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The black-hole collision that reshaped physics

The black-hole collision that reshaped physics | Amazing Science | Scoop.it

The event was catastrophic on a cosmic scale — a merger of black holes that violently shook the surrounding fabric of space and time, and sent a blast of space-time vibrations known as gravitational waves rippling across the Universe at the speed of light.

 

But it was the kind of calamity that physicists on Earth had been waiting for. On 14 September, when those ripples swept across the freshly upgraded Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO), they showed up as spikes in the readings from its two L-shaped detectors in Louisiana and Washington state. For the first time ever, scientists had recorded a gravitational-wave signal.

 

“There it was!” says LIGO team member Daniel Holz, an astrophysicist at the University of Chicago in Illinois. “And it was so strong, and so beautiful, in both detectors.” Although the shape of the signal looked familiar from the theory, Holz says, “it's completely different when you see something in the data. It's this transcendent moment”.

 

The signal, formally designated GW150914 after the date of its occurrence and informally known to its discoverers as 'the Event', has justly been hailed as a milestone in physics. It has provided a wealth of evidence for Albert Einstein's century-old general theory of relativity, which holds that mass and energy can warp space-time, and that gravity is the result of such warping. Stuart Shapiro, a specialist in computer simulations of relativity at the University of Illinois at Urbana–Champaign, calls it “the most significant confirmation of the general theory of relativity since its inception”.

 

But the Event also marks the start of a long-promised era of gravitational-wave astronomy. Detailed analysis of the signal has already yielded insights into the nature of the black holes that merged, and how they formed. With more events such as these — the LIGO team is analysing several other candidate events captured during the detectors' four-month run, which ended in January — researchers will be able to classify and understand the origins of black holes, just as they are doing with stars.

 

Still more events should appear starting in September, when Advanced LIGO is scheduled to begin joint observations with its European counterpart, the Franco–Italian-led Advanced Virgo facility near Pisa, Italy. (The two collaborations already pool data and publish papers together.) This detector will not only contribute crucial details to events, but could also help astronomers to make cosmological-distance measurements more accurately than before.

 

“It's going to be a really good ride for the next few years,” says Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics in Hanover, Germany.

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Scientists suggest a 100 times faster type of memory cell based on Josephson junctions

Scientists suggest a 100 times faster type of memory cell based on Josephson junctions | Amazing Science | Scoop.it

A group of scientists from Moscow Institute of Physics and Technology and from the Moscow State University has developed a fundamentally new type of memory cell based on superconductors -- this type of memory will be able to work hundreds of times faster than the types of memory devices commonly used today, according to an article published in the journal Applied Physics Letters.

 

"With the operational function that we have proposed in these memory cells, there will be no need for time-consuming magnetization and demagnetization processes. This means that read and write operations will take only a few hundred picoseconds, depending on the materials and the geometry of the particular system, while conventional methods take hundreds or thousands of times longer than this," said the corresponding author of the study, Alexander Golubov, the Head of MIPT's Laboratory of Quantum Topological Phenomena in Superconducting Systems.

 

Golubov and his colleagues have proposed creating basic memory cells based on quantum effects in "sandwiches" of a superconductor -- dielectric (or other insulating material) -- superconductor, which were predicted in the 1960s by the British physicist Brian Josephson. The electrons in these "sandwiches" (they are called "Josephson junctions") are able to tunnel from one layer of a superconductor to another, passing through the dielectric like balls passing through a perforated wall.

 

Today, Josephson junctions are used both in quantum devices and conventional devices. For example, superconducting qubits are used to build the D-wave quantum system, which is capable of finding the minima of complex functions using the quantum annealing algorithm. There are also ultra-fast analogue-to-digital converters, devices to detect consecutive events, and other systems that do not require fast access to large amounts of memory. There have also been attempts to use the Josephson Effect to create ordinary processors. An experimental processor of this type was created in Japan in the late 1980s. In 2014, the research agency IAPRA resumed its attempts to create a prototype of a superconducting computer.

 

Josephson junctions with ferromagnets used as the middle of the "sandwich" are currently of greatest practical interest. In memory elements that are based on ferromagnets the information is encoded in the direction of the magnetic field vector in the ferromagnet. However, there are two fundamental flaws with this process: firstly, the low density of the "packaging" of the memory elements -- additional chains need to be added to provide extra charge for the cells when reading or writing data, and secondly the magnetization vector cannot be changed quickly, which limits the writing speed.

 

The group of physicists from MIPT and MSU proposed encoding the data in Josephson cells in the value of the superconducting current. By studying the superconductor-normal metal/ferromagnet-superconductor-insulator-superconductor junctions, the scientists discovered that in certain longitudinal and transverse dimensions the layers of the system may have two energy minima, meaning they are in one of two different states. These two minima can be used to record data -- zeros and ones.

 

In order to switch the system from "zero" to "one" and back again, the scientists have suggested using injection currents flowing through one of the layers of the superconductor. They propose to read the status using the current that flows through the whole structure. These operations can be performed hundreds of times faster than measuring the magnetization or magnetization reversal of a ferromagnet.

 

"In addition, our method requires only one ferromagnetic layer, which means that it can be adapted to so-called single flux quantum logic circuits, and this means that there will be no need to create an entirely new architecture for a processor. A computer based on single flux quantum logic can have a clock speed of hundreds of gigahertz, and its power consumption will be dozens of times lower," said Golubov.

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Tiny failure: Ultrasmall nano-engines bend second law of thermodynamics

Tiny failure: Ultrasmall nano-engines bend second law of thermodynamics | Amazing Science | Scoop.it
When French engineer Sadi Carnot calculated the maximum efficiency of a heat engine in 1824, he had no idea what heat was. In those days, physicists thought heat was a fluid called caloric. But Carnot, later lauded as a pioneer in establishing the second law of thermodynamics, didn’t have to know those particulars, because thermodynamics is insensitive to microscopic details. Heat flows from hot to cold regardless of whether it consists of a fluid or, as it turns out, the collective motion of trillions of trillions of molecules. Thermodynamics, the laws and equations governing energy and its usefulness to do work, concerns itself only with the big picture.

It’s a successful approach. As thermodynamics requires, energy is always conserved (the first law), and when it flows from hot to cold it can do work, limited by the generation of disorder, or entropy (the second law). These laws dictate everything from the miles per gallon a car engine gets to the battery life of a smartphone. They help physicists better understand black holes and why time moves forward but not backward (SN: 7/25/15, p. 15).

Yet the big picture approach, considering the forest rather than the trees, has made physicists wonder if thermodynamics holds at all scales. Would it work if an engine consisted of three molecules rather than the typical trillion trillion? In the realm of the very small, governed by the quirky rules of quantum mechanics, perhaps the thermodynamic code is not so rigid.

 

It goes back to statistics, says University College London quantum theoretical physicist Jonathan Oppenheim. If the trillion trillion gas molecules in a steam engine were represented by that many coins, then the result of flipping all those coins would be a homogenous mixture of heads and tails, the equivalent of stable temperature and maximum entropy. That’s why steam engines always follow the rules. But flip three minicoins inside a tiny quantum engine and all three could easily land on heads, as if all the fast molecules stayed in one compartment rather than mixing with the other — a violation of the second law.

 

Experiments over the years had suggested that if the second law of thermodynamics does break down at small scales, the violation is not very drastic. Last year, Oppenheim and colleagues got more specific, publishing a detailed analysis in the Proceedings of the National Academy of Sciences. Their results indicate that not only does the second law actually hold at the quantum scale, it is also more demanding.

 

Rather than analyzing entropy directly, Oppenheim’s team looked at how much energy a system has available to do work, a quantity called free energy. In our macroscopic world, the amount of free energy depends only on a system’s temperature and entropy. But by zooming in toward smaller and smaller collections of particles, the researchers found that they had to take into account several more varieties of free energy. Every one of them decreases over time. In other words, the second law requires adherence to even more rules at the quantum level.

Recent experiments have made it clear that attempts to circumvent the second law at any scale are doomed.

 

In the Dec. 31 Physical Review Letters, Jonne Koski, a physicist at Aalto University in Finland, and colleagues created the laboratory equivalent of the heat-manipulating “demon” conjured by Scottish physicist James Clerk Maxwell in 1867. Maxwell wondered whether a hypothetical microscopic entity tracking the particles flitting around two adjacent containers could separate the fast-moving particles from the slow ones. The demon’s actions would minimize the system’s total entropy, a violation of the second law, and create a temperature difference that could be exploited to do work for free.

 

Koski’s team built a demonic device that deprived an electronic circuit of heat and thus its entropy as well. The demon did its job: A visitor to the lab observing the experiment would think  the circuit was violating the second law. But the researchers also noticed that the demon paid a price for its transgressions. As it performed its dirty deed, the demon itself heated up. The total entropy of the circuit and the demon together actually increased, just as the second law requires (SN Online: 12/1/15).

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Experiment shows magnetic chips could dramatically increase computing's energy efficiency

Experiment shows magnetic chips could dramatically increase computing's energy efficiency | Amazing Science | Scoop.it

In a breakthrough for energy-efficient computing, engineers at the University of California, Berkeley, have shown for the first time that magnetic chips can operate with the lowest fundamental level of energy dissipation possible under the laws of thermodynamics.

 

The findings, to be published Friday, March 11, 2016 in the peer-reviewed journal Science Advances, mean that dramatic reductions in power consumption are possible—as much as one-millionth the amount of energy per operation used by transistors in modern computers.

 

This is critical for mobile devices, which demand powerful processors that can run for a day or more on small, lightweight batteries. On a larger, industrial scale, as computing increasingly moves into 'the cloud,' the electricity demands of the giant cloud data centers are multiplying, collectively taking an increasing share of the country's—and world's—electrical grid.

 

"We wanted to know how small we could shrink the amount of energy needed for computing," said senior author Jeffrey Bokor, a UC Berkeley professor of electrical engineering and computer sciences and a faculty scientist at the Lawrence Berkeley National Laboratory. "The biggest challenge in designing computers and, in fact, all our electronics today is reducing their energy consumption."

 

Lowering energy use is a relatively recent shift in focus in chip manufacturing after decades of emphasis on packing greater numbers of increasingly tiny and faster transistors onto chips. "Making transistors go faster was requiring too much energy," said Bokor, who is also the deputy director the Center for Energy Efficient Electronics Science, a Science and Technology Center at UC Berkeley funded by the National Science Foundation. "The chips were getting so hot they'd just melt."

 

Researchers have been turning to alternatives to conventional transistors, which currently rely upon the movement of electrons to switch between 0s and 1s. Partly because of electrical resistance, it takes a fair amount of energy to ensure that the signal between the two states is clear and reliably distinguishable, and this results in excess heat.

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Triple entanglement in three dimensions: Three "twisted" photons entangled

Triple entanglement in three dimensions: Three "twisted" photons entangled | Amazing Science | Scoop.it

Researchers at the Institute of Quantum Optics and Quantum Information (IQOQI), the University of Vienna, and the Universitat Autonoma de Barcelona have achieved a new milestone in quantum physics: they were able to entangle three particles of light in a high-dimensional quantum property related to the "twist" of their wavefront structure. Just like Schrödinger's famous cat that is simultaneously dead and alive, all previous demonstrations of multi-particle entanglement have been with quantum objects in two discrete levels, or dimensions. The twisted photons used in the Vienna experiment have no such limit to their dimensionality, and can simultaneously exist in three or more quantum states. The three-photon entangled state created by the Vienna group breaks this previous record of dimensionality, and brings to light a new form of asymmetric entanglement that has not been observed before. The results from their experiment appear in the journal Nature Photonics.

Entanglement is a counterintuitive property of quantum physics that has long puzzled scientists and philosophers alike. Entangled quanta of light seem to exert an influence on each other, irrespective of how much distance is between them. Consider for example a metaphorical quantum ice dancer, who has the uncanny ability to pirouette both clockwise and counter-clockwise simultaneously. A pair of entangled ice-dancers whirling away from each other would then have perfectly correlated directions of rotation: If the first dancer twirls clockwise then so does her partner, even if skating in ice rinks on two different continents. "The entangled photons in our experiment can be illustrated by not two, but three such ice dancers, dancing a perfectly synchronized quantum mechanical ballet," explains Mehul Malik, the first author of the paper. "Their dance is also a bit more complex, with two of the dancers performing yet another correlated movement in addition to pirouetting. This type of asymmetric quantum entanglement has been predicted before on paper, but we are the first to actually create it in the lab."

The scientists created their three-photon entangled state by using yet another quantum mechanical trick: they combined two pairs of high-dimensionally entangled photons in such a manner that it became impossible to ascertain where a particular photon came from. Besides serving as a test bed for studying many fundamental concepts in quantum mechanics, multi-photon entangled states such as these have applications ranging from quantum computing to quantum encryption. Along these lines, the authors of this study have developed a new type of quantum cryptographic protocol using their state that allows different layers of information to be shared asymmetrically among multiple parties with unconditional security. "The experiment opens the door for a future quantum Internet with more than two partners and it allows them to communicate more than one bit per photon," says Anton Zeilinger. Many technical challenges remain before such a quantum communication protocol becomes a practical reality. However, given the rapid progress in quantum technologies today, it is only a matter of time before this type of entanglement finds a place in the quantum networks of the future.

Publication in "Nature Photonics": Multi-Photon Entanglement in High Dimensions: Mehul Malik, Manuel Erhard, Marcus Huber, Mario Krenn, Robert Fickler, Anton Zeilinger. Nature Photonics, 2016
http://dx.doi.org/10.1038/nphoton.2016.12.

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100 million-degrees essential for successful nuclear fusion

100 million-degrees essential for successful nuclear fusion | Amazing Science | Scoop.it

Some scientists believe fusion power -- the energy that powers the stars -- is the future of sustainable energy. Despite periodic breakthroughs, physicists have struggled to replicate the reaction in the lab. New research suggests scientists may have cleared another hurdle en route to synthesizing nuclear fusion.

The key, researchers say, is super hot fluid.

 

During fusion experiments, researchers have been frustrated by failing million-degree heating beams, destabilizing their fusion attempts before any energy is generated. A team of scientists at Australian National University believe they solved the problem using fluid dynamics.

 

"There was a strange wave mode which bounced the heating beams out of the experiment," researcher Zhisong Qu said in a news release. "This new way of looking at burning plasma physics allowed us to understand this previously impenetrable problem."

 

Qu is a theoretical physicist at the ANU Research School of Physics and Engineering and lead author of a new paper on fusion in the journal Physical Review Letters.

 

Earthbound scientists have been attempting to replicate stellar fusion using a strategy called magnetic confinement fusion, in which hydrogen is coaxed into plasma form and heated to temperatures ten times those found inside the center of the sun.

The problem is these super-heated beams of plasma sometimes behave in unexpected ways.

 

Qu and his colleagues have developed a model that simplifies how scientists explain and predict the behavior of the super-hot liquid hydrogen. The model makes sense of an unstable wave mode observed during the United States' largest fusion experiment, known as DIII-D.

 

The key to the model is that it attempts to explain the plasma's behavior by treating it as a liquid, instead of a collection of individual atoms. "When we looked at the plasma as a fluid we got the same answer, but everything made perfect sense," said Michael Fitzgerald, Qu's research partner and a physicist at the Culham Centre for Fusion Energy in England. "We could start using our intuition again in explaining what we saw, which is very powerful."

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Characterizing quantum Hall light zooming around a photonic chip

Characterizing quantum Hall light zooming around a photonic chip | Amazing Science | Scoop.it

The quantum Hall effect is best understood by peering through the lens of topology. In the 1980s, physicists discovered that electrons in some materials behave strangely when subjected to large magnetic fields at extreme cryogenic temperatures. Remarkably, the electrons at the boundary of the material will flow along avenues of travel called ‘edge states’, protected against defects that are most certainly present in the material. Moreover, the conductance--a measure of the current--is quantized. This means that when the magnetic field is ramped up, then the conductance does not change smoothly. Instead it stays flat, like a plateau, and then suddenly jumps to a new value. The plateaus occur at precise values that are independent of many of the material’s properties. This hopping behavior is a form of precise quantization and is what gives the quantum Hall effect its great utility, allowing it to provide the modern standard for calibrating resistance in electronics, for instance.

 

Researchers have engineered quantum Hall behavior in other platforms besides the solid-state realm in which it was originally discovered. Signatures of such physics have been spotted in ultracold atomic gases and photonics, where light travels in fabricated chips. Hafezi and colleagues have led the charge in the photonics field.

 

The group uses a silicon-based chip that is filled with an array of ring-shaped structures called resonators. The resonators are connected to each other via waveguides (figure). The chip design strictly determines the conditions under which light can travel along the edges rather than through the inner regions. The researchers measure the transmission spectrum, which is the fraction of light that successfully passes through an edge pathway. To circulate unimpeded through the protected edge modes, the light must possess a certain energy. The transmission increases when the light energy matches this criteria. For other parameters, the light will permeate the chip interior or get lost, causing the transmission signal to decrease. The compiled transmission spectrum looks like a set of bright stripes separated by darker regions (see figure). Using such a chip, this group previously collected images of light traveling in edge states, definitively demonstrating the quantum Hall physics for photons.

 

In this new experiment Hafezi’s team modified their design to directly measure the value of the topology-related property that characterizes the photonic edge states. This measurement is analogous to characterizing the quantized conductance, which was critical to understanding the electron quantum Hall effect. In photonics, however, conductance is not relevant as it pertains to electron-like behavior. Here the significant feature is the winding number, which is related to how light circulates around the chip. Its value equals to the number of available edge states and should not change in the face of certain disruptions.

 

To extract the winding number, the team adds 100 nanometer titanium heaters on a layer above the waveguides. Heat changes the index of refraction, namely how the light bends as it passes through the waveguides. In this manner, researchers can controllably imprint a phase shift onto the light. Phase can be thought of in terms of a time delay. For instance, when comparing two light waves, the intensity can be the same, but one wave may be shifted in time compared to the other. The two waves overlap when one wave is delayed by a full oscillation cycle—this is called a 2π phase shift.

 

On the chip, enough heat is added to add a 2π phase shift to the light. The researchers observe an energy shift in the transmission stripes corresponding to light traveling along the edge. Notably, in this chip design, the light can circulate either clockwise (CW) or counterclockwise (CCW), and the two travel pathways do not behave the same (in contrast to an interferometer). When the phase shift is introduced, the CW traveling light hops one direction in the transmission spectrum, and the CCW goes the opposite way. The winding number is the amount that these edge-state spectral features move and is exactly equivalent to the quantized jumps in the electronic conductance.

 

Sunil Mittal, lead author and postdoctoral researcher explains one future direction, “So far, our research has been focused on transporting classical [non-quantum] properties of light--mainly the power transmission. It is intriguing to further investigate if this topological system can also achieve robust transport of quantum information, which will have potential applications for on-chip quantum information processing.” 

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How to make electrons behave like a liquid

How to make electrons behave like a liquid | Amazing Science | Scoop.it
Physicists have found that electrons can sometimes show collective behavior to produce vortices and backward flow of electric current known as “negative resistance.”


Electrical resistance is a simple concept: Rather like friction slowing down an object rolling on a surface, resistance slows the flow of electrons through a conductive material. But two physicists have now found that electrons can sometimes cooperate to turn resistance on its head, producing vortices and backward flow of electric current.


The prediction of “negative resistance” is just one of a set of counterintuitive and bizarre fluid-like effects encountered under certain exotic circumstances, involving systems of strongly interacting particles in a sheet of graphene, a two-dimensional form of carbon. The findings are described in a paper appearing today in the journal Nature Physics, by MIT professor of physics Leonid Levitov and Gregory Falkovich, a professor at Israel’s Weizmann Institute of Science.


Electrons in graphene move in a neatly coordinated way, in many ways resembling the movement of viscous fluids through a tube where they are strongly affected by turbulence and vortices. This is due to interactions producing a long-range current-field response, quite different from the simple “individualist” behavior expected under ordinary circumstances, when electrons move in straight lines like pinballs bouncing among the ions, as described by Ohm's law, the researchers say.


The notion of electron viscosity had been suggested before in theory, but it had proven difficult to test because nobody had come up with a way to directly observe such phenomena. Now, Levitov and Falkovich say they have figured out a set of signs that can serve as an indicator of such collective effects in electron flows.


This work is “a remarkable application of theoretical insight to the prediction of a new experimentally observable effect,” says Subir Sachdev, a professor of physics at Harvard University who was not involved in this work. He says this insight is “very significant and opens a new chapter in the study of electron flow in metals.”

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Physicists Test the Response Time of Electrons

Physicists Test the Response Time of Electrons | Amazing Science | Scoop.it

Researchers from the Laboratory for Attosecond Physics generated for the first time visible flashes of light in attosecond dimensions. They dispatched the light-flashes to electrons in krypton atoms. Through the experiment the researchers have been able to display that the electrons, which are stimulated by the flashes, needed roughly 100 attoseconds to respond to the incident light. Until now it was assumed that particles respond to incident light without delay.


Light could be the driving force which makes electronics even faster in the future. This is how physicists pursue their goal of using short pulses of light to control electric currents in circuits at the same rate as the frequency of light. The attophysics discovery made by an international team working with Eleftherios Goulielmakis, Leader of the Attoelectronics Research Group at the Max Planck Institute of Quantum Optics, may make it possible in future to use light to control electrons much more precisely than ever before. This is because electrons apparently follow the electromagnetic forces of light with a slight delay. The researchers determined the time it takes the electrons to react to light by exciting electrons in krypton atoms with attosecond pulses of visible light. They observed that it takes around 100 attoseconds (one attosecond is a billionth of a billionth of a second) until the particles’ reaction to the light pulses becomes noticeable. Physicists previously had to assume that the force of light has an immediate effect because they were unable to measure the delay.


An electron weighs almost nothing at all. If you want to express its mass in grams, you have to write 27 zeros after the decimal point before you can write the first number. But even this lightweight is sluggish, a little bit at least. Quantum mechanics predicts that an electron also needs a certain, albeit very short, period of time to react to the forces of light. Since this takes only several tens to hundreds of attoseconds, this process was considered to be unmeasurably fast – until now. Researchers from the Max Planck Institute of Quantum Optics working with colleagues at Texas A&M University (USA) and Lomonosov Moscow State University (Russia) are now the first to have stopped this reaction time, as it were.


“Our research thereby puts an end to the decade-long debate about the fundamental dynamics of the light-matter interaction,” says Eleftherios Goulielmakis. In recent decades, researchers were already in a position to track both the rotations as well as the nuclear motions in molecules. “This is the first time that we are able to also track the reaction of the electrons bound in the atoms in real time,” stresses Goulielmakis. “But at the same time we are now standing on the threshold of a new era in which we will investigate and manipulate matter by influencing electrons.”


In the current publication, the researchers namely present not only the first measurements of how long an electron takes to respond to a light pulse. They also present the means that made this measurement possible in the first place, and which will enable completely new experiments with electrons to be carried out in the future: a way of tailoring pulses of visible light.

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Material deformation at atomic scale resembles avalanches

Material deformation at atomic scale resembles avalanches | Amazing Science | Scoop.it

The rearrangement of particles in materials during deformation, such as when a spoon is bent, doesn't occur independently, but rather resembles highly collective avalanches that span the entire material. This is the conclusion of experimental research conducted by researchers from the University of Amsterdam (UvA) and the University of Illinois at Urbana-Champaign. The team's findings, which are published in the latest edition of Nature Communications, offers a new universal theory of deformation.


Within the field of physics, the every-day deformation of materials has traditionally been described in very different contexts. For example, when a spoon is bent or a mobile phone cover shaped during production, small sporadic atomic rearrangements occur that ultimately give rise to the changing shape of the material. In soft materials such as cream or tooth paste, similar rearrangements occur with much larger constituent particles giving rise to the overall shape change. However, until now attempts to describe what exactly happens during the deformation process have been impeded by the large length-scale gap between microscopic rearrangements and macroscopic deformation. This has precluded a complete understanding of deformation processes.


'Avalanches are important phenomena that occur not only in the surge of snow down an incline, but also in a wider context such as through the spread of forest fires, diseases or in the dynamics of stock markets', says Peter Schall, professor of Soft Condensed Matter Physics at the UvA and one of the researchers who took part in the project. 'They typically develop in highly collective systems that are distinct by their critical state and in which a small event can trigger a large effect.'


The beauty of this finding is that deformation – like many other avalanche phenomena – are described by identical statistical distributions, thereby allowing unification of widely different phenomena, says Schall. 'For the process of deformation, this offers a new universal theory in which the gap between microscopic rearrangements and macroscopic flow is bridged by simple, self-similar scaling relations. These are independent of the material and can include anything from nanorods to rocks to everyday materials. This greatly reduces the complexity of the phenomenon into a unifying framework and should ultimately lead to the better prediction and design of material properties.

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Einstein’s Gravitational Waves Detected Originating from Merging Black Holes 1.3 Billion Years Ago

Einstein’s Gravitational Waves Detected Originating from Merging Black Holes 1.3 Billion Years Ago | Amazing Science | Scoop.it
Today, scientists announced that, for the first time in history, gravitational waves have been detected.

Gravitational waves are ripples in spacetime throughout the universe. What’s truly remarkable about this discovery is that Albert Einstein predicted the existence of gravitational waves 100 years ago, but scientists have never been able to detect them, until now.

The discovery came out of the U.S. based Laser Interferometer Gravitational Wave Observatory (LIGO). The mission of LIGO was to directly measure gravitational waves. In order to do that, LIGO scientists needed to construct the most precise measuring device the world had ever seen.

The LIGO project, which began in 1992, was the largest scientific investment the National Science Foundation (NSF) has ever made.

At an NSF press conference this morning, LIGO Laboratory Executive Director, David Reitze, said “This was a scientific moon shot. And we did it – we landed on the moon.”


LIGO consists of two 4 kilometer (2.5 mile) tunnels located in Louisiana and the state of Washington. Because gravitational waves stretch space in one direction and compress space in the other, LIGO was designed to measure changes in length across large land distances. If they could detect a stretch of land in the LIGO tunnels in one direction and compression in the other, they could theoretically detect a gravitational wave.


The “ruler” that scientists used to measure these tunnel lengths was the speed of light. The speed of light is constant, so LIGO can determine the length of the tunnels by measuring the time it takes for a laser to bounce from one end of the tunnel to the other.


Gravitational waves are created when masses accelerate. Measured back on September 14th, 2015, the gravitational wave signal that the LIGO scientists detected matches the exact signal they’d expect from two merging black holes accelerating at half the speed of light.


Reitze explained that the black holes that created this gravitational wave merged 1.3 billion years ago. It took that long for the wave to travel to the Earth. Each of the black holes were 30 times the mass of the sun and were accelerating at half the speed of light when they collided into each other. The ability to measure gravitational waves will open up an entirely new window for astronomy. Reitze explained that this will enable scientists to look at the universe in a new way.


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Physicists investigate the structure of time, with implications for quantum mechanics and philosophy

Physicists investigate the structure of time, with implications for quantum mechanics and philosophy | Amazing Science | Scoop.it

Although in theory it may seem possible to divide time up into infinitely tiny intervals, the smallest physically meaningful interval of time is widely considered to be the Planck time, which is approximately 10-43 seconds. This ultimate limit means that it is not possible for two events to be separated by a time smaller than this.


But now in a new paper, physicists have proposed that the shortest physically meaningful length of time may actually be several orders of magnitude longer than the Planck time. In addition, the physicists have demonstrated that the existence of such a minimum time alters the basic equations of quantum mechanics, and as quantum mechanics describes all physical systems at a very small scale, this would change the description of all quantum mechanical systems.


The researchers, Mir Faizal at the University of Waterloo and University of Lethbridge in Canada, Mohammed M. Khalil at Alexandria University in Egypt, and Saurya Das at the University of Lethbridge, have recently published a paper called "Time crystals from minimum time uncertainty" in The European Physical Journal C.


"It might be possible that, in the universe, the minimum time scale is actually much larger than the Planck time, and this can be directly tested experimentally," Faizal explainsThe Planck time is so short that no experiment has ever come close to examining it directly—the most precise tests can access a time interval down to about 10−17 seconds.


Nevertheless, there is a great deal of theoretical support for the existence of the Planck time from various approaches to quantum gravity, such as string theory, loop quantum gravity, and perturbative quantum gravity. Almost all of these approaches suggest that it is not possible to measure a length shorter than the Planck length, and by extension not possible to measure a time shorter than the Planck time, since the Planck time is defined as the time it takes light to travel a single unit of the Planck length in a vacuum.


Motivated by several recent theoretical studies, the scientists further delved into the question of the structure of time—in particular, the long-debated question of whether time is continuous or discrete. "In our paper, we have proposed that time is discrete in nature, and we have also suggested ways to experimentally test this proposal," Faizal said.


One possible test involves measuring the rate of spontaneous emission of a hydrogen atom. The modified quantum mechanical equation predicts a slightly different rate of spontaneous emission than that predicted by the unmodified equation, within a range of uncertainty. The proposed effects may also be observable in the decay rates of particles and of unstable nuclei.


Based on their theoretical analysis of the spontaneous emission of hydrogen, the researchers estimate that the minimum time may be orders of magnitude larger than the Planck time, but no greater than a certain amount, which is fixed by previous experiments. Future experiments could lower this bound on the minimum time or determine its exact value.


The scientists also suggest that the proposed changes to the basic equations of quantum mechanics would modify the very definition of time. They explain that the structure of time can be thought of as a crystal structure, consisting of discrete, regularly repeating segments.


On a more philosophical level, the argument that time is discrete suggests that our perception of time as something that is continuously flowing is just an illusion.

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Solving hard quantum problems: Everything is connected

Solving hard quantum problems: Everything is connected | Amazing Science | Scoop.it
Quantum physics is a game of luck and randomness. Initially, the atoms in a cold atom cloud do not have a predetermined position. Much like a die whirling through the air, where the number is yet to be determined, the atoms are located at all possible positions at the same time. Only when they are measured, their positions are fixed. "We shine light on the atom cloud, which is then absorbed by the atoms", says Kaspar Sakmann. "The atoms are photographed, and this is what determines their position. The result is completely random."

There is, however, an important difference between quantum randomness and a game of dice: if different dice are thrown at the same time, they can be seen as independent from each other. Whether or not we roll a six with die number one does not influence the result of die number seven. The atoms in the atom cloud on the other hand are quantum physically connected. It does not make sense to analyse them individually, they are one big quantum object. Therefore, the result of every position measurement of any atom depends on the positions of all the other atoms in a mathematically complicated way.

"It is not hard to determine the probability that a particle will be found at a specific position", says Kaspar Sakmann. "The probability is highest in the centre of the cloud and gradually diminishes towards the outer fringes." In a classically random system, this would be all the information that is needed. If we know that in a dice roll, any number has the probability of one sixth, then we can also determine the probability of rolling three ones with three dice. Even if we roll five ones consecutively, the probability remains the same the next time. With quantum particles, it is more complicated than that.

"We solve this problem step by step", says Sakmann. "First we calculate the probability of the first particle being measured on a certain position. The probability distribution of the second particle depends on where the first particle has been found. The position of the third particle depends on the first two, and so on." In order to be able to describe the position of the very last particle, all the other positions have to be known. This kind of quantum entanglement makes the problem mathematically extremely challenging.


But these correlations between many particles are extremely important - for example for calculating the behaviour of colliding Bose-Einstein-condensates. "The experiment shows that such collisions can lead to a special kind of quantum waves. On certain positions we find many particles, on an adjacent position we do not find any", says Kaspar Sakmann. "If we consider the atoms separately, this cannot be explained. Only if we take the full quantum distribution into account, with all its higher correlations, these waves can be reproduced by our calculations."


Also other phenomena have been calculated with the same method, for instance Bose-Einstein-condensates which are stirred with a laser beam, so that little vortices emerge - another typical quantum many-particle-effect. "Our results show how important theses correlations are and that it is possible to include them in quantum calculations, in spite of all mathematical difficulties", says Sakmann. With certain modifications, the approach can be expected to be useful for many other quantum systems as well.

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Black Holes and Black Hole Tech. How far have we progressed?

Black Holes and Black Hole Tech. How far have we progressed? | Amazing Science | Scoop.it
In celebration of the detection of gravitational waves, Stephen Wolfram looks forward and discusses what technology black holes could make possible.
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Revealing the Nature of Dark Matter

Dr. Dan Hooper, a Theoretical Astrophysicist at Fermilab, explores the current status of the dark matter search and some new thoughts on the nature of this mystery.

A signal of gamma rays has been observed from the center of the Milky Way, and it may be the breakthrough that we have long been waiting for. If these gamma-rays are in fact being produced by the interactions of dark matter particles, they promise to reveal much about this elusive substance, and may be a major step toward identifying of the underlying nature of our universe's dark matter.
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Fundamentally accurate quantum thermometer created

Fundamentally accurate quantum thermometer created | Amazing Science | Scoop.it

While the method is not yet ready for commercialization, it reveals how an object's thermal energy—its heat—can be determined precisely by observing its physical properties at the quantum scale. While the initial demonstration has an absolute accuracy only within a few percentage points, the NIST approach works over a wide temperature range encompassing cryogenic and room temperatures. It is also accomplished with a small, nanofabricated photonic device, which opens up possible applications that are not practical with conventional temperature standards.

 

The NIST team's approach arose from their efforts to observe the vibrations of a small transparent beam of silicon nitride using laser light. Thermal energy—often expressed as temperature—makes all objects vibrate; the warmer the object, the more pronounced the vibrations, though they are still on the order of just a picometer (trillionths of a meter) in size for the beam at room temperature. To observe these tiny perturbations, the team carved a small reflective cavity into the beam. When they shone a laser through the crystal, the light reflecting from the cavity experienced slight shifts in color or frequency due to the beam's temperature-induced vibrations, making the light's color change noticeably in time with the movement.

 

But these were not the only vibrations the team members could see. The team also spotted the much more subtle vibrations that all objects possess due to a quantum-mechanical property called zero-point motion: Even at its lowest possible energy, the beam vibrates ever so slightly due to the inherent uncertainty at the heart of quantum mechanics. This motion is independent of temperature, and has a well-known amplitude fundamentally dictated by quantum mechanics. By comparing the relative size of the thermal vibration to the quantum motion, the absolute temperature can be determined.

 

These intrinsic quantum fluctuations are thousands of times fainter and ordinarily get lost in the noise of the thermal energy-induced vibrations typical of ordinary temperatures, but the process of measuring the beam provides a method to distinguish quantum and thermal fluctuations. When photons from the laser bounce off the sides of the beam, they give it slight kicks, inducing correlations that make the quantum motion more pronounced.

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Majorana 'zero modes' quasiparticle spotted in superconducting nanowires for the first time

Majorana 'zero modes' quasiparticle spotted in superconducting nanowires for the first time | Amazing Science | Scoop.it
Topological protection could lead to better quantum computers

 

An important property of Majorana quasiparticles has been measured for the first time by physicists at the Niels Bohr Institute in Denmark. They found evidence that electrons in tiny nanowires form entangled states that are highly isolated from noise and other external stimuli. Because they are protected from outside influences, these Majorana "zero modes" could be used as quantum bits (qubits) in quantum computers.

 

First predicted by the Italian physicist Ettore Majorana in 1937, the Majorana particle obeys "non-Abelian" statistics, which means that quantum information encoded in the particles would be highly resistant to decoherence. Decoherence is the bane of physicists who are trying to develop practical quantum computers, and so devices based on Majorana particles could be used in future quantum-information systems.

 

While physicists have yet to see isolated Majorana particles, some collective excitations of electrons in solids have the same properties as Majorana particles. These "Majorana quasiparticles" have already been glimpsed in several systems, including semiconductor nanowires coated in a superconducting layer. When these nanowires are cooled to near absolute zero, superconducting electrons can exist within the semiconductor. An electron in the wire becomes entangled with electrons on either side of it, creating an uninterrupted chain of entangled electrons along the entire length of the wire.

 

At either end of this chain are electrons that are entangled only with one electron, which can each be thought of as "half" an electron and are called Majorana modes. Together they form a Majorana quasiparticle. Quantum information stored in such a quasiparticle would be distributed between both ends of the nanowire, meaning it should be protected from being destroyed by external noise.

 

"The protection is related to the exotic property of the Majorana mode that it simultaneously exists on both ends of the nanowire, but not in the middle," explains Sven Albrecht, who was part of the Danish team. "To destroy its quantum state, you have to act on both ends at the same time, which is unlikely," he adds.

 

An important feature of the Majorana modes is that the energy required to add another electron to the nanowire decreases exponentially with the length of the nanowire. This exponential decay is a signature of the protected nature of the Majorana modes and is something that previous studies have not measured.

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Star Trek’s Vision Becomes Reality: First-Time Teleportation of Classical Object

Star Trek’s Vision Becomes Reality: First-Time Teleportation of Classical Object | Amazing Science | Scoop.it

"Beam me up, Scotty" - even if Captain Kirk supposedly never said this exact phrase, it remains a popular catch-phrase to this day. Whenever the chief commander of the television series starship USS Enterprise (NCC-1701) wanted to go back to his control centre, this command was enough to take him back to the control centre instantly-travelling through the infinity of outer space without any loss of time. But is all of this science fiction that was thought up in the 1960s? Not quite: Physicists are actually capable of beaming-or "teleporting" as it is called in technical language - if not actual solid particles at least their properties.

 

Transmission of information without loss of time

"Many of the ideas from Star Trek that back then appeared to be revolutionary have become reality," explains Prof. Dr Alexander Szameit from the University of Jena (Germany). "Doors that open automatically, video telephony or flip phones-all things we have first seen on the starship USS Enterprise," exemplifies the Junior-professor of Diamond-/Carbon-Based Optical Systems. So why not also teleporting? "Elementary particles such as electrons and light particles exist per se in a spatially delocalized state," says Szameit. For these particles, it is with a certain probability thus possible to be in different places at the same time. "Within such a system spread across multiple locations, it is possible to transmit information from one location to another without any loss of time." This process is called quantum teleportation and has been known for several years.

 

The team of scientists lead by science fiction fan Szameit has now for the first time demonstrated in an experiment that the concept of teleportation does not only persist in the world of quantum particles, but also in our classical world. Szameit and his colleagues report about these achievements in the scientific journal "Laser & Photonics Reviews" (DOI: 10.1002/lpor.201500252).


To entangle properties of light beams

They used a special form of laser beams in the experiment. "As can be done with the physical states of elementary particles, the properties of light beams can also be entangled," explains Dr Marco Ornigotti, a member of Prof. Szameit's team. For physicists, "entanglement" means a sort of codification. "You link the information you would like to transmit to a particular property of the light," clarifies Ornigotti who led the experiments for the study that was now presented.

 

In their particular case, the physicists have encoded some information in a particular polarisation direction of the laser light and have transmitted this information to the shape of the laser beam using teleportation. "With this form of teleportation, we can, however, not bridge any given distance," admits Szameit. "On the contrary, classic teleportation only works locally." But just like it did at the starship USS Enterprise or in quantum teleportation, the information is transmitted fully and instantly, without any loss of time. And this makes this kind of information transmission a highly interesting option in telecommunication for instance, underlines Szameit.


Original publication:
Diego Guzman-Silva et al. Demonstration of local teleportation using classical entanglement, Laser Photonics Rev. 2016, DOI 10.1002/lpor.201500252

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Physicists find extreme violation of local realism in quantum hypergraph states

Physicists find extreme violation of local realism in quantum hypergraph states | Amazing Science | Scoop.it
Many quantum technologies rely on quantum states that violate local realism, which means that they either violate locality (such as when entangled particles influence each other from far away) or realism (the assumption that quantum states have well-defined properties, independent of measurement), or possibly both. Violation of local realism is one of the many counterintuitive, yet experimentally supported, characteristics of the quantum world.

 

Determining whether or not multiparticle quantum states violate local realism can be challenging. Now in a new paper, physicists have shown that a large family of multiparticle quantum states called hypergraph states violates local realism in many ways. The results suggest that these states may serve as useful resources for quantum technologies, such as quantum computers and detecting gravitational waves.

 

The physicists, Mariami Gachechiladze, Costantino Budroni, and Otfried Gühne at the University of Siegen in Germany, have published their paper on the quantum hypergraph states in a recent issue of Physical Review Letters.

 

The properties of multiparticle quantum systems are described by quantum states, some of which can be represented on a graph where each point corresponds to a particle and each edge to the interaction between particles. While some quantum states can be represented by ordinary graphs, others are represented by hypergraphs. On an ordinary graph, two points can be connected by an edge, while on a hypergraph, a hyperedge can connect more than two vertices. Whereas an ordinary edge is usually drawn as a straight line between two vertices, a hyperedge is depicted as a curve that wraps around three or more vertices.

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Physicists Discover New Tetraquark Particle: X(5568)

Physicists Discover New Tetraquark Particle: X(5568) | Amazing Science | Scoop.it

Physicists on the DZero international collaboration at Fermilab, the U.S. Department of Energy’s laboratory specializing in high-energy particle physics, have discovered a new subatomic particle, X(5568), whose quark content appears to be qualitatively different from normal.


Quarks are point-like elementary particles that typically come in packages of two or three, the most familiar of which are the proton and neutron – each is made of three quarks. There are six types — or flavors — of quark to choose from: up, down, strange, charm, bottom and top. Each of these also has an antimatter counterpart. The newly-discovered tetraquark particle X(5568), named for its mass – 5568 megaelectronvolts, contains four distinct flavors – bottom, strange, up and down.


“It is exciting to discover a new and unusual particle that will help us understand the strong interaction- one of the four known fundamental interactions in physics,” said team member Prof. Iain Bertram, of Lancaster University, UK. “The discovery of a unique member of the tetraquark family with four different quark flavors will help theorists develop models that will allow for a deeper understanding of these particles,” said Fermilab Director Nigel Lockyer.


The discovery will be published in the journal Physical Review Letters, but have been published on arXiv.org ahead of time.


X(5568) decays via the strong interaction into a Bs and pi mesons, according to the DZero physicists. The Bs meson decays into a J/psi and a phi meson, and these in turn decay into two muons and two kaons, respectively. Several other previously observed particles are good candidates to be tetraquark or pentaquark states, but all of these have a quark and antiquark of the same flavor, and thus their character as an exotic particle is less certain.


The scientists said that the detailed internal structure of X(5568) is not yet understood.


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Pulsar Web Could Detect Low-Frequency Gravitational Waves

Pulsar Web Could Detect Low-Frequency Gravitational Waves | Amazing Science | Scoop.it
Monitoring a vast network of rapidly spinning pulsars is key to finding very-low-frequency gravitational waves, researchers say.


Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation. Astronomers detect this as a rapid pulse of radio emission. Most pulsars rotate several times a second. But some, called millisecond pulsars, rotate hundreds of times faster.


"Millisecond pulsars have extremely predictable arrival times, and our instruments are able to measure them to within a ten-millionth of a second," said Maura McLaughlin, a radio astronomer at West Virginia University in Morgantown and member of the NANOGrav team. "Because of that, we can use them to detect incredibly small shifts in Earth's position."


But astrophysicists at JPL and Caltech caution that detecting faint gravitational waves would likely require more than a few pulsars. "We're like a spider at the center of a web," said Michele Vallisneri, another member of the JPL/Caltech research group. "The more strands we have in our web of pulsars, the more likely we are to sense when a gravitational wave passes by."


Vallisneri said accomplishing this feat will require international collaboration. "NANOGrav is currently monitoring 54 pulsars, but we can only see some of the southern hemisphere. We will need to work closely with our colleagues in Europe and Australia in order to get the all-sky coverage this search requires."


The feasibility of this approach was recently called into question when a group of Australian pulsar researchers reported that they were unable to detect such signals when analyzing a set of pulsars with the most precise timing measurements. After studying this result, the NANOGrav team determined that the reported non-detection was not a surprise, and resulted from the combination of optimistic gravitational wave models and analysis of too few pulsars. Theirone-page response was released recently via the arXiv electronic print service.


Despite the technical challenges, Taylor is confident their team is on the right track. "Gravitational waves are washing over Earth all the time," Taylor said. "Given the number of pulsars being observed by NANOGrav and other international teams, we expect to have clear and convincing evidence of low-frequency gravitational waves within the next decade."


NANOGrav is a collaboration of over 60 scientists at more than a dozen institutions in the United States and Canada. The group uses radio pulsar timing observations acquired at NRAO's Green Bank Telescope in West Virginia and at Arecibo Radio Observatory in Puerto Rico to search for ripples in the fabric of spacetime. In 2015, NANOGrav was awarded $14.5 million by the National Science Foundation to create and operate a Physics Frontiers Center.


"With the recent detection of gravitational waves by LIGO, the outstanding work of the NANOGrav collaboration is particularly relevant and timely," said Pedro Marronetti, National Science Foundation program director for gravitational wave research. "This NSF-funded Physics Frontier Center is poised to complement LIGO observations, extending the window of gravitational wave detection to very low frequencies."

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Three new gravitational wave projects unveiled in China

Three new gravitational wave projects unveiled in China | Amazing Science | Scoop.it
Chinese scientists have unveiled three separate projects to investigate gravitational waves, state media said Wednesday, days after earthshaking US discoveries that confirmed Einstein's century-old predictions.


Space officials said such research would give China—which has an ambitious, military-run, multi-billion-dollar space programme that Beijing sees as symbolising the country's progress—an opportunity to become a "world leader" in the field.


Gravitational waves are direct evidence of ripples in the fabric of space-time, and their first-ever observation was announced by US scientists last week. The Chinese Academy of Sciences (CAS) rolled out a proposal for a space-based gravitational wave detection project, the official Xinhua news agency reported.


The proposed Taiji programme, named after the "supreme ultimate" of Chinese philosophy symbolised by the yin-yang sign, would send satellites of its own into orbit or share equipment with the European Space Agency's eLISA initiative.


Separately, Sun Yat-sen University in Guangzhou also proposed to launch satellites into space, while the Institute of High Energy Physics at CAS suggested a land-based scheme in Tibet. All three projects have yet to obtain government approval, state media said.

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A Toolkit for Silicon-based Quantum Computing

A Toolkit for Silicon-based Quantum Computing | Amazing Science | Scoop.it
Before quantum computing becomes practical, researchers will need to find a practical way to store information as quantum bits, or qubits. Researchers are making significant progress toward the creation of electronic devices based on qubits made of single ions implanted in silicon, one of the most practical of all materials.


“Bit” is a contraction of “binary digit,” but unlike a classical bit, which is plain-vanilla binary with a value of either 0 or 1, a quantum bit, or qubit — the theoretical basis of quantum computing — holds both 0 and 1 in a superposed state until it is measured.


A vast computational space can be created with relatively few quantum-mechanically entangled qubits, and the measurement of one qubit can instantly resolve an intricate calculation when all the entangled qubits are “collapsed” to a specific value by the measurement.


So how does one make and measure a qubit? The problem has engaged scientists for years. Many arrangements have been proposed and some demonstrated, each with its advantages and disadvantages, including tricky schemes involving superconducting tunnel junctions, quantum dots, neutral atoms in optical lattices, trapped ions probed by lasers, and so on.


In the long run, however, qubits based on individual dopant atoms implanted in silicon may have the edge. The materials and methods of silicon-chip manufacturing are familiar and, when applied to quantum-computer devices, have the potential for easy scale-up.


“There are three pillars to the development program my colleagues and I have been following,” says Thomas Schenkel of Berkeley Lab’s Accelerator and Fusion Research Division. “One is the theory of quantum measurement in the devices we build, led by Professor Birgitta Whaley from the Department of Chemistry at UC Berkeley; another is the fabrication of these devices, headed by myself and Professor Jeff Bokor from UC Berkeley’s Department of Electrical Engineering and Computer Science; and the third is to actually measure quantum states in these devices, an effort led by Professor Steve Lyon from Princeton’s Department of Electrical Engineering. Of course, things don’t necessarily happen in that order.”

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Revolutionizing heat transport: Quantum-limited heat conduction over macroscopic distances

Revolutionizing heat transport: Quantum-limited heat conduction over macroscopic distances | Amazing Science | Scoop.it

Scientists at Aalto University, Finland, have made a breakthrough in physics. They succeeded in transporting heat maximally effectively ten thousand times further than ever before. The discovery may lead to a giant leap in the development of quantum computers.


Heat conduction is a fundamental physical phenomenon utilized, for example, in clothing, housing, car industry, and electronics. Thus our day-to-day life is inevitably affected by major shocks in this field. The research group, led by quantum physicist Mikko Möttönen has now made one of these groundbreaking discoveries. This new invention revolutionizes quantum-limited heat conduction which means as efficient heat transport as possible from point A to point B. This is great news especially for the developers of quantum computers.


Quantum technology is still a developing research field, but its most promising application is the super-efficient quantum computer. In the future, it can solve problems that a normal computer can never crack. The efficient operation of a quantum computer requires that it can be cooled down efficiently. At the same time, a quantum computer is prone to errors due to external noise.


Möttönen's innovation may be utilized in cooling quantum processors very efficiently and so cleverly that the operation of the computer is not disturbed.


"Our research started already in 2011 and advanced little by little. It feels really great to achieve a fundamental scientific discovery that has real practical applications", Professor Mikko Möttönen rejoices.


In the QCD Labs in Finland, Möttönen's research group succeeded in measuring quantum-limited heat transport over distances up to a meter. A meter doesn't sound very long at first, but previously scientists have been able to measure such heat transport only up to distances comparable to the thickness of a human hair.


"For computer processors, a meter is an extremely long distance. Nobody wants to build a larger processor than that", stresses Möttönen.

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Physicists control electrons at femtosecond timescales

Physicists control electrons at femtosecond timescales | Amazing Science | Scoop.it

When you shine a light on a conducting surface like silicon or graphene, that light jump-starts certain electrons into high-energy states and kicks off a cascade of interactions that happens faster than the blink of an eye. Within just a few femtoseconds — a thousand trillionth of a second — these energized electrons can scatter among other electrons like balls on a billiard table, quickly dissipating energy in an ultrafast process known as thermalization.


Now physicists at MIT have come up with a way to manipulate electrons in graphene within the first few femtoseconds of photo-excitation. With their technique, the researchers can redirect these high-energy electrons before they interact with other electrons in the material. The team’s ultrafast control of high-energy electrons may ultimately lead to more efficient photovoltaic and energy-harvesting devices, which capture photo-excited electrons before they lose their energy to thermalization.


“We’re intellectually excited about whether this will have technological applications,” says Pablo Jarillo-Herrero, associate professor of physics at MIT. “It’s too soon to know, but there are certain angles of looking at this where it's clear there might be ways to engineer energy flow or transfer in ways that are novel. Now we need more people thinking about this.”


The group’s results are published this week in the journal Nature Physics. Jarillo-Herrero’s co-authors include lead author and graduate student Qiong Ma, along with Jing Kong, professor of electrical engineering and computer science, and Nuh Gedik, associate professor of physics.


Via Mariaschnee
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