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

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

The province said growth in the quantum technologies sector would help attract talent to the province, create long-term jobs, and help commercialize new technologies in areas like molecular chemistry, large-scale biological research, geological exploration, space technology and quantum satellite communications.

Diversifying our economy has never been more important, Schweitzer said.

Thats why we are investing in the U of Cs quantum technology project. Establishing Alberta as a leader in quantum technologies will give a competitive boost to our economy and create new jobs today and for the future.

Another $3.9 million will be dedicated for research on antimicrobial resistance, which is when bacteria or viruses stop responding as effectively to treatment. The research will support infection prevention and control strategies.

The other $4.9 million in funding, through the Research Capacity Program, will support U of CsSMILE-UVI satellite project.

The province said this funding would contribute to the international space mission. It would also fund research to study how space radiation impacts the upper atmosphere, industrial infrastructure, and technology in applications like enhanced GPS and satellite imaging in oil and gas mining.

That research is just critical for us in our diversification efforts, said Schweitzer.

So many of us can rattle off names of oil and gas companies, but many of us, were just starting to scratch the surface on our potential here when it comes to these emerging companies.

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Province gives $11.8M to U of C for quantum research, other projects - Calgary Herald

In China, I was fascinated by the use of electric scooters everywhere. Students were zipping past me at considerable speed, with tires making the only sound. At night, walking across campus could be a challenge. Like phantoms, people on dark scooters crossed my path unexpectedly, making me jump aside. They were reluctant to turn their lights on because it would use some of the battery power that they needed for travel.

And theres the problem. When you run low on gas, a 5-minute fill-up at a gas station will get you going again for a long time. Electric vehicles require a recharge, and depending on the kind of charger thats used, it can take hours. Batteries for electric cars are improving significantly, though. The latest lithium-ion types provide a range of more than 200 miles.

For those of us who are planning to build their own electric car, there are some choices. One could make do with a 100-mile range, using 14 standard lead-acid batteries. This comes with a substantial amount of weight, although it eliminates the need for a fuel system, exhaust pipes, and a transmission. A high-grade lithium-ion battery will double the range. Prices have been dropping continuously, currently at $156 per kilowatt-hour (kWh) according to Bloomberg New Energy Finance. This means that if you want the latest 68 kWh battery pack like the one used in the 2020 Nissan Leaf Plus, youll still pay $10,000 for that part alone. The engine-less 1971 VW Beetle body I have waiting to be converted into an electric car will probably be more modest. Classic Beetles have traditionally been near-impossible to heat and air-condition anyway, so theres no anticipation of electricity use by those two power-hungry consumers.

A new light on the horizon comes in the form of the quantum battery. This latest invention relies on quantum physics instead of chemical reactions like the current batteries. Essentially, the principle is based on the energy exchange between electrons and photons on the atomic scale. Quantum batteries dont lose power over time. Companies working on this innovation, including Tesla, Panasonic and Toyota, are tight-lipped about details and current status of the project. Dont expect to be able to buy a quantum battery at your local autoparts store soon. But it looks like a new, more powerful option for running electric vehicles may be coming.

Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenaus Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.

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Column: A new era of electric vehicles could be on the way - Gainesville Times