Daily Archives: May 6, 2023

Were not getting to absolute zero anytime soon. The temperature at which all energy in an object drops to zero, our inability to reach it is enshrined in the third law of thermodynamics.

One version of the law states that in order to reach absolute zero, wed have to either have infinite time or infinite energy. Thats not happening any time soon, so out the window go our hopes of achieving a total lack of energy.

Or do they?

A team from the Vienna University of Technology in Austria wanted to see if there was alternate route to absolute zero. And they found one in an interesting placequantum computing.

The researchers entered into their research with the intent of trying to generate a version of the third law of thermodynamics that jived cleanly with quantum physics. Because the regular version that so many physicists know and love doesnt quite fit nicely into the quantum world.

Disagreements between classical and quantum physics happen all the timeits why so much time and effort goes into trying to find a unified theory of physics that encompasses both sets of rules. That doesnt mean classical physics is wrong, it just means its limited in ways that we didnt expect when we first were figuring out how the universe works.

The third law of thermodynamics, despite how fundamental it is, is one of those surprisingly limited aspects of classical physics. In saying that we cant reach absolute zero without infinite time or infinite energy, it doesnt fully take a fundamental aspect quantum physicsinformation theoryinto account.

A principle of information theory called the Landauer principle states that there is a minimum, and finite, amount of energy that it takes to delete a piece of information. The catch here is that deleting information from a particle is the exact same thing as taking that particle to absolute zero. So, how is it possible that it takes a finite amount of energy to delete information and an infinite amount of energy to reach absolute zero, if those two things are the same?

It's not a total paradoxyou could take an infinitely long time. But that doesnt tell the whole story. The team discovered a key parameter that would get it done a whole lot fastercomplexity. It turns out that if you have complete, infinite control over an infinitely complex system, you can bring fully delete information from a quantum particle without the need for infinite energy or infinite time.

Now, is infinite complexity with infinite control more achievable than infinite time or infinite energy? No. Were still dealing with infinities here.

But this discovery does emphasize known limitations in the functionality of quantum computers. Namely, once we start saving information on those things, were never going to be able to fully scrub the information from the quantum bits (known as qubits) making up our information storage centers.

According to experts, thats not going to present a practical issue. Machines that operate absolutely perfectly already dont exist, so theres no reason to hold quantum computers to an unreachable standard. But it does teach us a bit more about exactly what building and operating these futuristic machines is going to take.

When it comes to quantum, were just getting started.

Associate News Editor

Jackie is a writer and editor from Pennsylvania. She's especially fond of writing about space and physics, and loves sharing the weird wonders of the universe with anyone who wants to listen. She is supervised in her home office by her two cats.

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There's a Secret Way to Get to Absolute Zero. Scientists Just Found It. - Popular Mechanics

A team at the University of Portsmouth has achieved unprecedented precision in measurements through a method involving quantum interference and frequency-resolving sampling measurements. This breakthrough could enhance imaging of nanostructures and biological samples, and improve quantum-enhanced estimation in optical networks.

A team of researchers has demonstrated the ultimate sensitivity allowed by quantum physics in measuring the time delay between two photons.

By measuring their interference at a beam-splitter through frequency-resolving sampling measurements, the team has shown that unprecedented precision can be reached within current technology with an error in the estimation that can be further decreased by decreasing the photonic temporal bandwidth.

This breakthrough has significant implications for a range of applications, including more feasible imaging of nanostructures, including biological samples, and nanomaterial surfaces, as well as quantum-enhanced estimation based on frequency-resolved boson sampling in optical networks.

The research was conducted by a team of scientists at the University of Portsmouth, led by Dr. Vincenzo Tamma, Director of the UniversitysQuantum Science and Technology Hub.

Dr. Tamma said: Our technique exploits the quantum interference occurring when two single photons impinging on the two faces of a beam-splitter are indistinguishable when measured at the beam-splitter output channels. If, before impinging on the beam splitter, one photon is delayed in time with respect to the other by going through or being reflected by the sample, one can retrieve in real time the value of such a delay and therefore the structure of the sample by probing the quantum interference of the photons at the output of the beam splitter.

We showed that the best precision in the measurement of the time delay is achieved when resolving such two-photon interference with sampling measurements of the two photons in their frequencies. Indeed, this ensures that the two photons remain completely indistinguishable at detectors, irrespective of their delay at any value of their sampled frequencies detected at the output.

The team proposed the use of a two-photon interferometer to measure the interference of two photons at a beam splitter. They then introduced a technique based on frequency-resolving sampling measurements to estimate the time delay between the two photons with the best possible precision allowed by nature, and with an increasing sensitivity at the decreasing of the photonic temporal bandwidth.

Dr. Tamma added: Our technique overcomes the limitations of previous two-photon interference techniques not retrieving the information on the photonic frequencies in the measurement process.

It allows us to employ photons of the shortest duration experimentally possible without affecting the distinguishability of the time-delayed photons at the detectors, and therefore maximizing the precision of the delay estimation with a remarkable reduction in the number of required pairs of photons. This allows a relatively fast and efficient characterization of the given sample paving the way to applications in biology and nanoengineering.

The applications of this breakthrough research are significant. It has the potential to significantly improve the imaging of nanostructures, including biological samples, and nanomaterial surfaces. Additionally, it could lead to quantum-enhanced estimation based on frequency-resolved boson sampling in optical networks.

The findings of the study are published in the journal Physical Review Applied.

Reference: Ultimate Quantum Sensitivity in the Estimation of the Delay between two Interfering Photons through Frequency-Resolving Sampling by Danilo Triggiani, Giorgos Psaroudis and Vincenzo Tamma, 24 April 2023, Physical Review Applied.DOI: 10.1103/PhysRevApplied.19.044068

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Photon Precision: How Quantum Physicists Shattered the Bounds of Sensitivity - SciTechDaily

IN NOVEMBER 1997, a young physicist named Juan Maldacena proposed an almost ludicrously bold idea: that space-time, the fabric of the universe and apparently the backdrop against which reality plays out, is a hologram.

For many working in the fields of particle physics and gravity at the time, Maldacenas proposal was as surprising as it was ingenious. Before it was published, the notion of a holographic universe was way out there, says Ed Witten, a mathematical physicist at the Institute for Advanced Studies in Princeton (IAS), New Jersey. I would have described it as wild speculation.

And yet today, just over 25 years on, the holographic universe is widely revered as one of the most important breakthroughs of the past few decades. The reason is that it strikes at the mystery of quantum gravity the long-sought unification of quantum physics, which governs particles and their interactions, and general relativity, which casts gravity as the product of warped space-time.

Then again, you might wonder why the idea is held in such high regard given that it remains a mathematical conjecture, which means it is unproven, and that the model universe it applies to has a bizarre geometry that doesnt resemble our universe.

The answer, it turns out, is twofold. First, the holographic conjecture has helped to make sense of otherwise intractable problems in particle physics and black holes. Second, and more intriguing perhaps, physicists have finally begun to make headway in their attempts to demonstrate that the holographic principle applies to the cosmos we actually reside in.

Maldacena, now also at the IAS, was originally inspired by two separate branches of

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Do we live in a hologram? Why physics is still mesmerised by this idea - New Scientist

My friend, Richard is a curmudgeonly physicist, who sends me science-y things he finds online. Richard loves making the point that if you dont understand something mathematically, you dont understand it. This claim bugs me, perhaps because I studied literature in college and teach humanities here at Stevens. My rebuttal follows.

Richard is in fancy company when he contends that the deepest truths are mathematical. Pythagoras and Plato both implied as much, and Galileo famously wrote that you can only read the grand book of the universe if you understand the language in which the book is written: mathematics. In 1931 James Jeans, a British physicist, proposed that the Great Architect of the universe, that is, God, seems to be a mathematician.

Richard sent me the Galileo and Jeans quotes, plus similar comments from physicist Richard Feynman. To those who do not know mathematics, Feynman wrote in The Character of Physical Law, it is difficult to get across a real feeling as to the beauty, the deepest beauty, of nature. But heres an irony: Feynmans comments on quantum physics contradict the claim that mathematics illuminates nature.

In a book on quantum electrodynamics, which he helped formulate, Feynman reiterates that you cant comprehend quantum theory without the math. But he adds that you cant understand it with the math either! I dont understand quantum physics, Feynman confesses. Nobody does. He suggests that physicists advanced mathematical tricks, although they make calculations easier, can obscure what is actually happening in nature.

Also, if God is a mathematician, in what dialect does She/He/They/It speak? Quantum phenomena are described with differential equations, matrices and path integrals, a method invented by Feynman. Each of these dialects employs imaginary numbers, which are constructed from the square roots of negative numbers.

Moreover, quantum theory accounts for electromagnetism and the nuclear forces, and general relativity describes gravity. Quantum theory and general relativity are conveyed in radically different lingos that are hard to translate into each other. Some physicists still dream of a unified theory, possibly embodied in a single formula, that describes reality. That is the theme of Michio Kakus recent bestseller The God Equation: The Quest for a Theory of Everything.

But Kakus vision of a mathematical theory of everything seems increasingly quaint, given all weve learned about the limits of mathematics. In the 1930s, Kurt Gdel proved that all but the simplest mathematical systems are inconsistent, posing problems that cannot be solved within the axioms of that system. Extending the work of Gdel, mathematician Gregory Chaitin points out that mathematics, rather than being a unified, logically consistent whole, is riddled with randomness, contradictions and paradoxes.

Philosopher Bertrand Russell, early in his career, revered mathematics, which he thought is our best route to absolute truth. Toward the end of his life, perhaps because of the influence of Gdel, Russell arrived at a darker view of mathematics. I fear that, to a mind of sufficient intellectual power, he wrote, the whole of mathematics would appear trivial, as trivial as the statement that a four-footed animal is an animal.

Thats far too bleak a view. If mathematics reduces to a tautology, 1 = 1, it is a fantastically fecund tautology. Mathematics has led to countless intellectual, aesthetic and material advances, on which our civilization depends. But mathematics, like ordinary language, is a human invention, a powerful but limited tool, not a divine gift. Many mysteries resist mathematical analysis, especially those related to the human mind. And some great scientific advances have been non-mathematical. Charles Darwins On the Origin of Species does not include a single equation.

For all these reasons, we should doubt physicists who say that truth must be expressed in equations. Physicists would say that, wouldnt they? Thats like a poet saying that truth can only be expressed in meter and rhyme, or an economist saying that everything comes down to money.

Back for a moment to my grouchy pal Richard. Although a math-o-phile, Richard does not share the belief of Kaku and others that there ismust be!a single, true mathematical description of the world. Richard adheres to a position called theoretical pluralism. There can be many ways to model nature and to solve a scientific problem, Richard says, and insisting that there must be one correct way can impede scientific progress. On this point, Richard and I agree.

John Horgan directs the Stevens Center for Science Writings. This column is adapted from one posted on johnhorgan.org.

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Is Ultimate Truth an Equation? Nah. The Stute - The Stute

Published on Thursday, May 4, 2023

How can integrating the arts with science and technology cultivate something new and unexpected? This question is one that Nancy Kawalek has been answering in several ways throughout her career most recently, with a suite of engaging games focused on teaching the principles of quantum science and engineering.

Kawalek, a professionally trained actor, brings her unique perspective from a background in theater to explore the myriad possibilities of a different stage: Scientists,Technologists, andArtistsGeneratingExploration.

Aptly shortened to STAGE, the collective laboratory was initially launched by Kawalek during her time at the California Nanosystems Institute at the University of California, Santa Barbara (UCSB). Today, it is embedded in the Pritzker School of Molecular Engineering (PME)at theUniversity of Chicago where Kawalek is a professor and Distinguished Fellow in Arts, Science, and Technology.

A true testament to the interdisciplinary tenant on which the PME was established, Kawalek was encouraged to expand her work at UChicago by a former UCSB colleague, Matthew Tirrell, who has been the dean of PME since 2011. Her team includes distinguished scientists, engineers, professional actors, technology experts, students, and diverse theatrical, visual, media, and performing artists.

At that time I had no idea that the University of Chicago would be such a good place, that the fit was just right, said Kawalek, who stressed that the aim is to explore how to get people to think and work in new ways, in addition to getting them excited about science.

Importantly, we are never going to get everyone excited about science just by sharing the facts. Weve seen this happen in such a bold way recently. I believe the only way to engage the general public in the sciences is to grab them emotionally. And I think the way to do that is always with a good story, said Kawalek. Its critical that we move people or entertain them and thats what the games do.

The Quantum Casino

A betting card game for two to seven players, Chicago Quantem is based on the popular poker variant Texas Holdem. The experiential game immerses players in the world of quantum physics and qubits.

With these concepts superposition, entanglement, operations, and measurement built into the game mechanics, the goal is to collect, change, and arrange the cards into a winning hand. Cards and colors are used to represent these complex ideas. As one example, having more entanglement in the game is better because more entangled qubits are desirable in quantum applications.

For Kawalek, it has been gratifying to see the games out in the world and being enjoyed by a diverse range of players. The STAGE team debuted the games at the 2022 American Physical Society (APS) Annual Meeting and featured them later that year at the South Side Science Festival where five- and ten-year-olds sat down with the game. Its amazing when you can create something that really spans all ages and levels of education, Kawalek said.

In six months, Kawalek and her team, including more than 40 students, created three card games with custom decks and three digital games. The project is aptly called the Quantum Casino and also includes a Quantum Photo Booth, which is used to aid in explaining quantum key distribution, a mechanism for sharing encryption keys between remote parties.

The work drew from three important research papers: Quantum Poker:a game for quantum computers suitable for benchmarking error mitigation techniques on NISQ devices; Quantum blackjack:advantages offered by quantum strategies in communication-limited games; and Investigation of quantum roulette.

But why quantum specifically? Kawalek wants more people to engage with quantum science and engineering an area that promises to provide growing opportunities and jobs, including many that dont require a PhD. To know that you can get some training and have a job that is interesting and that pays well its a huge opportunity to level the playing field for a large swath of the population who might never think they could engage with science, or be a scientist, she explained.

This approach means making the games accessible to schools and teachers. You really cant make an impact unless your work is out in the world, said Kawalek, who is collaborating with the Polsky Center for Entrepreneurship and Innovation to commercialize and patent the Quantum Casino games. We are eager to reach as many people as possible. If you can engage a few people, and they start to talk to others, it creates a ripple effect.

INTERESTED IN THIS TECHNOLOGY?ContactMichael Hinton, Manager, Technology Marketing, who can provide more detail aboutthis technology, discuss the licensing process, and connect you with the inventor.

//Polsky Patentedis a column highlighting research and inventions from University of Chicago faculty. For more information about available technologies,click here.

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UChicago Lab Creates 'Quantum Casino,' a Win-Win to Educate and ... - Polsky Center for Entrepreneurship and Innovation

May 5, 2023• Physics 16, 75

A new kind of 3D optical lattice traps atoms using focused laser spots replicated in multiple planes and could eventually serve as a quantum computing platform.

Researchers have produced 3D lattices of trapped atoms for possible quantum computing tasks, but the standard technology doesnt allow much control over atom spacing. Now a team has created a new type of 3D lattice by combining optical tweezerspoints of focused light that trap atomswith an optical phenomenon known as the Talbot effect [1]. The teams 3D tweezer lattice has sites for 10,000 atoms, but with some straightforward modifications, the system could reach 100,000 atoms. Such a large atom arrangement could eventually serve as a platform for a quantum computer with error correction.

3D optical lattices have been around for decades. The standard method for creating them involves crossing six laser beams to generate a 3D interference pattern that traps atoms in either the high- or low-intensity spots (see Synopsis: Pinpointing Qubits in a 3D Lattice). These cold-atom systems have been used as precision clocks and as models of condensed-matter systems. However, the spacing between atoms is fixed by the wavelength of the light, which can limit the control researchers have over the atomic behavior.

Optical tweezers offer an alternative method for trapping and controlling atoms. To form a tweezer array, researchers pass a single laser beam through a microlens array (or similar device) that focuses the beam into a 2D pattern of multiple bright spots. Atoms are automatically drawn to the centers of these spots, forming an array in a single plane (see Viewpoint: Alkaline Atoms Held with Optical Tweezers). We take these tweezer arrays to the third dimension, says Malte Schlosser from the Technical University of Darmstadt, Germany.

To obtain a 3D lattice, Schlosser and his colleagues took advantage of the Talbot effect, which is an interference phenomenon that occurs when light strikes a periodic structure, such as a diffraction grating or a microlens array. The light exiting the structure produces a 2D interference pattern of bright spots at some fixed distance beyond the structure but also generates additional planes of spots parallel to the first one. The Talbot effect had long been considered a nuisance for tweezer array research, as it creates extra bright spots that trap stray atoms, which interferes with measurements. The researchers turned this bug into a feature by deliberately tuning their optical system to trap atoms in the extra bright spots, Schlosser explains.

The researchers shined an 800-milliwatt laser onto a microlens array, which produced a 2D square array of 777 atom traps at the focal plane of the lens. But thanks to the Talbot effect, this 2D array was reproduced in 17 parallel planes, giving a total of 10,000 atom traps. These Talbot planes come for free, so we dont have to put in additional laser power or additional laser beams, Schlosser says.

As a demonstration of their system, Schlosser and his colleagues showed that they could load around 50% of the traps with rubidium atoms and induce an optical transition in all the atoms in a sublattice. In the future, the team plans to use a focused laser beam to selectively excite a single atom. Such optical control could allow researchers to read the atoms state or to place it in a so-called Rydberg state that would let it interact with its neighbors. Control of atomatom interactions has been previously demonstrated in 2D tweezer arrays. Schlosser foresees having atomatom interactions in the 3D lattice, but currently the spacing between the planes is too large (around 100 m); a distance of 10 m or less would be required.

Besides squeezing down the spacing of the lattice, the team plans to explore other trap geometries, such as hexagonal patterns that could mimic materials like graphene. The researchers are also working to boost the laser power. More light will increase the number of traps in the lattice. They estimate that doubling the power would provide 30,000 traps and that quadrupling it should produce close to 100,000.

Schlosser and his colleagues are tackling one of the most important challenges any quantum computing technology will face, which is scaling, says Ben Bloom, founder and chief technology officer of Atom Computing, a quantum technology company in California. He says that the new design can create a large number of atom quantum bits at essentially no cost, but there will be challenges ahead in trying to control the atoms within the lattice. Still, controlling so many atoms will have practical benefits. Pushing to large numbers of individually controlled atoms in 3D will allow for the exploration of new quantum error-correction codes, Bloom says.

Michael Schirber

Michael Schirber is a Corresponding Editor forPhysics Magazine based in Lyon, France.

A new experiment follows the trajectories of electrons as pulsed laser light yanks them away from their atoms and slams them back. Read More

The electric-field distribution within a cold-ion cloud has been characterized using Rydberg atoms embedded in the cloudan approach that could be harnessed to optimize ion-beam sources. Read More

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Physics - Tweezers in Three Dimensions - Physics

Less than three decades into the 21st century, the world is at the edge of a second quantum revolution one that integrates with the Fourth Industrial Revolution to create new technologies, new materials, and new, clean energy storage mechanisms.

It is also deepening humankinds understanding of life-generating biological processes such as photosynthesis, said Professor Jeff Murugan in his 19April inaugural lecture, The Future is Quantum How I learnt to stop worrying and embrace chaos.

It was the first in the reconfigured UCT Inaugural Lecture Series.

The term quantum revolution was coined by quantum physicists Jonathan Dowling and Gerard Milburn in 2002. It refers to quantum mechanics, a framework used to describe the dynamics of matter, such as electrons in atoms and molecules at a fundamental level.

The study of quantum matter the kind found in materials such as superconductors, magnets and graphene sits at the nexus of a number of overlapping disciplines, including condensed matter physics.

The title of Professor Murugans lecture was a play on words; chaos referring to both the realm of the everyday and the chaos that exists in realm of quantum particles because of their sometimes unpredictable properties.

The future is quantum

Early examples of quantum inventions include the transistor and laser. Lasers perhaps provide the easiest vehicle to demonstrate the enigma and potential of quantum mechanics. Lasers were developed in the 1950s by optical physicists who found that hitting certain kinds of atoms at the right energy could lead these to emit more photons with the same energy and direction as the initial photons. The effect would cause a cascade of photons, creating a stable, straight beam of light.

Suddenly were talking about material science, computing, batteries, cryptography, and all things quantum.

Harnessing the potential of a second quantum revolution has far-reaching implications, said Murugan, the founder and director of the Laboratory for Quantum Gravity & Strings (QGaSlab) in the Department of Mathematics and Applied Mathematics.

Suddenly were talking about material science, computing, batteries, cryptography, and all things quantum, he said. And in other things, were better able to understand chemistry and biology in terms of quantum mechanics, for example, why photosynthesis is the most efficient energy-harvesting system known in nature is best understood in terms of a property of quantum systems known as superposition.

Quantum computing has led big companies such as Google and Microsoft to invest heavily in quantum technologies,many teaming up with academic research institutions to create partnerships that will advance this technology.

Early developments

Murugan describes the mathematics at the heart of quantum matter as beautiful.

He and his talented young research group at QGaSlab, which corrals researchers in string theory, quantum gravity and cosmology, have made small but important breakthroughs in the field.

Theres been a flurry of activity over the past five to six years, building this up.

The result has been several research papers that explore the properties of these novel quantum systems.

Among these, quantum batteries are perhaps the most exciting possibility on South Africas radar right now: next-generation battery technology that can potentially revolutionise the nature of energy generation and storage.

No South African needs to be convinced that alternative energy storage is a good thing to invest in, said Murugan.

Unlike the batteries we know, such as the lithium-ion battery in smartphones that rely on classical electrochemical principles, quantum batteries rely solely on quantum mechanics.

They have a remarkable set of properties, he explained. Charging an ensemble of quantum batteries no longer scale linearly with the number of cells, but rather, exponentially. The more batteries there are, the faster they charge and the more batteries there are, the more energy you can deposit into that system, but exponentially faster. Remarkably, this quantum advantage of these batteries is because they are quantum chaotic!

In the current era of rolling blackouts and Eskoms uncertain future, the power of quantum batteries holds enormous potential for clean, reliable energy, he added.

Even though the possibilities are manifold, including new portable power sources for electric vehicles, which charge almost instantly, it is the fundamentally quantum aspect of these processes that intrigues Murugan, the mathematical physicist.

Chaos and purpose

But his beginnings as a mathematical physicist were not promising. At school he hated mathematics.

It was boring, uninspired and disconnected from anything. Physics, on the other hand, was amazing. It was curious and made me think about the world around us.

The turning point in his relationship with mathematics came with his introduction to calculus. It showed him that mathematics and physics were inextricably interwoven.

Here was motion; things were happening. There was cause and effect.

Mathematics is really a language to understand the universe around us.

From this, Murugan drew one of several life lessons that peppered his lecture, part of a legacy he would like to impart to his students (he is a 2018 Distinguished Teacher Awardee) and his children, he said.

Mathematics is really the language of nature. And like any language, it can be learnt in two ways. You can learn it like a linguist, understanding the structure of the language and the etymology of its lexicon, or immerse yourself in a population, where you will learn how to speak the language, swear-words and all.

Following undergraduate and postgraduate studies at UCT, in 2000 Murugan travelled to the United Kingdom on a Lindbury Fellowship to pursue a PhD in non-commutative geometry in string theory, jointly at UCT and Worchester College, Oxford. He was co-supervised by UCTs Emeritus Distinguished Professor of Complex Systems George Ellis and Philip Candelas, until recently Rouse-Ball Professor of Mathematics University of Oxford.

Postdoctoral studies followed at the High Energy Theory Group at Brown University in the United States. He returned to UCT in 2006 to join the Cosmology and Gravity Group, founded by Emeritus Professor Ellis. He left to begin QGaSlAB in 2012. In doing so, he had entered a new world of possibilities, perhaps too many, he said.

I am a mathematical physicist with a very short attention span so, unlike many of my colleagues, I dont spend too long thinking about any particular problem. My career has basically been a random walk through interesting problems in mathematical physics that include gravity, condensed matter, neurophysics, and even traffic flow.

This underpinned his final lesson in his lecture: Never stop learning!

Family business

The vote of thanks following Murugans presentation was delivered by his wife, UCT cosmologist Professor Amanda Weltman, the director of the High Energy Physics, Cosmology & Astrophysics Theory group at UCT andSARChI Chair in Physical Cosmology.

He takes very complex mathematical topics and unwraps them strand by strand.

Their three young children also attended the lecture, the littlest charming the audience over her fathers shoulder while another put his mind to bossing a Rubiks speed cube (a love of the abstract runs in the family).

In her address, Professor Weltman said, Theres never any doubt that Jeff was destined to be a professor of mathematical physics. His innate talent and great curiosity for understanding the universe and our world within it are two qualities that have helped him become a leader in the field and one of the most sought-after professors in the country.

Part of his appeal is that he takes very complex mathematical topics and unwraps them strand by strand. But best of all, he does so with great humour and there would be thunderous applause regularly coming from his lectures. Youd be forgiven for thinking you were at a comedy festival. And I would know that I would have to go in [to teach] next.

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Brave new world: On the edge of a second quantum revolution - University of Cape Town News

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Northeastern researchers have made what they describe as a groundbreaking discovery in the field of quantum mechanics.

Wei-Chi Chiu, a postdoctoral researcher at Northeastern reporting to Arun Bansil, university distinguished professor of physics at Northeastern, tells Northeastern Global News that his team has published a novel study examining the nature of a specific class of subatomic particles, whose very existence has eluded quantum physicists for nearly a century.

Chiu and his colleagues propose a new theoretical framework to explain how these particles, called Weyl fermions, interact with each other in certain materials. The findings, published in Nature Communications earlier this month, look beyond the framework of Albert Einstein's theory of relativity to probe these mysterious particles, Chiu says.

Weyl fermions were first discovered in 2015 by a group of physicists at Northeastern and Princeton universities. The discovery capped off an 85-year search for the massless particle, considered a basic building block of other subatomic particles, since its existence was first theorized by physicist Hermann Weyl in 1929.

In June of 2015, Bansil and the team of researchers predicted that a specific crystalline material, called Tantalum arsenide (TaAs), would host Weyl fermions. Soon after, the researchers demonstrated in an experimental paper the presence of the particles in TaAs through photoemission spectroscopy.

The discovery prompted a surge of experimental and theoretical explorations of Weyl fermions in different materials for want of a mechanical explanation of how they actually behave in real-time.

"Weyl fermions are relativistic particles that had actually never been seen, or observed, until 2015," Chiu says. "Our main focus in this work is understanding how these kinds of quasiparticles are interacting, and what the mechanisms are behind these interactions."

The most significant part of the researchers' findings, he says, is that the new framework for these quantum-level interactions challenges the longstanding view of "causality" as existing in spacetime. In Einstein's theory of relativity, the traditional view of causalityor mere cause-and-effectis that it is "time-ordered," meaning it is established in relation to chronological time. Under this view, causality refers to the principle that an event can only be influenced by other events that occur within its past light cone, Chiu says.

"This means that if 'A' causes event 'B,' then event 'A' must occur before event 'B' in both space and time," he says. "The light cone forms the event horizon or the boundary in spacetime which distinguishes between events that are and are not causally connected."

In other words, no object or signal can travel faster than the speed of light. This principle is sometimes referred to as the causality principle in relativity. The concept of causality in relativity is important, Chiu says, because it sets fundamental limits on what can be observed and measured in the universe.

Instead of thinking about the behavior of Weyl fermions in terms of spacetime, Chiu and his associates say these causal interactions are better understood as a result of measurable changes in the "energy-momentum" space.

"Our study, for the first time, shows how key concepts of causality and the associated event horizon in spacetime can be carried over into the field of correlated Weyl materials, and thus unveils fundamental connections between condensed matter and high-energy physics," Chiu says.

The work, he says, "opens up opportunities for exploring new connections between the world of particles and the larger world we experience every day."

"This study reveals for the first time how the ideas of causality that are enshrined in Einstein's theory of relativityand lead to the concepts of 'light cones' and 'event horizons' that have become the stuff of movies and common sci-fi workscan be generalized and expanded into the world of quantum materials," Bansil says,

More information: Wei-Chi Chiu et al, Causal structure of interacting Weyl fermions in condensed matter systems, Nature Communications (2023). DOI: 10.1038/s41467-023-37931-w

Journal information: Nature Communications

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Researchers pull back the quantum curtain on 'Weyl fermions' - Phys.org

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In physics, one often has to deal with different scales that can be described separately from one another: For the Earth's orbit around the sun, it makes absolutely no difference whether an elephant in the zoo walks to the left or to the right. And the movement of the elephant can be described without having to know anything about the properties of the electrons in its ear. The world can be divided into different scales.

In materials research, too, it is important to describe the behavior of particles on the appropriate scales. However, you first have to find out which scales are the decisive onesa difficult task for which there was previously no clear solution strategy. One could only hope to guess the solution with a lot of experience.

However, a mathematical method has now been found by an international research cooperation with the participation of the TU Wien and Saitama University in Japan to calculate the appropriate scalesan important step in the search for better materials for different areas of application, from microchips to photovoltaics. The method has now been published in the journal Physical Review X.

"In materials physics, electrons often cannot be viewed separately from one another," says Anna Kauch, who heads an FWF research project on this topic. "Particularly exciting phenomena such as magnetism or superconductivity can only be understood if many particles and their complex interactions are described together."

However, this is usually not possible with complete accuracy: If many particles are involved, then the formulas of quantum theory quickly become so big and so complex that even the best supercomputers in the world cannot solve them exactlynot even the state of the particles can then be written down exactly, because that would require more storage space than we will ever have available.

One must therefore look for certain approximations. These approximations often consist in being able to disregard certain size scales in certain cases. "Sometimes you can find quite simple physical arguments for it," says Markus Wallerberger, one of the authors of the paper. "A typical example of this are electrons and atomic nuclei in a crystal: the electrons are very light and move quickly. The atoms are much heavier, so on the time scale used to describe the motion of the electrons, the atoms can be considered rigid and immobile.

"In this case, we have split a complicated problem into two much simpler problems: we can now think about the fast movement of the electrons on the one hand and the much slower movement of the atoms on the otherand think about how the two are related." (a) QTT representation in momentum space. The rightmost bits (indices) represent fine structures in momentum space. Low entanglement structures are assumed between different length scales. (b) Schematic illustration of the bond dimensions along the chain representing the momentum dependence. The dashed line indicates the maximum bond dimensions in maximally entangled cases. (c) Fourier transform from momentum space to real space by applying a MPO. The orange diamonds represent the MPO tensors. Credit: Physical Review X (2023). DOI: 10.1103/PhysRevX.13.021015

But what do you do if you cannot see such an intuitive solution? So far, one could only guess in this case. But now it has been possible to develop a mathematical recipe for this situation. "In our paper, we show how to break down the complete description of such a system into different scales," explains Hiroshi Shinaoka, professor at Saitama University in Japan and leader of the study.

"It then automatically shows which scales are important and which ones can be left out. At the same time, the calculation method also tells us what the coupling between the different scales looks like and how we can then use it for further calculations."

More information: Hiroshi Shinaoka et al, Multiscale Space-Time Ansatz for Correlation Functions of Quantum Systems Based on Quantics Tensor Trains, Physical Review X (2023). DOI: 10.1103/PhysRevX.13.021015

Journal information: Physical Review X

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Scale separation: Breaking down unsolvable problems into solvable ones - Phys.org

About the opportunity

The University of Sydney's School of Physics are welcoming applicants for a Postdoctoral Research Associate in Quantum Optics, funded by Dr Sahand Mahmoodian's Australian Reserch Council grant, "Emergent many-body phenomena in engineered quantum optical systems". The field of research is quantum many-body physics of photons. The candidate can choose to undertake research on a range of topics within this area both focusing on fundamental research and for applications in developing quantum technologies.

Your key responsibilities will be to:

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About you

The University values courage and creativity; openness and engagement; inclusion and diversity; and respect and integrity. As such, we see the importance of recruiting talent aligned to these values and are looking for a Postdoctoral Research Associate who has:

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Your employment is conditional upon the completion of all role required pre-employment or background checks in terms satisfactory to the University. Similarly, your ongoing employment is conditional upon the satisfactory maintenance of all relevant clearances and background check requirements. If you do not meet these conditions, the University may take any necessary step, including the termination of your employment.

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Applications Close

Sunday 04 June 2023 11:59 PM

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Postdoctoral Research Associate in Quantum Optics job with ... - Times Higher Education