Category Archives: Quantum Physics

Albert Einsteins twin paradox is one of the most famous thought experiments in physics. It postulates that if you send one of two twins on a return trip to a star at near light speed, they will be younger than their identical sibling when they return home. The age difference is a consequence of something called time dilation, which is described by Einsteins special theory of relativity: the faster you travel, the slower time appears to pass.

But what if we introduce quantum theory into the problem? Physicists Alexander Smith of Saint Anselm College and Dartmouth College and Mehdi Ahmadi of Santa Clara University tackle this idea in a study published today in the journal Nature Communications. The scientists imagine measuring a quantum atomic clock experiencing two different times while it is placed in superpositiona quirk of quantum mechanics in which something appears to exist in two places at once. We know from Einsteins special theory of relativity that when a clock moves relative to another clock, the time shown on it slows down, Smith says. But quantum mechanics allows you to start thinking about what happens if this clock were to move in a superposition of two different speeds.

Superposition is a strange aspect of quantum physics where an object can initially be in multiple locations simultaneously, yet when it is observed, only one of those states becomes true. Particles can be placed in superposition in certain experiments, such as those using a beam splitter to divide photons of light, to show the phenomenon in action. Both of the particles in superposition appear to share information until they are observed, making the phenomenon useful for applications such as encryption and quantum communications.

Some atoms, meanwhile, can act as atomic clocks, with their rate of decay noting the passage of time. In their paper, Smith and Ahmadi describe how an atomic clock placed in superposition could experience time dilation, just like Einsteins twins experiment, if one of the superposition states is moved at several meters per second while the other remains stationary. Instead of the atom simply being in two states at onceas described in the Schrdingers cat experimentthe states would actually age differently. Its kind of like Schrdingers clock, Smith says.

Vlatko Vedral, a physicist at the University of Oxford, who was not involved in the study, says the idea allows for a rare opportunity to merge quantum mechanics with relativitytwo areas of physics that infamously do not mix well. You can actually combine the superposition principle in quantum mechanics with this notion of time dilation in relativity, he says. Its exactly Einsteins twins but now applied to the same system. Thats the twist. The final state is really amazing, because the atom is back in the same position where you started, but internally, it feels two different times. Its in a superposition of being older and younger at the same time.

Though the effect is far too small to be noticeable to humans, this idea of quantum time dilation could have repercussions for high-precision quantum clocks. And crucially, the new study suggests it might be possible to measure the effect experimentally. Im hoping this paper really prompts people to try to do this in the lab, Vedral says. And Smith suggests an experimental proposal could be drafted in the near future, perhaps using spectroscopy to split light, to look for this signature of quantum time dilation. We might be able to see this in the next five to 10 years, he says. I dont think its science fiction by any means.

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Quantum Time Twist Offers a Way to Create Schrdinger's Clock - Scientific American

No sooner had the radical equations of quantum mechanics been discovered than physicists identified one of the strangest phenomena the theory allows.

Quantum tunneling shows how profoundly particles such as electrons differ from bigger things. Throw a ball at the wall and it bounces backward; let it roll to the bottom of a valley and it stays there. But a particle will occasionally hop through the wall. It has a chance of slipping through the mountain and escaping from the valley, as two physicists wrote in Nature in 1928, in one of the earliest descriptions of tunneling.

Physicists quickly saw that particles ability to tunnel through barriers solved many mysteries. It explained various chemical bonds and radioactive decays and how hydrogen nuclei in the sun are able to overcome their mutual repulsion and fuse, producing sunlight.

But physicists became curious mildly at first, then morbidly so. How long, they wondered, does it take for a particle to tunnel through a barrier?

The trouble was that the answer didnt make sense.

The first tentative calculation of tunneling time appeared in print in 1932. Even earlier stabs might have been made in private, but when you get an answer you cant make sense of, you dont publish it, noted Aephraim Steinberg, a physicist at the University of Toronto.

It wasnt until 1962 that a semiconductor engineer at Texas Instruments named Thomas Hartman wrote a paper that explicitly embraced the shocking implications of the math.

Hartman found that a barrier seemed to act as a shortcut. When a particle tunnels, the trip takes less time than if the barrier werent there. Even more astonishing, he calculated that thickening a barrier hardly increases the time it takes for a particle to tunnel across it. This means that with a sufficiently thick barrier, particles could hop from one side to the other faster than light traveling the same distance through empty space.

In short, quantum tunneling seemed to allow faster-than-light travel, a supposed physical impossibility.

After the Hartman effect, thats when people started to worry, said Steinberg.

The discussion spiraled for decades, in part because the tunneling-time question seemed to scratch at some of the most enigmatic aspects of quantum mechanics. Its part of the general problem of what is time, and how do we measure time in quantum mechanics, and what is its meaning, said Eli Pollak, a theoretical physicist at the Weizmann Institute of Science in Israel. Physicists eventually derived at least 10 alternative mathematical expressions for tunneling time, each reflecting a different perspective on the tunneling process. None settled the issue.

But the tunneling-time question is making a comeback, fueled by a series of virtuoso experiments that have precisely measured tunneling time in the lab.

In the most highly praised measurement yet, reported in Nature in July, Steinbergs group in Toronto used whats called the Larmor clock method to gauge how long rubidium atoms took to tunnel through a repulsive laser field.

The Larmor clock is the best and most intuitive way to measure tunneling time, and the experiment was the first to very nicely measure it, said Igor Litvinyuk, a physicist at Griffith University in Australia who reported a different measurement of tunneling time in Nature last year.

Luiz Manzoni, a theoretical physicist at Concordia College in Minnesota, also finds the Larmor clock measurement convincing. What they measure is really the tunneling time, he said.

The recent experiments are bringing new attention to an unresolved issue. In the six decades since Hartmans paper, no matter how carefully physicists have redefined tunneling time or how precisely theyve measured it in the lab, theyve found that quantum tunneling invariably exhibits the Hartman effect. Tunneling seems to be incurably, robustly superluminal.

How is it possible for [a tunneling particle] to travel faster than light? Litvinyuk said. It was purely theoretical until the measurements were made.

Tunneling time is hard to pin down because reality itself is.

At the macroscopic scale, how long an object takes to go from A to B is simply the distance divided by the objects speed. But quantum theory teaches us that precise knowledge of both distance and speed is forbidden.

In quantum theory, a particle has a range of possible locations and speeds. From among these options, definite properties somehow crystallize at the moment of measurement. How this happens is one of the deepest questions.

The upshot is that until a particle strikes a detector, its everywhere and nowhere in particular. This makes it really hard to say how long the particle previously spent somewhere, such as inside a barrier. You cannot say what time it spends there, Litvinyuk said, because it can be simultaneously two places at the same time.

To understand the problem in the context of tunneling, picture a bell curve representing the possible locations of a particle. This bell curve, called a wave packet, is centered at position A. Now picture the wave packet traveling, tsunami-like, toward a barrier. The equations of quantum mechanics describe how the wave packet splits in two upon hitting the obstacle. Most of it reflects, heading back toward A. But a smaller peak of probability slips through the barrier and keeps going toward B. Thus the particle has a chance of registering in a detector there.

But when a particle arrives at B, what can be said about its journey, or its time in the barrier? Before it suddenly showed up, the particle was a two-part probability wave both reflected and transmitted. It both entered the barrier and didnt. The meaning of tunneling time becomes unclear.

And yet any particle that starts at A and ends at B undeniably interacts with the barrier in between, and this interaction is something in time, as Pollak put it. The question is, what time is that?

Steinberg, who has had a seeming obsession with the tunneling-time question since he was a graduate student in the 1990s, explained that the trouble stems from the peculiar nature of time. Objects have certain characteristics, like mass or location. But they dont have an intrinsic time that we can measure directly. I can ask you, What is the position of thebaseball? but it makes no sense to ask, What is the time of thebaseball? Steinberg said. The time is not a property any particle possesses. Instead, we track other changes in the world, such as ticks of clocks (which are ultimately changes in position), and call these increments of time.

But in the tunneling scenario, theres no clock inside the particle itself. So what changes should be tracked? Physicists have found no end of possible proxies for tunneling time.

Hartman (and LeRoy Archibald MacColl before him in 1932) took the simplest approach to gauging how long tunneling takes. Hartman calculated the difference in the most likely arrival time of a particle traveling from A to B in free space versus a particle that has to cross a barrier. He did this by considering how the barrier shifts the position of the peak of the transmitted wave packet.

But this approach has a problem, aside from its weird suggestion that barriers speed particles up. You cant simply compare the initial and final peaks of a particles wave packet. Clocking the difference between a particles most likely departure time (when the peak of the bell curve is located at A) and its most likely arrival time (when the peak reaches B) doesnt tell you any individual particles time of flight, because a particle detected at B didnt necessarily start at A. It was anywhere and everywhere in the initial probability distribution, including its front tail, which was much closer to the barrier. This gave it a chance to reach B quickly.

Since particles exact trajectories are unknowable, researchers sought a more probabilistic approach. They considered the fact that after a wave packet hits a barrier, at each instant theres some probability that the particle is inside the barrier (and some probability that its not). Physicists then sum up the probabilities at every instant to derive the average tunneling time.

As for how to measure the probabilities, various thought experiments were conceived starting in the late 1960s in which clocks could be attached to the particles themselves. If each particles clock only ticks while its in the barrier, and you read the clocks of many transmitted particles, theyll show a range of different times. But the average gives the tunneling time.

All of this was easier said than done, of course. They were just coming up with crazy ideas of how to measure this time and thought it would never happen, said Ramn Ramos, the lead author of the recent Nature paper. Now the science has advanced, and we were happy to make this experiment real.

Although physicists have gauged tunneling times since the 1980s, the recent rise of ultraprecise measurements began in 2014 in Ursula Kellers lab at the Swiss Federal Institute of Technology Zurich. Her team measured tunneling time using whats called an attoclock. In Kellers attoclock, electrons from helium atoms encounter a barrier, which rotates in place like the hands of a clock. Electrons tunnel most often when the barrier is in a certain orientation call it noon on the attoclock. Then, when electrons emerge from the barrier, they get kicked in a direction that depends on the barriers alignment at that moment. To gauge the tunneling time, Kellers team measured the angular difference between noon, when most tunneling events began, and the angle of most outgoing electrons. They measured a difference of 50 attoseconds, or billionths of a billionth of a second.

Then in work reported in 2019, Litvinyuks group improved on Kellers attoclock experiment by switching from helium to simpler hydrogen atoms. They measured an even shorter time of at most two attoseconds, suggesting that tunneling happens almost instantaneously.

But some experts have since concluded that the duration the attoclock measures is not a good proxy for tunneling time. Manzoni, who published an analysis of the measurement last year, said the approach is flawed in a similar way to Hartmans tunneling-time definition: Electrons that tunnel out of the barrier almost instantly can be said, in hindsight, to have had a head start.

Meanwhile, Steinberg, Ramos and their Toronto colleagues David Spierings and Isabelle Racicot pursued an experiment that has been more convincing.

This alternative approach utilizes the fact that many particles possess an intrinsic magnetic property called spin. Spin is like an arrow that is only ever measured pointing up or down. But before a measurement, it can point in any direction. As the Irish physicist Joseph Larmor discovered in 1897, the angle of the spin rotates, or precesses, when the particle is in a magnetic field. The Toronto team used this precession to act as the hands of a clock, called a Larmor clock.

The researchers used a laser beam as their barrier and turned on a magnetic field inside it. They then prepared rubidium atoms with spins aligned in a particular direction, and sent the atoms drifting toward the barrier. Next, they measured the spin of the atoms that came out the other side. Measuring any individual atoms spin always returns an unilluminating answer of up or down. But do the measurement over and over again, and the collected measurements will reveal how much the angle of the spins precessed, on average, while the atoms were inside the barrier and thus how long they typically spent there.

The researchers reported that the rubidium atoms spent, on average, 0.61 milliseconds inside the barrier, in line with Larmor clock times theoretically predicted in the 1980s. Thats less time than the atoms would have taken to travel through free space. Therefore, the calculations indicate that if you made the barrier really thick, Steinberg said, the speedup would let atoms tunnel from one side to the other faster than light.

In 1907, Albert Einstein realized that his brand-new theory of relativity must render faster-than-light communication impossible. Imagine two people, Alice and Bob, moving apart at high speed. Because of relativity, their clocks tell different times. One consequence is that if Alice sends a faster-than-light signal to Bob, who immediately sends a superluminal reply to Alice, Bobs reply could reach Alice before she sent her initial message. The achieved effect would precede the cause, Einstein wrote.

Experts generally feel confident that tunneling doesnt really break causality, but theres no consensus on the precise reasons why not. I dont feel like we have a completely unified way of thinking about it, Steinberg said. Theres a mystery there, not a paradox.

Some good guesses are wrong. Manzoni, on hearing about the superluminal tunneling issue in the early 2000s, worked with a colleague to redo the calculations. They thought they would see tunneling drop to subluminal speeds if they accounted for relativistic effects (where time slows down for fast-moving particles). To our surprise, it was possible to have superluminal tunneling there too, Manzoni said. In fact, the problem was even more drastic in relativistic quantum mechanics.

Researchers stress that superluminal tunneling is not a problem as long as it doesnt allow superluminal signaling. Its similar in this way to the spooky action at a distance that so bothered Einstein. Spooky action refers to the ability of far-apart particles to be entangled, so that a measurement of one instantly determines the properties of both. This instant connection between distant particles doesnt cause paradoxes because it cant be used to signal from one to the other.

Considering the amount of hand-wringing over spooky action at a distance, though, surprisingly little fuss has been made about superluminal tunneling. With tunneling, youre not dealing with two systems that are separate, whose states are linked in this spooky way, said Grace Field, who studies the tunneling-time issue at the University of Cambridge. Youre dealing with a single system thats traveling through space. In that way it almost seems weirder than entanglement.

In a paper published in the New Journal of Physics in September, Pollak and two colleagues argued that superluminal tunneling doesnt allow superluminal signaling for a statistical reason: Even though tunneling through an extremely thick barrier happens very fast, the chance of a tunneling event happening through such a barrier is extraordinarily low. A signaler would always prefer to send the signal through free space.

Why, though, couldnt you blast tons of particles at the ultra-thick barrier in the hopes that one will make it through superluminally? Wouldnt just one particle be enough to convey your message and break physics? Steinberg, who agrees with the statistical view of the situation, argues that a single tunneled particle cant convey information. A signal requires detail and structure, and any attempt to send a detailed signal will always be faster sent through the air than through an unreliable barrier.

Pollak said these questions are the subject of future study. I believe the experiments of Steinberg are going to be an impetus for more theory. Where that leads, I dont know.

The pondering will occur alongside more experiments, including the next on Steinbergs list. By localizing the magnetic field within different regions in the barrier, he and his team plan to probe not only how long the particle spends in the barrier, but where within the barrier it spends that time, he said. Theoretical calculations predict that the rubidium atoms spend most of their time near the barriers entrance and exit, but very little time in the middle. Its kind of surprising and not intuitive at all, Ramos said.

By probing the average experience of many tunneling particles, the researchers are painting a more vivid picture of what goes on inside the mountain than the pioneers of quantum mechanics ever expected a century ago. In Steinbergs view, the developments drive home the point that despite quantum mechanics strange reputation, when you see where a particle ends up, that does give you more information about what it was doing before.

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Quantum Tunnels Show How Particles Can Break the Speed of Light - Quanta Magazine

Lets get subatomic. In philanthropic circles, arcane topics such as theoretical physics and quantum mechanics have a tough time attracting significant funding. Grantseekers can find it challenging to convey to potential donors the importance of subjects that are not only outside the ken of most non-scientists, but which may not seem as pressing as emergencies like global pandemics, poverty or climate change. Even within science funding, public and private, the life sciences dominate.

But the Perimeter Institute, a center for theoretical physics based in Waterloo, Ontario, has been successfully attracting funding through a pioneering public-private funding model. We wrote about Perimeter and its approach last year in the wake of the 20-year-old institutes contribution to developing the worlds first image of a black hole.

In short, Perimeter draws a blend of support from government, industry and private funders, and has become a worldwide leader in advancing talent and new discoveries in theoretical physics.

Just last week, Perimeter announced its new Clay Riddell Centre for Quantum Matter, a research hub where scientists will study the subatomic world of quantum mechanics to understand and discover new states of matteryou know, states of matter other than the familiar solid, liquid, gas and plasma that you learned about in high school. (Dont ask us to explain plasma.)

The new center is the culmination of a 10-year, $25 million investment in quantum matter research, made possible by a $10 million founding donation from the Riddell Family Charitable Foundation. Clay Riddell, who died in 2018, was a Canadian entrepreneur and philanthropist. Physicists believe that study of quantum science and matter will eventually lead to useful technologies and abilities that stretch the imagination.

That the theoretical science of today leads to the technologies of tomorrow is a key message in basic scienceand especially funding for basic science, explained Greg Dick, Perimeters executive director of advancement and senior director of public engagement. Consider the theory of special relativity and curved space: One hundred years after Einstein proposed it, Dick said, special relativity is a necessary element of GPS navigation systems in cars and other settings. The theories of quantum mechanics led in just a few decades to the computer age. And before all that, the theories of magnetism and electricity eventually translated into practically every single thing we use every day.

When electricity and magnetism were discovered, the problem of the day was air pollution in New York City from the manure that horse hoofs pulverized into dust, said Dick. But fortunately, people were thinking about esoteric questions of electricity and magnetism, and that changed society.

In other words, society can ill afford to stop funding basic and theoretical science. The exciting thing is that the time from new theory to useful technology is getting shorter, Dick said. Perhaps in a decade, the study of quantum matter could lead to solutions for next-generation quantum computers, medical diagnostics, transportation, superconductors for energy grids and cryptography for data security and communications.

But just as likely, said Dick, the study of quantum matter will enable the creation of exotic materials and technologies no one currently expects or imagines.

And this brings us to why the coronavirus pandemic, which has demanded so much of the worlds attention, is helping science grantseekers connect with funders.

Obviously, when COVID started, there was a pause (in fundraising), but interestingly, COVID has also moved the relevance and value of foundational science to the forefront of peoples minds, said Dick. Yes, the theoretical physics that we do is nuanced, but COVID has put science on a pedestal. Its actually easier to have that conversation about the value of science.

Whatever their understanding of physics, prospective donors can easily grasp the importance of the basic research that has enabled todays search for treatments and vaccines for COVID-19.

In a related manner, the COVID-19 pandemic changed the nature of the social interactions with potential donors, said Dick. In the past, wed host big events and parties, but now, the pivot to digital communication has really opened up new ways to connect with supporters. Those person-to-person video calls can actually enable more personal and deeper conversations, he said.

Perimeter was established in 1999, seeded with $100 million from Mike Lazaridis, the founder of the Blackberry smartphone pioneer Research In Motion. Bringing the public along as enthusiastic partners was always a requirement, said Dick. Mikes vision right at the beginning was world-class research, for sure, but he also wanted that message of foundational science baked into Perimeter from the very beginning.

As a result, Perimeter also offers classroom-ready educational resources used by teachers around the world, reaching millions of students.

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The Importance of Funding Quantum Physics, Even in a Pandemic - Inside Philanthropy

Note: For at least a while, based upon discussion with folks at Patheos, Ill be experimenting with a new approach to my blogging: Fewer posts, but longer. Well see how it works.

What follows here is inspired by and indebted to Chapter 5, Spacetime is Quantum, in Carlo Rovelli,Reality Is Not What It Seems: The Journey to Quantum Gravity, translated by Simon Carnell and Erica Segre (Penguin, 2017), 125-137:

Physics made enormous progress, almost literally unthinkable strides, in the twentieth century. Most of these strides can be grouped under two main headings: general relativity and quantum mechanics. From relativity which is essentially a theory of gravity, and which sees the reality around us as a continuum that is warped or curved by the objects in it flow such fields of inquiry as the study of black holes and gravitational waves, astrophysics, and cosmology. From quantum theory which views reality as an assemblage of discrete, particular packets or quanta we derive such things as atomic physics, nuclear physics, the study of elementary particles and of condensed matter, and a significant amount of cutting-edge technology. And each theory, general relativity and quantum mechanics, has passed test after confirming test. Both work extremely well

But there is a disturbing problem. Its not only that quantum theory is probabilistic, something that Albert Einstein absolutely loathed. (I, at any rate, am convinced that [God] does not throw dice, he wrote in a 1926 letter to Max Born. [Jedenfalls bin ich berzeugt, da der nicht wrfelt.])

The more fundamental issue is that the view of reality provided by the two theories, when theyre taken together (or, better, when scientists attempt to take them together), is schizophrenic. Theyre incompatible. As Rovelli, himself a prominent European theoretical physicist, puts it,

They cannot both be true, at least not in their present forms, because they appear to contradict each other. . . .

A university student attending lectures on general relativity in the morning, and others on quantum mechanics in the afternoon, might be forgiven for concluding that his professors are fools, or that they havent talked to each other for at least a century. In the morning, the world is a curved spacetime where everything is continuous; in the afternoon, the world is a flat one where discrete quanta of energy leap and interact. (125, italics in the original)

In most cases, the contradictions can be safely ignored. Microcosm and macrocosm are far enough apart that issues really dont arise. In studying the lunar orbit, for example, the Moon is so large that tiny quantum issues neednt be noticed. And atoms are too light to curve space significantly, so the overall curvature of spacetime described by general relativity plays no role worthy of attention.

But there are situations where both curvature of space and quantum granularity matter, and for these we do not yet have an established physical theory that works.

An example is the interior of black holes. Another is what happened to the universe during the Big Bang. In more general terms, we do not know how time and space behave at very small scale. In all these instances, todays theories become confused and no longer tell us anything reasonable: quantum mechanics cannot deal with the curvature of spacetime, and general relativity cannot account for quanta. (126)

For a non-physicist such as I, who will never make any significant contribution in this life toward bridging the gap, one obvious lesson can be drawn from the present state of things: humility. For all of our successes and technological marvels, there are enormous and fundamental things that still elude us. There is so much that we dont know!

Strikingly, though, Rovelli is not at all discouraged. In fact, he seems positively exuberant. He points out that a band of theoretical physicists scattered across five continents is laboriously seeking to solve the problem (127). He cites previous examples in the history of physics where massive contradictions have forced harmonizing breakthroughs. Newtons discovery of universal gravitation, for instance, came as he reconciled Galileos description of terrestrial motion with Keplers laws of motion for the heavens. Maxwell and Faraday combined what was known about electricity with what was known about magnetism in order to formulate the equations of electromagnetism. But there seemed to be a conflict between Maxwells equations on electromagnetism and Newtons mechanics; Einstein formulated special relativity to reconcile the two, and then, because his own special relativity had problems with Newtons mechanics, he discovered general relativity through his attempt to resolve those problems.

Theoretical physicists are thus only too happy when they discover a conflict of this type: it is an extraordinary opportunity. (127)

I myself would note that many fields of modern science seem to work fruitfully on the boundaries or borders between previously distinct disciplines (e.g., geophysics, biochemistry, biophysics, astrophysics, perhaps paleobotany, and so forth).

Rovellis discussion in these pages is not merely scientific but historical and, to an important extent, biographical. He concentrates particularly on two significant physicists of earlier generations. John Archibald Wheeler (1911-2008) is one of the two; he is discussed in a chapter section called, simply, John (132-136).For what its worth, among those who have contributed to my Latter-day Saint Scholars Testify websiteisB. Kent Harrison, who earned his doctorate at Princeton University, studying under Wheeler and with fellow students Masami Wakano and 2017 Nobel laureate Kip Thorne co-authoring a 1965 book with him onGravitation Theory and Gravitational Collapse:

The scientist who has most contributed to quantum gravity is John Wheeler, a legendary figure who has traversed the physics of the past century. A pupil of and contributor with Niels Bohr in Copenhagen; a collaborator with Einstein when Einstein moved to the United States; a teacher who can count among his students figures such as Richard Feynman . . . Wheeler was at the heart of the physics of the twentieth century. (133-134)

Before that, though, in a section simply called Matvei (128-131), Rovelli describes the contribution and the tragically short life of Matvei Bronstein (or Matvei Brontejn; ), and it is on him that I wish to concentrate here.

Matvei Bronstein wrote three books for children: Solar Matter ( ), X Rays ( X), and Inventors of Radio ( ). But he wasnt only a popularizer. He was atheoreticalphysicist who also authored works on astrophysics,semiconductors,quantum electrodynamics, andcosmology. Most directly relevant to Rovellis purposes, he was a pioneer in the field ofquantum gravity.

Matvei was a younger friend of Lev Landau the scientist who would go on to become the best theoretical physicist of the Soviet Union. Colleagues who knew them both would claim that, of the two, Matvei was the more brilliant. (128)

Heres the problem that Bronstein intuited, as described by Carlo Rovelli:

Energy makes space curve. A lot of energy means that space will curve a great deal. A lot of energy in a small region results in curving space so much that it collapses into a black hole, like a collapsing star. But if a particle plummets into a black hole, I can no longer see it. (129, italics in the original)

Perhaps, here, science has discovered that space itself is discontinuous, quantized, particular, granular, and has done so applying general relativity at the microcosmic level.

Modern physicists talk about Planck length,the minimum size of a particle before it falls into its own black hole (130), the smallest distance about which current experimentally corroborated models in physics can make any meaningful statement.At such small distances, the conventional laws of macro-physics no longer apply, and evenrelativistic physicsrequires special treatment. Rovelli contends that, in truth and justice, Planck length should be called Brontejn length, since it was Matvei Bronstein who identified it.

In numerical terms, it is equivalent to approximately one millionth of a billionth of a billionth of a billionth of a centimetre (10-33centimetres). So, that is to say . . . small.

It is at this extremely minute scale that quantum gravity manifests itself. To give an idea of the smallness of the scale we are discussing: if we enlarged a walnut shell until it had become as big as the whole observable universe, we would still not see the Planck length. Even after having been enormously magnified thus, it would still be a million times smaller than the actual walnut shell was before magnification. At this scale, space and time change their nature. They become something different; they become quantum space and time, and understanding what this means is the problem.

Matvei Brontejn understands all of this in the 1930s and writes two short and illuminating articles in which he points out that quantum mechanics and general relativity, taken together, are incompatible with our customary idea of space as an infinitely divisible continuum. (131)

Unfortunately, like his friend Lev Landau, Matvei Bronstein was a nave young idealist. He was really convinced that Communism would introduce a better world, without inequality and injustice. He believed incorrectly, as we now plainly see that Lenin was moving Russia toward that better world. When Stalin assumed power after Lenins death, however, both Matvei Bronstein and Lev Landau were disappointed and, eventually, horrified. Gently and cautiously, they dissented.

Landau suffered under Stalin, but survived. Matvei Bronstein was not so fortunate.

In August 1937, during Stalins Great Purge, Bronstein was arrested for disloyalty. In February 1938, he was convicted in a summary trial. Then, although his wife was told that he had been sentenced to ten years in a labor camp with no right of correspondence, he was executed later that same day. He was thirty-one years old.

Mattvei Bronsteins unjust early death was a painful loss to science. Who can possibly know what contributions he might have made? (Gloriously, though, his books for children were eventually republished after his reputation had been rehabilitated by Stalins successors and Soviet censors in 1957.)

Moreover, his case should certainly be counted among the enormous damages visited upon the world by Marxism and Communism indeed by socialism itself, which tends to lop off any and all heads that rise above the crowd or diverge from the mass, a tendency that Communism simply made more obvious and more violent. But it is also a specimen of the vast pain and injustice of this mortal world generally and an illustration of the desirability, if not the reality, of a world beyond this one, in which oppression will be abolished, wrongs wil be righted, injustices will be recompensed, and there will be no obstacles to delighted learning and progress, and in which God shall wipe away all tears from [our] eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away (Revelation 21:4).

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Quantum Physics and Early Death | Dan Peterson - Patheos

One property of quantum mechanics is superposition, which explains how a system could be in multiple states at the same time until the instant it is observed or measured. A theoretical study suggests that this phenomenon affects high-precision clocks.

A team from Dartmouth College, Saint Anselm College, and Santa Clara University has conducted an inquiry on superposition and how it creates a correction in atomic clocks called "quantum time dilation." Their study, published in the journal Nature Communications on Friday, October 23, might reconcile Albert Einstein's predictions from the theory of relativity with new quantum effects beyond his theory about the properties of time.

(Photo: Ciacho5 via Wikimedia Commons)National Laboratory of Atomic, Molecular, and Optical Physics in Nicolaus Copernicus University in Toru (Poland). Part of the optical atomic clock.

"Whenever we have developed better clocks, we've learned something new about the world," shared Alexander Smith, who led the research as a junior fellow in Dartmouth's Society of Fellows. Smith also serves as an adjunct assistant professor at Dartmouth, as well as an assistant professor of physics with Saint Anselm College. He explains quantum time dilation as a consequence of both Einstein's relativity and quantum mechanics, offering a unique opportunity to examine physics at the intersection of these two "physics."

Albert Einstein is perhaps best known for his "theory of relativity," which is actually a combination of two interrelated theories - special and general relativity. These theories largely revolutionized classical physics and the theory of mechanics most defined by the works of Isaac Newton. Among its main propositions include spacetime as an entity made of both time and space. One of his experiments illustrated the time dilation - that a clock's time depends on the speed of its movement, making it relative. As it moves faster, the rate of its ticking starts to decrease. This largely differentiates from the linear and absolute nature of time proposed by Newton.

RELATED: 30 Things You Didn't Know About Einstein

On the other hand, quantum mechanics attempts to characterize the behavior of matter and energy at atomic and subatomic scales. It attempts to explain phenomena that are either not covered, or directly in contrast, with predictions from classical physics. While relativity remains mostly classical, mainly because it maintains causality - or the relationship between cause and effect - quantum mechanics does not. Under the context of quantum mechanics, a clock could move as if it simultaneously moves at two different speeds or a superposition.

To arrive at the quantum time dilation theory, researchers combined modern methods derived from works in quantum information science together with a work from the 1980s, suggesting how time might be characterized by a quantum theory of gravity.

"Physicists have sought to accommodate the dynamical nature of time in quantum theory for decades," explained Mehdi Ahmadi, co-author of the study and a lecturer with Santa Clara University. In their work, they predicted possible corrections to relativistic time dilation coming from the fact that clocks used to observe this behavior are in the context of quantum mechanics.

RELATED: New Measurement Technology Paves Way For Nuclear Clocks

The clock they refer to in their model does not work by mechanical parts or oscillators used in conventional timekeeping devices. If an atom exhibits superposition, moving at different velocities simultaneously, its lifetime will change - either increasing or decreasing - depending on the nature of the superimposed system relative to a reference atom at a defined speed.

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A New Timekeeping Theory Reconciles Einstein's Relativity and Quantum Clocks - Science Times

The Australian materials technology company said its latest development work on its 12CQ cubit chip modelling, directly addressed a key area of priority to accelerate the development of quantum computing globally.

() (OTCMKTS:ARRXF) (FRA:38A) is very well aligned with the strategic direction of the US in the field of quantum computing.

The Australian materials technology company said its latest development work on its 12CQ qubit chip modelling, directly addresseda key area of priority to accelerate the development of quantum computing globally.

Archer is developing the12CQ chip for quantum computing operation at room-temperature and integration on-board modern electronic devices.

Archer Materials chief executive officer Dr Mohammad Choucair said: "The US is taking significant action in growing the quantum technology industry in America, and in maintaining its global leadership position.

This gives Archer and its shareholders confidence moving forward with our strategy, aswe work with global giants like IBMto realise our innovative quantum computing deep tech.

Archer is a member of the International Business Machines Corporation (IBM) () (LON:IBM)Q Network.

As part of anagreement with the global IT giant, it plans to use IBMs Qiskit quantum development platform as the software stack for its12CQ qubit processors.

US makes quantum technology critical priorityThe UShas made it clear that several quantum technology areas remain in an early phase of development, including quantum computing, where the engineering of a core technology is relatively immature.

It is therefore taking significant action to strengthen investments in quantum tech and prepare a quantum-ready workforce.It has made quantum technology a critical priority for ensuring Americas long-term economic prosperity and national security.

Harnessing the novel properties of quantum physics has the potential to yield transformative new technologies, such as quantum computers, quantum sensors, and quantum networks.

The newquantum.govwebsite provides centralised information and reports detailing leading indicators of success in the quantum technology ecosystem, pointing to specific goals and focused efforts in the short term (5 years) and in the longer term (20 years) being made in the US.

Earlier this month, Archer Materials announced the development of a computational quantum mechanical theory that accurately models the behaviour of the qubit material at the core of Archers 12CQ quantum computing qubit processor (chip).

The computational models validate the origins of experimentally observed quantum phenomena in the qubit material and allow Archer to predict future quantum behaviour.

Choucair said: In the global multi-billion-dollar quantum computing ecosystem, this type of theoretical validation is a technological prerequisite and demonstrates that Archer operates under a high degree of certainty in its qubit chip development.

We can now accurately predict the 12CQ qubit materials future behaviour, performance, and overcome potential limitations in device operation from an early stage, to drastically reduce technological risk and assist in moving forward with our partners.

Archer is working with world-leading theoretical physicists at the prestigious research institute cole Polytechnique Fdrale de Lausanne, Switzerland (EPFL), to computationally model Archers unique qubit material.

The results of the work validate Archers global competitive advantage in quantum computing processor technology development.

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Archer Materials well-aligned with strategic direction of the US in quantum computing - Proactive Investors Australia

Have you ever been in more than one place at the same time? If you are much bigger than an atom, the answer will be no.

But atoms and particles are governed by the rules of quantum mechanics, in which several different possible situations can coexist at once. Quantum systems are ruled by what is called a wave function: a mathematical object that describes the probabilities of these different possible situations.

And these different possibilities can coexist in the wave function as what is called a superposition of different states. For example, a particle existing in several different places at once is what we call spatial superposition.

It is only when a measurement is carried out that the wave function collapses and the system ends up in one definite state.

Generally, quantum mechanics applies to the tiny world of atoms and particles. The jury is still out on what it means for large-scale objects.

In our research, published in Optica, we propose an experiment that may resolve this thorny question once and for all.

In the 1930s, Austrian physicist Erwin Schrdinger came up with his famous thought experiment about a cat in a box which, according to quantum mechanics, could be alive and dead at the same time.

In it, a cat is placed in a sealed box in which a random quantum event has a 5050 chance of killing it. Until the box is opened and the cat is observed, the cat is both dead and alive at the same time.

In other words, the cat exists as a wave function (with multiple possibilities) before it is observed. When it is observed, it becomes a definite object.

After much debate, the scientific community at the time reached a consensus with the Copenhagen interpretation. This basically says quantum mechanics can only apply to atoms and molecules, but cannot describe much larger objects.

Turns out they were wrong.

In the past two decades or so, physicists have created quantum states in objects made of trillions of atoms large enough to be seen with the naked eye. Although, this has not yet included spatial superposition.

But how does the wave function become a real object? This is what physicists call the quantum measurement problem. It has puzzled scientists and philosophers for about a century.

If there is a mechanism that removes the potential for quantum superposition from large-scale objects, it would require somehow disturbing the wave function and this would create heat.

If such heat is found, this implies large-scale quantum superposition is impossible. If such heat is ruled out, then its likely nature doesnt mind being quantum at any size.

If the latter is the case, with advancing technology we could put large objects, maybe even sentient beings, into quantum states.

Physicists do not know what a mechanism preventing large-scale quantum superpositions would look like. According to some, it is an unknown cosmological field. Others suspect gravity could have something to do with it.

This years Nobel Prize winner for physics, Roger Penrose, thinks it could be a consequence of living beings consciousness.

Over the past decade or so, physicists have been feverishly seeking a trace amount of heat which would indicate a disturbance in the wave function.

To find this out, we would need a method that can suppress (as perfectly as is possible) all other sources of excess heat that may get in the way of an accurate measurement. We would also need to keep an effect called quantum backaction in check, in which the act of observing itself creates heat.

In our research, we have formulated such an experiment, which could reveal whether spatial superposition is be possible for large-scale objects. The best experiments thus far have not been able to achieve this.

Our experiment would use resonators at much higher frequencies than have been used. This would remove the issue of any heat from the fridge itself.

As was the case in previous experiments, we would need to use a fridge at 0.01 degrees kelvin above absolute zero. (Absoloute zero is the lowest temperature theoretically possible).

With this combination of very low temperatures and very high frequencies, vibrations in the resonators undergo a process called Bose condensation.

You can picture this as the resonator becoming so solidly frozen that heat from the fridge cant wiggle it, not even a bit.

We would also use a different measurement strategy that doesnt look at the resonators movement at all, but rather the amount of energy it has. This method would strongly suppress backaction heat, too.

Single particles of light would enter the resonator and bounce back and forth a few million times, absorbing any excess energy. They would eventually leave the resonator, carrying the excess energy away.

By measuring the energy of the light particles coming out, we could determine if there was heat in the resonator.

If heat was present, this would indicate an unknown source (which we didnt control for) had disturbed the wave function. And this would mean its impossible for superposition to happen at a large scale.

The experiment we propose is challenging. It is not the kind of thing you can casually set up on a Sunday afternoon. It may take years of development, millions of dollars and a whole bunch of skilled experimental physicists.

Nonetheless, it could answer one of the most fascinating questions about our reality: is everything quantum? And so, we certainly think it is worth the effort.

As for putting a human, or cat, into quantum superposition there is really no way for us to know how this would effect that being.

Luckily, this is a question we do not have to think about, for now.

Stefan Forstner is a Postdoctoral Research Fellow at the The University of Queensland.

This article first appeared on The Conversation.

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Could Schrdingers cat exist in real life? We propose an experiment to find out - Scroll.in

Quantum computersare machines that use the properties of quantum physics to store data and perform calculations based on the probability of an objects state before it is measured. This can be extremely advantageous for certain tasks where they could vastlyoutperform even the best supercomputers.

Quantum computers canprocess massive and complex datasetsmore efficiently than classical computers. They use the fundamentals of quantum mechanics to speed up the process of solving complex calculations. Often, these computations incorporate a seemingly unlimited number of variables and the potential applications span industries from genomics to finance.

Classic computers, which include smartphones and laptops, carry out logical operations using the definite position of a physical state. They encode information in binary bits that can either be 0s or 1s. In quantum computing, operations instead use the quantum state of an object to produce the basic unit of memory called as a quantum bit or qubit. Qubits are made using physical systems, such as the spin of an electron or the orientation of a photon. These systems can be in many different arrangements all at once, a property known as quantum superposition. Qubits can also be inextricably linked together using a phenomenon called quantum entanglement. The result is that a series of qubits can represent different things simultaneously. These states are the undefined properties of an object before theyve been detected, such as the spin of an electron or the polarization of a photon.

Instead of having a clear position, unmeasured quantum states occur in a mixed superposition that can be entangled with those of other objects as their final outcomes will be mathematically related even. The complex mathematics behind these unsettled states of entangled spinning coins can be plugged into special algorithms to make short work of problems that would take a classical computer a long time to work out.

American physicist andNobel laureate Richard Feynmangave a note about quantum computers as early as 1959. He stated that when electronic components begin to reach microscopic scales, effects predicted by quantum mechanics occur, which might be exploited in the design of more powerful computers.

During the 1980s and 1990s, the theory of quantum computers advanced considerably beyond Feynmans early speculation. In 1985,David Deutschof the University of Oxford described the construction of quantum logic gates for a universal quantum computer.Peter Shor of AT&T devised an algorithmto factor numbers with a quantum computer that would require as few as six qubits in 1994. Later in 1998, Isaac Chuang of Los Alamos National Laboratory, Neil Gershenfeld of Massachusetts Institute of Technology (MIT) and Mark Kubince of the University of Californiacreated the first quantum computerwith 2 qubits, that could be loaded with data and output a solution.

Recently, Physicist David Wineland and his colleagues at the US National Institute for Standards and Technology (NIST) announced that they havecreated a 4-qubit quantum computerby entangling four ionized beryllium atoms using an electromagnetic trap. Today, quantum computing ispoised to upend entire industriesstarting from telecommunications to cybersecurity, advanced manufacturing, finance medicine and beyond.

There are three primary types of quantum computing. Each type differs by the amount of processing power (qubits) needed and the number of possible applications, as well as the time required to become commercially viable.

Quantum annealing is best for solving optimization problems. Researchers are trying to find the best and most efficient possible configuration among many possible combinations of variables.

Volkswagen recently conducted a quantum experiment to optimize traffic flows in the overcrowded city of Beijing, China. The experiment was run in partnership with Google and D-Wave Systems. Canadian company D-Wave developed quantum annealer. But, it is difficult to tell whether it actually has any real quantumness so far. The algorithm could successfully reduce traffic by choosing the ideal path for each vehicle.

Quantum simulations explore specific problems in quantum physics that are beyond the capacity of classical systems. Simulating complex quantum phenomena could be one of the most important applications of quantum computing. One area that is particularly promising for simulation is modeling the effect of a chemical stimulation on a large number of subatomic particles also known as quantum chemistry.

Universal quantum computers are the most powerful and most generally applicable, but also the hardest to build. Remarkably, a universal quantum computer would likely make use of over 100,000 qubits and some estimates put it at 1M qubits. But to the disappointment, the most qubits we can access now is just 128. The basic idea behind the universal quantum computer is that you could direct the machine at any massively complex computation and get a quick solution. This includes solving the aforementioned annealing equations, simulating quantum phenomena, and more.

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Every Thing You Need to Know About Quantum Computers - Analytics Insight

Scientists have discovered the fastest possible speed of sound, a zippy 22 miles (36 kilometers) per second.

Sound waves move at different speeds in solids, liquids and gases, and within those states of matter for instance, they travel faster in warmer liquids compared with colder ones. Physicist Kostya Trachenko of Queen Mary University of London and his colleagues wanted to figure out the upper limits of how fast sound could travel.

This exercise was largely theoretical: The researchers found that the answer, which is about twice as fast as sound moves through solid diamond, depends on some fundamental numbers in the universe. The first is the fine structure constant, which is a number that describes the electromagnetic force that holds together elementary particles such as electrons and protons. (It happens to be approximately 1/137.) The second is the proton-to-electron mass ratio of a material, which, as it sounds, is the ratio of mass from protons and mass from electrons within the atomic structure of the material.

Related: In photos: Large numbers that define the universe

It's not possible to test this theoretical top speed in the real world, because the math predicts that sound moves at its top speed in the lowest-mass atoms. The lowest-mass atom is hydrogen, but hydrogen isn't solid unless it's under super-duper pressure that's a million times stronger than that of Earth's atmosphere. That might happen at the core of a gas giant like Jupiter, but it doesn't happen anywhere nearby where scientific testing is possible.

So instead, Trachenko and his colleagues turned to quantum mechanics and math to calculate what would happen to sound zipping through a solid atom of hydrogen. They found that sound could travel close to the theoretical limit of 79,200 mph (127,460 km/h), confirming their initial calculations. In contrast, the speed of sound in air is roughly 767 mph (1,235 km/h).

The movement of sound in such extreme and specific environments may seem unimportant, but because sound waves are traveling vibrations of molecules, the speed of sound is related to many other properties of materials, such as the ability to resist stress, study co-author Chris Pickard, a materials scientist at the University of Cambridge, said in a statement. Thus, understanding the fundamentals of sound could help illuminate other fundamental properties of materials in extreme circumstances, Trachenko added in the statement.

For instance, previous research has suggested that solid atomic hydrogen could be a superconductor. So knowing its fundamental properties could be important for future superconductivity research. Sound could also reveal more about the hot mix of quarks and gluons that made up the universe an instant after the Big Bang, and could be applied to the strange physics around the gravity wells that are black holes. (Other researchers have studied "sonic black holes" to gather insight into these cosmic objects.)

"We believe the findings of this study could have further scientific applications by helping us to find and understand limits of different properties, such as viscosity and thermal conductivity, relevant for high-temperature superconductivity, quark-gluon plasma, and even black hole physics," Trachenko said.

The researchers reported their findings Oct. 9 in the journal Science Advances.

Originally published on Live Science.

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Physicists clock the fastest possible speed of sound - Live Science

Work type:Full-timeDepartment:Department of Physics (25600)Categories:Academic-related Staff, Research Support Staff

Applications are invited for appointment asPost-doctoral Fellow in the Department of Physics(Ref.: 502419) to commence as soon as possible for one year, with the possibility of renewal subject to satisfactory performance.

Applicants should possess a Ph.D. degree in Physics or equivalent, and be able to demonstrate a strong research track record including refereed publications in top journals.They should have excellent communication skills, interpersonal skills and research leadership, the ability to work independently and in a team, and supervise Ph.D. students. Applicants with experience in multi-wavelength data analysis from radio to gamma rays (e.g. Chandra, XMM, Swift, AstroSat, HXMT, FAST, GMRT), space-astronomy missions and large ground based facilities in terms of winning telescope time, and publishing related papers as well as expertise in gamma-ray astronomy, both with ground-based (e.g. MAGIC, HAWC) and space-based (e.g. Fermi-LAT) instruments would have an advantage. The appointee will conduct research in collaboration with the Laboratory for Space Research (LSR). He/She will work with Dr. Pablo Saz Parkinson, Dr. Stephen C.Y. Ng and other members of the Department and LSR to pursue research in areas primarily related but not necessarily limited to neutron stars, pulsar wind nebulae, supernova remnants, gravitational waves, searches for electromagnetic counterparts of gravitational wave events, multi-wavelength, radio, X-ray, and gamma-ray data analysis.Enquiries about the post should be sent to Dr. Saz Parkinson atpablosp@hku.hk.

The Department of Physics is committed to excellence in teaching and research.There are five major areas of research in the Department, including Astronomy and Astrophysics, Atomic, Optical and Quantum Physics Group, Experimental Condensed Matter and Material Science Group, Theoretical and Computational Condensed Matter Group, and the Experimental Nuclear and Particle Physics Group.LSR is a multidisciplinary research group under the Faculty of Science at the University of Hong Kong. Information about the Department of Physicsand LSRcan be obtained athttps://www.physics.hku.hkandhttps://www.lsr.hku.hkrespectively.

A highly competitive salary commensurate with qualifications and experience will be offered, in addition to annual leave and medical benefits. At current rates, salaries tax does not exceed 15% of gross income.

The University only accepts online application for the above post. Applicants should apply online and upload a cover letter, an up-to-date C.V., a detailed publication list and a research proposal.Review of applications will commence as soon as possible and continue untilDecember 31, 2020, or until the post is filled, whichever is earlier.

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Post-doctoral Fellow, Department of Physics job with THE UNIVERSITY OF HONG KONG | 230760 - Times Higher Education (THE)