Tyler O'Neal, Staff Editor GOVERNMENT

Chinese modeling work demonstrates Tonga volcano to have smaller cooling impact on climate change than first thought

A fresh analysis of the possible cooling effect of the sulfur dioxide injected into the atmosphere by the Hunga Tonga-Hunga Ha'apai volcano in January 2022 has concluded that the impact will be much smaller than initially thought—but the researchers responsible add some major caveats to this conclusion. FY-4B Satellite captured the eruption of Hunga Tonga-Hunga Ha’apai volcano and monitored the diffusion of volcanic ash clouds.

An undersea volcano at Hunga Tonga-Hunga Ha'apai (HTHH) erupted violently on 15th January 2022, which raised wide public concern about its impact on global climate. Sulfur dioxide (SO2) injected into the stratosphere after volcanic eruptions are oxidized and converted to sulfate aerosols. These aerosols linger there for one or two years and while there, work to reduce incoming solar radiation, resulting in a short period of global cooling.

The surface temperature returns to normal as the volcanic aerosols dissipate, and so a single volcanic eruption is not enough to alter the long-term global warming trend, unless there are clusters of a volcanic eruption that can persist through centuries as is suggested have happened during the Little Ice Age in the past millennium. 

{media id=277,layout=solo}

The largest volcanic eruption of the last 500 years, the eruption of Mount Tambora in Indonesia in April 1815 caused the so-called “Year Without a Summer” in the following year in many parts of the world. There is a reduction in annual mean surface temperature over the tropics and northern hemisphere by 0.4-0.8°C.

But the Tambora eruption emitted 53-58 teragrams (Tg) of SO2. Satellite measurements of the eruption at HTHH—which has erupted multiple times over the past century—showed that its volcanic ash has reached an altitude of 30 kilometers deep into the stratosphere, with a total mass of only about 0.4 Tg.

One previously reported initial estimate placed the reduction in global surface air temperature at between 0.03 and 0.1°C over the next one to two years as a result of the HTHH eruption.

 “This reported initial estimate may have overestimated the impact as it did not take into account the location where the eruption occurred, which alters the spatial distribution of stratospheric sulfate aerosols—a variable that can alter results substantially”, said Tianjun Zhou of the Institute of Atmospheric Physics at the Chinese Academy of Sciences, “This is because southern hemisphere volcanic eruption emissions are largely confined to circulating in the same hemisphere and the tropics, with less of an impact on the northern hemisphere. This, in turn, leads to a weaker global cooling than those of northern hemispheric and tropical volcanoes”.

To arrive at a more accurate assessment, modeling needs to take into account the latitude of the release of sulfate aerosols. Correcting for this however was something of a challenge, as there are few southern volcanic eruptions similar to that of HTHH in the historical record. Fortunately, climate-model simulations that use large southern volcanic eruptions in the last millennium overall provided a useful reference. In this way, the researchers found a significant correlation between the intensity of 70 selected volcanic eruptions over the last millennium and the global mean surface temperature response in the first year after the eruption.

They then picked six particularly large tropical eruptions in model simulations and scaled the surface temperature response in line with the intensity of the 1991 Mount Pinatubo eruption where 20 Tg of SO2 were ejected. The results of the model simulations were found to be similar to real-world observations, suggesting their modeling work was on the right track.

These results were then scaled down for the HTHH eruption with its stratospheric injection of 0.4 Tg of SO2. The final results showed that the global mean surface temperature will decrease by only 0.004°C in the first year after the HTHH eruption. This is within the scope of the internal variability of the climate system.

The cooling in the southern hemisphere will be stronger than in other parts of the world, with the strongest cooling of more than 0.01°C occurring in parts of Australia and South America. The cooling over most of China will be less than 0.01°C.

This means that the eruption of HTHH will not be strong enough to overwhelm the longer-term global warming tendency.

The researchers did include one caveat however to these conclusions: This would be the case if the HTHH eruption is a one-time-only event. No explosive eruptions have been detected at HTHH since the Jan. 15 event so far. However, it may become active again in the future as this volcano has erupted many times over the past 100 years.

“As a result, we should keep monitoring the activity of HTHH in the coming days, months, and years,” said Professor Zhou.

In line with such monitoring efforts, the team will be extending their research by running some experiments based on ideal cases (scenario hypothesis in their simplification, but useful to make the models easier to understand) to try to reveal the potential climate impact of a larger HTHH volcanic eruption should they occur soon.

Goethe University Frankfurt identifies materials that have fast properties for spintronics

Tyler O'Neal, Staff Editor GOVERNMENT

While modern computers are already very fast, they also consume vast amounts of electricity. For some years now a new technology has been much talked about, which although it is still in its infancy could one day revolutionize computer technology – spintronics. The word is a portmanteau meaning “spin” and “electronics”, because with these components electrons no longer flow through computer chips, but the spin of the electrons serves as the information carrier. A team of researchers with staff from Goethe University Frankfurt has now identified materials that have surprisingly fast properties for spintronics. Researchers at Goethe University develop novel materials to minimize power consumption of electronic elements. Photo: raigvi/Shutterstock

“You have to imagine the electron spins as if they were tiny magnetic needles which are attached to the atoms of a crystal lattice and which communicate with one another,” says Cornelius Krellner, Professor for Experimental Physics at Goethe University Frankfurt. How these magnetic needles react with one another fundamentally depends on the properties of the material. To date ferromagnetic materials have been examined in spintronics above all; with these materials – similarly to iron magnets – the magnetic needles prefer to point in one direction. In recent years, however, the focus has been placed on so-called antiferromagnets to a greater degree, because these materials are said to allow for even faster and more efficient switchability than other spintronic materials.

With antiferromagnetic, the neighboring magnetic needles always point in opposite directions. If an atomic magnetic needle is pushed in one direction, the neighboring needle turns to face in the opposite direction. This in turn causes the next but one neighbor to point in the same direction as the first needle again. “As this interplay takes place very quickly and with virtually no friction loss, it offers considerable potential for entirely new forms of electronic componentry,” explains Krellner.

Above all crystals with atoms from the group of rare earth are regarded as interesting candidates for spintronics as these comparatively heavy atoms have strong magnetic moments – chemists call the corresponding states of the electrons 4f orbitals. Among the rare-earth metals – some of which are neither rare nor expensive – are elements such as praseodymium and neodymium, which are also used in magnet technology. The research team has now studied seven materials with differing rare-earth atoms in total, from praseodymium to holmium.

The problem in the development of spintronic materials is that perfectly designed crystals are required for such components as the smallest discrepancies immediately hurt the overall magnetic order in the material. This is where the expertise in Frankfurt came into play. “The rare earth melts at about 1000 degrees Celsius, but the rhodium that is also needed for the crystal does not melt until about 2000 degrees Celsius,” says Krellner. “This is why customary crystallization methods do not function here.”

Instead, the scientists used hot indium as a solvent. The rare earth, as well as the rhodium and silicon that are required, dissolve in this at about 1500 degrees Celsius. The graphite crucible was kept at this temperature for about a week and then gently cooled. As a result, the desired crystals grew in the form of thin disks with an edge length of two to three millimeters. These were then studied by the team with the aid of X-rays produced on the Berlin synchrotron BESSY II and the Swiss Light Source of the Paul Scherrer Institute in Switzerland.

“The most important finding is that in the crystals which we have grown the rare-earth atoms react magnetically with one another very quickly and that the strength of these reactions can be specifically adjusted through the choice of atoms,” says Krellner. This opens up the path for further optimization – ultimately spintronics is still purely fundamental research and years away from the production of commercial components.

There are still a great many problems to be solved on the path to market maturity, however. Thus, the crystals – which are produced in blazing heat – only deliver convincing magnetic properties at temperatures of less than minus 170 degrees Celsius. “We suspect that the operating temperatures can be raised significantly by adding iron atoms or similar elements,” says Krellner. “But it remains to be seen whether the magnetic properties are then just as positive.” Thanks to the new results the researchers now have a better idea of where it makes sense to change parameters, however.

Stanford researchers showcase a new level of control over how atoms interact

Tyler O'Neal, Staff Editor GOVERNMENT

In a new study, Stanford researchers demonstrate how to manipulate atoms so they interact with an unprecedented degree of control. Using precisely delivered light and magnetic fields, the researchers programmed a straight line of atoms into treelike shapes, a twisted loop called a Möbius strip, and other patterns. From left, Eric Cooper, Philipp Kunkel, Avikar Periwal and Monika Schleier-Smith. (Image credit: Khoi Huynh)

These shapes were produced not by physically moving the atoms, but by controlling the way atoms exchange particles and “sync up” to share certain properties. By carefully manipulating these interactions, researchers can generate a vast range of geometries. Importantly, they found that atoms at the far ends of the straight line could be programmed to interact just as strongly as the atoms located right next to each other at the center of the line. To the researchers’ knowledge, the ability to program nonlocal interactions to this degree, irrespective of the atoms’ actual spatial locations, had never been demonstrated before.

The findings could prove a key step forward in the development of advanced technologies for computation and simulation based on the laws of quantum mechanics – the mathematical description of how particles move and interact on the atomic scale.

“In this paper, we’ve demonstrated a whole new level of control over the programmability of interactions in a quantum mechanical system,” said study senior author Monika Schleier-Smith, the Nina C. Crocker Faculty Scholar and associate professor in the Department of Physics in Stanford’s School of Humanities and Sciences. “It’s an important milestone that we’ve long been working towards, while at the same time it’s a starting point for new opportunities.”

Two graduate students, Avikar Periwal and Eric Cooper, as well as a postdoctoral scholar, Philipp Kunkel, are co-led authors of the paper. Periwal, Cooper, and Kunkel are researchers in Schleier-Smith’s lab at Stanford.

“Avikar, Eric, and Philipp worked tremendously well together as a team in running the experiments, devising clever ways of analyzing and visualizing the data, and developing the theoretical models,” said Schleier-Smith. “We’re all very excited about these results.”

“We chose some simple geometries, like rings and disconnected chains, just as a proof of principle, but we also formed more complex geometries including ladder-like structures and treelike interactions, which have applications to open problems in physics,” Periwal, Cooper, and Kunkel said in a group statement.

Syncing up atoms on command

Periwal, Cooper, Kunkel, and colleagues performed experiments for the study on apparatuses known as optical tables, a pair of which dominate the floor space in Schleier-Smith’s lab. The tables are inset with intricate arrays of electronic components strung together by multicolored wires. At the heart of one optical table is a vacuum chamber, consisting of a metallic cylinder studded with porthole windows. A pump expels all air from this chamber so that no other atoms can disturb the small bunches of rubidium atoms carefully placed inside it. The Stanford researchers beamed lasers into this airless chamber to trap the rubidium atoms, slowing the atoms’ movement and cooling them down to within whiskers of absolute zero – the lowest temperature theoretically possible where particle movement comes to a virtual standstill. The extremely cold realm just above absolute zero is where quantum mechanical effects can dominate over those of classical physics, and thus where the atoms can be quantum mechanically manipulated.

Shining light through the bunches of atoms in this way also serves as a means of getting the atoms to “talk” to each other. As the light strikes each atom, it conveys information between them, generating patterns called “correlations” wherein every atom shares a certain desired quantum mechanical property. An example of a quantum mechanical property is the total angular momentum, known as the spin of an atom and which can have values of, for example, +1, 0, or –1.

Researchers at Stanford and elsewhere have correlated atomic networks before using systems of laser-cooled atoms, but, until recently, only two basic kinds of atomic networks could be made. In one, called an all-to-all network, every atom talks to every other atom. The second kind of network operates on what’s known as the nearest neighbor principle, where laser-suspended atoms interact most strongly with adjacent atoms.

In this new study, the Stanford researchers debut a far more dynamic method that conveys information over specific distances between discrete groups of atoms. This way, spatial location does not matter, and a vastly richer set of correlations can be programmed.

“With an all-to-all network, it’s like I’m sending a worldwide bulletin to everyone, while in a nearest-neighbor network, it’s like I’m only talking to the person who lives next door,” said Schleier-Smith. “With the programmability that we have now demonstrated in our lab, it’s like I’m picking up a phone and dialing the exact person I want to talk to located anywhere in the world.”

The researchers succeeded in creating these nonlocal interactions and correlations by controlling the frequencies of light shone at the trapped bunches of rubidium atoms and varying the strength of an applied magnetic field in the optical table. As the magnetic field strengthened in intensity from one end of the vacuum chamber to the other, it caused each bunch of atoms along the line to spin a bit faster than the prior, neighboring bunch. Although each atomic bunch had a unique rotation rate, every so often, certain bunches would nonetheless periodically arrive at the same orientation – rather like how a row of clocks with progressively faster-spinning hands will still momentarily read off the same times. The researchers used light to selectively enable and measure interactions between these momentarily synced-up atomic clouds. Overall, using a straight line of 18 clouds of atoms, the researchers could generate interactions between clouds at any specified set of distances along the line.

“The ability to generate and control these kinds of nonlocal interactions is powerful,” Schleier-Smith added. “It fundamentally changes the way information can travel and the quantum systems we can engineer.”

Benefitting from versatile control

One of the many applications of the Stanford team’s work is the crafting of optimization algorithms for quantum computers – machines that rely on the laws of quantum mechanics for crunching numbers. Quantum computing has applications in artificial intelligence, machine learning, cybersecurity, financial modeling, drug development, climate change forecasting, logistics, and scheduling optimization. For example, quantum computer-tailored algorithms could efficiently solve scheduling problems by finding the shortest possible routes for deliveries, or optimal scheduling of university classes so the greatest number of students can attend.

Another highly promising application is testing out theories of quantum gravity. The treelike shapes in this study were expressly designed for this purpose – they serve as basic models of space-time curved by a hypothetical new concept of gravity based on quantum mechanical principles that would revamp our understanding of gravity as described in Albert Einstein’s theory of relativity. A similar approach can also be applied to investigate the light-trapping, ultra-dense cosmic objects called black holes.

Schleier-Smith and colleagues are now working on showing that their experiments can produce quantum entanglement, where quantum states among atoms are correlated in a manner that can be harnessed for applications ranging from ultraprecise sensors to quantum computation.

“We made a lot of progress with this study and we’re looking to build on it,” said Schleier-Smith. “Our work demonstrates a new level of control that can help bridge the gap, in several areas of physics, between elegant theoretical ideas and actual experiments.”