Daily Archives: June 28, 2017

Quantum states reveal themselves with measurable 'fingerprint'

Researchers working in Singapore and the United States have discovered that all entangled states of two particles have a classical 'fingerprint'. This breakthrough could help engineers guard against errors and devices that ...

Quantum physic can guarantee that a message has not be intercepted before reaching its destination. Thanks to the laws of quantum physic, a particle of light a photon can be in two distinct states simultaneously, ...

Phase transitions include common phenomena like water freezing or boiling. Similarly, quantum systems at a temperature of absolute zero also experience phase transitions. The pressure or magnetic field applied to such systems ...

Quantum computers are experimental devices that offer large speedups on some computational problems. One promising approach to building them involves harnessing nanometer-scale atomic defects in diamond materials.

Our computers, even the fastest ones, seem unable to withstand the needs of the enormous quantity of data produced in our technological society. That's why scientists are working on computers using quantum physics, orquantum ...

When a ballerina pirouettes, twirling a full revolution, she looks just as she did when she started. But for electrons and other subatomic particles, which follow the rules of quantum theory, that's not necessarily so. When ...

(Phys.org)A team at Harvard University has found a way to create a cold-atom FermiHubbard antiferromagnet, which offers new insight into how electrons behave in solids. In their paper published in the journal Nature, ...

The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are brokenparticles can exist in two places at once, they can react to each other over ...

The 'quantized magneto-electric effect' has been demonstrated for the first time in topological insulators at TU Wien, which is set to open up new and highly accurate methods of measurement.

As if by magic, seemingly independent pendulum clocks can come together to tick simultaneously and in synchrony. The phenomenon of "self-organized synchronization" frequently occurs in nature and engineering and is one of ...

Scientists at Amherst College (USA) and Aalto University (Finland) have made the first experimental observations of the dynamics of isolated monopoles in quantum matter.

Quantum field theories are often hard to verify in experiments. Now, there is a new way of putting them to the test. Scientists have created a quantum system consisting of thousands of ultra cold atoms. By keeping them in ...

(Phys.org)Stars, quasars, and other celestial objects generate photons in a random way, and now scientists have taken advantage of this randomness to generate random numbers at rates of more than one million numbers per ...

Energy dissipation is a key ingredient in understanding many physical phenomena in thermodynamics, photonics, chemical reactions, nuclear fission, photon emissions, or even electronic circuits, among others.

In a recent experiment at EPFL, a microwave resonator, a circuit that supports electric signals oscillating at a resonance frequency, is coupled to the vibrations of a metallic micro-drum. By actively cooling the mechanical ...

Research from The University of Manchester has thrown new light on the use of miniaturised 'heat engines' that could one day help power nanoscale machines like quantum computers.

By precisely measuring the entropy of a cerium copper gold alloy with baffling electronic properties cooled to nearly absolute zero, physicists in Germany and the United States have gleaned new evidence about the possible ...

A well-known computational problem seeks to find the most efficient route for a traveling salesman to visit clients in a number of cities. Seemingly simple, it's actually surprisingly complex and much studied, with implications ...

In our solar system, an asteroid orbits the sun in the opposite direction to the planets. Asteroid 2015 BZ509, also known as Bee-Zed, takes 12 years to make one complete orbit around the sun. This is the same orbital period ...

Producing biofuels like ethanol from plant materials requires various enzymes to break down the cellulosic fibers. Scientists using neutron scattering have identified the specifics of an enzyme-catalyzed reaction that could ...

Throughout its 4.5-billion-year history, Earth has been repeatedly pummelled by space rocks that have caused anything from an innocuous splash in the ocean to species annihilation.

Using five different scientific approaches, a team including University of Wyoming researchers has given considerable support to the idea that humans lived year-round in the Andean highlands of South America over 7,000 years ...

Scientists have developed a new biological tool for examining molecules - the building blocks of life - which they say could provide new insights and other benefits such as reducing the numbers of animals used in experiments.

For the first time ever, astronomers at The University of New Mexico say they've been able to observe and measure the orbital motion between two supermassive black holes hundreds of millions of light years from Earth - a ...

Many geckos inhabit trees, often living high in the canopy. Relying on their incredible adhesive strength to help them break their fall, they jump from trees, and land on either leaves or relatively smooth tree trunks. How ...

(Phys.org)A pair of researchers, one with the Weizmann Institute of Science in Israel the other with Princeton University in the U.S. has come up with a possible explanation for the inability of space scientists to find ...

Building transient electronics is usually about doing something to make them stop working: blast them with light, soak them with acid, dunk them in water.

(Phys.org)A new study recently published on arXiv.org reveals that the fossil group galaxy NGC 1132 (also known as UGC 2359) has a disturbed and asymmetrical hot halo. The findings provide new insights into the formation ...

A new, highly virulent strain of malicious software that is crippling computers globally appears to have been sown in Ukraine, where it badly hobbled much of the government and private sector on the eve of a holiday celebrating ...

When insects skip the light fandango their romantic foreplay often involves some pretty crazy things like hypnotic dance moves and flashy colors. In some species it ends with a complex ejaculate package that does more than ...

A study of yeast reveals new mechanism that allows cells to adapt to environmental changes more rapidly by accelerating genetic changes around genes that boost fitness, publishing 27 June in the open access journal PLOS Biology, ...

New research finds large earthquakes can trigger underwater landslides thousands of miles away, weeks or months after the quake occurs.

Proteins found in tick saliva could be used to treat a potentially fatal form of heart disease, according to new Oxford University research.

For us humans, it goes without saying that we reward others as an indication of the gratitude we feel towards them. Scientists from the Max Planck Institutes for Evolutionary Anthropology and for Mathematics in the Sciences ...

Researchers in China have developed a genetic engineering approach capable of delivering many genes at once and used it to make rice endospermseed tissue that provides nutrients to the developing plant embryoproduce ...

In the world of heavy metal poisoning, arsenic may have found a sidekickand it's one that needs more research to understand its influence on human health, according to Kansas State University researchers.

Recent increases in an unregulated ozone-depleting substance, could delay recovery of Antarctic ozone levels by 5-30 years, depending on emissions scenarios.

A team of researchers has found a way to detect trace gases down to concentrations at the parts-per-quadrillion level using a new variation on the photoacoustic effect, a technique that measures the sound generated when light ...

In the fight against the viruses that invade everyday life, seeing and understanding the battleground is essential. Scientists at the Morgridge Institute for Research have, for the first time, imaged molecular structures ...

A warming climate is not just melting the Arctic's sea ice; it is stirring the remaining ice faster, increasing the odds that ice-rafted pollution will foul a neighboring country's waters, says a new study.

Researchers from the University of Zurich and the University Hospital Zurich have discovered the protein that enables natural embryonic stem cells to form all body cells. In the case of embryonic stem cells maintained in ...

Israel is subjected to sand and dust storms from several directions: northeast from the Sahara, northwest from Saudi Arabia and southwest from the desert regions of Syria. The airborne dust carried in these storms affects ...

Under anaerobic conditions, certain bacteria can produce electricity. This behavior can be exploited in microbial fuel cells, with a special focus on wastewater treatment schemes. A weak point is the dissatisfactory power ...

A team of three Dutch astronomers from the University of Amsterdam and Leiden University found a new way to form two black holes that orbit each other for quite a while and then merge. Their publication with computer simulations ...

Scientists have reconstructed in detail the collapse of the Eurasian ice sheet at the end of the last ice age. The big melt wreaked havoc across the European continent, driving home the original Brexit 10,000 years ago.

As NASA's Parker Solar Probe spacecraft begins its first historic encounter with the sun's corona in late 2018flying closer to our star than any other mission in historya revolutionary cooling system will keep its solar ...

A diagnostic technique that can detect tiny molecules signalling the presence of cancer could be on the horizon.

Having minority middle school students write a series of self-affirmation exercises focusing on core values improved the odds that the students would pursue college tracks in school, according to Stanford scholars.

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Intern Katherine Dunne with mentor Maurice Garcia-Sciveres. (Credit: Marilyn Chung/Berkeley Lab)

As a high school student in Birmingham, Alabama, Berkeley Lab Undergraduate Research (BLUR) intern Katie Dunne first dreamed of becoming a physicist after reading Albert Einsteins biography, but didnt know anyone who worked in science. I felt like the people who were good at math and science werent my friends, she said. So when it came time for college, she majored in English, and quickly grew dissatisfied because it wasnt challenging enough. Eventually, she got to know a few engineers, but none of them were women, she recalled.

She still kept physics in the back of her mind until she read an article about The First Lady of Physics, Chien-Shiung Wu, an experimental physicist who worked on the Manhattan Project, and later designed the Wu experiment, which proved that the conservation of parity is violated by weak interactions. Two male theorists who proposed parity violation won the 1957 Nobel Prize in physics, and Wu did not, Dunne said. When I read about her, I decided that thats what I want to do design experiments.

Katie Dunne, left, and mentor Maurice Garcia-Sciveres. (Credit: Marilyn Chung/Berkeley Lab)

So she put physics front and center, and about four years ago, transferred as a physics major to the City College of San Francisco. With Silicon Valley nearby, there are many opportunities here to get work experience in instrumentation and electrical engineering, Dunne said. In the summers of 2014 and 2015, she landed internships in the Human Factors division at NASA Ames Research Center in Mountain View, where she streamlined the development of a printed circuit board for active infrared illumination.

But it wasnt until she took a class in modern physics when she discovered her true passion particle physics. When we got to quantum physics, it was great. Working on the problems of quantum physics is exciting, she said. Its so elegant and dovetails with math. Its the ultimate mystery because we cant observe quantum behavior.

When it came time to apply for her next summer internship in 2016, instead of reapplying for a position at NASA, she googled ATLAS, the name of a 7,000-ton detector for the Large Hadron Collider (LHC). Her search drummed up an article about Beate Heinemann, who, at the time, was a researcher with dual appointments at UC Berkeley and Berkeley Lab and was deputy spokesperson of the ATLAS collaboration. (Heinemann is also one of the 20percent of female physicists working on the ATLAS experiment.)

When Dunne contacted Heinemann to ask if she would consider her for an internship, she suggested that she contact Maurice Garcia-Sciveres, a physicist at Berkeley Lab whose research specializes in pixel detectors for ATLAS, and who has mentored many students interested in instrumentation.

Garcia-Sciveres invited Dunne to a meeting so she could see the kind of work that they do. I could tell I would get a lot of hands-on experience, she said. So she applied for her first internship with Garcia-Sciveres through the Community College Internship (CCI) program which, like the BLUR internship program, is managed by Workforce Development & Education at Berkeley Lab and started to work with his team on building prototype integrated circuit (IC) test systems for ATLAS as part of the High Luminosity Large Hadron Collider (HL-LHC) Project, an international collaboration headed by CERN to increase the LHCs luminosity (rate of collisions) by a factor of 10 by 2020.

A quad module with a printed circuit board (PCB) for power and data interface to four FE-I4B chips. Dunne designed the PCB. (Credit: Katie Dunne/Berkeley Lab)

For the ATLAS experiment, we work with the Engineering Division to build custom electronics and integrated circuits for silicon detectors. Our work is focused on improving the operation, testing, and debugging of these ICs, said Garcia-Sciveres.

During Dunnes first internship, she analyzed threshold scans for an IC readout chip, and tested their radiation hardness or threshold for tolerating increasing radiation doses at the Labs 88-Inch Cyclotron and at SLAC National Accelerator Laboratory. Berkeley Lab is a unique environment for interns. They throw you in, and you learn on the job. The Lab gives students opportunities to make a difference in the field theyre working in, she said.For the ATLAS experiment, we work with the Engineering Division to build custom electronics and integrated circuits for silicon detectors. Our work is focused on improving the operation, testing, and debugging of these ICs, said Garcia-Sciveres.

For Garcia-Sciveres, it didnt take long for Dunne to prove she could make a difference for his team. Just after her first internship at Berkeley Lab, the results from her threshold analysis made their debut as data supporting his presentation at the 38th International Conference on High Energy Physics (ICHEP) in August 2016. The results were from her measurements, he said. This is grad student-level work shes been doing. Shes really good.

Katie Dunne delivers a poster presentation in spring 2017. (Credit: Marilyn Chung/Berkeley Lab)

After the conference, Garcia-Sciveres asked Dunne to write the now published proceedings (he and the other authors provided her with comments and suggested wording). And this past January, Dunne presented Results of FE65-P2 Stability Tests for the High Luminosity LHC Upgrade during the HL-LHC, BELLE2, Future Colliders session of the American Physical Society (APS) Meeting in Washington, D.C.

This summer, for her third and final internship at the Lab, Dunne is working on designing circuit boards needed for the ATLAS experiment, and assembling and testing prototype multi-chip modules to evaluate system performance. She hopes to continue working on ATLAS when she transfers to UC Santa Cruz as a physics major in the fall, and would like to get a Ph.D. in physics one day. I love knowing that the work I do matters. My internships and work experience as a research assistant at Berkeley Lab have made me more confident in the work Im doing, and more passionate about getting things done and sharing my results, she said.

Goherefor more information about internships hosted by Workforce Development & Education at Berkeley Lab, or contact them ateducation@lbl.gov.

This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Community College Internship (CCI) program.

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Berkeley Lab Intern Finds Her Way in Particle Physics | Berkeley Lab - Lawrence Berkeley National Laboratory

Albert Einstein is heading out for his daily stroll and has to pass through two doorways. First he walks through the green door, and then through the red one. Or wait did he go through the red first and then the green? It must have been one or the other. The events had have to happened in a sequence, right?

Not if Einstein were riding on one of the photons ricocheting through Philip Walther's lab at the University of Vienna. Walther's group has shown that it is impossible to say in which order these photons pass through a pair of gates as they zip around the lab. It's not that this information gets lost or jumbled it simply doesn't exist. In Walther's experiments, there is no well-defined order of events.

This finding1 in 2015 made the quantum world seem even stranger than scientists had thought. Walther's experiments mash up causality: the idea that one thing leads to another. It is as if the physicists have scrambled the concept of time itself, so that it seems to run in two directions at once.

In everyday language, that sounds nonsensical. But within the mathematical formalism of quantum theory, ambiguity about causation emerges in a perfectly logical and consistent way. And by creating systems that lack a clear flow of cause and effect2, researchers now think they can tap into a rich realm of possibilities. Some suggest that they could boost the already phenomenal potential of quantum computing. A quantum computer free from the constraints of a predefined causal structure might solve some problems faster than conventional quantum computers, says quantum theorist Giulio Chiribella of the University of Hong Kong.

What's more, thinking about the 'causal structure' of quantum mechanics which events precede or succeed others might prove to be more productive, and ultimately more intuitive, than couching it in the typical mind-bending language that describes photons as being both waves and particles, or events as blurred by a haze of uncertainty.

And because causation is really about how objects influence one another across time and space, this new approach could provide the first steps towards uniting the two cornerstone theories of physics and resolving one of the most profound scientific challenges today. Causality lies at the interface between quantum mechanics and general relativity, says Walther's collaborator aslav Brukner, a theorist at the Institute for Quantum Optics and Quantum Information in Vienna, and so it could help us to think about how one could merge the two conceptually.

Causation has been a key issue in quantum mechanics since the mid-1930s, when Einstein challenged the apparent randomness that Niels Bohr and Werner Heisenberg had installed at the heart of the theory. Bohr and Heisenberg's Copenhagen interpretation insisted that the outcome of a quantum measurement such as checking the orientation of a photon's plane of polarization is determined at random, and only in the instant that the measurement is made. No reason can be adduced to explain that particular outcome. But in 1935, Einstein and his young colleagues Boris Podolsky and Nathan Rosen (now collectively denoted EPR) described a thought experiment that pushed Bohr's interpretation to a seemingly impossible conclusion.

The EPR experiment involves two particles, A and B, that have been prepared with interdependent, or 'entangled', properties. For example, if A has an upward-pointing 'spin' (crudely, a quantum property that can be pictured a little bit like the orientation of a bar magnet), then B must be down, and vice versa.

Both pairs of orientations are possible. But researchers can discover the actual orientation only when they make a measurement on one of the particles. According to the Copenhagen interpretation, that measurement doesn't just reveal the particle's state; it actually fixes it in that instant. That means it also instantly fixes the state of the particle's entangled partner however far away that partner is. But Einstein considered this apparent instant action at a distance impossible, because it would require faster-than-light interaction across space, which is forbidden by his special theory of relativity. Einstein was convinced that this invalidated the Copenhagen interpretation, and that particles A and B must already have well-defined spins before anybody looks at them.

Measurements of entangled particles show, however, that the observed correlation between the spins can't be explained on the basis of pre-existing properties. But these correlations don't actually violate relativity because they can't be used to communicate faster than light. Quite how the relationship arises is hard to explain in any intuitive cause-and-effect way.

But what the Copenhagen interpretation does at least seem to retain is a time-ordering logic: a measurement can't induce an effect until after it has been made. For event A to have any effect on event B, A has to happen first. The trouble is that this logic has unravelled over the past decade, as researchers have realized that it is possible to imagine quantum scenarios in which one simply can't say which of two related events happens first.

Classically, this situation sounds impossible. True, we might not actually know whether A or B happened first but one of them surely did. Quantum indeterminacy, however, isn't a lack of knowledge; it's a fundamental prohibition on pronouncing on any 'true state of affairs' before a measurement is made.

Brukner's group in Vienna, Chiribella's team and others have been pioneering efforts to explore this ambiguous causality in quantum mechanics3, 4. They have devised ways to create related events A and B such that no one can say whether A preceded and led to (in a sense 'caused') B, or vice versa. This arrangement enables information to be shared between A and B in ways that are ruled out if there is a definite causal order. In other words, an indeterminate causal order lets researchers do things with quantum systems that are otherwise impossible.

The trick they use involves creating a special type of quantum 'superposition'. Superpositions of quantum states are well known: a spin, for example, can be placed in a superposition of up and down states. And the two spins in the EPR experiment are in a superposition in that case involving two particles. It's often said that a quantum object in a superposition exists in two states at once, but more properly it simply cannot be said in advance what the outcome of a measurement would be. The two observable states can be used as the binary states (1 and 0) of quantum bits, or qubits, which are the basic elements of quantum computers.

The researchers extend this concept by creating a causal superposition. In this case, the two states represent sequences of events: a particle goes first through gate A and then through gate B (so that A's output state determines B's input), or vice versa.

In 2009, Chiribella and his co-workers came up with a theoretical way to do an experiment like this using a single qubit as a switch that controls the causal order of events experienced by a particle that acts as second qubit3. When the control-switch qubit is in state 0, the particle goes through gate A first, and then through gate B. When the control qubit is in state 1, the order of the second qubit is BA. But if that qubit is in a superposition of 0 and 1, the second qubit experiences a causal superposition of both sequences meaning there is no defined order to the particle's traversal of the gates (see 'Trippy journeys').

Nik Spencer/Nature

Three years later, Chiribella proposed an explicit experimental procedure for enacting this idea5; Walther, Brukner and their colleagues subsequently worked out how to implement it in the lab1. The Vienna team uses a series of 'waveplates' (crystals that change a photon's polarization) and partial mirrors that reflect light and also let some pass through. These devices act as the logic gates A and B to manipulate the polarization of a test photon. A control qubit determines whether the photon experiences AB or BA or a causal superposition of both. But any attempt to find out whether the photon goes through gate A or gate B first will destroy the superposition of gate ordering.

Having demonstrated causal indeterminacy experimentally, the Vienna team wanted to go further. It's one thing to create a quantum superposition of causal states, in which it is simply not determined what caused what (that is, whether the gate order is AB or BA). But the researchers wondered whether it is possible to preserve causal ambiguity even if they spy on the photon as it travels through various gates.

At face value, this would seem to violate the idea that sustaining a superposition depends on not trying to measure it. But researchers are now realizing that in quantum mechanics, it's not exactly what you do that matters, but what you know.

Last year, Walther and his colleagues devised a way to measure the photon as it passes through the two gates without immediately changing what they know about it6. They encode the result of the measurement in the photon itself, but do not read it out at the time. Because the photon goes through the whole circuit before it is detected and the measurement is revealed, that information can't be used to reconstruct the gate order. It's as if you asked someone to keep a record of how they feel during a trip and then relay the information to you later so that you can't deduce exactly when and where they were when they wrote it down.

As the Vienna researchers showed, this ignorance preserves the causal superposition. We don't extract any information about the measurement result until the very end of the entire process, when the final readout takes place, says Walther. So the outcome of the measurement process, and the time when it was made, are hidden but still affect the final result.

Other teams have also been creating experimental cases of causal ambiguity by using quantum optics. For example, a group at the University of Waterloo in Canada and the nearby Perimeter Institute for Theoretical Physics has created quantum circuits that manipulate photon states to produce a different causal mash-up. In effect, a photon passes through gates A and B in that order, but its state is determined by a mixture of two causal procedures: either the effect of B is determined by the effect of A, or the effects of A and B are individually determined by some other event acting on them both, in much the same way that a hot day can increase sunburn cases and ice-cream sales without the two phenomena being directly causally related. As with the Vienna experiments, the Waterloo group found that it's not possible to assign a single causal 'story' to the state the photons acquire7.

Some of these experiments are opening up new opportunities for transmitting information. A causal superposition in the order of signals travelling through two gates means that each can be considered to send information to the other simultaneously. Crudely speaking, you get two operations for the price of one, says Walther. This offers a potentially powerful shortcut for information processing.

An indeterminate causal order lets researchers do things with quantum systems that are otherwise impossible.

Although it has long been known that using quantum superposition and entanglement could exponentially increase the speed of computation, such tricks have previously been played only with classical causal structures. But the simultaneous nature of pathways in a quantum-causal superposition offers a further boost in speed. That potential was apparent when such superpositions were first proposed: quantum theorist Lucien Hardy at the Perimeter Institute8 and Chiribella and his co-workers3 independently suggested that quantum computers operating with an indefinite causal structure might be more powerful than ones in which causality is fixed.

Last year, Brukner and his co-workers showed9 that building such a shortcut into an information-processing protocol with many gates should give an exponential increase in the efficiency of communication between gates, which could be beneficial for computation. We haven't reached the end yet of the possible speed-ups, says Brukner. Quantum mechanics allows way more.

It's not terribly complicated to build the necessary quantum-circuit architectures, either you just need quantum switches similar to those Walther has used. I think this could find applications soon, Brukner says.

The bigger goal, however, is theoretical. Quantum causality might supply a point of entry to some of the hardest questions in physics such as where quantum mechanics comes from.

Quantum theory has always looked a little ad hoc. The Schrdinger equation works marvellously to predict the outcomes of quantum experiments, but researchers are still arguing about what it means, because it's not clear what the physics behind it is. Over the past two decades, some physicists and mathematicians, including Hardy10 and Brukner11, have sought to clarify things by building 'quantum reconstructions': attempts to derive at least some characteristic properties of quantum-mechanical systems such as entanglement and superpositions from simple axioms about, say, what can and can't be done with the information encoded in the states (see Nature 501, 154156; 2013).

The framework of causal models provides a new perspective on these questions, says Katja Ried, a physicist at the University of Innsbruck in Austria who previously worked with the University of Waterloo team on developing systems with causal ambiguity. If quantum theory is a theory about how nature processes and distributes information, then asking in which ways events can influence each other may reveal the rules of this processing.

And quantum causality might go even further by showing how one can start to fit quantum theory into the framework of general relativity, which accounts for gravitation. The fact that causal structure plays such a central role in general relativity motivates us to investigate in which ways it can 'behave quantumly', says Ried.

Most of the attempts to understand quantum mechanics involve trying to save some aspects of the old classical picture, such as particle trajectories, says Brukner. But history shows us that what is generally needed in such cases is something more, he says something that goes beyond the old ideas, such as a new way of thinking about causality itself. When you have a radical theory, to understand it you usually need something even more radical.

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How quantum trickery can scramble cause and effect - Nature.com