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Category: quantum physics

Scientists from the Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter have developed a new understanding of how electrons behave in strong magnetic fields. Their results explain measurements of electric currents in three-dimensional materials that signal a quantum Hall effect – a phenomenon thus far only associated with two-dimensional metals. This new 3D effect can be the foundation for topological quantum phenomena, which are believed to be particularly robust and therefore promising candidates for extremely powerful quantum technologies. These results have just been published in the scientific journal Nature Communications.

Dr. Tobias Meng and Dr. Johannes Gooth are early career researchers in the Würzburg-Dresdner Cluster of Excellence ct.qmat that researches topological quantum materials since 2019. They could hardly believe the findings of a recent publication in Nature claiming that electrons in the topological metal zirconium pentatelluride (ZrTe5) move only in two-dimensional planes, despite the fact that the material is three-dimensional. Meng and Gooth therefore started their own research and experiments on the material ZrTe5. Meng from the Technische Universität Dresden (TUD) developed the theoretical model, Gooth from the Max Planck Institute for Chemical Physics of Solids designed the experiments. Seven measurements with different techniques always lead to the same conclusion.

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For that, they will need the quantum equivalent of optical repeaters, the components of today’s telecommunications networks that keep light signals strong across thousands of kilometers of optical fiber. Several teams have already demonstrated key elements of quantum repeaters and say they’re well on their way to building extended networks. “We’ve solved all the scientific problems,” says Mikhail Lukin, a physicist at Harvard University. “I’m extremely optimistic that on the scale of 5 to 10 years… we’ll have continental-scale network prototypes.”

Advance could precisely link telescopes, yield hypersecure banking and elections, and make quantum computing possible from anywhere.

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TAMPA, Fla. — Europe has tasked an Airbus-led group to devise its own quantum communications network as startup Arqit raises $400 million for a space-based system.

Airbus said May 31 the European Commission awarded the group a contract to study a quantum technology-powered network, called EuroQCI, to secure critical infrastructure across Europe.

The 15-month agreement is worth several millions of euros, Airbus Defence and Space spokesperson Bruno Daffix told SpaceNews.

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What is time? What is humankind’s role in the universe? What is the meaning of life? For much of human history, these questions have been the province of religion and philosophy. What answers can science provide?

In this talk, Sean Carroll will share what physicists know, and don’t yet know, about the nature of time. He’ll argue that while the universe might not have purpose, we can create meaning and purpose through how we approach reality, and how we live our lives.

Sean Carroll is a Research Professor of theoretical physics at the California Institute of Technology, and an External Professor at the Santa Fe Institute. His research has focused on fundamental physics and cosmology, especially issues of dark matter, dark energy, spacetime symmetries, and the origin of the universe.

Recently, Carroll has worked on the foundations of quantum mechanics, the emergence of spacetime, and the evolution of entropy and complexity. Carroll is the author of Something Deeply Hidden, The Big Picture, The Particle at the End of the Universe amongst other books and hosts the Mindscape podcast.

“The Passage of Time and the Meaning of Life” was given on May 4, 02021 as part of Long Now’s Seminar series. The series was started in 02003 to build a compelling body of ideas about long-term thinking from some of the world’s leading thinkers. The Seminars take place in San Francisco and are curated and hosted by Stewart Brand. To follow the talks, you can:

Explore the full series: http://longnow.org/seminars.
More ideas on long-term thinking: http://blog.longnow.org.

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JÜLICH, Germany, May 28, 2021 — Quantum systems are considered extremely fragile. Even the smallest interactions with the environment can result in the loss of sensitive quantum effects. In the renowned journal Science, however, researchers from TU Delft, RWTH Aachen University and Forschungszentrum Jülich now present an experiment in which a quantum system consisting of two coupled atoms behaves surprisingly stable under electron bombardment. The experiment provide an indication that special quantum states might be realised in a quantum computer more easily than previously thought.

The so-called decoherence is one of the greatest enemies of the quantum physicist. Experts understand by this the decay of quantum states. This inevitably occurs when the system interacts with its environment. In the macroscopic world, this exchange is unavoidable, which is why quantum effects rarely occur in daily life. The quantum systems used in research, such as individual atoms, electrons or photons, are better shielded, but are fundamentally similarly sensitive.

“Systems subject to quantum physics, unlike classical objects, are not sharply defined in all their properties. Instead, they can occupy several states at once. This is called superposition,” Markus Ternes explains. “A famous example is Schrödinger’s thought experiment with the cat, which is temporarily dead and alive at the same time. However, the superposition breaks down as soon as the system is disturbed or measured. What is left then is only a single state, which is the measured value,” says the quantum physicist from Forschungszentrum Jülich and RWTH Aachen University.

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Scientists from the Cluster of Excellence ct.qmat—Complexity and Topology in Quantum Matter have developed a new understanding of how electrons behave in strong magnetic fields. Their results explain measurements of electric currents in three-dimensional materials that signal a quantum Hall effect—a phenomenon thus far only associated with two-dimensional metals. This new 3D effect can be the foundation for topological quantum phenomena, which are believed to be particularly robust and therefore promising candidates for extremely powerful quantum technologies. These results have just been published in the scientific journal Nature Communications.

Dr. Tobias Meng and Dr. Johannes Gooth are early career researchers in the Würzburg-Dresdner Cluster of Excellence ct.qmat that researches topological quantum materials since 2019. They could hardly believe the findings of a recent publication in Nature claiming that electrons in the topological zirconium pentatelluride (ZrTe5) move only in two-dimensional planes, despite the fact that the material is three-dimensional. Meng and Gooth therefore started their own research and experiments on the material ZrTe5. Meng from the Technische Universität Dresden (TUD) developed the theoretical model, Gooth from the Max Planck Institute for Chemical Physics of Solids designed the experiments. Seven measurements with different techniques always lead to the same conclusion.

Read more | >

How materials behave depends on the interactions between countless atoms. You could see this as a giant group chat in which atoms are continuously exchanging quantum information. Researchers from Delft University of Technology in collaboration with RWTH Aachen University and the Research Center Jülich have now been able to intercept a chat between two atoms. They present their findings in Science on May 28, 2021.

Atoms, of course, don’t really talk. But they can feel each other. This is particularly the case for magnetic atoms. “Each atom carries a small magnetic moment called spin. These spins influence each other, like compass needles do when you bring them close together. If you give one of them a push, they will start moving together in a very specific way,” explains Sander Otte, leader of the team that performed the research. “But according to the laws of quantum mechanics, each spin can be simultaneously point in various directions, forming a superposition. This means that actual transfer of quantum information takes place between the atoms, like some sort of conversation.”

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## SCIENCE ADVANCES • MAY 24, 2021 # *by Vienna University of Technology*

In everyday life, phase transitions usually have to do with temperature changes--for example, when an ice cube gets warmer and melts. But there are also different kinds of phase transitions, depending on other parameters such as magnetic field. In order to understand the quantum properties of materials, phase transitions are particularly interesting when they occur directly at the absolute zero point of temperature. These transitions are called "quantum phase transitions" or a "quantum critical points."

Such a quantum critical point has now been discovered by an Austrian-American research team in a novel material, and in an unusually pristine form. The properties of this material are now being further investigated.

It is suspected that the material could be a so-called Weyl-Kondo semimetal, which is considered to have great potential for quantum technology due to special quantum states (so-called topological states). If this proves to be true, a key for the targeted development of topological quantum materials would have been found.

This surprising result is probably related to the fact that the behavior of electrons in this material has some special features. "It is a highly correlated electron system. This means that the electrons interact strongly with each other, and that you cannot explain their behavior by looking at the electrons individually.

If there are only relatively few free electrons, as is the case in a semimetal, then the Kondo effect is unstable. This could be the reason for the quantum critical behavior of the material: the system fluctuates between a state with and a state without the Kondo effect, and this has the effect of a phase transition at zero temperature.

**Quantum fluctuations could lead to Weyl particles**

The main reason why the result is of such central importance is that it is suspected to be closely connected to the phenomenon of “Weyl fermions.” In solids, Weyl fermions can appear in the form of quasiparticles–i.e. as collective excitations such as waves in a pond. According to theoretical predictions, such Weyl fermions should exist in this material.

We suspect that the quantum criticality we observed favors the occurrence of such Weyl fermions,” says Silke Bühler-Paschen. “Quantum critical fluctuations could therefore have a stabilizing effect on Weyl fermions, in a similar way to quantum critical fluctuations in high-temperature superconductors holding superconducting Cooper pairs together.

It seems to us that certain quantum effects–namely quantum critical fluctuations, the Kondo effect and Weyl fermions–are tightly intertwined in the newly discovered material and, together, give rise to exotic Weyl-Kondo states. These are ‘topological’ states of great stability that, unlike other quantum states, cannot be easily destroyed by external disturbances. This makes them particularly interesting for quantum computers.

Thanks to folkstone design inc. & zoomers of the sunshine coast BC

**Relevant Stories**

https://www.youtube.com/channel/UCpEBFr960dwZqR-9HtCWIcQ

## ORIGINAL PAPER

Wesley T. Fuhrman et al, **Pristine quantum criticality in a Kondo semimetal**, Science Advances (2021). DOI: 10.1126/sciadv.abf9134

https://advances.sciencemag.org/content/7/21/eabf9134

#WeylKondoStates #KondoEffect #QuantumComputers.

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In the last few years, several technology companies including Google, Microsoft, and IBM, have massively invested in quantum computing systems based on microwave superconducting circuit platforms in an effort to scale them up from small research-oriented systems to commercialized computing platforms. But fulfilling the potential of quantum computers requires a significant increase in the number of qubits, the building blocks of quantum computers, which can store and manipulate quantum information.

But quantum signals can be contaminated by thermal noise generated by the movement of electrons. To prevent this, superconducting quantum systems must operate at ultra-low temperatures—less than 20 milli-Kelvin—which can be achieved with cryogenic helium-dilution refrigerators.

The output microwave signals from such systems are amplified by low-noise high-electron mobility transistors (HEMTs) at low temperatures. Signals are then routed outside the refrigerator by microwave , which are the easiest solutions to control and read but are poor heat isolators, and take up a lot of space; this becomes a problem when we need to scale up qubits in the thousands.

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