarely achieved in diffraction gratings used for astronomy, where every bit of efficiency gain really matters due to photon starvation,” said Lee.

Another advantage of using the RIPLE process to produce diffraction gratings is that the grating structure is embedded directly into the glass substrate, which means that they share the same material characteristics.

“Our gratings can be very robust optically, thermally, and mechanically, which makes them ideal for harsh environments, such as those found in space observatories and cryogenic systems,” said Poutous, “This allows for their application in a broad range of scientific and engineering spectroscopic measurements.”

Overall, the results of this study showcase the potential of the RIPLE process to revolutionize the way in which diffraction gratings are fabricated. The researchers are optimistic about the future use of such high-efficiency gratings in the upcoming era of ground-based ELTs with apertures over of 30 meters. With any luck, these gratings will be instrumental for astronomers to observe extremely faint objects far out in space in upcoming years.

More information: Hanshin Lee et al, Reactive ion plasma etched surface relief gratings for low/medium/high resolution spectroscopy in astronomy, Journal of Astronomical Telescopes, Instruments, and Systems (2022). DOI: 10.1117/1.JATIS.8.4.045002

Chirality is the breaking of reflection and inversion symmetries. Simply put, it is when an object’s mirror images cannot be superimposed over each other. A common example are your two hands—while mirror images of each other, they can never overlap. Chirality appears at all levels in nature and is ubiquitous.

In addition to static chirality, chirality can also occur due to dynamic motion including rotation. With this in mind, we can distinguish true and false chirality. A system is truly chiral if—when translating—space inversion does not equate to time reversal combined with a proper spatial rotation.

Phonons are quanta (or small packets) of energy associated with the vibration of atoms in a crystal lattice. Recently, phonons with chiral properties have been theorized and experimentally discovered in two-dimensional (2D) materials such as tungsten diselenide. The discovered chiral phonons are rotating—yet not propagating—atomic motions. But, truly chiral phonons would be atomic motions that are both rotating and propagating, and these have never been observed in three-dimensional (3D) bulk systems.

Now, a team of researchers led by scientists from Tokyo Institute of Technology (Tokyo Tech) has identified truly chiral phonons, both theoretically and experimentally. Their work is published in Nature Physics. The team, led by Professor Takuya Satoh of the Department of Physics at Tokyo Tech, observed the chiral phonons in cinnabar (α-HgS). This was achieved using a combination of first-principles calculations and an experimental technique called circularly polarized Raman scattering.

“Chiral structures can be probed using chiral techniques. So, using circularly polarized light, which has its own handedness (i.e., right-handed or left-handedness), is critical. Dynamic chiral structures can be mapped using pseudo-angular momentum (PAM). Pseudo-momentum and PAM originate from the phase factors acquired by discrete translation and rotation symmetry operations, respectively,” explains Professor Satoh.

The researchers’ novel experimental approach also allowed them to probe the fundamental traits of PAM. They found that the law of the conservation of PAM—one of the key laws of physics—holds between circularly polarized photons and chiral phonons.

“Our work also provides an optical method to identify the handedness of chiral materials using PAM. Namely, we can determine the handedness of materials with better resolution than X-ray diffraction (XRD) can achieve. Moreover, XRD requires a large-enough crystal, is invasive, and can be destructive. Circularly polarized Raman scattering, on the other hand, allowed us to determine the chirality of structures XRD could not, in a non-contact and non-destructive manner,” concludes Professor Satoh.

This study is the first to identify truly chiral phonons in 3D materials, which are clearly distinct from those seen previously in 2D hexagonal systems. The knowledge gained here could drive new research into developing ways for transferring the PAM from photons to electron spins via propagating chiral phonons in future devices. Furthermore, this approach enables the determination of the true chirality of a crystal in an improved manner, providing a new critical tool for experimentalists’ and researchers.

More information: Kyosuke Ishito et al, Truly chiral phonons in α-HgS, Nature Physics (2022). DOI: 10.1038/s41567-022-01790-x

Journal information: Nature Physics 

Provided by Tokyo Institute of Technology 

On July 5, the LHC roared to life for its third run after three years of continual improvements to the machine as well as to the experiments’ detectors and analysis tools, and immediately reached a record energy of 13.6 TeV. Just three weeks later, the compact muon solenoid (CMS) collaboration was ready for its physics data-taking period.

The CMS collaboration recently presented its first Run 3 physics results of the production rate of pairs of the heaviest elementary particle, the top quark. In just one week, from July 28 to 3August 3, the CMS collaboration collected data equivalent to almost 12% of the data set that had been required for the Higgs boson discovery in 2012.

Before Run 3 began, it was hoped—and has now been confirmed—that it would be possible to gather such a vast amount of data in a very short time. It took physicists two years to collect the data used to announce the Higgs boson discovery in 2012. But now, thanks to developments in data acquisition and selection systems and to the unprecedented speed of the analyses, the Run 3 data can now be analyzed in almost real time.

Due to the high number of top-quark pairs created at the LHC, physics analysis can start with even a small amount of data. The production rate of this heavy system of particles has been enhanced by about 10% thanks to the collision energy increase from 13 TeV in Run 2 to 13.6 TeV in Run 3.

The CMS results, which agree with the Standard Model prediction, are important because precise measurements of top-quark properties provide, among other things, crucial input for various searches for new phenomena in Run 3. Because of its high mass, the top quark decays immediately to a b quark and a W boson, which is also an unstable particle. The decay products leave traces as they pass through the detector, making it possible to observe them and to test the detector performance.

Precision measurements of the Standard Model are an essential part of the Run 3 program, as any significant deviation could hint at new physics. The measurement of top-quark pair production rate is only the first step into the unexplored territory of the new energy regime, where answers to fundamental physics questions may be found.

Provided by CERN 

Terahertz light, radiation in the far-infrared part of the emission spectrum, is currently not fully exploited in technology, although it shows great potential for many applications in sensing, homeland security screening, and future (sixth generation) mobile networks.

Indeed, this radiation is harmless due to its small photon energy, but it can penetrate many materials (such as skin, packaging, etc.). In the last decade, a number of research groups have focused their attention on identifying techniques and materials to efficiently generate THz electromagnetic waves: among them is the wonder material graphene, which, however, does not provide the desired results. In particular, the generated terahertz output power is limited.

Better performance has now been achieved by topological insulators (TIs)—quantum materials that behave as insulators in the bulk while exhibiting conductive properties on the surface—according to a paper recently published in Light: Science & Applications.

This study was carried out by members of the ICN2 Ultrafast Dynamics in Nanoscale Systems Group, led by Dr. Klaas-Jan Tielrooij, and of the High-field THz Driven Phenomena Group at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR, Germany), led by Dr. Sergey Kovalev, in collaboration with researchers from the ICN2 Physics and Engineering of Nanodevices Group, headed by ICREA Prof. Sergio O. Valenzuela, from the School of Physics and Astronomy of the University of Manchester (UK), and the Physics Institute of the University of Würzburg (Germany). The experiments were performed at the TELBE THz facility in Dresden.

Earlier studies had shown that materials which host electrons with zero effective mass enable efficient generation of terahertz harmonics, including the aforementioned graphene and topological insulators. The phenomenon of harmonic generation occurs when photons of the same frequency and energy interact non-linearly with matter, leading to the emission of photons whose energy is a multiple of that of the incident ones. This can be exploited, for example, to upconvert electronically generated signals in the high GHz regime into signals in the THz regime.

Dr. Tielrooij and colleagues investigated the behavior of two topological insulators—the prototypical Bi₂Se₃ and Bi₂Te₃—in direct comparison with a reference graphene sample.

They observed that, while the maximum power of the harmonics generated in graphene is limited by saturation effects (which arise at high incident powers), in these quantum materials it continued to increase with the incident fundamental power. The performed experiments revealed an improvement in generated output power by orders of magnitude over graphene, approaching the milliwatt regime.

This significant divergence in behavior is due to the fact that topological insulators can rely on a highly efficient cooling mechanism, in which the massless charges on the surface dissipate their electronic heat to those in the rest of the thin film. In other words, bulk electrons lend a helping hand to the surface-state electrons by sinking electronic heat.

The highest output power for the terahertz third-harmonic –i.e. radiation with three times the same energy– was achieved in a metamaterial that contained a topological insulator film together with a metallic grating –consisting of metal strips separated by gaps on the surface of the material.

“In this work we were able to demonstrate that the saturation effect occurring in graphene is much less present in topological insulators. This occurs thanks to a novel cooling mechanism between surface and bulk electrons of topological insulators,” explains Dr. Klaas-Jan Tielrooij, first author of the paper. “These quantum metamaterials thus bring nonlinear terahertz photonics technology a big step closer.”

Sergey Kovalev, last author of the paper, adds that “the obtained results furthermore offer interesting possibilities towards studying the quantum properties of these materials with prospects towards quantum technologies.”

More information: Klaas-Jan Tielrooij et al, Milliwatt terahertz harmonic generation from topological insulator metamaterials, Light: Science & Applications (2022). DOI: 10.1038/s41377-022-01008-y

Journal information: Light: Science & Applications 

Provided by Chinese Academy of Sciences 

Astronomers led by the University of Warwick have identified the oldest star in our galaxy that is accreting debris from orbiting planetesimals, making it one of the oldest rocky and icy planetary systems discovered in the Milky Way.

Their findings are published today (Nov. 5) in the Monthly Notices of the Royal Astronomical Society and conclude that a faint white dwarf located 90 light years from Earth, as well as the remains of its orbiting planetary system, are over 10 billion years old.

The fate of most stars, including those like our sun, is to become a white dwarf. A white dwarf is a star that has burnt up all of its fuel and shed its outer layers and is now undergoing a process of shrinking and cooling. During this process, any orbiting planets will be disrupted and in some cases destroyed, with their debris left to accrete onto the surface of the white dwarf.

For this study the team of astronomers, led by the University of Warwick, modeled two unusual white dwarfs that were detected by the space observatory GAIA of the European Space Agency. Both stars are polluted by planetary debris, with one of them being found to be unusually blue, while the other is the faintest and reddest found to date in the local galactic neighborhood—the team subjected both to further analysis.

Using spectroscopic and photometric data from GAIA, the Dark Energy Survey and the X-Shooter instrument at the European Southern Observatory to work out how long it has been cooling for, the astronomers found that the “red” star WDJ2147-4035 is around 10.7 billion years old, of which 10.2 billion years has been spent cooling as a white dwarf.

Spectroscopy involves analyzing the light from the star at different wavelengths, which can detect when elements in the star’s atmosphere are absorbing light at different colors and helps determine what elements those are and how much is present. By analyzing the spectrum from WDJ2147-4035, the team found the presence of the metals sodium, lithium, potassium and tentatively detected carbon accreting onto the star—making this the oldest metal-polluted white dwarf discovered so far.

The second “blue” star WDJ1922+0233 is only slightly younger than WDJ2147-4035 and was polluted by planetary debris of a similar composition to the Earth’s continental crust. The science team concluded that the blue color of WDJ1922+0233, despite its cool surface temperature, is caused by its unusual mixed helium-hydrogen atmosphere.

The debris found in the otherwise nearly pure-helium and high-gravity atmosphere of the red star WDJ2147-4035 are from an old planetary system that survived the evolution of the star into a white dwarf, leading the astronomers to conclude that this is the oldest planetary system around a white dwarf discovered in the Milky Way.

Lead author Abbigail Elms, a Ph.D. student in the University of Warwick Department of Physics, said, “these metal-polluted stars show that Earth isn’t unique, there are other planetary systems out there with planetary bodies similar to the Earth. 97% of all stars will become a white dwarf and they’re so ubiquitous around the universe that they are very important to understand, especially these extremely cool ones. Formed from the oldest stars in our galaxy, cool white dwarfs provide information on the formation and evolution of planetary systems around the oldest stars in the Milky Way.”

“We’re finding the oldest stellar remnants in the Milky Way that are polluted by once Earth-like planets. It’s amazing to think that this happened on the scale of 10 billion years, and that those planets died way before the Earth was even formed.”

Astronomers can also use the star’s spectra to determine how quickly those metals are sinking into the star’s core, which allows them to look back in time and determine how abundant each of those metals were in the original planetary body. By comparing those abundances to astronomical bodies and planetary material found in our own solar system, we can guess at what those planets would have been like before the star died and became a white dwarf—but in the case of WDJ2147-4035, that has proven challenging.

Abbigail explains, “The red star WDJ2147-4035 is a mystery as the accreted planetary debris are very lithium and potassium rich and unlike anything known in our own solar system. This is a very interesting white dwarf as its ultra-cool surface temperature, the metals polluting it, its old age, and the fact that it is magnetic, makes it extremely rare.”

Professor Pier-Emmanuel Tremblay of the Department of Physics at the University of Warwick said, “when these old stars formed more than 10 billion years ago, the universe was less metal-rich than it is now, since metals are formed in evolved stars and gigantic stellar explosions. The two observed white dwarfs provide an exciting window into planetary formation in a metal poor and gas-rich environment that was different to the conditions when the solar system was formed.”

More information: Abbigail Elms et al, Spectral analysis of ultra-cool white dwarfs polluted by planetary debris, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac2908

Journal information: Monthly Notices of the Royal Astronomical Society 

Provided by University of Warwick 

In 1842, the famous British researcher Michael Faraday made an amazing observation by chance: A thin layer of water forms on the surface of ice, even though it is well below zero degrees. The temperature is below the melting point of ice, yet the surface of the ice has melted. This liquid layer on ice crystals is also why snowballs stick together.

It was not until about 140 years later, in 1985, that this “surface melting” could be scientifically confirmed under controlled laboratory conditions. By now, surface melting has been demonstrated in a variety of crystalline materials and is scientifically well understood: Several degrees below the actual melting point, a liquid layer only a few nanometers thick forms on the surface of the otherwise solid material.

Because the surface properties of materials play a crucial role in their use as, e.g. catalysts, sensors, battery electrodes and more, surface melting is not only of fundamental importance but also in view of technical applications.

It must be emphasized that this process has absolutely nothing to do with the effect of, say, taking an ice cube out of the freezer and exposing it to ambient temperature. The reason why an ice cube melts on its surface first under such conditions is that the surface is significantly warmer than the ice cube’s interior.

Surface melting detected in glass

In crystals with periodically arranged atoms, the thin liquid layer on the surface is typically detected by scattering experiments, which are very sensitive to the presence of atomic order. Since liquids are not arranged in a regular pattern, such techniques can therefore clearly resolve the appearance of a thin liquid film on top of the solid.

This approach, however, does not work for glasses (i.e. disordered, amorphous materials) because there is no difference in the atomic order between the solid and the liquid. Therefore, surface melting of glasses has remained rather unexplored with experiments.

To overcome the above-mentioned difficulties, Clemens Bechinger, physics professor at the University of Konstanz, and his colleague Li Tian used a trick: instead of studying an atomic glass, they produced a disordered material made of microscopic glass spheres known as colloids. In contrast to atoms, these particles are about 10,000 times larger and can be observed directly under a microscope.

The researchers were able to demonstrate the process of surface melting in such a colloidal glass because the particles near the surface move much faster compared to the solid below. At first glance, such behavior is not entirely unexpected, since the particle density at the surface is lower than in the underlying bulk material. Therefore, particles close to the surface have more space to move past each other, which makes them faster.

A surprising discovery

What surprised Clemens Bechinger and Li Tian, however, was the fact that even far below the surface, where the particle density has reached the bulk value, the particle mobility is still significantly higher compared to the bulk material.

The microscope images show that this previously unknown layer is up to 30 particle diameters thick and continues from the surface into the deeper regions of the solid in a streak-like pattern. “This layer which reaches far into the material has interesting material properties since it combines liquid and solid features,” Bechinger explains.

As a consequence, the properties of thin, disordered films depend very much on their thickness. In fact, this property is already being exploited in their use as thin ionic conductors in batteries, which are found to have a significantly higher ionic conductivity compared to thick films. With the new insights gained from the experiments, however, this behavior can now be understood quantitatively and thus be optimized for technical applications.

The research was published in Nature Communications.

More information: Li Tian et al, Surface melting of a colloidal glass, Nature Communications (2022). DOI: 10.1038/s41467-022-34317-2

Provided by University of Konstanz 

Single crystals are materials in which the crystal lattice is continuous and unbroken to the edges of the sample, with no grain boundaries. The atoms occupy regular positions, which are repeated indefinitely in space. While polycrystals are made up of many crystal grains or crystallites of varying sizes and orientations, monocrystals consist of a single grain.

A large supply of high-quality monocrystals is of the utmost importance to the study of the intrinsic physical properties of materials. They can be synthesized by various techniques. The most widely used method of growing single crystals of intermetallic compounds is known as chemical vapor transport (CVT).

An alternative technique has been designed and successfully tried out by a team led by researchers at the University of São Paulo’s Lorena School of Engineering (EEL-USP) in Brazil. An article on the study is published in the Journal of Crystal Growth.

“Conventional CVT consists of a chemical reaction in which the compound reacts with the chemical agent to form a volatile complex. This complex moves to a different region of the experimental apparatus with a different temperature from that of the zone in which the first chemical reaction occurred and is eventually deposited in the form of a single crystal. A temperature gradient is required in order for the single crystal to grow as it creates the necessary thermodynamic potential. In the novel technique, which we call isothermal chemical vapor transport [ICVT], growth occurs without the need for a temperature gradient,” said Lucas Eduardo Corrêa, first author of the article.

The study was part of Corrêa’s Ph.D. research, supervised by Professor Antonio Jefferson da Silva Machado.

“In the method we developed, the chemical potential gradient is what drives the growth of the single crystal,” said Machado, last author of the article.

“In a closed environment, a pellet of polycrystalline material and a transport agent are placed in contact at a constant temperature high enough to produce a reaction and form gaseous complexes. It’s reasonable to consider that the transport agent initially reacts with the surface of the polycrystalline material, creating a chemical potential gradient between the interior of the grains and the interface with the gas phase. Owing to this gradient, thermodynamic equilibrium can’t be obtained between the gas and solid phases.”

“When the gas phase reaches saturation point—which is facilitated by the use of very small amounts of the transport agent—the chemical potential of the pellet is lower than that of the gas. At this point, inversion of the gas flux occurs, and the surface of the pellet serves as a point for single crystal nucleation.”

According to the researchers, the isothermal growth process has a number of advantages over conventional CVT. The first is that there is no need for a two-zone furnace since in isothermal growth the temperature is kept constant throughout the experimental apparatus. Generally speaking, growth can be promoted using a simple uniform furnace. Second, there is no need for chemical attack on the tube since the pellet itself is the nucleation point, simplifying the growth process.

“It’s important to note that the crystallographic quality of the crystals obtained is very high. No seeded crystals occur. In sum, the isothermal growth process is a simplified version of conventional CVT that can grow much larger crystals,” Corrêa said.

Although growth was obtained for such materials as ZrTe₂, TiTe₂ and HfTe₂, which are almost two-dimensional, the researchers believe the method can be applied to other systems under the right thermodynamic conditions.

“The relevance of the materials in question lies in the gap between the tellurium atoms, so that other atoms or molecules can be intercalated into the material,” Machado said. “Indeed, the electronic structure of the compound ZrTe₂ exhibits a non-trivial topology. We discovered that intercalation of nickel [Ni] into this gap leads to superconductor behavior with a critical temperature close to 4.0 K.”

Another instability observed in the material—and one that competes with superconductivity—is the existence of charge density waves (CDWs). In addition to potential quantum computing applications, these properties make such materials attractive for the study of the fundamentals of solid-state physics. Other intercalations were tested by the researchers and are being analyzed as part of Corrêa’s Ph.D. research.

More information: Lucas E. Correa et al, Growth of pure and intercalated ZrTe₂, TiTe₂ and HfTe₂ dichalcogenide single crystals by isothermal chemical vapor transport, Journal of Crystal Growth (2022). DOI: 10.1016/j.jcrysgro.2022.126819

Provided by FAPESP 

Cell organelles are involved in a variety of cellular life activities. Their dysfunction is closely related to the development and metastasis of cancer. Exploration of subcellular structures and their abnormal states facilitates insights into the mechanisms of pathologies, which may enable early diagnosis for more effective treatment.

The optical microscope, invented more than 400 years ago, has become an indispensable and ubiquitous instrument for the investigation of microscale objects in many areas of science and technology. In particular, fluorescence microscopy has achieved several leaps—from 2D wide-field, to 3D confocal, and then to super-resolution fluorescence microscopy, greatly promoting the development of modern life sciences.

Using conventional microscopes, researchers currently struggle to generate sufficient intrinsic contrast for unstained cells, due to their low absorption or weak scattering properties. Specific dyes or fluorescent labels can help with visualization, but long-term observation of live cells remains difficult to achieve.

Recently, quantitative phase imaging (QPI) has shown promise with its unique ability to quantify the phase delay of unlabeled specimens in a nondestructive way. Yet the throughput of an imaging platform is fundamentally limited by its optical system’s space-bandwidth product (SBP), and the SBP increase of a microscope is fundamentally confounded by the scale-dependent geometric aberrations of its optical elements. This results in a tradeoff between achievable image resolution and field of view (FOV).

Lead author Linpeng Lu, a PhD student in the SCILab, provides a vivid hand-painted animation as a helpful summary of the report. Credit: Lu et al., doi 10.1117/1.AP.4.5.056002.

An approach to achieving label-free, high-resolution, and large FOV microscopic imaging is needed to enable precise detection and quantitative analysis of subcellular features and events. To this end, researchers from Nanjing University of Science and Technology (NJUST) and the University of Hong Kong recently developed a label-free high-throughput microscopy method based on hybrid bright/darkfield illuminations.

As reported in Advanced Photonics, the “hybrid brightfield-darkfield transport of intensity” (HBDTI) approach for high-throughput quantitative phase microscopy significantly expands the accessible sample spatial frequencies in the Fourier space, extending the maximum achievable resolution by approximately fivefold over the coherent imaging diffraction limit.

Based on the principle of illumination multiplexing and synthetic aperture, they establish a forward imaging model of nonlinear brightfield and darkfield intensity transport. This model endows HBDTI with the ability to provide features beyond the coherent diffraction limit.

Using a commercial microscope with a 4x, 0.16NA objective lens, the team demonstrated HBDTI high-throughput imaging, attaining 488-nm half-width imaging resolution within an FOV of approximately 7.19 mm², yielding a 25× increase in SBP over the case of coherent illumination.

Noninvasive high-throughput imaging enables delineation of subcellular structures in large-scale cell studies. According to corresponding author Chao Zuo, principal investigator of the Smart Computational Imaging Laboratory (SCILab) at NJUST, “HBDTI offers a simple, high-performance, low-cost, and universal imaging tool for quantitative analysis in life sciences and biomedical research. Given its capability for high-throughput QPI, HBDTI is expected to provide a powerful solution for cross-scale detection and analysis of subcellular structures in a large number of cell clusters.”

Zuo notes that further efforts are needed to promote the high-speed implementation of HBDTI in large-group live cell analysis.

More information: Linpeng Lu et al, Hybrid brightfield and darkfield transport of intensity approach for high-throughput quantitative phase microscopy, Advanced Photonics (2022). DOI: 10.1117/1.AP.4.5.056002

Provided by SPIE 

Highly charged ions are a common form of matter in the cosmos, where they are found, for example, in the sun or other stars. They are so called because they have lost many electrons and therefore have a high positive charge. This is why the outermost electrons are more strongly bound to the atomic nucleus than in neutral or weakly charged atoms.

For this reason, highly charged ions react less strongly to interference from external electromagnetic fields, but become more sensitive probes of fundamental effects of special relativity, quantum electrodynamics and the atomic nucleus.

“Therefore, we expected that an optical atomic clock with highly charged ions would help us to better test these fundamental theories”, explains PTB physicist Lukas Spieß. This hope has already been fulfilled: “We were able to detect the quantum electrodynamic nuclear recoil, an important theoretical prediction, in a five-electron system, which has not been achieved in any other experiment before.”

Beforehand, the team had to solve some fundamental problems, such as detection and cooling, in years of work: For atomic clocks, one has to cool the particles down extremely in order to stop them as much as possible and thus read out their frequency at rest. Highly charged ions, however, are produced by creating an extremely hot plasma.

Because of their extreme atomic structure, highly charged ions can’t be cooled directly with laser light, and standard detection methods can’t be used either. This was solved by a collaboration between MPIK in Heidelberg and the QUEST Institute at PTB by isolating a single highly charged argon ion from a hot plasma and storing it in an ion trap together with a singly charged beryllium ion.

This allows the highly charged ion to be cooled indirectly and studied by means of the beryllium ion. An advanced cryogenic trap system was then built at MPIK and finalized at PTB for the following experiments, which were carried out in part by students switching between the institutions.

Subsequently, a quantum algorithm developed at PTB succeeded in cooling the highly charged ion even further, namely close to the quantum mechanical ground state. This corresponded to a temperature of 200 millionths of a Kelvin above absolute zero. These results were already published in Nature in 2020 and in Physical Review X in 2021.

Now the researchers have successfully taken the next step: They have realized an optical atomic clock based on thirteen-fold charged argon ions and compared the ticking with the existing ytterbium ion clock at PTB. To do this, they had to analyze the system in great detail in order to understand, for example, the movement of the highly charged ion and the effects of external interference fields.

They achieved a measurement uncertainty of 2 parts in 1017—comparable to many currently operated optical atomic clocks. “We expect a further reduction of the uncertainty through technical improvements, which should bring us into the range of the best atomic clocks,” says research group leader Piet Schmidt.

The researchers have thus created a serious competitor to existing optical atomic clocks based on, for example, individual ytterbium ions or neutral strontium atoms. The methods used are universally applicable and allow many different highly charged ions to be studied. These include atomic systems that can be used to search for extensions of the Standard Model of particle physics.

Other highly charged ions are particularly sensitive to changes in the fine structure constant and to certain dark matter candidates that are required in models beyond the Standard Model but could not be detected with previous methods.

More information: Lukas Spieß, An optical atomic clock based on a highly charged ion, Nature (2022). DOI: 10.1038/s41586-022-05245-4. www.nature.com/articles/s41586-022-05245-4

Journal information: Physical Review X , Nature

Provided by Physikalisch-Technische Bundesanstalt

The weak nuclear force is currently not entirely understood, despite being one of the four fundamental forces of nature. In a pair of Physical Review Letters articles, a multi-institutional team, including theorists and experimentalists from Louisiana State University, Lawrence Livermore National Laboratory, Argonne National Laboratory and other institutions worked closely together to test physics beyond the “Standard Model” through high-precision measurements of nuclear beta decay.

By loading lithium-8 ions, an exotic heavy isotope of lithium with a less than one second half-life, in an ion trap, the experimental team was able to detect the energy and directions of the particles emitted in the beta decay of lithium-8 produced with the ATLAS accelerator at Argonne National Laboratory and held in an ion trap. Different underlying mechanisms for the weak nuclear force would give rise to distinct energy and angular distributions, which the team determined to unrivaled precision.

State-of-the-art calculations with the ab initio symmetry-adapted no-core shell model, developed at Louisiana State University, had to be performed to precisely account for typically neglected effects that are 100 times smaller than the dominant decay contributions. However, since the experiments have achieved remarkable precision, it is now required to confront the systematic uncertainties of such corrections that are difficult to be measured.

In their paper, “Impact of Clustering on the 8Li Beta Decay and Recoil Form Factors,” the LSU-led collaboration places unprecedented constraints on recoil corrections in the β decay of 8Li, by identifying a strong correlation between them and the 8Li ground state quadrupole moment in large-scale ab initio calculations.

The results are essential for improving the sensitivity of high-precision experiments that probe the weak interaction theory and test physics beyond the Standard Model. Dr. Grigor Sargsyan led the theoretical developments while he was a Ph.D. student at LSU, and is currently a postdoctoral researcher at Lawrence Livermore National Laboratory (LLNL).

In “Improved Limit on Tensor Currents in the Weak Interaction from 8Li β Decay,” researchers present the most precise measurement of tensor currents in the low-energy regime by examining the β−¯ν correlation of trapped 8Li ions with the Beta-decay Paul Trap. The results are found to be consistent with the Standard Model prediction, ruling out certain possible sources of “new” physics and setting the bar for precision measurements of this kind.

“This has important implications for understanding the physics of the tensor current contribution to the weak interaction,” said LSU Assistant Professor Alexis Mercenne. “Heretofore, the data has favored only vector and axial-vector couplings in the electroweak Lagrangian, but it has been suggested that other Lorentz-invariant interactions such as tensor, scalar, and pseudoscalar, can arise in the Standard Model extensions.”

“These are remarkable findings—the level of theoretical precision reached in ab initio theory beyond the lightest nuclei is unprecedented, and opens the path to novel high-precision predictions in atomic nuclei rooted in first principles,” said LSU Associate Professor Kristina Launey.

“In addition, no one expected that these theoretical developments would unveil a new state in 8Be nucleus that has not been measured yet. This nucleus is notoriously difficult to model due to its cluster structure and collective correlations, but become feasible for calculations in the ab initio symmetry-adapted no-core shell-model framework.”

The excitement of modern nuclear physics is its interdisciplinary nature and the use of a wide range of techniques and tools. LSU has both experimental and theoretical research groups in nuclear physics, with strong connections to the high-energy physics and astrophysics/space science groups. The principal focus of the experimental and theoretical groups is in the area of low-energy nuclear structure and reactions, including the study of nuclei far from stability and applications to astrophysics.

More information: G. H. Sargsyan et al, Impact of Clustering on the Li8 β Decay and Recoil Form Factors, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.202503

M. T. Burkey et al, Improved Limit on Tensor Currents in the Weak Interaction from Li8 β Decay, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.202502

Journal information: Physical Review Letters

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