Daily Archives: July 17, 2024

The study of quantum phase transitions, specifically the quantum Griffith singularity, has advanced with a team led by Jian-Hao Chen investigating this phenomenon in unconventional high-temperature superconducting bulk single crystals of CaFe1-xNixAsF. They observed robust quantum Griffith singularities influenced by magnetic fields, suggesting the potential universality of this phenomenon in three-dimensional and unconventional superconductors, which could enhance the understanding of high-temperature superconductivity mechanisms.

A new paper explores the quantum Griffith singularity in phase transitions, focusing on recent studies that could expand our understanding of high-temperature superconductivity in unconventional materials.

Exploring exotic quantum phase transitions has long been a key focus in condensed matter physics. A critical phenomenon in a phase transition is determined entirely by its universality class, which is governed by spatial and/or order parameters and remains independent of microscopic details. Quantum phase transitions, a subset of phase transitions, occur due to quantum fluctuations and are tuned by specific system parameters at the zero-temperature limit.

The superconductor-insulator/metal phase transition is a classic example of quantum phase transition, which has been intensely studied for more than 40 years. Disorder is considered one of the most important influencing factors, and therefore has received widespread attention. During the phase transitions, the system usually satisfies scaling invariance, so the universality class will be characterized by a single critical exponent. In contrast, the peculiarity of quantum Griffith singularity is that it breaks the traditional scaling invariance, where exotic physics emerges.

Figure 1Magnetic-field-driven superconductor-metal phase transition with multiple quantum critical points in CaFe1-xNixAsF. Credit: Science China Press

The physics of Griffiths singularity dates back to 1969, when American physicist Robert B. Griffiths proposed a type of phase transition in which the scaling invariance is broken. In this case, the critical exponent tends to diverge rather than remain constant. The quantum Griffith singularity refers to the Griffith singularity in a quantum phase transition.

Since the proposal of quantum Griffith singularity, it has only been observed in conventional low-dimensional superconducting films and in a few three-dimensional ferromagnets. The existence of quantum Griffith singularity in three-dimensional superconductors and in unconventional high-temperature superconductors has yet to be confirmed experimentally. Such confirmation will shed light on the understanding of mechanisms in unconventional high-temperature superconductivity.

Figure 2BT phase diagram of quantum Griffiths singularity in a three-dimensional anisotropic superconductor. Credit: Science China Press

Recently, a research group led by Jian-Hao Chen, a researcher at the International Center for Quantum Materials at the School of Physics at Peking University, the Beijing Academy of Quantum Information Sciences, and the Key Laboratory for the Physics and Chemistry of Nanodevices of Peking University, conducted a study on the quantum Griffith singularity in unconventional high-temperature superconducting bulk single crystal CaFe1-xNixAsF. They and their collaborators grew a series of high-quality underdoped CaFe1-xNixAsF bulk single crystals for the first time and observed the evolution of quasi-two-dimensional to three-dimensional anisotropic quantum Griffith singularities in the superconductor-metal phase transitions driven by magnetic fields.

They found robust quantum Griffith singularity which can last up to 5.3 K, and it can be induced in the crystals by both parallel and vertical magnetic fields. This study not only reveals the universality of quantum Griffith singularity in three-dimensional and unconventional high-temperature superconducting systems, but also predicts the possibility of finding quantum Griffith states in more unconventional high-temperature superconducting families (i.e., nickel-based and copper-based superconductors), which may further promote the understanding of unconventional high-temperature superconductivity mechanisms.

Reference: Three-dimensional quantum Griffiths singularity in bulk iron-pnictide superconductors by Shao-Bo Liu, Congkuan Tian, Yongqing Cai, Hang Cui, Xinjian Wei, Mantang Chen, Yang Zhao, Yuan Sui, Shuyue Guan, Shuang Jia, Yu Zhang, Ya Feng, Jiankun Li, Jian Cui, Yuanjun Song, Tingting Hao, Chaoyu Chen and Jian-Hao Chen, 25 June 2024, National Science Review. DOI: 10.1093/nsr/nwae220

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Unconventional Superconductivity: The Peculiar Case of Griffith Singularity - SciTechDaily

One of the most epic claims Ray Kurzweil makes in his new book, The Singularity Is Nearer is that the first person who will live to 1,000 may have already been born. Thats because, he writes, by 2030, humans will attain longevity escape velocity, and science will have figured out how to add more than a year to lifespan for each year that passes thanks to AI-led medical and pharmaceutical innovations.

Of course, Kurzweil is no stranger to outrageous predictions about the future and there are many more here, some of which, were they to pass, would make the prospect of such incredible longevity a little more palatable. By the late 2020s, he writes, data-driven vertical farming will cause the cost of food to plummet and 3-D printing will make housing shortages a thing of the past. In the 2030s, he asserts, it will be relatively inexpensive to live at a level that is considered luxurious today.

Kurzweil hasnt changed his tone or expectations much over the past 20 years. In his 2005 book The Singularity Is Near, he predicted that the Singularitythe term applied to the theoretical threshold when technology would outpace its human creators, resulting in an unpredictable, possibly uncontrollable explosion of superintelligent machineswould arrive by 2045. Now he writes it will arrive some time in the 2040s.

AI will change the way we approach a fundamental question: Who am I?

Early on in the new book, Kurzweil clarifies that his definition for the Singularity differs somewhat from other conceptions. While many futurists consider it the moment AI becomes capable of self-guided replication and growth, Kurzweil conceives of it as more of a fusion between tech and humanity, a time when this technology will let us merge with the superintelligence, allowing us to be freed from the enclosure of our skulls by artificial augmentation to our biology, ultimately expanding our intelligence millions-fold.

Along the way, he claims, several key innovations will happen. His new book essentially charts the path this snowballing technological revolution will take, providing rough estimates for when we may encounter certain landmark developments.

On that note, he explores at length present concerns about the future of work, claiming that, As AI unlocks unprecedented material abundance across countless areas, the struggle for physical survival will fade into history. Instead, our main struggle will be for purpose and meaning, and by the 2030s, we will be able to create meaningful expressions that we cannot imagine or understand today.

Around that same time, he writes that we will master the concept of atom-by-atom placement which will let us reorganize matter as we see fit, essentially allowing us to print clothing, furniture, solar panels, hot meals, and even human organs. Within a decade, this micro-manipulation will extend to medical nanobots who will regulate and repair our bodies from within, and by the 2040s and 2050s, we will rebuild our bodies and brains to go vastly beyond what our biological bodies are capable of.

This is the singularity as Kurzweil imagines it, when the AIs will become part of us, and thus it is we who will be doing those things.

At the heart of Kurzweils framework is the suggestion that AIs progressive arrival will change the way we approach a fundamental question: Who am I? This technology, he claims, will, through both its material and conceptual impacts, alter the way we think of ourselves.

Consider our phones, which already augment the otherwise limited capacity of our memories. You dont need to remember driving directions, because theyre stored in the cloud. Increasingly, writes Kurzweil, we will exist more and more in or even as this cloud, especially when the biological crutches afforded by AI become integrated into our bodies via implants and nanobots. Who are you if your identity is partially stored in the cloud, and if it can even be restored into a newly fabricated body in the event of accidental death?

If Kurzweil is even remotely right, then 10 years from now our livesour very societywill be totally unrecognizable.

One shortcoming of Kurzweils vision, of course, is that he seems to believe that technological progress proceeds in a straight line, when its history is chock full of diversions and dead endsa criticism levered at his earlier work.

And then there is the question of his enthusiasm itself. In Nearer, Kurzweil is unabashedly optimistic about the potential benefits afforded by AI. While he does devote some 20 pages to its perilsnotably a misalignment of programming values resulting in undesirable AI behavior, the misuse of AI-powered biotech by terrorists to create novel viruses or other large scale hazards, or nanobots loosed to violent ends or perhaps even total, if accidental, planetary devastationhe dismisses these as unlikely incidentals on the way to our grand utopia.

Wide-eyed optimism and inattention to the nonlinear path of progress aside, its hard to escape the appeal of Kurzweils vision. Nanorobots keeping us all healthy forever on our techno-quest for meaning? Sounds exciting on paper! And who doesnt want to believe in the powers of science to improve, enhance, and extend our lives?

But look back in time as far as you like, and you will see that history is decidedly short on utopias.

Lead image: DannyOliva / Shutterstock

Posted on July 17, 2024

Arts, science, and travel writer Nick Hilden contributes to the likes of the Washington Post, Scientific American, Esquire, Popular Science, National Geographic, and more. You can follow him on Twitter at @nickhilden or Instagram at @nick.hilden.

Cutting-edge science, unraveled by the very brightest living thinkers.

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Ray Kurzweil Still Lives in Utopia - Nautilus

A new generation of flying cars promises to revolutionize urban mobility, but limited battery power holds them back from plying longer routes. A new hydrogen-powered variant from Joby Aviation could soon change that.

Rapid advances in battery technology and electric motors have opened the door to a new class of aircraft known as eVTOLs, which stands for electric vertical takeoff and landing. The companies making the aircraft tout them as a quieter, greener alternative to helicopters.

However, current battery technology means theyre limited to ranges of approximately 150 miles. Thats why they have primarily been envisaged as a new form of urban mobility, allowing quick hops across cities congested with traffic.

Joby is already developing a battery-powered eVTOL that it expects to start commercial operations next year. But this week, the company announced it has created a hydrogen-powered version of the aircraft, which recently completed a 523-mile test flight. The company says this could allow eVTOLs to break into regional travel as well.

With our battery-electric air taxi set to fundamentally change the way we move around cities, were excited to now be building a technology stack that could redefine regional travel using hydrogen-electric aircraft, JoeBen Bevirt, founder and CEO of Joby, said in a press release.

Imagine being able to fly from San Francisco to San Diego, Boston to Baltimore, or Nashville to New Orleans without the need to go to an airport and with no emissions except water.

Jobys demonstrator is a converted battery-electric aircraft that had already completed 25,000 miles of test flights. It features the same airframe with six electric-motor-powered tilting propellers that allow it to take off vertically like a helicopter but cruise like a light aircraft. Joby says this should significantly speed up the certification process if the company decides to commercialize the technology.

Whats new is the addition of a hydrogen fuel cell system designed by H2FLY, a German startup Joby acquired in 2021, and a liquid hydrogen fuel tank that can store about 40 kilograms of fuel. The fuel cell combines the liquid hydrogen with oxygen from the air to generate the electricity that powers the aircrafts motors. The H2FLY team used the same underlying technology in a series of demonstration flights with a more conventional aircraft design last year.

The new Joby aircraft will still carry some batteries to provide additional power during takeoff and landing. But hydrogen has a much higher energy densityor specific energythan batteries, which makes it possible to power the aircraft for significantly longer.

Hydrogen has one hundred times the specific energy of todays batteries and three times that of jet fuel, Bevirt wrote in a blog post. The result is an electric aircraft that can travel much fartherand carry a greater payloadthan is possible not only with any battery cells currently under development, but even with the same mass of jet fuel.

However, switching to hydrogen fuel poses some challenges. For a start, hydrogen requires complicated cooling equipment, which means airports or other landing facilities would need to invest significant amounts in new fueling infrastructure.

The industry is already scratching its head figuring out how to support battery electric aircraft with charging infrastructure at airports, Cyrus Sigari, co-founder and managing partner of VC Up.Partners, told TechCrunch. Adding hydrogen filling stations into that equation will present even more challenges.

Hydrogens green credentials are also somewhat weaker than those of batteries. While its possible to generate hydrogen from water using only renewable electricity, at present the vast majority is produced from fossil fuels.

However, efforts are underway to increase the supply of green hydrogen, and the Bipartisan Infrastructure Law passed in 2021 set aside $9.5 billion to help boost these efforts. And if hydrogen-powered flight can piggyback on innovations in eVTOL technology, it could prove a powerful way to curb emissions in one of the worlds most polluting sectors.

Image Credit: Joby

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Jobys New Hydrogen-Powered Aircraft Can Fly You From San Francisco to San Diego - Singularity Hub

Roughly 52,000 years ago, a woolly mammoth died in the Siberian tundra. As her body flash froze in the biting cold, something remarkable happened: Her DNA turned into a fossil. It wasnt only genetic letters that were memorializedthe cold preserved their intricate structure too.

Fast forward to 2018, when an international expedition to the area found her preserved body. The team took little bits of skin from her head and ear, hairs still intact.

From these samples, scientists built a three-dimensional reconstruction of a woolly mammoths genome down to the nanometer. The results were published in Cell today.

Like humans, the mammoths DNA strands are tightly packed into chromosomes inside cells. These sophisticated structures are hard to analyze in detail, even for humans, but they contain insights into which genes are turned on or off and how theyre organized in different cell types.

Previous attempts to reconstruct ancient DNA only had tiny snippets of genetic sequences. Like trying to put together a puzzle with missing pieces, the resulting DNA maps were incomplete.

Thanks to the newly discovered flash-frozen DNA, this mammoth projectpun intendedis the first to assemble an enormous ancient genome in 3D.

This is a new type of fossil, and its scale dwarfs that of individual ancient DNA fragmentsa million times more sequence, said study author Erez Lieberman Aiden at Baylor College of Medicine in a statement.

Aidens team heavily collaborated with Love Daln at the Center of Palaeogenetics in Sweden. In a separate study, Dalns team analyzed 21 Siberian woolly mammoth genomes and charted how the species survived for six millennia after a potentially catastrophic genetic bottleneck.

The mammoth genomes werent that different than those of todays Asian and African elephants. All have 28 pairs of chromosomes, and their X chromosomes twist into unique structures unlike most mammals. Digging deeper, the team found genes that were turned on or off in the mammoth compared to its elephant cousins.

Our analyses uncover new biology, wrote Aidens team in their paper.

Ancient DNA is hard to come by, but it offers invaluable clues about the evolutionary past. In the 1980s, scientists eager to probe genetic history showed ancient DNA, however fragmented, could be extracted and sequenced in samples from an extinct member of the horse family and Egyptian mummies.

Thanks to modern DNA sequencing, the study of ancient DNA has subsequently undergone a remarkable expansion, wrote Aidens team. Its now possible to sequence whole genomes from extinct humans, animals, plants, and even pathogens spanning a million years.

Making sense of the fragments is another matter. One way to decipher ancient genetic codes is to compare them to the genomes of their closest living cousins, such as woolly mammoths and elephants. This way, scientists can figure out which parts of the DNA sequence remained unchanged and where evolution swapped letters or small fragments.

These analyses can link genetic changes to function, such as identifying which genes made mammoths woolly. But they cant capture large-scale differences at the chromosomal level. Because DNA relies on the chromosomes 3D structure to function, sequencing its letters alone misses valuable information, such as when and where genes are turned on or off.

Enter Hi-C. Developed in 2009 to reconstruct human genomes, the technique detects interactions between different genetic sites inside the cells nucleus.

Heres roughly how it works. DNA strands are like ribbons that twirl around proteins in a structure resembling beads on a string. Because of this arrangement, different parts of the DNA strand are closer to each other in physical space. Hi-C glues together sections that are near one another and tags the pairs. Alongside modern DNA sequencing, the technique produces a catalog of DNA fragments that interact in physical space. Like a 3D puzzle, scientists can then put the pieces back together.

Imagine you have a puzzle that has three billion pieces, but you dont have the picture of the final puzzle to work from, study author Marc A. Marti-Renom said in the press release. Hi-C allows you to have an approximation of that picture before you start putting the puzzle pieces together.

But Hi-C can be impossible to use in ancient samples because the surviving fragments are so short theyve erased any chromosome shapes. Theyve literally withered away over time.

In the new study, the team developed a new technique, called PaleoHi-C, to analyze ancient DNA specifically.

Scientists immediately treated samples in the field to reduce contamination. They generated roughly 4.4 billion pairs of physically aligned DNA sequencessome interacting within a single chromosome, others between two. Overall, they painted a 3D snapshot of the woolly mammoths genetic material and how it looked inside cells with nanoscale detail.

In the new reconstructions, the team identified chromosome territoriescertain chromosomes are located in different regions of the nucleusalongside other quirks, such as loops that bring pairs of distant genomic sites into close physical proximity to alter gene expression. These patterns differed between cell types, suggesting its possible to learn which genes are active, not just for the mammoth but also compared to its closest living relative, the Asian elephant.

Roughly 820 genes differed between the two, with 425 active in the mammoth but not in elephants, and a similar number inactivated in one but not the other. One inactive mammoth gene thats active in elephants has a human variant that is also shut down in the Nunavik Inuit, an indigenous people who thrive in the arctic. The gene may be relevant for adaptation to a cold environment, wrote the team.

Another inactive gene may explain how the woolly mammoth got its name. In humans and sheep, shutting down the same gene can result in excessive hair or wool growth.

For the first time, we have a woolly mammoth tissue for which we know roughly which genes were switched on and which genes were off, said Marti-Renom in the release. This is an extraordinary new type of data, and its the first measure of cell-specific gene activity of the genes in any ancient DNA sample.

How did the mammoths genome architecture remain so well preserved for over 50,000 years?

Dehydration, often used to preserve food, may have been key. Using Hi-C on fresh beef, beef after 96 hours sitting on a desk, or jerky after a year at room temperature, the jerky took the win for resiliency. Even after getting run over by a car, immersed in acid, and pulverized by a shotgun (no joke), the dehydrated beefs genomic architecture remained intact.

Dehydration could also partly be why the mammoth sample lasted so long. A chemical process called glass transition is widely used to produce shelf-stable food such as tortilla chips and instant coffee. It prevents pathogens from taking over or breaking down food. The mammoths DNA may also have been preserved in a glassy state called chromoglass. In other words, the sample was preserved across millennia by being freeze-dried.

Its hard to say how long DNA architecture can survive as chromoglass, but the authors estimate its likely over two million years. Whether PaleoHi-C can work on hot-air-dried specimens, such as ancient Egyptian samples, remains to be seen.

As for mammoths, the next step is to examine gene expression patterns in other tissues and compare them to Asian elephants. Besides building an evolutionary throughline, the efforts could also guide ongoing studies looking to revive some version of the majestic animals.

These results have obvious consequences for contemporary efforts aimed at woolly mammoth de-extinction, said study author Thomas Gilbert at the University of Copenhagen in the release.

Image Credit: Beth Zaiken

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First Woolly Mammoth Genome Reconstructed in 3D Could Help Bring the Species Back to Life - Singularity Hub