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Category: quantum physics – Page 634

One of the fundamental challenges of physics is the reconciliation of Einstein’s theory of relativity and quantum mechanics. The necessity to critically question these two pillars of modern physics arises, for example, from extremely high-energy events in the cosmos, which so far can only ever be explained by one theory at a time, but not both theories in harmony. Researchers around the world are therefore searching for deviations from the laws of quantum mechanics and relativity that could open up insights into a new field of physics.

For a recent publication, scientists from Leibniz University Hannover and Ulm University have taken on the twin paradox known from Einstein’s special theory of relativity. This thought experiment revolves around a pair of twins: While one brother travels into space, the other remains on Earth. Consequently, for a certain period of time, the twins are moving in different orbits in space. The result when the pair meets again is quite astounding: The twin who has been travelling through space has aged much less than his brother who stayed at home. This phenomenon is explained by Einstein’s description of time dilation: Depending on the speed and where in the gravitational field two clocks move relative to each other, they tick at different speeds.

For the publication in Science Advances, the authors assumed a quantum-mechanical variant of the twin paradox with only one twin. Thanks to the superposition principle of , this twin can move along two paths at the same time. In the researchers’ , the twin is represented by an . “Such clocks use the quantum properties of atoms to measure time with high precision. The atomic clock itself is therefore a quantum-mechanical object and can move through space-time on two paths simultaneously due to the superposition principle. Together with colleagues from Hannover, we have investigated how this situation can be realised in an experiment,” explains Dr. Enno Giese, research assistant at the Institute of Quantum Physics in Ulm. To this end, the researchers have developed an experimental setup for this scenario on the basis of a quantum-physical model.

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Research led by University of Texas at Dallas physicists has altered the understanding of the fundamental properties of perovskite crystals, a class of materials with great potential as solar cells and light emitters.

Published in July in Nature Communications, the study presents evidence that questions existing models of the behavior of perovskites on the .

“Our enhanced understanding of the physics of perovskites will help determine how they are best used,” said Dr. Anton Malko, associate professor of physics in the School of Natural Sciences and Mathematics and a corresponding author of the paper.

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Researchers from the University of Maryland, the National Institute of Standards and Technology (NIST), the National High Magnetic Field Laboratory (NHMFL) and the University of Oxford have observed a rare phenomenon called re-entrant superconductivity in the material uranium ditelluride. The discovery furthers the case for uranium ditelluride as a promising material for use in quantum computers.

Nicknamed “Lazarus ” after the biblical character who rose from the dead, the phenomenon occurs when a arises, breaks down, then re-emerges in a material due to a change in a specific parameter—in this case, the application of a very strong magnetic field. The researchers published their results on October 7, 2019, in the journal Nature Physics.

Once dismissed by physicists for its apparent lack of interesting physical properties, uranium ditelluride is having its own Lazarus moment. The current study is the second in as many months (both published by members of the same research team) to demonstrate unusual and surprising superconductivity states in the material.

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The standard model of physics remains incomplete. Could supersymmetry fill the gaps? From whether supersymmetric particles could fix the mass of the Higgs Boson to what this would mean for string theory, the world’s leading thinkers explain all.

John Ellis is a British theoretical physicist who is currently Clerk Maxwell Professor of Theoretical Physics at King’s College London. He was Division Leader for the CERN theory division, a founding member of the LEPC and of the LHCC at CERN and currently chair of the committee to investigate physics opportunities for future proton accelerators.

Catherine Heymans is a Professor of Astrophysics and European Research Council Fellow at the University of Edinburgh. She is also the Director of the German Centre for Cosmological Lensing at the Ruhr-University Bochum, Germany.

Ben Allanach is a member of the Department of Applied Mathematics and Theoretical Physics High Energy Physics research group and The Cambridge SUSY Working Group based at the Cavendish Laboratory.

Continue reading “On Supersymmetry | John Ellis, Catherine Heymans, Ben Allanach, Subir Sakar, Cumrun Vafa” | >

An international team of researchers recently placed an entire molecule into a state of quantum superposition. This huge breakthrough represents the largest object to ever be observed in such a state – essentially occupying two places at once. And it may just be the eureka moment that defines our species’ far-future technology.

Quantum physics is about as close to a faith-based field of scientific study as there is. It’s not our fault, the universe is infinite and complex and we’ve been here for a relatively short amount of time. It’s excusable that we still don’t understand all the rules and, in lieu of a blueprint, we’re forced to come up with theories to explain the things we don’t know.

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As quantum objects are susceptible to their surrounding environment, quantum coherence and quantum states can easily be destroyed due to the impact of external signals, which can include thermal noise and backscattered signals in the measurement circuit. Researchers have thus been trying to develop techniques to enable nonreciprocal signal propagation, which could help to block the undesired effects of backward noise.

In a recent study, members of the dynamic spintronics group at the University of Manitoba in Canada have proposed a new method to produce dissipative coupling in hybrid quantum systems. Their technique, presented in a paper published in Physical Review Letters, enables nonreciprocal signal propagation with a substantial isolation ratio and flexible controllability.

“Our recent work on nonreciprocity in cavity magnonics is grounded in a research area combining cavity spintronics and hybrid quantum systems, which holds promise for constructing new quantum information processing platforms,” Yi-Pu Wang, a postdoctoral researcher at the University of Manitoba who was involved in the study, told Phys.org.

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The inability of scientists to create a theory of quantum gravity arises from long-standing tensions between general relativity and quantum mechanics. There have been few approaches with any success. In this video, Fermilab’s Dr. Don Lincoln explains one of the few promising ideas, called loop quantum gravity.

Further reading:
http://www.einstein-online.info/spotlights/spin_networks.1.html

Full Quantum series: https://www.youtube.com/playlist?list=PLCfRa7MXBEsq5JoO2gU3yWhxTr06SY2De

Continue reading “Loop Quantum Gravity” | >

Some researchers have raised the possibility that, if quantum computers fail to deliver anything of use soon, a quantum winter will descend: enthusiasm will wane and funding will dry up before researchers get anywhere close to building full-scale machines. “Quantum winter is a real concern,” Preskill says. But he remains upbeat, because the slow progress has forced researchers to adjust their focus and see whether the devices they already have might be able to do something interesting in the near future.

Researchers search for ways to put today’s small noisy quantum systems to work. The hunt for useful quantum computers.

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Energy is a quantity that must always be positive—at least that’s what our intuition tells us. If every single particle is removed from a certain volume until there is nothing left that could possibly carry energy, then a limit has been reached. Or has it? Is it still possible to extract energy even from empty space?

Quantum physics has shown time and again that it contradicts our intuition, which is also true in this case. Under certain conditions, negative energies are allowed, at least in a certain range of space and time. An international research team at the TU Vienna, the Université libre de Bruxelles (Belgium) and the IIT Kanpur (India) have now investigated the extent to which negative is possible. It turns out that no matter which quantum theories are considered, no matter what symmetries are assumed to hold in the universe, there are always certain limits to “borrowing” energy. Locally, the energy can be less than zero, but like money borrowed from a bank, this energy must be “paid back” in the end.

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