From Science News: “Trapping atoms in a laser beam offers a new way to measure gravity”

From Science News

November 7, 2019
Maria Temming

The technique can measure slight gravitational variations, which could help in mapping terrain.

A new type of experiment to measure the strength of gravity uses atoms suspended in laser light (with the machinery pictured above), rather than free-falling atoms. V. Xu.

By watching how atoms behave when they’re suspended in midair, rather than in free fall, physicists have come up with a new way to measure Earth’s gravity.

Traditionally, scientists have measured gravity’s influence on atoms by tracking how fast atoms tumble down tall chutes. Such experiments can help test Einstein’s theory of gravity and precisely measure fundamental constants (SN: 4/12/18). But the meters-long tubes used in free-fall experiments can be unwieldy and difficult to shield from environmental interference such as stray magnetic fields. With a new tabletop setup, physicists can gauge the strength of Earth’s gravity by monitoring atoms suspended a couple millimeters in the air by laser light.

This redesign, described in the Nov. 8 Science, could better probe the gravitational forces exerted by small objects. The technique also could be used to measure slight gravitational variations at different places in the world, which may help in mapping the seafloor or finding oil and minerals underground (SN: 2/12/08).

Physicist Victoria Xu and colleagues at the University of California, Berkeley began by launching a cloud of cesium atoms into the air and using flashes of light to split each atom into a superposition state. In this weird quantum limbo, each atom exists in two places at once: one version of the atom hovering a few micrometers higher than the other. Xu’s team then trapped these split cesium atoms in midair with light from a laser.

Got you, atom. To measure gravity, physicists split atoms into a weird quantum state called superposition — where one version of the atom is slightly higher than the other (blue dots connected by vertical yellow bands in this illustration). The researchers trap these atoms in midair using laser light (horizontal blue bands). While held in the light, each version of a single atom behaves slightly differently, due to their different positions in Earth’s gravitational field. Measuring those differences allows physicists to determine the strength of Earth’s gravity at that location.

Measuring the strength of gravity with atoms that are held in place, rather than being tugged downward by a gravitational field, requires tapping into the atoms’ wave-particle duality (SN: 11/5/10). That quantum effect means that, much as light waves can act like particles called photons, atoms can act like waves. And for each cesium atom caught in superposition, the higher version of the atom wave undulates a little faster than its lower counterpart, due to the atoms’ slightly different positions in Earth’s gravitational field. By tracking how fast the waviness of the two versions of an atom gets out of sync, physicists can calculate the strength of Earth’s gravity at that spot.

“Very impressive,” says physicist Alan Jamison of MIT. To him, one big promise of the new technique is more controlled measurements. “It’s quite a challenge to work on these drop experiments, where you have a 10-meter-long tower,” he says. “Magnetic fields are hard to shield, and the environment produces them all over the place — all the electrical systems in your building, and so forth. Working in a smaller volume makes it easier to avoid those environmental noises.”

More compact equipment can also measure shorter-range gravity effects, says study coauthor Holger Müller. “Let’s say you don’t want to measure the gravity of the entire Earth, but you want to measure the gravity of a small thing, such as a marble,” he says. “We just need to put the marble close to our atoms [and hold it there]. In a traditional free-fall setup, the atoms would spend a very short time close to our marble — milliseconds — and we would get much less signal.”

Physicist Kai Bongs of the University of Birmingham in England imagines using the new kind of atomic gravimeter to investigate the nature of dark matter or test a fundamental facet of Einstein’s theory of gravity called the equivalence principle (SN: 4/28/17). Many unified theories of physics proposed to reconcile quantum mechanics and Einstein’s theory of gravity — which are incompatible — violate the equivalence principle in some way. “So looking for violations might guide us to the grand unified theory,” he says. “That’s one of the Holy Grails in physics.”

See the full article here .

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From MIT News: “Chemists observe “spooky” quantum tunneling”

From MIT News

November 4, 2019
Anne Trafton

MIT chemists have observed, for the first time, inversion of the umbrella-like ammonia molecule by quantum tunneling. Image: Chelsea Turner, MIT.

Extremely large electric fields can prevent umbrella-shaped ammonia molecules from inverting.

A molecule of ammonia, NH3, typically exists as an umbrella shape, with three hydrogen atoms fanned out in a nonplanar arrangement around a central nitrogen atom. This umbrella structure is very stable and would normally be expected to require a large amount of energy to be inverted.

However, a quantum mechanical phenomenon called tunneling allows ammonia and other molecules to simultaneously inhabit geometric structures that are separated by a prohibitively high energy barrier. A team of chemists that includes Robert Field, the Robert T. Haslam and Bradley Dewey Professor of Chemistry at MIT, has examined this phenomenon by using a very large electric field to suppress the simultaneous occupation of ammonia molecules in the normal and inverted states.

“It’s a beautiful example of the tunneling phenomenon, and it reveals a wonderful strangeness of quantum mechanics,” says Field, who is one of the senior authors of the study.

Heon Kang, a professor of chemistry at Seoul National University, is also a senior author of the study, which appears this week in the Proceedings of the National Academy of Sciences. Youngwook Park and Hani Kang of Seoul National University are also authors of the paper.

Suppressing inversion

The experiments, performed at Seoul National University, were enabled by the researchers’ new method for applying a very large electric field (up to 200,000,000 volts per meter) to a sample sandwiched between two electrodes.

This assembly is only a few hundred nanometers thick, and the electric field applied to it generates forces nearly as strong as the interactions between adjacent molecules.

“We can apply these huge fields, which are almost the same magnitude as the fields that two molecules experience when they approach each other,” Field says. “That means we’re using an external means to operate on an equal playing field with what the molecules can do themselves.”

This allowed the researchers to explore quantum tunneling, a phenomenon often used in undergraduate chemistry courses to demonstrate one of the “spookinesses” of quantum mechanics, Field says.

As an analogy, imagine you are hiking in a valley. To reach the next valley, you need to climb a large mountain, which requires a lot of work. Now, imagine that you could tunnel through the mountain to get to the next valley, with no real effort required. This is what quantum mechanics allows, under certain conditions. In fact, if the two valleys have exactly the same shape, you would be simultaneously located in both valleys.

In the case of ammonia, the first valley is the low-energy, stable umbrella state. For the molecule to reach the other valley — the inverted state, which has exactly the same low-energy — classically it would need to ascend into a very high-energy state. However, quantum mechanically, the isolated molecule exists with equal probability in both valleys.

Under quantum mechanics, the possible states of a molecule, such as ammonia, are described in terms of a characteristic energy level pattern. The molecule initially exists in either the normal or inverted structure, but it can tunnel spontaneously to the other structure. The amount of time required for that tunneling to occur is encoded in the energy level pattern. If the barrier between the two structures is high, the tunneling time is long. Under certain circumstances, such as application of a strong electric field, tunneling between the regular and inverted structures can be suppressed.

For ammonia, exposure to a strong electric field lowers the energy of one structure and raises the energy of the other (inverted) structure. As a result, all of the ammonia molecules can be found in the lower energy state. The researchers demonstrated this by creating a layered argon-ammonia-argon structure at 10 kelvins. Argon is an inert gas which is solid at 10 K, but the ammonia molecules can rotate freely in the argon solid. As the electric field is increased, the energy states of the ammonia molecules change in such a way that the probabilities of finding the molecules in the normal and inverted states become increasingly far apart, and tunneling can no longer occur.

This effect is completely reversible and nondestructive: As the electric field is decreased, the ammonia molecules return to their normal state of being simultaneously in both wells.

“This manuscript describes a burgeoning frontier in our ability to tame molecules and control their underlying dynamics,” says Patrick Vaccaro, a professor of chemistry at Yale University who was not involved in the study. “The experimental approach set forth in this paper is unique, and it has enormous ramifications for future efforts to interrogate molecular structure and dynamics, with the present application affording fundamental insights into the nature of tunneling-mediated phenomena.”

Lowering the barriers

For many molecules, the barrier to tunneling is so high that tunneling would never happen during the lifespan of the universe, Field says. However, there are molecules other than ammonia that can be induced to tunnel by careful tuning of the applied electric field. His colleagues are now working on exploiting this approach with some of those molecules.

“Ammonia is special because of its high symmetry and the fact that it’s probably the first example anybody would ever discuss from a chemical point of view of tunneling,” Field says. “However, there are many examples where this could be exploited. The electric field, because it’s so large, is capable of acting on the same scale as the actual chemical interactions,” offering a powerful way of externally manipulating molecular dynamics.

The research was funded by the Samsung Science and Technology Foundation and the National Science Foundation.

See the full article here .

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From Caltech: “Untangling Quantum Entanglement”

From Caltech

Caltech Magazine Fall 2019
Whitney Clavin

In Erwin Schrödinger’s famous thought experiment, a cat is trapped in a box with a bit of poison the release of which is controlled by a quantum process. The cat therefore exists in a quantum state of being both dead and alive until somebody opens the box and finds the cat either dead or alive.

The perplexing phenomenon of quantum entanglement is central to quantum computing, quantum networking, and the fabric of space and time.

The famous “Jim twins,” separated soon after birth in the 1940s, seemed to live parallel lives even though they grew up miles apart in completely different families. When they were reunited at the age of 39, they discovered many similarities between their life stories, including the names of their sons, wives, and childhood pets, as well as their preferences for Chevrolet cars, carpentry, and more.

A similar kind of parallelism happens at a quantum level, too. The electrons, photons, and other particles that make up our universe can become inextricably linked, such that the state observed in one particle will be identical for the other. That connection, known as entanglement, remains strong even across vast distances.

“When particles are entangled, it’s as if they are born that way, like twins,” says Xie Chen, associate professor of theoretical physics at Caltech. “Even though they might be separated right after birth, [they’ll] still look the same. And they grow up having a lot of personality traits that are similar to each other.”

The phenomenon of entanglement was first proposed by Albert Einstein and colleagues in the 1930s. At that time, many questioned the validity of entanglement, including Einstein himself. Over the years and in various experiments, however, researchers have generated entangled particles that have supported the theory. In these experiments, researchers first entangle two particles and then send them to different locations miles apart. The researchers then measure the state of one particle: for instance, the polarization (or direction of vibration) of a photon. If that entangled photon displays a horizontal polarization, then so too will its faithful partner.

“It may be tempting to think that the particles are somehow communicating with each other across these great distances, but that is not the case,” says Thomas Vidick, a professor of computing and mathematical sciences at Caltech. “There can be correlation without communication.” Instead, he explains, entangled particles are so closely connected that there is no need for communication; they “can be thought of as one object.”

As baffling as the concept of two entangled particles may be, the situation becomes even more complex when more particles are involved. In natural settings such as the human body, for example, not two but hundreds of molecules or even more become entangled, as they also do in various metals and magnets, making up an interwoven community. In these many-body entangled systems, the whole is greater than the sum of its parts.

“The particles act together like a single object whose identity lies not with the individual components but in a higher plane. It becomes something larger than itself,” says Spyridon (Spiros) Michalakis, outreach manager of Caltech’s Institute for Quantum Information and Matter (IQIM) and a staff researcher. “Entanglement is like a thread that goes through every single one of the individual particles, telling them how to be connected to one another.”

Associate Professor of Theoretical Physics Xie Chen specializes in the fields of condensed matter physics and quantum information.

At Caltech, researchers are focusing their studies on many-body entangled systems, which they believe are critical to the development of future technologies and perhaps to cracking fundamental physics mysteries. Scientists around the world have made significant progress applying the principles of many-body entanglement to fields such as quantum computing, quantum cryptography, and quantum networks (collectively known as quantum information); condensed-matter physics; chemistry; and fundamental physics. Although the most practical applications, such as quantum computers, may still be decades off, according to John Preskill, the Richard P. Feynman Professor of Theoretical Physics at Caltech and the Allen V.C. Davis and Lenabelle Davis Leadership Chair of the Institute of Quantum Science and Technology (IQST), “entanglement is a very important part of Caltech’s future.”

Entanglement Passes Tests with Flying Colors

In 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen published a paper on the theoretical concept of quantum entanglement, which Einstein called “spooky action at a distance.” The physicists described the idea, then argued that it posed a problem for quantum mechanics, rendering the theory incomplete. Einstein did not believe two particles could remain connected to each other over great distances; doing so, he said, would require them to communicate faster than the speed of light, something he had previously shown to be impossible.

Today, experimental work leaves no doubt that entanglement is real. Physicists have demonstrated its peculiar effects across hundreds of kilometers; in fact, in 2017, a Chinese satellite named Micius sent entangled photons to three different ground stations, each separated by more than 1,200 kilometers, and broke the distance record for entangled particles.

Entanglement goes hand in hand with another quantum phenomenon known as superposition, in which particles exist in two different states simultaneously. Photons, for example, can display simultaneously both horizontal and vertical states of polarization.

Or, to simplify, consider two “entangled” quarters, each hidden under a cup. If two people, Bob and Alice, were each to take one of those quarters to a different room, the quarters would remain both heads and tails until one person lifted the cup and observed his or her quarter; at that point, it would randomly become either heads or tails. If Alice were to lift her cup first and her quarter was tails, then when Bob observed his quarter, it would also be tails. If you repeated the experiment and the coins are covered once more, they would go back to being in a state of superposition. Alice would lift her cup again and might find her quarter as heads this time. Bob would then also find his quarter as heads. Whether the first quarter is found to be heads or tails is entirely random.

Similarly, when a researcher entangles two photons and then sends each one in different directions under carefully controlled conditions, they will continue to be in a state of superposition, both horizontally and vertically polarized. Only when one of the photons is measured do both randomly adopt just one of the two possible polarization states.

“Quantum correlations are deeply different than ordinary correlations,” says Preskill. “And randomness is the key. This spooky intrinsic randomness is actually what bothered Einstein. But it is essential to how the quantum world works.”

“Scientists often use the word correlation to explain what is happening between these particles,” adds Oskar Painter, the John G Braun Professor of Applied Physics and Physics at Caltech. “But, actually, entanglement is the perfect word.”

Entanglement to the Nth Degree

Untangling the relationship between two entangled particles may be difficult, but the real challenge is to understand how hundreds of particles, if not more, can be similarly interconnected.

According to Manuel Endres, an assistant professor of physics at Caltech, one of the first steps toward understanding many-body entanglement is to create and control it in the lab. To do this, Endres and his team use a brute force approach: they design and build laboratory experiments with the goal of creating a system of 100 entangled atoms.

“This is fundamentally extremely difficult to do,” says Endres. In fact, he notes, it would be difficult even at a much smaller scale. “If I create a system where I generate, for instance, 20 entangled particles, and I send 10 one way and 10 another way, then I have to measure whether each one of those first 10 particles is entangled with each of the other set of 10. There are many different ways of looking at the correlations.”

While the task of describing those correlations is difficult, describing a system of 100 entangled atoms with classical computer bits would be unimaginably hard. For instance, a complete classical description of all the quantum correlations among as many as 300 entangled particles would require more bits than the number of atoms in the visible universe. “But that’s the whole point and the reason we are doing this,” Endres says. “Things get so entangled that you need a huge amount of space to describe the information. It’s a complicated beast, but it’s useful.”

“Generally, the number of parameters you need to describe the system is going to scale up exponentially,” says Vidick, who is working on mathematical and computational tools to describe entanglement. “It blows up very quickly, which, in general, is why it’s hard to make predictions or simulations, because you can’t even represent these systems in your laptop’s memory.”

To solve that problem, Vidick and his group are working on coming up with computational representations of entangled materials that are simpler and more succinct than models that currently exist.

“Quantum mechanics and the ideas behind quantum computing are forcing us to think outside the box,” he says.

A Fragile Ecosystem

Another factor in creating and controlling quantum systems has to do with their delicate nature. Like Mimosa pudica ,a member of the pea family also known as the “sensitive plant,” which droops when its leaves are touched, entangled states can easily disappear, or collapse, when the environment changes even slightly. For example, the act of observing a quantum state destroys it. “You don’t want to even look at your experiment, or breathe on it,” jokes Painter. Adds Preskill, “Don’t turn on the light, and don’t even dare walk into the room.”

The problem is that entangled particles become entangled with the environment around them quickly, in a matter of microseconds or faster. This then destroys the original entangled state a researcher might attempt to study or use. Even one stray photon flying through an experiment can render the whole thing useless.

“You need to be able to create a system that is entangled only with itself, not with your apparatus,” says Endres. “We want the particles to talk to one another in a controlled fashion. But we don’t want them to talk to anything in the outside world.”

In the field of quantum computing, this fragility is problematic because it can lead to computational errors. Quantum computers hold the promise of solving problems that classical computers cannot, including those in cryptography, chemistry, financial modeling, and more. Where classical computers use binary bits (either a “1” or a “0”) to carry information, quantum computers use “qubits,” which exist in states of “1” and “0” at the same time. As Preskill explains, the qubits in this mixed state, or superposition, would be both dead and alive, a reference to the famous thought experiment proposed by Erwin Schrödinger in 1935, in which a cat in a box is both dead and alive until the box is opened, and the cat is observed to be one or the other. What’s more, those qubits are all entangled. If the qubits somehow become disentangled from one another, the quantum computer would be unable to execute its computations.

To address these issues, Preskill and Alexei Kitaev (Caltech’s Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics and recipient of a 2012 Breakthrough Prize in Fundamental Physics), along with other theorists at Caltech, have devised a concept to hide the quantum information within a global entangled state, such that none of the individual bits have the answer. This approach is akin to distributing a code among hundreds of people living in different cities. No one person would have the whole code, so the code would be much less vulnerable to discovery.

Manuel Endres, assistant professor of physics, here pictured with Adam Shaw (left) and Ivaylo Madjarov (right), uses laser-based techniques in his lab to create many-body entanglement.

“The key to correcting errors in entangled systems is, in fact, entanglement,” says Preskill. “If you want to protect information from damage due to the extreme instability of superpositions, you have to hide the information in a form that’s very hard to get at,” he says. “And the way you do that is by encoding it in a highly entangled state.”

Spreading the Entanglement

At Caltech, this work on the development of quantum-computing systems is conducted alongside with research into quantum networks in which each quantum computer acts as a separate node, or connection point, for the whole system. Painter refers to this as “breaking a quantum computer into little chunks” and then connecting them together to create a distributed network. In this approach, the chunks would behave as if they were not separated. “The network would be an example of many-body entanglement, in which the bodies are the different nodes in the network,” says Painter.

Quantum networks would enhance the power of quantum computers, notes Preskill.

“We’d like to build bigger and bigger quantum computers to solve harder and harder problems. And it’s hard to build one piece of hardware that can handle a million qubits,” he says. “It’s easier to make modular components with 100 qubits each or something like that. But then, if you want to solve harder problems, you’ve got to get these different little quantum computers to communicate with one another. And that would be done through a quantum network.”

Quantum networks could also be used for cryptography purposes, to make it safer to send sensitive information; they would also be a means by which to distribute and share quantum information in the same way that the World Wide Web works for conventional computers. Another future use might be in astronomy. Today’s telescopes are limited. They cannot yet see any detail on, for instance, the surface of distant exoplanets, where astronomers might want to look for signs of life or civilization. If scientists could combine telescopes into a quantum network, it “would allow us to use the whole Earth as one big telescope with a much-improved resolution,” says Preskill.

“Up until about 20 years ago, the best way to explore entanglement was to look at what nature gave us and try to study the exotic states that emerged,” notes Painter. “Now our goal is to try to synthesize these systems and go beyond what nature has given us.”

At the Root of Everything

While entanglement is the key to advances in quantum-information sciences, it is also a concept of interest to theoretical physicists, some of whom believe that space and time itself are the result of an underlying network of quantum connections.

“It is quite incredible that any two points in space-time, no matter how far apart, are actually entangled. Points in space-time that we consider closer to each other are just more entangled than those further apart,” says Michalkis.

The link between entanglement and space-time may even help solve one of the biggest challenges in physics: establishing a unifying theory to connect the macroscopic laws of general relativity (which describe gravity) with the microscopic laws of quantum physics (which describe how subatomic particles behave).

The quantum error-correcting schemes that Preskill and others study may play a role in this quest. With quantum computers, error correction ensures that the computers are sufficiently robust and stable. Something similar may occur with space-time. “The robustness of space may come from a geometry where you can perturb the system, but it isn’t affected much by the noise, which is the same thing that happens in stable quantum-computing schemes,” says Preskill.

“Essentially, entanglement holds space together. It’s the glue that makes the different pieces of space hook up with one another,” he adds.

At Caltech, the concept of entanglement connects various labs and buildings across campus. Theorists and experimentalists in computer science, quantum-information science, condensed-matter physics, and other fields regularly work across disciplines and weave together their ideas.

“We bring our ideas from condensed-matter physics to quantum-information folks, and we say, ‘Hey, I have a material you can use for quantum computation,’” says Chen. “Sometimes we borrow ideas from them. Many of us from different fields have realized that we have to deal with entanglement head-on.”

Preskill echoes this sentiment and is convinced entanglement is an essential part of Caltech’s future: “We are making investments and betting on entanglement as being one of the most important themes of 21st-century science.”

See the full article here .

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From Stanford University and SLAC: “Stanford developing a radio that searches for dark matter”

From Stanford University

and

SLAC National Accelerator Lab

The dark matter radio is a tabletop device that could explain the mysterious matter that makes up 85 percent of the mass of our universe. (Image credit: Harrison Truong)

September 25, 2019
Taylor Kubota

A team of Stanford University researchers are on a mission to identify dark matter once and for all. But first, they’ll need to build the world’s most sensitive radio.

“Dark matter is most of the matter in our universe. We don’t know what it is but we know it’s there because we can see its gravitational effects,” explained Peter Graham, an associate professor of physics in Stanford’s School of Humanities and Sciences and one of the leaders of this search for dark matter. “We also know it has to be made out of a totally different particle with different properties than anything we’ve ever found.”

Graham and Savas Dimopoulos, the Hamamoto Family Professor in physics at Stanford, have developed theories about dark matter that advocate for high-precision experiments focused on finding axions, theorized particles that are among the most likely candidates for dark matter. Their theories – once considered “interesting but out there,” according to Graham – are gaining popularity as other candidates for dark matter get ruled out and new technologies are making their exacting experiments possible. Now the Gordon and Betty Moore Foundation have granted Stanford researchers roughly $2.5 million to prototype a new kind of dark matter sensor.

Guided by Graham and Dimopoulos’ theories, Kent Irwin, a professor of physics, of particle physics and astrophysics and of photon science at Stanford and SLAC National Accelerator Laboratory, is building the Dark Matter Radio, which will search for the signal of axions the same way a standard AM radio picks up a broadcast. Like an AM radio station, axion dark matter has a precise frequency, but this frequency is unknown. Due to advances in quantum sensors, the radio will be much more sensitive than past dark matter experiments, and able to scan a large swath of the frequencies that are most likely to reveal axions.

Peter Graham and Kent Irwin are building a tabletop-sized device to detect dark matter. (Image credit: Harrison Truong)

“This project is a really beautiful example of people with very different expertise coming together to solve a hard problem,” said Risa Wechsler, director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) and professor of physics and of particle physics and astrophysics.

Risa Wechsler, professor of physics and of particle physics and astrophysics. (Image credit: Holly Hernandez)

“Dark matter is 85 percent of the mass in the universe and I think it’s very unlikely that we would exist without it. The exciting thing about this experiment is that it opens up so much discovery space that was previously inaccessible.”

Even if the researchers don’t find the axion, their work would have the distinction of searching a significant fraction of its possible frequency range. The researchers are also excited to see how their sensor development will contribute to spinoff applications in various fields.

The Dark Matter Radio

Dark matter makes up most of the mass in the universe, but each axion is theorized to have such a low mass – falling in the category of ultra-light dark matter – that it might spread out over kilometers. Quantum mechanics, which is the study of behavior of extremely small particles, contends that every particle also behaves like a wave. So, if axions do exist, they’re rippling all around us like a radio signal. The Dark Matter Radio team will scan for the frequency that carries the signal from the wave-like undulations of this ocean of overlapping axions.

The first trick is to convert axion waves into radio waves – carried out by a strong magnetic field inside the Dark Matter Radio. The Dark Matter Radio is also surrounded by a superconducting shield of niobium that blocks out regular radio signals, but will let axions through.

Even with all these enhancements, axions will give off a very weak signal. So, the radio’s tuning has to be incredibly sharp – the equivalent of a car radio that can detect stations separated by one one-millionth of a decimal place. As part of achieving this level of sensitivity and precision, Irwin is working with a new type of quantum sensor that is capable of picking up magnetic signals a hundred million trillion times smaller than what is produced by a typical refrigerator magnet.

“There’s been a breakthrough in the ability to control, create and manipulate quantum states in ways that allow us to take advantage of theory that’s been around for many decades,” said Irwin. “These are some of the same techniques that are being used to develop quantum computers. Instead of using them to compute, we can measure things much more sensitively and precisely than we could before, and the techniques we’re using will have broad applications.”

The same quantum sensors that the researchers are building into the radio could also enhance the precision of medical scanning techniques that measure the properties of magnetic and electric fields in the human body.

Beyond the whiteboard

So far, the researchers have successfully built a soda-can-sized prototype of the dark matter radio that works as an extra-sensitive AM radio. They are currently working on a larger version that will be able to scan all the frequencies of interest with enough sensitivity to measure axion dark matter.

“Most of the ideas that we theorists have fail before they ever get anywhere, so it was a big deal to see this crazy idea that we had on a whiteboard become a physical thing,” said Graham. “The experimentalists, like Kent, still have a lot of work ahead of them but for me, it feels like the culmination of so many years of work. The Dark Matter Radio is going to be real. It’s going to happen.”

See the full article here .

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SLAC/LCLS II projected view

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

Stanford University campus. No image credit

Stanford University

Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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From University of Vienna: “Quantum gravity’s tangled time”

From University of Vienna

22. August 2019

Scientific contact
Univ.-Prof. Mag. Dr. Caslav Brukner
Institute for Quantum Optics and Quantum Information Vienna
Universität Wien
1090 – Wien, Boltzmanngasse 5
+43-1-4277-725 82
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A pair of starships train for a mission. They are asked to fire at each other at a specified time, and immediately start their engines in order to dodge each other’s attack. If either of the ships fires too early, it will destroy the other, and this establishes an unmistakable time order between the firing events. If a powerful agent could place a sufficiently massive object, say a planet, closer to one ship it would slow down its counting of time. As a result, the ship farther away from the mass will fire too early for the first one to escape. © Magdalena Zych.

The theories of quantum mechanics and gravity are notorious for being incompatible, despite the efforts of scores of physicists over the past fifty years. However, recently an international team of researchers led by physicists from the University of Vienna, the Austrian Academy of Sciences as well as the University of Queensland (AUS) and the Stevens Institute of Technology (USA) have combined the key elements of the two theories describing the flow of time and discovered that temporal order between events can exhibit genuine quantum features.

According to general relativity, the presence of a massive object slows down the flow of time. This means that a clock placed close to a massive object will run slower as compared to an identical one that is further away.

However, the rules of quantum theory allow for any object to be prepared in a superposition state. A superposition state of two locations is different to placing an object in one or the other location randomly – it is another way for an object to exist, allowed by the laws of quantum physics.

One of the open questions in physics is: What happens when an object massive enough to influence the flow of time is placed in a quantum superposition state?

This is a controversial topic: some physicists claim that such scenarios are fundamentally impossible – some new mechanism must block the superposition from forming in the first place – while others develop entire theories based on the assumption that this is possible.

“We started by tackling a question: what would a clock measure if it was influenced by a massive object in a quantum superposition state?” explains Magdalena Zych from the University of Queensland.

The scientists were expecting to face the roadblocks making the scenario impossible, but surprisingly, using standard textbook physics they were able to exactly describe what happens.

They so discovered that when a massive object is placed in a quantum superposition in the vicinity of a set of clocks, their time order can become genuinely quantum, defying any classical description.

Caslav Brukner, coauthor from the University of Vienna and the Austrian Academy of Sciences added that the regime where quantum time order could arise is quite remote from our everyday experience, “but the most important insight from our work is that quantum time order is at all possible, and that it results in new physical effects.”

To illustrate what happens, imagine a pair of starships training for a mission. They are asked to fire at each other at a specified time, and immediately start their engines in order to dodge each other’s attack. If either of the ships fires too early, it will destroy the other, and this establishes an unmistakable time order between the firing events. If a powerful agent could place a sufficiently massive object, say a planet, closer to one ship it would slow down its counting of time. As a result, the ship farther away from the mass will fire too early for the first one to escape.

The laws of quantum physics and gravity predict that by manipulating a quantum superposition state of the planet, the ships can end up in a superposition of either of them being destroyed. Such a superposition state, involving two systems, is called entangled. The new work shows that the temporal order among events can exhibit superposition and entanglement – genuinely quantum features of particular importance for testing quantum theory against alternatives. The result can now be used as a theoretical testing ground for frameworks for quantum gravity, and thus help to move forward in formulating the correct theory of quantum gravity.

The study will also be relevant for future quantum technologies. Quantum computers that exploit quantum order of performing operations might beat devices that operate using only fixed sequences. Practical implementations of quantum temporal order do not require extreme conditions—such as planets in superposition—and can be simulated without the use of gravity. The discovery of quantum properties of time can lead to better quantum devices in the upcoming era of quantum computers.

Science paper:
Bell’s theorem for temporal order
Nature Communications

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The University of Vienna (German: Universität Wien) is a public university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is one of the oldest universities in the German-speaking world. With its long and rich history, the University of Vienna has developed into one of the largest universities in Europe, and also one of the most renowned, especially in the Humanities. It is associated with 15 Nobel prize winners and has been the academic home to a large number of scholars of historical as well as of academic importance.

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From UC Santa Barbara: “A Quantum Leap”

From UC Santa Barbara

September 16, 2019
James Badham

$25M grant makes UC Santa Barbara home to the nation’s first NSF-funded Quantum Foundry, a center for development of materials and devices for quantum information-based technologies.

Professors Stephen Wilson and Ania Bleszynski Jayich will co-direct the campus’s new Quantum Foundry

We hear a lot these days about the coming quantum revolution. Efforts to understand, develop, and characterize quantum materials — defined broadly as those displaying characteristics that can be explained only by quantum mechanics and not by classical physics — are intensifying.

Researchers around the world are racing to understand these materials and harness their unique qualities to develop revolutionary quantum technologies for quantum computing, communications, sensing, simulation and other quantum technologies not yet imaginable.

This week, UC Santa Barbara stepped to the front of that worldwide research race by being named the site of the nation’s first Quantum Foundry.

Funded by an initial six-year, $25-million grant from the National Science Foundation (NSF), the project, known officially as the UC Santa Barbara NSF Quantum Foundry, will involve 20 faculty members from the campus’s materials, physics, chemistry, mechanical engineering and computer science departments, plus myriad collaborating partners. The new center will be anchored within the California Nanosystems Institute (CNSI) in Elings Hall.

California Nanosystems Institute

The grant provides substantial funding to build equipment and develop tools necessary to the effort. It also supports a multi-front research mission comprising collaborative interdisciplinary projects within a network of university, industry, and national-laboratory partners to create, process, and characterize materials for quantum information science. The Foundry will also develop outreach and educational programs aimed at familiarizing students at all levels with quantum science, creating a new paradigm for training students in the rapidly evolving field of quantum information science and engaging with industrial partners to accelerate development of the coming quantum workforce.

“We are extremely proud that the National Science Foundation has chosen UC Santa Barbara as home to the nation’s first NSF-funded Quantum Foundry,” said Chancellor Henry T. Yang. “The award is a testament to the strength of our University’s interdisciplinary science, particularly in materials, physics and chemistry, which lie at the core of quantum endeavors. It also recognizes our proven track record of working closely with industry to bring technologies to practical application, our state-of-the-art facilities and our educational and outreach programs that are mutually complementary with our research.

“Under the direction of physics professor Ania Bleszynski Jayich and materials professor Stephen Wilson the foundry will provide a collaborative environment for researchers to continue exploring quantum phenomena, designing quantum materials and building instruments and computers based on the basic principles of quantum mechanics,” Yang added.

Said Joseph Incandela, the campus’s vice chancellor for research, “UC Santa Barbara is a natural choice for the NSF quantum materials Foundry. We have outstanding faculty, researchers, and facilities, and a great tradition of multidisciplinary collaboration. Together with our excellent students and close industry partnerships, they have created a dynamic environment where research gets translated into important technologies.”

“Being selected to build and host the nation’s first Quantum Foundry is tremendously exciting and extremely important,” said Rod Alferness, dean of the College of Engineering. “It recognizes the vision and the decades of work that have made UC Santa Barbara a truly world-leading institution worthy of assuming a leadership role in a mission as important as advancing quantum science and the transformative technologies it promises to enable.”

“Advances in quantum science require a highly integrated interdisciplinary approach, because there are many hard challenges that need to be solved on many fronts,” said Bleszynski Jayich. “One of the big ideas behind the Foundry is to take these early theoretical ideas that are just beginning to be experimentally viable and use quantum mechanics to produce technologies that can outperform classical technologies.”

Doing so, however, will require new materials.

“Quantum technologies are fundamentally materials-limited, and there needs to be some sort of leap or evolution of the types of materials we can harness,” noted Wilson. “The Foundry is where we will try to identify and create those materials.”

Research Areas and Infrastructure

Quantum Foundry research will be pursued in three main areas, or “thrusts”:

• Natively Entangled Materials, which relates to identifying and characterizing materials that intrinsically host anyon excitations and long-range entangled states with topological, or structural, protection against decoherence. These include new intrinsic topological superconductors and quantum spin liquids, as well as materials that enable topological quantum computing.

• Interfaced Topological States, in which researchers will seek to create and control protected quantum states in hybrid materials.

• Coherent Quantum Interfaces, where the focus will be on engineering materials having localized quantum states that can be interfaced with various other quantum degrees of freedom (e.g. photons or phonons) for distributing quantum information while retaining robust coherence.

Developing these new materials and assessing their potential for hosting the needed coherent quantum state requires specialized equipment, much of which does not exist yet. A significant portion of the NSF grant is designated to develop such infrastructure, both to purchase required tools and equipment and to fabricate new tools necessary both to grow and characterize the quantum states in the new materials, Wilson said.

UC Santa Barbara’s deep well of shared materials growth and characterization infrastructure was also a factor in securing the grant. The Foundry will leverage existing facilities, such as the large suite of instrumentation shared via the Materials Research Lab and the California Nanosystems Institute, multiple molecular beam epitaxy (MBE) growth chambers (the university has the largest number of MBE apparatuses in academia), unique optical facilities such as the Terahertz Facility, state-of-the-art clean rooms, and others among the more than 300 shared instruments on campus.

Data Science

NSF is keenly interested in both generating and sharing data from materials experiments. “We are going to capture Foundry data and harness it to facilitate discovery,” said Wilson. “The idea is to curate and share data to accelerate discovery at this new frontier of quantum information science.”

Industrial Partners

Industry collaborations are an important part of the Foundry project. UC Santa Barbara’s well-established history of industrial collaboration — it leads all universities in the U.S. in terms of industrial research dollars per capita — and the application focus that allows it to to transition ideas into materials and materials into technologies, was important in receiving the Foundry grant.

Another value of industrial collaboration, Wilson explained, is that often, faculty might be looking at something interesting without being able to visualize how it might be useful in a scaled-up commercial application. “If you have an array of directions you could go, it is essential to have partners to help you visualize those having near-term potential,” he said.

“This is a unique case where industry is highly interested while we are still at the basic-science level,” said Bleszynski Jayich. “There’s a huge industry partnership component to this.”

Among the 10 inaugural industrial partners are Microsoft, Google, IBM, Hewlett Packard Enterprises, HRL, Northrop Grumman, Bruker, SomaLogic, NVision, and Anstrom Science. Microsoft and Google have substantial campus presences already; Microsoft’s Quantum Station Q lab is here, and UC Santa Barbara professor and Google chief scientist John Martinis and a team of his Ph.D. student researchers are working with Google at its Santa Barbara office, adjacent to campus, to develop Google’s quantum computer.

Undergraduate Education

In addition, with approximately 700 students, UC Santa Barbara’s undergraduate physics program is the largest in the U.S. “Many of these students, as well as many undergraduate engineering and chemistry students, are hungry for an education in quantum science, because it’s a fascinating subject that defies our classical intuition, and on top of that, it offers career opportunities. It can’t get much better than that,” Bleszynski Jayich said.

Graduate Education Program

Another major goal of the Foundry project is to integrate quantum science into education and to develop the quantum workforce. The traditional approach to quantum education at the university level has been for students to take physics classes, which are focused on the foundational theory of quantum mechanics.

“But there is an emerging interdisciplinary component of quantum information that people are not being exposed to in that approach,” Wilson explained. “Having input from many overlapping disciplines in both hard science and engineering is required, as are experimental touchstones for trying to understand these phenomena. Student involvement in industry internships and collaborative research with partner companies is important in addressing that.”

“We want to introduce a more practical quantum education,” Bleszynski Jayich added. “Normally you learn quantum mechanics by learning about hydrogen atoms and harmonic oscillators, and it’s all theoretical. That training is still absolutely critical, but now we want to supplement it, leveraging our abilities gained in the past 20 to 30 years to control a quantum system on the single-atom, single-quantum-system level. Students will take lab classes where they can manipulate quantum systems and observe the highly counterintuitive phenomena that don’t make sense in our classical world. And, importantly, they will learn various cutting-edge techniques for maintaining quantum coherence.

“That’s particularly important,” she continued, “because quantum technologies rely on the success of the beautiful, elegant theory of quantum mechanics, but in practice we need unprecedented control over our experimental systems in order to observe and utilize their delicate quantum behavior.”

See the full article here .

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The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

#computer-science, #data-science, #nsf, #quantum-mechanics, #quantum-science, #ucsb

From Nature: “The bizarre logic of the many-worlds theory”

From Nature

02 September 2019
Robert P. Crease

Originating in the 1950s, the many-worlds theory posits that parallel worlds constantly branch off from each other, moment by moment.Credit: Shutterstock

Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime
Sean M Carroll Oneworld (2019)

At the beginning of Something Deeply Hidden, Sean M Carroll cites the tale of the fox and the grapes from Aesop’s Fables. A hungry fox tries to reach a bunch of grapes dangling from a vine. Finding them beyond his grasp, but refusing to admit failure, the fox declares the grapes to be inedible and turns away. That, Carroll declares, encapsulates how physicists treat the wacky implications of quantum mechanics.

Carroll wants that to stop. The fox can reach the grapes, he argues, with the many-worlds theory. Originated by US physicist Hugh Everett in the late 1950s, this envisions our Universe as just one of numerous parallel worlds that branch off from each other, nanosecond by nanosecond, without intersecting or communicating. (The many-worlds theory differs from the concept of the multiverse, which pictures many self-contained universes in different regions of space-time.)

Six decades on, the theory is one of the most bizarre yet fully logical ideas in human history, growing directly out of the fundamental principles of quantum mechanics without introducing extraneous elements. It has become a staple of popular culture, although the plots of the many films and television series inspired by it invariably flout the theory by relying on contact between the parallel worlds, as in the 2011 movie Another Earth.

In Something Deeply Hidden, Carroll cogently explains the many-worlds theory and its post-Everett evolution, and why our world nevertheless looks the way it does. Largely because of its purely logical character, Carroll calls Everett’s brainchild “the best view of reality we have”.

Catch a wave

Quantum mechanics is the basic framework of modern subatomic physics. It has successfully withstood almost a century of tests, including French physicist Alain Aspect’s experiments confirming entanglement, or action at a distance between certain types of quantum phenomena. In quantum mechanics, the world unfolds through a combination of two basic ingredients. One is a smooth, fully deterministic wave function: a mathematical expression that conveys information about a particle in the form of numerous possibilities for its location and characteristics. The second is something that realizes one of those possibilities and eliminates all the others. Opinions differ about how that happens, but it might be caused by observation of the wave function or by the wave function encountering some part of the classical world.

Many physicists accept this picture at face value in a conceptual kludge known as the Copenhagen interpretation, authored by Niels Bohr and Werner Heisenberg in the 1920s. But the Copenhagen approach is difficult to swallow for several reasons. Among them is the fact that the wave function is unobservable, the predictions are probabilistic and what makes the function collapse is mysterious.

Hugh Everett (second from right) originated the many-worlds theory. (Also pictured, left to right: Charles Misner, Hale Trotter, Niels Bohr and David Harrison.)Credit: Alan Richards/AIP Emilio Segre Visual Archives.

What are we to make of that collapsing wave? The equations work, but what the wave function ‘is’ is the key source of contention in interpreting quantum mechanics. Carroll outlines several alternatives to the Copenhagen interpretation, along with their advantages and disadvantages.

One option, the ‘hidden variables’ approach championed by Albert Einstein and David Bohm, among others, basically states that the wave function is just a temporary fix and that physicists will eventually replace it. Another tack, named quantum Bayesianism, or QBism, by Christopher Fuchs, regards the wave function as essentially subjective. Thus it is merely a guide to what we should believe about the outcome of measurements, rather than a name for a real feature of the subatomic world. Late in his life, Heisenberg proposed that we have to change our notion of reality itself. Reaching back to a concept developed by Aristotle — ‘potency’, as in an acorn’s potential to become an oak tree, given the right context — he suggested that the wave function represents an “intermediate” level of reality.

Carroll argues that the many-worlds theory is the most straightforward approach to understanding quantum mechanics. It accepts the reality of the wave function. In fact, it says that there is one wave function, and only one, for the entire Universe. Further, it states that when an event happens in our world, the other possibilities contained in the wave function do not go away. Instead, new worlds are created, in which each possibility is a reality. The theory’s sheer simplicity and logic within the conceptual framework of quantum mechanics inspire Carroll to call it the “courageous” approach. Don’t worry about those extra worlds, he asserts — we can’t see them, and if the many-worlds theory is true, we won’t notice the difference. The many other worlds are parallel to our own, but so hidden from it that they “might as well be populated by ghosts”.

Branching cats

For physicists, the theory is attractive because it explains many puzzles of quantum mechanics. With Erwin Schrödinger’s thought experiment concerning a dead-and-alive cat, for instance, the cats simply branch into different worlds, leaving just one cat-in-a-box per world. Carroll also shows that the theory offers simpler explanations of certain complex phenomena, such as why black holes emit radiation. Furthermore, the theory might help to develop still-speculative ideas about conundrums such as how to combine quantum mechanics with relativity theory.

Something Deeply Hidden is aimed at non-scientists, with a sidelong glance at physicists still quarrelling over the meaning of quantum mechanics. Carroll brings the reader up to speed on the development of quantum physics from Max Planck to the present, and explains why it is so difficult to interpret, before expounding the many-worlds theory. Dead centre in the book is a “Socratic dialogue” about the theory’s implications. This interlude, between a philosophically sensitive physicist and a scientifically alert philosopher, is designed to sweep away intuitive reservations that non-scientists might have.

Nevertheless, non-scientists might have lingering problems with Carroll’s breezy, largely unexamined ideas about “reality”. Like many physicists, he assumes that reality is whatever a scientific theory says it is. But what gives physicists a lock on this concept, and the right to say that the rest of us (not to mention, say, those in extreme situations such as refugees, soldiers and people who are terminally ill) are living through a less fundamental reality? Could it be that we have to follow Heisenberg’s lead? That is, must we rely on tools for talking about the complexities of reality that philosophers have developed over millennia to explain why the fox has such a tough time reaching those grapes?

What a wacky idea.

See the full article here .

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Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

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