Daily Archives: November 29, 2020

Credit: University of Nottingham

Researchers have developed a new theory for observing a quantum vacuum that could lead to new insights into the behavior of black holes.

The Unruh effect combines quantum physics and the theory of relativity. So far it has not been possible to measure or observe it, but now new research from a team led by the University of Nottingham has shed light on how this could be achieved using sound particles. The teams research has been published today in the journal Physical Review Letters.

The Unruh effect suggests that if you fly through a quantum vacuum with extreme acceleration, the vacuum no longer looks like a vacuum: rather, it looks like a warm bath full of particles. This phenomenon is closely related to the Hawking radiation from black holes.

A research team from the University of Nottinghams Black Hole Laboratory in collaboration with University of British Columbia and Vienna University of Technology has shown that instead of studying the empty space in which particles suddenly become visible when accelerating, you can create a two-dimensional cloud of ultra-cold atoms (Bose-Einstein condensate) in which sound particles, phonons, become audible to an accelerated observer in the silent phonon vacuum. The sound is not created by the detector, rather it is hearing what is there just because of the acceleration (a non-accelerated detector would still hear nothing).

One of the basic ideas of Albert Einsteins theory of relativity is: Measurement results can depend on the state of motion of the observer. How fast does a clock tick? How long is an object? What is the wavelength of a ray of light? There is no universal answer to this, the result is relative it depends on how fast the observer is moving. But what about the question of whether a certain area of space is empty or not? Shouldnt two observers at least agree on that?

No because what looks like a perfect vacuum to one observer can be a turbulent swarm of particles and radiation to the other. The Unruh effect, discovered in 1976 by William Unruh, says that for a strongly accelerated observer the vacuum has a temperature. This is due to so-called virtual particles, which are also responsible for other important effects, such as Hawking radiation, which causes black holes to evaporate.

To observe the Unruh effect directly, as William Unruh described it, is completely impossible for us today, explains Dr. Sebastian Erne who came from the University of Nottingham to the Atomic Institute of the Vienna University of Technology as an ESQ Fellow a few months ago. You would need a measuring device accelerated to almost the speed of light within a microsecond to see even a tiny Unruh-effect -we cant do that. However, there is another way to learn about this strange effect: using so-called quantum simulators.

Many laws of quantum physics are universal. They can be shown to occur in very different systems. One can use the same formulas to explain completely different quantum systems, says Jrg Schmiedmayer from the Vienna University of Technology. This means that you can often learn something important about a particular quantum system by studying a different quantum system.

Simulating one system with another has been especially useful for understanding black holes, since real black holes are effectively inaccessible, Dr. Cisco Gooding from the Black Hole laboratory emphasizes. In contrast, analog black holes can be readily produced right here in the lab.

This is also true for the Unruh effect: If the original version cannot be demonstrated for practical reasons, then another quantum system can be created and examined in order to see the effect there.

Just as a particle is a disturbance in empty space, there are disturbances in the cold Bose-Einstein condensate small irregularities (sound waves) that spread out in waves. As has now been shown, such irregularities should be detectable with special laser beams. Using special tricks, the Bose-Einstein condensate is minimally disturbed by the measurement, despite the interaction with the laser light.

Jrg Schmiedmayer explains: If you move the laser beam, so that the point of illumination moves over the Bose-Einstein condensate, that corresponds to the observer moving through the empty space. If you guide the laser beam in accelerated motion over the atomic cloud, then you should be able to detect disturbances that are not seen in the stationary case just like an accelerated observer in a vacuum would perceive a heat bath that is not there for the stationary observer.

Until now, the Unruh effect was an abstract idea, says Professor Silke Weinfurtner who leads the Black Hole laboratory at the University of Nottingham, Many had given up hope of experimental verification. The possibility of incorporating a particle detector in a quantum simulation will give us new insights into theoretical models that are otherwise not experimentally accessible.

Preliminary planning is already underway to carry out a version of the experiment using superfluid helium at the University of Nottingham. It is possible, but very time-consuming and there are technical hurdles for us to overcome, explains Jrg Schmiedmayer. But it would be a wonderful way to learn about an important effect that was previously thought to be practically unobservable.

Reference: Interferometric Unruh Detectors for Bose-Einstein Condensates by Cisco Gooding, Steffen Biermann, Sebastian Erne, Jorma Louko, William G. Unruh, Joerg Schmiedmayer and Silke Weinfurtner, 20 November 2020, Physical Review Letters.DOI: 10.1103/PhysRevLett.125.213603

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Combining Quantum Physics and the Theory of Relativity: Sound-Waves From a Quantum Vacuum at the Black Hole Laboratory - SciTechDaily

Visualization of quantum dots in bilayer graphene using scanning tunneling microscopy and spectroscopy reveals a three-fold symmetry. In this three-dimensional image, the peaks represent sites of high amplitude in the waveform of the trapped electrons. Credit: Zhehao Ge, Frederic Joucken, and Jairo Velasco Jr.

Researchers used a scanning tunneling microscope to visualize quantum dots in bilayer graphene, an important step toward quantum information technologies.

Trapping and controlling electrons in bilayer graphene quantum dots yields a promising platform for quantum information technologies. Researchers at UC Santa Cruz have now achieved the first direct visualization of quantum dots in bilayer graphene, revealing the shape of the quantum wave function of the trapped electrons.

The results, published on November 23, 2020, in Nano Letters, provide important fundamental knowledge needed to develop quantum information technologies based on bilayer graphene quantum dots.

There has been a lot of work to develop this system for quantum information science, but weve been missing an understanding of what the electrons look like in these quantum dots, said corresponding author Jairo Velasco Jr., assistant professor of physics at UC Santa Cruz.

While conventional digital technologies encode information in bits represented as either 0 or 1, a quantum bit, or qubit, can represent both states at the same time due to quantum superposition. In theory, technologies based on qubits will enable a massive increase in computing speed and capacity for certain types of calculations.

A variety of systems, based on materials ranging from diamond to gallium arsenide, are being explored as platforms for creating and manipulating qubits. Bilayer graphene (two layers of graphene, which is a two-dimensional arrangement of carbon atoms in a honeycomb lattice) is an attractive material because it is easy to produce and work with, and quantum dots in bilayer graphene have desirable properties.

These quantum dots are an emergent and promising platform for quantum information technology because of their suppressed spin decoherence, controllable quantum degrees of freedom, and tunability with external control voltages, Velasco said.

Understanding the nature of the quantum dot wave function in bilayer graphene is important because this basic property determines several relevant features for quantum information processing, such as the electron energy spectrum, the interactions between electrons, and the coupling of electrons to their environment.

Velascos team used a method he had developed previously to create quantum dots in monolayer graphene using a scanning tunneling microscope (STM). With the graphene resting on an insulating hexagonal boron nitride crystal, a large voltage applied with the STM tip creates charges in the boron nitride that serve to electrostatically confine electrons in the bilayer graphene.

The electric field creates a corral, like an invisible electric fence, that traps the electrons in the quantum dot, Velasco explained.

The researchers then used the scanning tunneling microscope to image the electronic states inside and outside of the corral. In contrast to theoretical predictions, the resulting images showed a broken rotational symmetry, with three peaks instead of the expected concentric rings.

We see circularly symmetric rings in monolayer graphene, but in bilayer graphene the quantum dot states have a three-fold symmetry, Velasco said. The peaks represent sites of high amplitude in the wave function. Electrons have a dual wave-particle nature, and we are visualizing the wave properties of the electron in the quantum dot.

This work provides crucial information, such as the energy spectrum of the electrons, needed to develop quantum devices based on this system. It is advancing the fundamental understanding of the system and its potential for quantum information technologies, Velasco said. Its a missing piece of the puzzle, and taken together with the work of others, I think were moving toward making this a useful system.

Reference: Visualization and Manipulation of Bilayer Graphene Quantum Dots with Broken Rotational Symmetry and Nontrivial Topology by Zhehao Ge, Frederic Joucken, Eberth Quezada, Diego R. da Costa, John Davenport, Brian Giraldo, Takashi Taniguchi, Kenji Watanabe, Nobuhiko P. Kobayashi, Tony Low and Jairo Velasco Jr., 23 November 2020, Nano Letters.DOI: 10.1021/acs.nanolett.0c03453

In addition to Velasco, the authors of the paper include co-first authors Zhehao Ge, Frederic Joucken, and Eberth Quezada-Lopez at UC Santa Cruz, along with coauthors at the Federal University of Ceara, Brazil, the National Institute for Materials Science in Japan, University of Minnesota, and UCSCs Baskin School of Engineering. This work was funded by the National Science Foundation and the Army Research Office.

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Direct Visualization of Quantum Dots Reveals Shape of Quantum Wave Function of the Trapped Electrons - SciTechDaily

The central unifying, overarching factor or cause is God himself.

Recently, I watched a fascinating NOVA episode entitled Einsteins Quantum Riddle. It was about advances in the area of quantum mechanics specifically, what is called quantum entanglement. Wikipedia has a long, complicated article about it. But the gist of it (which the TV special summarized for the layperson) is as follows:

Bottom line (beyond all the technical mumbo-jumbo of modern physics), is that even assuming that this phenomenon is true and a fact scientists have no explanation for how it could happen as it does. Its one of those things where the knowledge of science comes to an end: like the origin of life, the causes of the origins of the Big Bang, DNA and higher intelligence, and dark matter.

Einstein, as is well-known, had serious problems with quantum mechanics, with regard to its seemingly random and irrational nature, in relation to traditional notions of cause-and-effect. He famously stated, God doesnt play dice. Einsteins god was a pantheist one at best, but he was no atheist, and recognized that the universe had an unexplainable higher order and beauty of design that any thinking person couldnt deny. I have argued that this was a broad, bare-bones version of the classic theistic teleological (design) argument.

Science often gets to a place where it is completely baffled, but because it methodologically excludes God (which has essentially been the case since Darwin), and so often doesnt recognize its own inherent philosophical limitations (empiricism being only one form of knowledge among many), it rules out what is as plausible an explanation as anything else: God.

The most obvious example of this is Big Bang cosmology. This theory was formulated by a Catholic priest-scientist, Father Georges Lematre. It expressed in scientific detail what had already long since been present in the Bible: creatio ex nihilo (creation from nothing).

The theory of evolution runs into the same insuperable difficulties when it comes to describing exact sequences and causes for evolutionary change: especially across large gaps, such as the origins of life and DNA and of large classification groups to other ones. Its entirely possible as a method that God used to create (theistic evolution), but without the inclusion of God, science cannot explain many key aspects of it.

Intelligent design advocate and scientist Dr. Michael Behe believes that intelligent design doesnt necessarily require additional intervention by God after His initial act of creation.

All Christians, it seems to me, have to believe that (1) God created (Genesis, etc.), and (2) he in some sense sustains or upholds his creation.

Its a belief in a non-material or immaterial force or power or spirit, that profoundly influences the material universe and its creative processes, and which itself seems ultimately beyond purely scientific or empirical analysis.

In this view, of intelligent design and/or theistic evolution, God designed or foreordained that complex structures would evolve, and life and consciousness, etc., by some unknown non-material, overarching, guiding principle that transcends science, or concerning which science (presently) can give us no clues or answers.

He not only created scientific laws that work essentially on their own (hence can be observed and studied scientifically), but also supervises or ordains the entire project though not in an interventionist or supernatural/miraculous way. The processes and potentialities were there from the beginning, as a manifestation of his omnipotence and omniscience. Its just that some of them are supra-scientific.

I submit that the same explanation that suggests itself with regard to the Big Bang and the unexplained mysteries of evolutionary process: the creative and upholding/omnipotent power of God, is applicable and plausible also as the explanation of how quantum entanglement is possible at all. Here are biblical passages along these lines:

This is inspired revelation from God. God either does these things: establishes, preserves, holds together, allows to endure, and upholds all of his creation (which he brought into being from nothing) or he does not. Christians if they are consistent cannot disbelieve this. And Gods power is as plausible an explanation of quantum entanglement as anything else: if only methodologically atheist science will allow him to be discussed at all.

If scientists seek the vaunted unified theory in physics, its right in front of them: the central unifying, overarching factor or cause is God himself. The Bible has taught it these past 2000 or more years. Modern science keeps indirectly verifying it, in effect, by its inability to explain origins or (as in our present example) the basis and ultimate causes of experimentally verified quantum mechanics.

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Quantum Mechanics and the Upholding Power of God - National Catholic Register

The magic squares reflect the magic of mathematics. Magic Squares are square grids with a special arrangement of numbers in them. These numbers are special because every row, column, and diagonal adds up to the same number.

Recently, quantum physicist Gemma De las Cuevas and mathematicians Tim Netzer and Tom Drescher introduced the quantum magic square notion. For the first time, physicists studied the properties of this quantum version of magic squares in detail.

Tim Netzer and Tom Drescher from the Department of Mathematics and Gemma De las Cuevas from the Department of Theoretical Physics have introduced the quantum magic square, which is a magic square. Still, instead of numbers, one puts in matrices. This is a non-commutative, and thus quantum, a generalization of a magic square.

In the study, physicists show that quantum magic squares cannot be as quickly characterized as their classical cousins. More precisely, quantum magic squares are not convex combinations of quantum permutation matrices. Instead, they are richer and more complicated to understand.

Tom Drescher said,This is the general theme when generalizations to the non-commutative case are studied.

The work is at the intersection of algebraic geometry and quantum information and showcases the benefits of interdisciplinary collaboration.

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Physicists introduced the notion of the quantum magic square - Tech Explorist

Clifford Johnson spends his days dissecting some of sciences most inscrutable mysteries. How does quantum physics apply to our understanding of space and time? What is the true nature of black holes? What are the origins of the universe?

But, as the Marvel Cinematic Universe (MCU) ventures further into quantum realms, time travel and space exploration, Johnson has added to his daily musings. Hes become the MCUs go-to guy when its producers need to sprinkle a little scientific realism into their superhero stories.

With credits on television shows and films from Thor: Ragnarok and Avengers: Endgame to the forthcoming Ms. Marvel, Johnson has helped shape some of the MCUs most memorable depictions of science and scientists in action. With The Falcon and The Winter Soldier due for release on Disney+ this autumn, we spoke to the Los Angeles-based advisor about getting science right in the biggest movie franchise of all time.

Qualifications aside, how does one become Marvels go-to science advisor?

My involvement varies from project to project and Im by no means the only scientist they have on speed dial. The US National Academy of Science set up The Science and Entertainment Exchange to try and get better representation of science and scientists in entertainment media, and I came to the MCU through them. Marvel has been extremely smart in how they try to represent science. I call it Marvel science. Its obviously not real science, but it is rooted in things from the real world.

Is your involvement consistent from film to film?

It varies. The first thing I do is read the script and make copious notes and suggestions on every bit that I can. Sometimes they just want some scientific buzzwords, and to know what certain things might look like. In Thor: Ragnarok I was brought in to advise on wormholes. I suggested that each wormhole has a different character and visuals depending on what kind of astrophysical object we find at its end.

Whats the most direct impact youve had on the story?

Its fun when you get to work with the filmmakers from an early stage and can do a deep dive into the story. In that way, the science can get into the DNA of the storytelling. An example is in Agent Carter: they had this exotic material they wanted to use throughout the second series which I advised on based on knowledge of real life exotic materials. This was everything from containment of a substance you cant touch to how they might move this substance (I suggested magnetic fields) and designing machines which they actually built and used on set.

How detailed does it get? Do you sneak things in?

In season two of Agent Carter I filled the blackboards in Howard Starks lab with period-appropriate equations, modified slightly to relate to the problems they were trying to solve. Maybe me and one other person would appreciate whats in those equations, but it was fun.

As a huge comics fan, to what degree have you tried to influence the direction of the MCU?

As Agent Carter was about the early days of what would become SHIELD, I started suggesting to whoever would listen that this would be a good point to start building a reference framework that could be used for the future films, particularly with regards to the energy sources that later became the Infinity Stones. I offered to help them write the physics rules for them, so that they would be consistent from film to film, but no one got back to me. I think I was being a little bit optimistic about how much they wanted me to worry about that stuff!

Whats the most important thing to get right?

I want to give people the opportunity to recognise that everyone can be involved in science. In the comics, people like Tony Stark do science, meaning they can do anything in any scientific discipline. I wanted to change that because science is a collaborative field. In Infinity War they did a really good job of bringing in Shuri to help them save Vision (although I cant claim thats a result of my suggestion). Representation of people doing science in the MCU has evolved from just white men.

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This physicist keeps the science in Marvel's movies accurate (ish) - Wired.co.uk