From Symmetry: “LHCb discovers matter-antimatter asymmetry in charm quarks”

From Symmetry

03/21/19
Sarah Charley

A new observation by the LHCb experiment finds that charm quarks behave differently than their antiparticle counterparts.

Artwork by Sandbox Studio, Chicago with Ana Kova

CERN/LHCb detector

Scientists on the LHCb experiment at the Large Hadron Collider at CERN have discovered a new way in which matter and antimatter behave differently.

With 99.9999 percent statistical certainty, LHCb scientists have observed a difference between the decays of matter and antimatter particles containing charm quarks. This discovery opens up a new realm to study the differences between matter and antimatter and could help explain why we live in a matter-dominated universe.

“This is a major breakthrough in experimental physics,” says Sheldon Stone, a professor at Syracuse University and collaborator on the LHCb experiment. “There’s been many attempts to make this measurement, but until now, no one had ever seen it. It’s a huge milestone in antimatter research.”

Every structure in the universe—from the tiniest speck of dust to the mightiest star—is built from matter. But there is an equally qualified material for the job: antimatter. Antimatter is nearly identical to matter, except that its charge and magnetic properties are reversed. Precision studies of antihydrogen atoms, for example, have shown that their characteristics are identical to hydrogen atoms to beyond the billionth decimal place.

Matter and antimatter cannot coexist in the same physical space because if they come into contact, they annihilate each other. This equal-but-opposite nature of matter and antimatter poses a conundrum for cosmologists, who theorize that the same amount of matter and antimatter should have exploded into existence during the birth of our universe. But if that’s true, all of that matter and antimatter should have annihilated one another, leaving nothing but energy behind.

Particle physicists are looking for any tiny differences between matter and antimatter which could help explain why matter won out over antimatter in the early universe.

Lucky for them, antimatter is not a totally extinct species. “We don’t usually see antimatter in our world,” says Ivan Polyakov, a postdoc at Syracuse University and internal LHCb reviewer for this new analysis. “But it can be produced when ordinary matter particles are smashed together at high energies, such as they do inside the Large Hadron Collider.”

The main way scientists study the tiny and rare particles produced during the LHC’s collisions is by mapping how they decay and transform into more-stable byproducts.

“This gives us a sort of family lineage for our ­particle of interest,” says Cesar da Silva, a scientist from Los Alamos National Lab and also a LHCb collaborator. “Once stable particles are measured by the detector, we can trace their ancestors to find the primordial generation of particles in the collision.

“Because of quantum mechanics, we cannot predict what each single unstable particle will decay into, but we can figure out the probabilities for each possible outcome.”

The new LHCb study looked at the decays of particles consisting of two bound quarks—the internal structural components of particles like protons and neutrons. One version of this particle (called D0 by scientists) contained a charm quark and the antimatter version of the up quark, called an anti-up quark. The other version contained the reverse, an up quark and an anti-charm quark.

Scientists on the LHCb experiment identified tens of millions of both D0 and anti-D0 particles and counted how many times each transformed into one set of byproducts (a pair of particles called pions) versus another possible set (a pair of particles called kaons).

With everything else being equal, the ratio of these two possible outcomes should have been identical for both D0 and anti-D0 particles. But scientists found that the two ratios differed by about a tenth of a percent—evidence that these charmed matter and antimatter particles are not totally interchangeable.

“They might look nearly identical from the outside, but they behave differently,” Polyakov says. “This is the puzzle of antimatter.”

The idea that matter and antimatter particles behave slightly differently is not new and has been observed previously in studies of particles containing strange quarks and bottom quarks. What makes this study unique is that it is the first time this asymmetry has been observed in particles containing charm quarks.

Previous experiments—including BaBar, Belle and CDF—endeavored to make this same measurement but fell short of collecting enough data to to tease out such a subtle effect.

SLAC BaBar

Belle II KEK High Energy Accelerator Research Organization Tsukuba, Japan

FNAL/Tevatron CDF detector

The huge amount of data generated since the start of LHC Run 2 combined with the introduction of more advanced methods to tag the particles of interest enabled scientists to collect enough matter and antimatter D0 particles to finally see these decay differences beyond a shadow of a doubt.

The next step is to see how this measurement fits with the theoretical models, which are still a little fuzzy on this prediction.

“Theorists will need to figure out if the Standard Model can explain this,” Stone says.

Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

“We’re pushing our field and this result will certainly be in the history books.”

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Symmetry is a joint Fermilab/SLAC publication.

From Griffith University via COSMOS Magazine: “Quantum tunnelling is instantaneous, researchers find”

From Griffith University

via

COSMOS Magazine

19 March 2019
Alan Duffy

Physicists establish that electrons waste no time bashing through a barrier.

A diagrammatic representation of quantum tunnelling. Normaals/Getty Images

Researchers have found that electrons passing through solid matter in a quantum process known as “tunnelling” do so instantaneously.

The finding, led by scientists from Australia’s Griffith University, contradicts previous experiments [Nature] that suggested a degree of time elapses between the start and finish of a tunnelling event.

The work is detailed in a paper in the journal Nature.

Quantum tunnelling is one of the more bizarre differences between our everyday, classical world and the surprising realm of quantum mechanics.

“If you lean on a wall, that wall pushes back in force so that you don’t go through it,” co-author Robert Sang says.

“But when you go down to the microscopic level, things behave quite differently. This is where the laws of physics change from classical to quantum.”

A particle in the quantum world actually can pass through that wall. The experimental question was, how long does it take to transition through a given obstacle – in this case, the electric barrier potential of a hydrogen atom.

“We use the simplest atom, atomic hydrogen, and we’ve found that there’s no delay in what we can measure,” says Sang.

The Nature paper is the culmination of a three-year international project, in which the team shot a hydrogen atom and its lone electron with an enormously powerful, ultra-fast laser contained in Griffiths’ Australian Attosecond Science Facility. The laser was circularly polarised, meaning that it imparted a rotation to an emitted electron.

That resulting rotation in the electron’s “phase” could then be measured as if it were a clock hand ticking around – or in this case, more precisely, an atto-clock.

“There’s a well-defined point where we can start that interaction, and there’s a point where we know where that electron should come out if it’s instantaneous,” explains Sang.

“So anything that varies from that time we know that it’s taken that long to go through the barrier. That’s how we can measure how long it takes.

“It came out to agree with the theory within experimental uncertainty being consistent with instantaneous tunnelling.”

The precision of the clock to measure the tunnelling event was driven by the ultra-fast pulse of light in the attosecond laser – just a billionth of a billionth of a second long. The energy emitted by the laser during such a tiny amount of time is greater than that of the entire US power grid.

Sang notes about the attosecond timescale that “it’s hard to appreciate how short that is, but it takes an electron about a hundred attoseconds to orbit a nucleus in an atom”.

Tunnelling may be an unfamiliar effect in our everyday lives, yet common devices from electron microscopes to computer transistors rely on it.

“One limitation you might think of is how fast can I make a transistor work – the ultimate limit will be partly about how quickly quantum particles can tunnel,” says Sang.

“For a classical computer, it implies a limit as to how quickly you can switch a transistor.”

As we explore the realms, and limits, of these strange quantum mechanical processes, there may be a speed boost for personal computers, too.

Griffith University Australian Attosecond Science Facility laser

Griffith University a breakthrough ‘speed test’ in quantum tunnelling

The researchers have demonstrated that the electron spends no measurable time “under the potential” as it tunnels through the barrier, but noted that these events “are only as ‘instantaneous’ as the electron wave-function collapse that orthodox interpretations of quantum mechanics” predicts.

This, Sang adds, offers a tantalising possibility of future zeptosecond lasers – which would operate for a period of time a thousand times shorter than an attosecond – “obtaining information on the dynamics of the wave-function collapse itself”. Such a measurement would explore that most fundamental difference of the quantum to the classical world, where common sense expectations break down in the face of wave-functions describing particles.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

In 1971, Griffith was created to be a new kind of university—one that offered new degrees in progressive fields such as Asian studies and environmental science. At the time, these study areas were revolutionary—today, they’re more important than ever.

Since then, we’ve grown into a comprehensive, research-intensive university, ranking in the top 5% of universities worldwide. Our teaching and research spans five campuses in South East Queensland and all disciplines, while our network of more than 120,000 graduates extends around the world.

Griffith continues the progressive traditions of its namesake, Sir Samuel Walker Griffith, who was twice the Premier of Queensland, the first Chief Justice of the High Court of Australia, and the principal author of the Australian Constitution.

From UC Berkeley: “Can entangled qubits be used to probe black holes?”

From UC Berkeley

March 6, 2019
Robert Sanders
rlsanders@berkeley.edu

Someday, entangled quantum bits, or qubits, may allow us to explore the mysterious interior of a black hole, as represented in this artistic rendering. (Graphic by E. Edwards/Joint Quantum Institute)

Physicists have used a seven-qubit quantum computer to simulate the scrambling of information inside a black hole, heralding a future in which entangled quantum bits might be used to probe the mysterious interiors of these bizarre objects.

Scrambling is what happens when matter disappears inside a black hole. The information attached to that matter — the identities of all its constituents, down to the energy and momentum of its most elementary particles — is chaotically mixed with all the other matter and information inside, seemingly making it impossible to retrieve.

This leads to a so-called “black hole information paradox,” since quantum mechanics says that information is never lost, even when that information disappears inside a black hole.

So, while some physicists claim that information falling through the event horizon of a black hole is lost forever, others argue that this information can be reconstructed, but only after waiting an inordinate amount of time — until the black hole has shrunk to nearly half its original size. Black holes shrink because they emit Hawking radiation, which is caused by quantum mechanical fluctuations at the very edge of the black hole and is named after the late physicist Stephen Hawking.

Unfortunately, a black hole the mass of our sun would take about 10^67 years to evaporate — far, far longer than the age of the universe.

Can you extract information from a black hole? As part of a thought experiment, Alice, a physicist, drops a qubit into a black hole and asks whether Bob can reconstruct the qubit using only the outgoing Hawking radiation. (Graphic by Emily Elisa Edwards, University of Maryland)

However, there is a loophole — or rather, a wormhole — out of this black hole. It may be possible to retrieve this infalling information significantly faster by measuring subtle entanglements between the black hole and the Hawking radiation it emits.

Two bits of information — like the quantum bits, or qubits, in a quantum computer — are entangled when they are so closely linked that the quantum state of one automatically determines the state of the other, no matter how far apart they are. Physicists sometimes refer to this as “spooky action at a distance,” and measurements of entangled qubits can lead to the “teleportation” of quantum information from one qubit to another.

“One can recover the information dropped into the black hole by doing a massive quantum calculation on these outgoing Hawking photons,” said Norman Yao, a UC Berkeley assistant professor of physics and a faculty scientist at Lawrence Berkeley National Laboratory. “This is expected to be really, really hard, but if quantum mechanics is to be believed, it should, in principle, be possible. That’s exactly what we are doing here, but for a tiny three-qubit `black hole’ inside a seven-qubit quantum computer.”

By dropping an entangled qubit into a black hole and querying the emerging Hawking radiation, you could theoretically determine the state of a qubit inside the black hole, providing a window into the abyss.

Yao, who is a member of Berkeley Lab’s Quantum Algorithms Team, and his colleagues at the University of Maryland and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, will report their results in a paper appearing in the March 7 issue of the journal Nature.

Teleportation

Yao, who is interested in understanding the nature of quantum chaos, learned from friend and colleague Beni Yoshida, a theorist at the Perimeter Institute, that recovering quantum information falling into a black hole is possible if the information is scrambled rapidly inside the black hole. The more thoroughly it is mixed throughout the black hole, the more reliably the information can be retrieved via teleportation. Based on this insight, Yoshida and Yao proposed last year an experiment to provably demonstrate scrambling on a quantum computer.

A seven-qubit quantum computer circuit built by University of Maryland physicists uses quantum teleportation to detect information scrambling. This is analogous to information propagation through a traversable wormhole, which would allow Bob to identify the qubit that Alice threw into the black hole. (Graphic by Emily Elisa Edwards, University of Maryland)

“With our protocol, if you measure a teleportation fidelity that is high enough, then you can guarantee that scrambling happened within the quantum circuit,” Yao said. “So, then we called up my buddy, Chris Monroe.”

Monroe, a physicist at the University of Maryland in College Park who heads one of the world’s leading trapped-ion quantum information groups, decided to give it a try. His group implemented the protocol proposed by Yoshida and Yao and effectively measured an out-of-time-ordered correlation function.

Called OTOCs, these peculiar correlation functions are created by comparing two quantum states that differ in the timing of when certain kicks or perturbations are applied. The key is being able to evolve a quantum state both forward and backward in time to understand the effect of that second kick on the first kick.

Monroe’s group created a scrambling quantum circuit on three qubits within a seven-qubit trapped-ion quantum computer and characterized the resulting decay of the OTOC. While the decay of the OTOC is typically taken as a strong indication that scrambling has occurred, to prove that they had to show that the OTOC didn’t simply decay because of decoherence — that is, that it wasn’t just poorly shielded from the noise of the outside world, which also causes quantum states to fall apart.

Yao and Yoshida proved that the greater the accuracy with which they could retrieve the entangled or teleported information, the more stringently they could put a lower limit on the amount of scrambling that had occurred in the OTOC. This is because, if information is successfully teleported from one atom to another, it means that the state of the first atom is spread out across all of the atoms — something that only happens if the information is scrambled. If the information was lost, successful teleportation would not be possible. For an arbitrary process whose scrambling properties might not be known, this method could be used to test whether — or even how much — it scrambles.

Monroe and his colleagues measured a teleportation fidelity of approximately 80 percent, meaning that perhaps half of the quantum state was scrambled and the other half decayed by decoherence. Nevertheless, this was enough to demonstrate that genuine scrambling had indeed occurred in this three-qubit quantum circuit.

“One possible application for our protocol is related to the benchmarking of quantum computers, where one might be able to use this technique to diagnose more complicated forms of noise and decoherence in quantum processors,” Yao said. “The ability to diagnose how noise affects quantum simulations is key to building better fault-tolerant algorithms and getting accurate answers from current noisy quantum computers.”

Yao is also working with a UC Berkeley group led by Irfan Siddiqi to demonstrate scrambling in a different quantum system, superconducting qutrits: quantum bits that have three, rather than two, states. Siddiqi is a UC Berkeley professor of physics and a faculty scientist at Berkeley Lab, where he is leading the effort to build an advanced quantum computing test bed.

“At its core, this is a qubit or qutrit experiment, but the fact that we can relate it to cosmology is because we believe the dynamics of quantum information is the same,” he said. “The U.S. is launching a billion-dollar quantum initiative, and understanding the dynamics of quantum information connects many areas of research within this initiative: quantum circuits and computing, high energy physics, black hole dynamics, condensed matter physics and atomic, molecular and optical physics. The language of quantum information has become pervasive for our understanding of all these different systems.”

“Regardless of whether real black holes are very good scramblers, studying quantum scrambling in the lab could provide useful insights for the future development of quantum computing or quantum simulation,” Monroe said.

Aside from Yao, Yoshida and Monroe, other co-authors are graduate student Tommy Schuster of UC Berkeley and graduate student and first author Kevin Landsman, Caroline Figgatt and Norbert Linke of Maryland’s Joint Quantum Institute. The work was supported by the Department of Energy’s Office of Advanced Scientific Computing Research and Office of High Energy Physics and National Science Foundation.

RELATED INFORMATION

Ion experiment aces quantum scrambling test (JQI)
Verified Quantum Information Scrambling (Nature) [above]
Disentangling Scrambling and Decoherence via Quantum Teleportation (Physical Review X)
Norman Yao’s website

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

From WIRED: “Inside the High-Stakes Race to Make Quantum Computers Work”

From WIRED

03.08.19
Katia Moskvitch

View Pictures/Getty Images

Deep beneath the Franco-Swiss border, the Large Hadron Collider is sleeping.

LHC

CERN map

CERN LHC Tunnel

CERN LHC particles

But it won’t be quiet for long. Over the coming years, the world’s largest particle accelerator will be supercharged, increasing the number of proton collisions per second by a factor of two and a half.

Once the work is complete in 2026, researchers hope to unlock some of the most fundamental questions in the universe. But with the increased power will come a deluge of data the likes of which high-energy physics has never seen before. And, right now, humanity has no way of knowing what the collider might find.

To understand the scale of the problem, consider this: When it shut down in December 2018, the LHC generated about 300 gigabytes of data every second, adding up to 25 petabytes (PB) annually. For comparison, you’d have to spend 50,000 years listening to music to go through 25 PB of MP3 songs, while the human brain can store memories equivalent to just 2.5 PB of binary data. To make sense of all that information, the LHC data was pumped out to 170 computing centers in 42 countries [http://greybook.cern.ch/]. It was this global collaboration that helped discover the elusive Higgs boson, part of the Higgs field believed to give mass to elementary particles of matter.

CERN CMS Higgs Event

CERN ATLAS Higgs Event

To process the looming data torrent, scientists at the European Organization for Nuclear Research, or CERN, will need 50 to 100 times more computing power than they have at their disposal today. A proposed Future Circular Collider, four times the size of the LHC and 10 times as powerful, would create an impossibly large quantity of data, at least twice as much as the LHC.

CERN FCC Future Circular Collider map

In a bid to make sense of the impending data deluge, some at CERN are turning to the emerging field of quantum computing. Powered by the very laws of nature the LHC is probing, such a machine could potentially crunch the expected volume of data in no time at all. What’s more, it would speak the same language as the LHC. While numerous labs around the world are trying to harness the power of quantum computing, it is the future work at CERN that makes it particularly exciting research. There’s just one problem: Right now, there are only prototypes; nobody knows whether it’s actually possible to build a reliable quantum device.

Traditional computers—be it an Apple Watch or the most powerful supercomputer—rely on tiny silicon transistors that work like on-off switches to encode bits of data.

ORNL IBM AC922 SUMMIT supercomputer, No.1 on the TOP500. Credit: Carlos Jones, Oak Ridge National Laboratory/U.S. Dept. of Energy

Each circuit can have one of two values—either one (on) or zero (off) in binary code; the computer turns the voltage in a circuit on or off to make it work.

A quantum computer is not limited to this “either/or” way of thinking. Its memory is made up of quantum bits, or qubits—tiny particles of matter like atoms or electrons. And qubits can do “both/and,” meaning that they can be in a superposition of all possible combinations of zeros and ones; they can be all of those states simultaneously.

For CERN, the quantum promise could, for instance, help its scientists find evidence of supersymmetry, or SUSY, which so far has proven elusive.

Standard Model of Supersymmetry via DESY

At the moment, researchers spend weeks and months sifting through the debris from proton-proton collisions in the LCH, trying to find exotic, heavy sister-particles to all our known particles of matter. The quest has now lasted decades, and a number of physicists are questioning if the theory behind SUSY is really valid. A quantum computer would greatly speed up analysis of the collisions, hopefully finding evidence of supersymmetry much sooner—or at least allowing us to ditch the theory and move on.

A quantum device might also help scientists understand the evolution of the early universe, the first few minutes after the Big Bang. Physicists are pretty confident that back then, our universe was nothing but a strange soup of subatomic particles called quarks and gluons. To understand how this quark-gluon plasma has evolved into the universe we have today, researchers simulate the conditions of the infant universe and then test their models at the LHC, with multiple collisions. Performing a simulation on a quantum computer, governed by the same laws that govern the very particles that the LHC is smashing together, could lead to a much more accurate model to test.

Beyond pure science, banks, pharmaceutical companies, and governments are also waiting to get their hands on computing power that could be tens or even hundreds of times greater than that of any traditional computer.

And they’ve been waiting for decades. Google is in the race, as are IBM, Microsoft, Intel and a clutch of startups, academic groups, and the Chinese government. The stakes are incredibly high. Last October, the European Union pledged to give $1 billion to over 5,000 European quantum technology researchers over the next decade, while venture capitalists invested some $250 million in various companies researching quantum computing in 2018 alone. “This is a marathon,” says David Reilly, who leads Microsoft’s quantum lab at the University of Sydney, Australia. “And it’s only 10 minutes into the marathon.”

Despite the hype surrounding quantum computing and the media frenzy triggered by every announcement of a new qubit record, none of the competing teams have come close to reaching even the first milestone, fancily called quantum supremacy—the moment when a quantum computer performs at least one specific task better than a standard computer. Any kind of task, even if it is totally artificial and pointless. There are plenty of rumors in the quantum community that Google may be close, although if true, it would give the company bragging rights at best, says Michael Biercuk, a physicist at the University of Sydney and founder of quantum startup Q-CTRL. “It would be a bit of a gimmick—an artificial goal,” says Reilly “It’s like concocting some mathematical problem that really doesn’t have an obvious impact on the world just to say that a quantum computer can solve it.”

That’s because the first real checkpoint in this race is much further away. Called quantum advantage, it would see a quantum computer outperform normal computers on a truly useful task. (Some researchers use the terms quantum supremacy and quantum advantage interchangeably.) And then there is the finish line, the creation of a universal quantum computer. The hope is that it would deliver a computational nirvana with the ability to perform a broad range of incredibly complex tasks. At stake is the design of new molecules for life-saving drugs, helping banks to adjust the riskiness of their investment portfolios, a way to break all current cryptography and develop new, stronger systems, and for scientists at CERN, a way to glimpse the universe as it was just moments after the Big Bang.

Slowly but surely, work is already underway. Federico Carminati, a physicist at CERN, admits that today’s quantum computers wouldn’t give researchers anything more than classical machines, but, undeterred, he’s started tinkering with IBM’s prototype quantum device via the cloud while waiting for the technology to mature. It’s the latest baby step in the quantum marathon. The deal between CERN and IBM was struck in November last year at an industry workshop organized by the research organization.

Set up to exchange ideas and discuss potential collab­orations, the event had CERN’s spacious auditorium packed to the brim with researchers from Google, IBM, Intel, D-Wave, Rigetti, and Microsoft. Google detailed its tests of Bristlecone, a 72-qubit machine. Rigetti was touting its work on a 128-qubit system. Intel showed that it was in close pursuit with 49 qubits. For IBM, physicist Ivano Tavernelli took to the stage to explain the company’s progress.

IBM has steadily been boosting the number of qubits on its quantum computers, starting with a meagre 5-qubit computer, then 16- and 20-qubit machines, and just recently showing off its 50-qubit processor.

IBM iconic image of Quantum computer

Carminati listened to Tavernelli, intrigued, and during a much needed coffee break approached him for a chat. A few minutes later, CERN had added a quantum computer to its impressive technology arsenal. CERN researchers are now starting to develop entirely new algorithms and computing models, aiming to grow together with the device. “A fundamental part of this process is to build a solid relationship with the technology providers,” says Carminati. “These are our first steps in quantum computing, but even if we are coming relatively late into the game, we are bringing unique expertise in many fields. We are experts in quantum mechanics, which is at the base of quantum computing.”

The attraction of quantum devices is obvious. Take standard computers. The prediction by former Intel CEO Gordon Moore in 1965 that the number of components in an integrated circuit would double roughly every two years has held true for more than half a century. But many believe that Moore’s law is about to hit the limits of physics. Since the 1980s, however, researchers have been pondering an alternative. The idea was popularized by Richard Feynman, an American physicist at Caltech in Pasadena. During a lecture in 1981, he lamented that computers could not really simulate what was happening at a subatomic level, with tricky particles like electrons and photons that behave like waves but also dare to exist in two states at once, a phenomenon known as quantum superposition.

Feynman proposed to build a machine that could. “I’m not happy with all the analyses that go with just the classical theory, because nature isn’t classical, dammit,” he told the audience back in 1981. “And if you want to make a simulation of nature, you’d better make it quantum mechanical, and by golly it’s a wonderful problem, because it doesn’t look so easy.”

And so the quantum race began. Qubits can be made in different ways, but the rule is that two qubits can be both in state A, both in state B, one in state A and one in state B, or vice versa, so there are four probabilities in total. And you won’t know what state a qubit is at until you measure it and the qubit is yanked out of its quantum world of probabilities into our mundane physical reality.

In theory, a quantum computer would process all the states a qubit can have at once, and with every qubit added to its memory size, its computational power should increase exponentially. So, for three qubits, there are eight states to work with simultaneously, for four, 16; for 10, 1,024; and for 20, a whopping 1,048,576 states. You don’t need a lot of qubits to quickly surpass the memory banks of the world’s most powerful modern supercomputers—meaning that for specific tasks, a quantum computer could find a solution much faster than any regular computer ever would. Add to this another crucial concept of quantum mechanics: entanglement. It means that qubits can be linked into a single quantum system, where operating on one affects the rest of the system. This way, the computer can harness the processing power of both simultaneously, massively increasing its computational ability.

While a number of companies and labs are competing in the quantum marathon, many are running their own races, taking different approaches. One device has even been used by a team of researchers to analyze CERN data, albeit not at CERN. Last year, physicists from the California Institute of Technology in Pasadena and the University of Southern California managed to replicate the discovery of the Higgs boson, found at the LHC in 2012, by sifting through the collider’s troves of data using a quantum computer manufactured by D-Wave, a Canadian firm based in Burnaby, British Columbia. The findings didn’t arrive any quicker than on a traditional computer, but, crucially, the research showed a quantum machine could do the work.

One of the oldest runners in the quantum race, D-Wave announced back in 2007 that it had built a fully functioning, commercially available 16-qubit quantum computer prototype—a claim that’s controversial to this day. D-Wave focuses on a technology called quantum annealing, based on the natural tendency of real-world quantum systems to find low-energy states (a bit like a spinning top that inevitably will fall over). A D-Wave quantum computer imagines the possible solutions of a problem as a landscape of peaks and valleys; each coordinate represents a possible solution and its elevation represents its energy. Annealing allows you to set up the problem, and then let the system fall into the answer—in about 20 milliseconds. As it does so, it can tunnel through the peaks as it searches for the lowest valleys. It finds the lowest point in the vast landscape of solutions, which corresponds to the best possible outcome—although it does not attempt to fully correct for any errors, inevitable in quantum computation. D-Wave is now working on a prototype of a universal annealing quantum computer, says Alan Baratz, the company’s chief product officer.

Apart from D-Wave’s quantum annealing, there are three other main approaches to try and bend the quantum world to our whim: integrated circuits, topological qubits and ions trapped with lasers. CERN is placing high hopes on the first method but is closely watching other efforts too.

IBM, whose computer Carminati has just started using, as well as Google and Intel, all make quantum chips with integrated circuits—quantum gates—that are superconducting, a state when certain metals conduct electricity with zero resistance. Each quantum gate holds a pair of very fragile qubits. Any noise will disrupt them and introduce errors—and in the quantum world, noise is anything from temperature fluctuations to electromagnetic and sound waves to physical vibrations.

To isolate the chip from the outside world as much as possible and get the circuits to exhibit quantum mechanical effects, it needs to be supercooled to extremely low temperatures. At the IBM quantum lab in Zurich, the chip is housed in a white tank—a cryostat—suspended from the ceiling. The temperature inside the tank is a steady 10 millikelvin or –273 degrees Celsius, a fraction above absolute zero and colder than outer space. But even this isn’t enough.

Just working with the quantum chip, when scientists manipulate the qubits, causes noise. “The outside world is continually interacting with our quantum hardware, damaging the information we are trying to process,” says physicist John Preskill at the California Institute of Technology, who in 2012 coined the term quantum supremacy. It’s impossible to get rid of the noise completely, so researchers are trying to suppress it as much as possible, hence the ultracold temperatures to achieve at least some stability and allow more time for quantum computations.

“My job is to extend the lifetime of qubits, and we’ve got four of them to play with,” says Matthias Mergenthaler, an Oxford University postdoc student working at IBM’s Zurich lab. That doesn’t sound like a lot, but, he explains, it’s not so much the number of qubits that counts but their quality, meaning qubits with as low a noise level as possible, to ensure they last as long as possible in superposition and allow the machine to compute. And it’s here, in the fiddly world of noise reduction, that quantum computing hits up against one of its biggest challenges. Right now, the device you’re reading this on probably performs at a level similar to that of a quantum computer with 30 noisy qubits. But if you can reduce the noise, then the quantum computer is many times more powerful.

Once the noise is reduced, researchers try to correct any remaining errors with the help of special error-correcting algorithms, run on a classical computer. The problem is, such error correction works qubit by qubit, so the more qubits there are, the more errors the system has to cope with. Say a computer makes an error once every 1,000 computational steps; it doesn’t sound like much, but after 1,000 or so operations, the program will output incorrect results. To be able to achieve meaningful computations and surpass standard computers, a quantum machine has to have about 1,000 qubits that are relatively low noise and with error rates as corrected as possible. When you put them all together, these 1,000 qubits will make up what researchers call a logical qubit. None yet exist—so far, the best that prototype quantum devices have achieved is error correction for up to 10 qubits. That’s why these prototypes are called noisy intermediate-scale quantum computers (NISQ), a term also coined by Preskill in 2017.

For Carminati, it’s clear the technology isn’t ready yet. But that isn’t really an issue. At CERN the challenge is to be ready to unlock the power of quantum computers when and if the hardware becomes available. “One exciting possibility will be to perform very, very accurate simulations of quantum systems with a quantum computer—which in itself is a quantum system,” he says. “Other groundbreaking opportunities will come from the blend of quantum computing and artificial intelligence to analyze big data, a very ambitious proposition at the moment, but central to our needs.”

But some physicists think NISQ machines will stay just that—noisy—forever. Gil Kalai, a professor at Yale University, says that error correcting and noise suppression will never be good enough to allow any kind of useful quantum computation. And it’s not even due to technology, he says, but to the fundamentals of quantum mechanics. Interacting systems have a tendency for errors to be connected, or correlated, he says, meaning errors will affect many qubits simultaneously. Because of that, it simply won’t be possible to create error-correcting codes that keep noise levels low enough for a quantum computer with the required large number of qubits.

“My analysis shows that noisy quantum computers with a few dozen qubits deliver such primitive computational power that it will simply not be possible to use them as the building blocks we need to build quantum computers on a wider scale,” he says. Among scientists, such skepticism is hotly debated. The blogs of Kalai and fellow quantum skeptics are forums for lively discussion, as was a recent much-shared article titled “The Case Against Quantum Computing”—followed by its rebuttal, “The Case Against the Case Against Quantum Computing.

For now, the quantum critics are in a minority. “Provided the qubits we can already correct keep their form and size as we scale, we should be okay,” says Ray Laflamme, a physicist at the University of Waterloo in Ontario, Canada. The crucial thing to watch out for right now is not whether scientists can reach 50, 72, or 128 qubits, but whether scaling quantum computers to this size significantly increases the overall rate of error.

The Quantum Nano Centre in Canada is one of numerous big-budget research and development labs focussed on quantum computing. James Brittain/Getty Images

Others believe that the best way to suppress noise and create logical qubits is by making qubits in a different way. At Microsoft, researchers are developing topological qubits—although its array of quantum labs around the world has yet to create a single one. If it succeeds, these qubits would be much more stable than those made with integrated circuits. Microsoft’s idea is to split a particle—for example an electron—in two, creating Majorana fermion quasi-particles. They were theorized back in 1937, and in 2012 researchers at Delft University of Technology in the Netherlands, working at Microsoft’s condensed matter physics lab, obtained the first experimental evidence of their existence.

“You will only need one of our qubits for every 1,000 of the other qubits on the market today,” says Chetan Nayak, general manager of quantum hardware at Microsoft. In other words, every single topological qubit would be a logical one from the start. Reilly believes that researching these elusive qubits is worth the effort, despite years with little progress, because if one is created, scaling such a device to thousands of logical qubits would be much easier than with a NISQ machine. “It will be extremely important for us to try out our code and algorithms on different quantum simulators and hardware solutions,” says Carminati. “Sure, no machine is ready for prime time quantum production, but neither are we.”

Another company Carminati is watching closely is IonQ, a US startup that spun out of the University of Maryland. It uses the third main approach to quantum computing: trapping ions. They are naturally quantum, having superposition effects right from the start and at room temperature, meaning that they don’t have to be supercooled like the integrated circuits of NISQ machines. Each ion is a singular qubit, and researchers trap them with special tiny silicon ion traps and then use lasers to run algorithms by varying the times and intensities at which each tiny laser beam hits the qubits. The beams encode data to the ions and read it out from them by getting each ion to change its electronic states.

In December, IonQ unveiled its commercial device, capable of hosting 160 ion qubits and performing simple quantum operations on a string of 79 qubits. Still, right now, ion qubits are just as noisy as those made by Google, IBM, and Intel, and neither IonQ nor any other labs around the world experimenting with ions have achieved quantum supremacy.

As the noise and hype surrounding quantum computers rumbles on, at CERN, the clock is ticking. The collider will wake up in just five years, ever mightier, and all that data will have to be analyzed. A non-noisy, error-corrected quantum computer will then come in quite handy.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

From UC Santa Barbara: “Sensing Disturbances in the Force”

From UC Santa Barbara

March 5, 2019
Sonia Fernandez

UC Santa Barbara researchers receive U.S. Department of Energy grant to build atom-defect hybrid quantum sensor.

It will be a feat of engineering and physics at the smallest scales, but it could open the biggest doors — to new science and more advanced technologies. UC Santa Barbara physicists Ania Jayich and David Weld, and materials scientist Kunal Mukherjee, are teaming up to build an atom-defect hybrid quantum system — a sensor technology that would use the power of quantum science to unlock the mysteries of the atomic and subatomic world.

“We’re at this tipping point where we know there’s a lot of impactful and fundamentally exciting things we can do,” said Jayich, whose research investigates quantum effects at the nanoscale. The $1.5 million grant from the Department of Energy’s Office of Basic Sciences will kickstart the development of a system that will allow researchers an unusually high level of control over atoms while simultaneously leaving their “quantumness” untouched.

“In this whole field of quantum technology, that has been the big challenge,” Jayich said. In the quirky and highly unintuitive world of quantum mechanics, she explained, objects can exist in a superposition of many places at once, and entangled elements separated by thousands of miles can be inextricably linked — phenomena which, in turn, have opened up new and powerful possibilities for areas such as sensing, computing and the deepest investigations of nature.

However, the coherence that is the signature of these quantum behaviors — a state of information that is the foundation of quantum technology — is exceedingly fragile and fleeting.

“Quantum coherence is such a delicate phenomenon,” Jayich said. “Any uncontrolled interaction with the environment will kill it. And that’s the whole challenge behind advancing this field — how do we preserve the very delicate quantumness of an atom or defect, or anything?” To study a quantum element such as an atom, one would have to interrogate it, she explained, but the act of measuring can also destroy its quantum nature.

To Hold Without Touching

Fortunately, Jayich and colleagues see a way around this conundrum.

“It’s a hybrid atomic- and solid-state system,” Jayich said. Key to this technology is the nitrogen-vacancy (NV) center in diamond, an extensively studied point defect in diamond’s carbon atom lattice. The NV center is comprised of a vacancy created by a missing carbon atom next to another vacancy that is substituted with a nitrogen atom. With its several unpaired electrons, it is highly sensitive to and interactive with external perturbations, such as the minute magnetic or electric fields that would occur in the presence of individual atoms of interest.

“In the proposed experiment, we would have an atom on the diamond surface that couples to a shallow, subsurface NV center inside the material, in a highly controlled, cryogenic and ultra-high vacuum environment,” Jayich explained. The diamond surface provides a natural trapping that allows researchers to more easily hold the atom in place — a challenge for many quantum scientists who want to trap individual atoms. Further, upon reading the state of the defect, one could understand the quantum properties of the atom under interrogation — without touching the atom itself and destroying its coherence.

Previous methods aimed at interrogating individual adatoms (adsorbed atoms) relied on passing current through the atoms and necessitated metal surfaces, both of which, according to Jayich, reduce quantum coherence times.

“The past several decades of work in atomic physics have resulted in tools that allow exquisite quantum control of all degrees of freedom of atomic ensembles, but typically only when the atoms are gently held in a vacuum far away from all other matter,” added Weld. “This experiment seeks to extend this level of control into a much messier but also much more technologically relevant regime, by manipulating and sensing individual atoms that are chemically bonded to a solid surface.”

With the hybrid system, Jayich said, it would be “very easy to talk to the NV center defect with light, and the atoms have the benefit of retaining quantum information for very long periods of time. So we have a system where we leverage the best of both worlds — the best of the atom and the best of the defect — and put them together in a way that’s functional.”

A Foundation for Future Quantum Tech

Looking forward, the state-of-the-art spatial resolution and sensitivity of this atom-defect hybrid quantum system could offer researchers the deepest look at the workings of individual atoms, or structures of molecules at nanometer- and Angstrom scales.

“If you can see things on smaller scales with better sensitivity than anybody else, you’re going to find new physics,” Jayich said. The connections of microscopic structure to macroscopic behavior in materials synthesis could be elucidated. Quantum phenomena in condensed matter systems could be probed. Proteins that have evaded structural determination — such as membrane proteins — could be studied.

This project is a “natural fit” for UC Santa Barbara, say the researchers, due to the campus’s strengths in both physics and materials sciences. The technique is reminiscent of molecular beam epitaxy (MBE), a method of “growing” a material atom-by-atom on a substrate.

“There is a strong tradition of materials deposition at UCSB, ranging from metals, semiconductors to novel electronic materials,” Mukherjee said of the campus’s long record of materials growth and world-class MBE facilities. Among the first few atoms they intend to study are rare-earth types such as holmium or dysprosium “as they have unpaired electrons which are protected from environmental interactions by the atomic structure,” noted Mukherjee, adding that he is “particularly excited” about the challenge of removing the atoms from and resetting the diamond surface without breaking vacuum.

Additionally, the physical and materials knowledge gained by mastering the interface of such a hybrid system would contribute to the development of quantum computing systems. According to Jayich, future practicable quantum computers would likely be a hybrid of several elements, similar to how conventional computers are a mix of magnetic, electronic and solid-state components.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

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.

From University College London via Science Alert: “Physicists Are Rethinking a Fundamental Quantum Law to Help Us Understand Reality”

From University College London

via

Science Alert

2 MAR 2019
MIKE MCRAE

(gremlin/iStock)

Deep in the heart of physics there’s a lucky guess. It was an incredibly good guess, one that remains solid in the face of time and experiment, and is now a fundamental principle in quantum mechanics.

It’s called the Born rule, and while it’s used for predictions, nobody truly understands how it works. But a bold new attempt to rewrite it could be the break we’ve been looking for to finally understand it in full.

University College London physicists Lluís Masanes and Thomas Galley have teamed up with Markus Müller from the Austrian Academy of Sciences to find a new way to describe this basic law of physics.

They’re not the first to look for deeper truths to this most mind-boggling of quantum principles. And, let’s be honest, they won’t be the last. But if there is a solution to be found, it’ll probably require a unique approach like theirs.

First, to understand what’s so special about the Born rule, we need to back up a little.

It’s become a cliché to say quantum mechanics is weird. What with cats that are at once alive and dead and particles teleporting information across space and time, we’re used to seeing the basement of physics as a magic show.

Big names like Schrödinger, Heisenberg, and Einstein tend to get the glory, but it’s the German physicist and mathematician Max Born who truly deserves the credit for the monumental headache that quantum mechanics delivers.

Max Born (1882-1970), a German-Jewish physicist and mathematician who was instrumental in the development of quantum mechanics

To understand his contribution, we only need to look at the hot mess physicists found themselves in the early 1920s. The structure of the atom had recently been revealed to consist of a dense, positively charged nucleus surrounded by smaller negatively charged particles.

Why the whole system didn’t collapse was the Big Question being kicked around, until the French physicist Louis de Broglie came up with an audacious suggestion – just as light waves had a particle nature, those negative electrons could remain aloft if they were also wave-like.

The duality of light was already hard enough to swallow. But describing solid-seeming matter as if it was a wave on the ocean was just plain nuts. Still, experiments showed it was a good match.

Then, in 1926, Born came up with a simple suggestion – drawing insight from the mathematics of his colleagues, he showed how these waves reflected probability and came up with a rule that married observations with measures of chance. This rule allows physicists to predict the position of particles in experiments, using the probabilities reflected by the amplitudes of these wave functions.

But the Born rule wasn’t based on some basic set of axioms, or deeper truths of nature. In a lecture he gave on receiving a Nobel Prize in Physics for his work in 1954, Born explained the ‘aha!’ moment emerged from Einstein’s work.

“He had tried to make the duality of particles – light quanta or photons – and waves comprehensible by interpreting the square of the optical wave amplitudes as probability density for the occurrence of photons,” said Born.

It was an inspired guess, and an accurate one at that. But there were no basic axioms, no fundamental laws drawing Born to his conclusion. It was purely predictive, saying nothing about deeper principles that turn a multitude of maybes into a single actuality.

Einstein hated the implications, famously claiming God does not play dice, and felt quantum mechanics was an incomplete theory waiting for new pieces to make the picture clear.

Nearly a century on, those pieces are as elusive as ever. And the Born rule still sits at the heart of it, silently predicting without revealing the secret to its choice.

What’s needed is a reformulation of the famous law that retains its power of prediction while hinting at further truths. So Masanes, Galley, and Muller reworked the rule’s formulation based on a handful of seemingly trivial assumptions.

Firstly, they pointed out that quantum states are described according to measures of magnitude and direction.

Secondly, they showed how these states can be described according to what’s known as unitarity. This jargon refers to the information that connects a process’s start and end points. (To use a crude analogy, we might not know how we got home from the bar, but the method that got us there also describes the route back.)

Next, they assumed however we choose to group the parts of a complex quantum system, it shouldn’t make a difference to the measurement of the final state. Dividing a rainbow into seven colours is a choice we make subject to context; nature isn’t always concerned with convenient divisions.

Lastly, they affirmed that the measurement of a quantum state is unique. After all is said and done, a myriad of possibilities ends in a solid answer.

From these simple starting points, the trio logically built back up to the Born rule. Their work is available for anybody to read through on the pre-peer review website arxiv.org, but is already sparking discussion.

It’s not a solution in itself, mind you, as it falls short of explaining why a wave of possibility collapses into the reality we observe.

Instead, it shows how fundamental assumptions can give rise to the same law, providing a new perspective on how to approach the problem.

For now, God still rolls those dice fair and square. Maybe this is how we’ll catch him cheating.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

UCL was founded in 1826 to open up higher education in England to those who had been excluded from it – becoming the first university in England to admit women students on equal terms with men in 1878.

Academic excellence and research that addresses real-world problems inform our ethos to this day and are central to our 20-year strategy.

From University of Wisconsin-Madison and University of Chicago: “University of Wisconsin-Madison joins Chicago Quantum Exchange”

From University of Wisconsin Madison

via

University of Chicago

Feb 28, 2019

Photo by John Zich

UW-Madison adds expertise to hub for research and development of quantum technology.

The Chicago Quantum Exchange, a growing hub for the research and development of quantum technology, is adding the University of Wisconsin–Madison as its newest member.

UW-Madison is joining forces with the University of Chicago, the U.S. Department of Energy’s Argonne National Laboratory and Fermi National Accelerator Laboratory, and the University of Illinois at Urbana-Champaign in developing a national leading collaboration in the rapidly emerging field of quantum information.

The new partnership comes as UW-Madison makes significant investments in quantum science, a field with potential to revolutionize computing, communication, security and more using the powerful capabilities of quantum mechanics.

The federal government is increasingly interested in quantum technologies, launching late last year the National Quantum Initiative, which authorized an investment of more than $1.2 billion in quantum research over the next decade.

“I think quantum science is one of the most exciting areas in physics right now,” said Robert McDermott, a professor of physics at UW–Madison. “Joining the Chicago Quantum Exchange is going to put us in a very strong position in the landscape of academic institutions that are developing quantum technologies throughout the United States.”

The Chicago Quantum Exchange works toward advancing academic, industrial and governmental efforts in the science and engineering of quantum information, with the goal of applying research innovations to develop radically new types of devices, materials and computing techniques.

“Bringing UW-Madison’s expertise in qubits and quantum information to the Chicago Quantum Exchange allows us to strengthen one of the largest quantum research efforts in the U.S. and will help us accelerate scientific developments that can lead toward promising new technologies,” said David Awschalom, director of the Chicago Quantum Exchange, the Liew Family Professor in Molecular Engineering at UChicago and an Argonne senior scientist.

The Chicago Quantum Exchange’s continued growth enhances the position of the Chicago area, and the Midwest, to attract industry partnerships and government funding, while making it a leader in training the new quantum workforce.

UW–Madison has institutional research expertise in three areas of qubits, which is the basic unit of quantum information rendered as an electronic or optical device. These areas are neutral atom qubits, superconducting qubits and silicon quantum dot qubits—along with quantum sensing research being conducted by faculty such as College of Engineering Assistant Professor Jennifer Choy and Assistant Professor of Physics Shimon Kolkowitz, and condensed matter research being conducted in the Department of Physics by Professors Maxim Vavilov and Robert Joynt, Associate Professor Alex Levchenko and Senior Scientist Lara Faoro.

“We are looking forward to joint research projects within the CQE, which will give our students experience to enhance their education at UW–Madison,” said Mark Eriksson, a professor of physics at UW-Madison. “That collaboration is really important these days because a lot of expertise is needed to attack quantum computing problems from many different directions.”

As the field of quantum information science continues to grow, so will the demand for quantum engineers in industry, government and at universities. The Chicago Quantum Exchange, through its member institutions, offers both undergraduate and graduate students access to world-class expertise and research facilities in quantum science and engineering.

“Developing a next-generation quantum workforce is a huge priority nationally and worldwide,” Eriksson said. “We are training students to have this broad base of expertise that will equip them to make a high impact in this developing field of technology.”

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

An intellectual destination

One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

In achievement and prestige, the University of Wisconsin–Madison has long been recognized as one of America’s great universities. A public, land-grant institution, UW–Madison offers a complete spectrum of liberal arts studies, professional programs and student activities. Spanning 936 acres along the southern shore of Lake Mendota, the campus is located in the city of Madison.

From MIT News: “Quantum dots can spit out clone-like photons”

From MIT News

February 21, 2019
David L. Chandler

Scanning Transmission Electron Microscope image (STEM) of single perovskite quantum dots. New study shows that single perovskite quantum dots could be a fundamental building block for quantum-photonic technologies for computing or communications. Image courtesy of the authors.

System that generates coherent single particles of light could help pave the way for quantum information processors or communications.

In the global quest to develop practical computing and communications devices based on the principles of quantum physics, one potentially useful component has proved elusive: a source of individual particles of light with perfectly constant, predictable, and steady characteristics. Now, researchers at MIT and in Switzerland say they have made major steps toward such a single photon source.

The study, which involves using a family of materials known as perovskites to make light-emitting particles called quantum dots, appears today in the journal Science. The paper is by MIT graduate student in chemistry Hendrik Utzat, professor of chemistry Moungi Bawendi, and nine others at MIT and at ETH Zürich, Switzerland.

The ability to produce individual photons with precisely known and persistent properties, including a wavelength, or color, that does not fluctuate at all, could be useful for many kinds of proposed quantum devices. Because each photon would be indistinguishable from the others in terms of its quantum-mechanical properties, it could be possible, for example, to delay one of them and then get the pair to interact with each other, in a phenomenon called interference.

“This quantum interference between different indistinguishable single photons is the basis of many optical quantum information technologies using single photons as information carriers,” Utzat explains. “But it only works if the photons are coherent, meaning they preserve their quantum states for a sufficiently long time.”

Many researchers have tried to produce sources that could emit such coherent single photons, but all have had limitations. Random fluctuations in the materials surrounding these emitters tend to change the properties of the photons in unpredictable ways, destroying their coherence. Finding emitter materials that maintain coherence and are also bright and stable is “fundamentally challenging,” Utzat says. That’s because not only the surroundings but even the materials themselves “essentially provide a fluctuating bath that randomly interacts with the electronically excited quantum state and washes out the coherence,” he says.

“Without having a source of coherent single photons, you can’t use any of these quantum effects that are the foundation of optical quantum information manipulation,” says Bawendi, who is the Lester Wolfe Professor of Chemistry. Another important quantum effect that can be harnessed by having coherent photons, he says, is entanglement, in which two photons essentially behave as if they were one, sharing all their properties.

Previous chemically-made colloidal quantum dot materials had impractically short coherence times, but this team found that making the quantum dots from perovskites, a family of materials defined by their crystal structure, produced coherence levels that were more than a thousand times better than previous versions. The coherence properties of these colloidal perovskite quantum dots are now approaching the levels of established emitters, such as atom-like defects in diamond or quantum dots grown by physicists using gas-phase beam epitaxy.

One of the big advantages of perovskites, they found, was that they emit photons very quickly after being stimulated by a laser beam. This high speed could be a crucial characteristic for potential quantum computing applications. They also have very little interaction with their surroundings, greatly improving their coherence properties and stability.

Such coherent photons could also be used for quantum-encrypted communications applications, Bawendi says. A particular kind of entanglement, called polarization entanglement, can be the basis for secure quantum communications that defies attempts at interception.

Now that the team has found these promising properties, the next step is to work on optimizing and improving their performance in order to make them scalable and practical. For one thing, they need to achieve 100 percent indistinguishability in the photons produced. So far, they have reached 20 percent, “which is already very remarkable,” Utzat says, already comparable to the coherences reached by other materials, such as atom-like fluorescent defects in diamond, that are already established systems and have been worked on much longer.

“Perovskite quantum dots still have a long way to go until they become applicable in real applications,” he says, “but this is a new materials system available for quantum photonics that can now be optimized and potentially integrated with devices.”

It’s a new phenomenon and will require much work to develop to a practical level, the researchers say. “Our study is very fundamental,” Bawendi notes. “However, it’s a big step toward developing a new material platform that is promising.”

The work was supported by the U.S. Department of Energy, the National Science Foundation, and the Swiss Federal Commission for Technology and Innovation.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

From MIT News: “Study of quark speeds finds a solution for a 35-year physics mystery”

From MIT News

February 20, 2019
Jennifer Chu

MIT physicists find quarks move slower in atoms with more pairs of protons and neutrons. Courtesy of the researchers.

Number of proton-neutron pairs determine how fast the particles move, results suggest.

MIT physicists now have an answer to a question in nuclear physics that has puzzled scientists for three decades: Why do quarks move more slowly inside larger atoms?

Quarks, along with gluons, are the fundamental building blocks of the universe. These subatomic particles — the smallest particles we know of — are far smaller, and operate at much higher energy levels, than the protons and neutrons in which they are found. Physicists have therefore assumed that a quark should be blithely indifferent to the characteristics of the protons and neutrons, and the overall atom, in which it resides.

But in 1983, physicists at CERN, as part of the European Muon Collaboration (EMC), observed for the first time what would become known as the EMC effect: In the nucleus of an iron atom containing many protons and neutrons, quarks move significantly more slowly than quarks in deuterium, which contains a single proton and neutron. Since then, physicists have found more evidence that the larger an atom’s nucleus, the slower the quarks that move within.

“People have been wracking their brains for 35 years, trying to explain why this effect happens,” says Or Hen, assistant professor of physics at MIT.

Now Hen, Barak Schmookler, and Axel Schmidt, a graduate student and postdoc in MIT’s Laboratory for Nuclear Science, have led an international team of physicists in identifying an explanation for the EMC effect. They have found that a quark’s speed depends on the number of protons and neutrons forming short-ranged correlated pairs in an atom’s nucleus. The more such pairs there are in a nucleus, the more slowly the quarks move within the atom’s protons and neutrons.

Schmidt says an atom’s protons and neutrons can pair up constantly, but only momentarily, before splitting apart and going their separate ways. During this brief, high-energy interaction, he believes that quarks in their respective particles may have a “larger space to play.”

“In quantum mechanics, anytime you increase the volume over which an object is confined, it slows down,” Schmidt says. “If you tighten up the space, it speeds up. That’s a known fact.”

As atoms with larger nuclei intrinsically have more protons and neutrons, they also are more likely to have a higher number of proton-neutron pairs, also known as “short-range correlated” or SRC pairs. Therefore, the team concludes that the larger the atom, the more pairs it is likely to contain, resulting in slower-moving quarks in that particular atom.

Schmookler, Schmidt, and Hen as members of the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility, have published their results today in the journal Nature.

From a suggestion to a full picture

In 2011, Hen and collaborators, who has focused much of their research on SRC pairs, wondered whether this ephemeral coupling had anything to do with the EMC effect and the speed of quarks in atomic nuclei.

They gathered data from various particle accelerator experiments, some of which measured the behavior of quarks in certain atomic nuclei, while others detected SRC pairs in other nuclei. When they plotted the data on a graph a clear trend appeared: The larger an atom’s nucleus, the more SRC pairs there were, and the slower the quarks that were measured. The largest nucleus in the data — gold — contained quarks that moved 20 percent more slowly than those in the smallest measured nucleus, helium.

“This was the first time this connection was concretely suggested,” Hen says. “But we had to do a more detailed study to build a whole physical picture.”

So he and his colleagues analyzed data from an experiment that compared atoms of different sizes and allowed measuring both the quarks’ speed and the number of SRC pairs in each atom’s nucleus. The experiment was carried out at the CEBAF Large Acceptance Spectrometer, or CLAS detector, an enormous, four-story spherical particle accelerator at the Thomas Jefferson National Laboratory in Newport News, Virginia.

Jlab CEBAF

Within the detector, Hen describes the team’s target setup as a “kind of a Frankenstein-ish thing,” with mechanical arms, each holding a thin foil made from a different material, such as carbon, aluminum, iron, and lead, each made from atoms containing 12, 27, 67, and 208 protons and neutrons, respectively. An adjacent vessel held liquid deuterium, with atoms containing the lowest number of protons and neutrons of the group.

When they wanted to study a particular foil, they sent a command to the relevant arm to lower the foil of interest, following the deuterium cell and directly in the path of the detector’s electron beam. This beam shot electrons at the deuterium cell and solid foil, at the rate of several billion electrons per second. While a vast majority of electrons miss the targets, some do hit either the protons or neutrons inside the nucleus, or the much tinier quarks themselves. When they hit, the electrons scatter widely, and the angles and energies at which they scatter vary depending on what they hit — information that the detector captures.

Electron tuning

The experiment ran for several months and in the end amassed billions of interactions between electrons and quarks. The researchers calculated the speed of the quark in each interaction, based on the electron’s energy after it scattered, then compared the average quark speed between the various atoms.

By looking at much smaller scaterring angles, corresponding to momentum transfers of a different wave length, the team were able to “zoom out” so that electrons would scatter off the larger protons and neutrons, rather than quarks. SRC pairs are typically extremely energetic and would therefore scatter electrons at higher energies than unpaired protons and neutrons, which is a distinction the researchers used to detect SRC pairs in each material they studied.

“We see that these high-momentum pairs are the reason for these slow-moving quarks,” Hen says.

In particular, they found that the quarks in foils with larger atomic nuclei (and more proton-neutron pairs) moved at most 20 percent slower than deuterium, the material with the least number of pairs.

“These pairs of protons and neutrons have this crazy high-energy interaction, very quickly, and then dissipate,” Schmidt says. “In that time, the interaction is much stronger than normal and the nucleons have significant spatial overlap. So we think quarks in this state slow down a lot.”

Their data show for the first time that how much a quark’s speed is slowed depends on the number of SRC pairs in an atomic nucleus. Quarks in lead, for instance, were far slower than those in aluminum, which themselves were slower than iron, and so on.

The team is now designing an experiment in which they hope to detect the speed of quarks, specifically in SRC pairs.

“We want to isolate and measure correlated pairs, and we expect that will yield this same universal function, in that the way quarks change their velocity inside pairs is the same in carbon and lead, and should be universal across nuclei,” Schmidt says.

Ultimately, the team’s new explanation can help to illuminate subtle yet important differences in the behavior of quarks, the most basic building blocks of the visible world. Scientists have an incomplete understanding of how these tiny particles come to build the protons and neutrons that then come together to form the individual atoms that make up all the material we see in the universe.

“Understanding how quarks interact is really the essence of understanding the visible matter in the universe,” Hen says. “This EMC effect, even though 10 to 20 percent, is something so fundamental that we want to understand it.”

This research was funded, in part, by the U.S. Department of Energy, and the National Science Foundation.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

From Stanford University: “Q-FARM initiative to bolster quantum research at Stanford-SLAC

From Stanford University

February 8, 2019
Ker Than

Patrick Hayden and Jelena Vuckovic will direct Stanford’s new Q-FARM initiative centered around experimental and theoretical quantum science and engineering. (Image credit: L.A. Cicero)

There’s a new farm on the Farm.

Stanford and SLAC National Accelerator Laboratory have launched a new Quantum Fundamentals, ARchitecture and Machines (Q-FARM) initiative to leverage and expand the university’s strengths in quantum science and engineering and to train the field’s next generation of scientists.

“Our mission is not only to do research, it’s also to educate students, bring the community together, fill the gaps that we have in this space and connect to the world outside, both to industry and to other academic institutions,” said Q-FARM director Jelena Vuckovic, a professor of electrical engineering.

Q-FARM emerged from Stanford’s long-range planning process as part of a team focused on understanding the natural world. The idea for it originated from faculty across departments who recognized that the university is uniquely positioned to become a leader in the field of quantum research, said Q-FARM deputy director Patrick Hayden, a professor of physics in the School of Humanities and Sciences.

“I think it is very possible for Stanford to establish itself as the leading center in quantum science and engineering,” Hayden said. “We have advantages that other schools do not, including top-ranked science and engineering departments that are a short distance away from technology companies and SLAC, a renowned laboratory of the U.S. Department of Energy.”

A second wave

First formulated in the early 20th century, quantum mechanics deals with nature at its smallest scales. The theory describes with remarkable precision everything from the interactions between fundamental particles to the nature of chemical bonds and the electrical properties of materials. It even explains the origins of galaxies as tiny quantum ripples in spacetime that were stretched to enormous sizes during the first moments of the universe. Quantum mechanics is also the basis for some of our most transformative and ubiquitous technologies, including transistors and lasers.

As influential as the theory has been, it’s poised to be even more impactful in the future. Beginning in the 1990s, quantum mechanics entered a “second wave” of discovery and innovation driven by theoretical and technological advances.

On the theoretical front, quantum mechanics merged with computer science, mathematics and other branches of physics to give rise to a new field known as quantum information science (QIS). QIS aims to harness the spookier properties of quantum mechanics – superposition, wave-particle duality, entanglement – to manipulate information. Surprisingly, insights and techniques from QIS are proving useful not only for the design of quantum computers, algorithms and sensors but also for providing powerful new tools for investigating old questions in physics.

“I finally feel, after all these years, that I’m at a stage in my life where things are as interesting as the things I missed because I came into physics too late,” said Leonard Susskind, a theoretical physicist at the Stanford Institute for Theoretical Physics. Susskind and Hayden are using quantum information to model black hole interiors and probe the nature of spacetime.

As QIS has matured, so too has the ability of engineers to fabricate quantum-mechanical systems. Phenomena such as quantum teleportation that were once purely theoretical can now be created and studied in the lab. “This is what’s supposed to happen in science, that there is this feedback loop between theory and experiment, but it’s not always true,” Hayden said. “This is an area where it’s really happening and that’s very exciting.”

A strong foundation

Q-FARM will build upon Stanford and SLAC’s strong foundation in quantum science and engineering. The institutions include experts in the field, including Nobel laureate Robert Laughlin, and have played leading roles in a broad range of quantum research, including the discovery and characterization of new quantum materials, the use of quantum sensors to search for dark matter and exploration of the interface between QIS and fundamental physics.

Furthermore, SLAC, as a multi-purpose DOE laboratory, brings unique facilities and expertise for QIS research that will complement Q-FARM on many fronts.

Stanford and SLAC are also located in the heart of Silicon Valley, home to established companies like Google and to a long list of recent startups that are engaged in R&D efforts in quantum technologies. “Stanford has a history of strong interaction with Silicon Valley,” Hayden said. “All the big technology companies are investing in quantum computing. They are looking for the next major breakthrough in terms of computing power or communication power. Quantum mechanics seems to offer that.”

Priorities

With many world-leading research groups already established at Stanford, Q-FARM’s role will be to build bridges between them and create a community that can tackle the major emerging challenges in the area. Among Q-FARM’s initial priorities are the creation of postdoctoral and graduate fellowships and organizing research seminars where faculty, students and visiting scholars can present their research.

Q-FARM will also focus on developing an educational program for undergraduate and graduate students to bolster the current curriculum. “We already have an excellent collection of classes, but we want to coordinate the program between physics and engineering so that we can better educate our students,” Vuckovic said.

Demonstrating a united front on the research end will also help with faculty and student recruitment in an increasingly competitive field and attract some of the significant government funding that will target quantum research.

In 2018, the U.S. Senate unanimously passed the National Quantum Initiative, which authorizes $1.275 billion to be spent over the next five years to fund American quantum information science research and to create multiple centers dedicated to quantum research and education.

“Bringing one of those centers to Stanford and SLAC will help us maintain the strengths we already possess and establish ourselves more broadly in this field,” Vuckovic said.

“If we can sustain this pace, Stanford will be the place where people who work in this field will want to be,” she added. “We have leading physics and leading engineering. We are in Silicon Valley. This is what makes us the right place to carry this forward.”

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

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