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  • richardmitnick 2:21 pm on September 21, 2017 Permalink | Reply
    Tags: But quantum mechanics doesn’t really define what a measurement is, , Gravity at its most fundamental comes in indivisible parcels called quanta, GRW model-Ghirardi–Rimini–Weber theory, In quantum theory the state of a particle is described by its wave function, Much like the electromagnetic force comes in quanta called photons, , , Quantum Mechanics   

    From New Scientist: “Gravity may be created by strange flashes in the quantum realm” 

    NewScientist

    New Scientist

    20 September 2017
    Anil Ananthaswamy

    1
    Gravity comes about in a flash. Emma Johnson/Getty

    HOW do you reconcile the two pillars of modern physics: quantum theory and gravity? One or both will have to give way. A new approach says gravity could emerge from random fluctuations at the quantum level, making quantum mechanics the more fundamental of the two theories.

    Of our two main explanations of reality, quantum theory governs the interactions between the smallest bits of matter. And general relativity deals with gravity and the largest structures in the universe. Ever since Einstein, physicists have been trying to bridge the gap between the two, with little success.

    Part of the problem is knowing which strands of each theory are fundamental to our understanding of reality.

    One approach towards reconciling gravity with quantum mechanics has been to show that gravity at its most fundamental comes in indivisible parcels called quanta, much like the electromagnetic force comes in quanta called photons. But this road to a theory of quantum gravity has so far proved impassable.

    Now Antoine Tilloy at the Max Planck Institute of Quantum Optics in Garching, Germany, has attempted to get at gravity by tweaking standard quantum mechanics.

    In quantum theory, the state of a particle is described by its wave function. The wave function lets you calculate, for example, the probability of finding the particle in one place or another on measurement. Before the measurement, it is unclear whether the particle exists and if so, where. Reality, it seems, is created by the act of measurement, which “collapses” the wave function.

    But quantum mechanics doesn’t really define what a measurement is. For instance, does it need a conscious human? The measurement problem leads to paradoxes like Schrödinger’s cat, in which a cat can be simultaneously dead and alive inside a box, until someone opens the box to look.

    One solution to such paradoxes is a so-called GRW model that was developed in the late 1980s. It incorporates “flashes”, which are spontaneous random collapses of the wave function of quantum systems. The outcome is exactly as if there were measurements being made, but without explicit observers.

    Tilloy has modified this model to show how it can lead to a theory of gravity. In his model, when a flash collapses a wave function and causes a particle to be in one place, it creates a gravitational field at that instant in space-time. A massive quantum system with a large number of particles is subject to numerous flashes, and the result is a fluctuating gravitational field.

    It turns out that the average of these fluctuations is a gravitational field that one expects from Newton’s theory of gravity (arxiv.org/abs/1709.03809). This approach to unifying gravity with quantum mechanics is called semiclassical: gravity arises from quantum processes but remains a classical force. “There is no real reason to ignore this semiclassical approach, to having gravity being classical at the fundamental level,” says Tilloy.

    “I like this idea in principle,” says Klaus Hornberger at the University of Duisburg-Essen in Germany. But he points out that other problems need to be tackled before this approach can be a serious contender for unifying all the fundamental forces underpinning the laws of physics on scales large and small. For example, Tilloy’s model can be used to get gravity as described by Newton’s theory, but the maths still has to be worked out to see if it is effective in describing gravity as governed by Einstein’s general relativity.

    Tilloy agrees. “This is very hard to generalise to relativistic settings,” he says. He also cautions that no one knows which of the many tweaks to quantum mechanics is the correct one.

    Nonetheless, his model makes predictions that can be tested. For example, it predicts that gravity will behave differently at the scale of atoms from how it does on larger scales. Should those tests find that Tilloy’s model reflects reality and gravity does indeed originate from collapsing quantum fluctuations, it would be a big clue that the path to a theory of everything would involve semiclassical gravity.

    See the full article here .

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  • richardmitnick 8:27 am on September 14, 2017 Permalink | Reply
    Tags: , Brian Greene, Cosmology- origins of the universe, , , , , Quantum Mechanics, Superstring theory, Unified theory of physics,   

    From Harvard Gazette: “A master of explaining the universe” 

    Harvard University
    Harvard University

    September 13, 2017
    Colleen Walsh

    1
    Brian Greene ’84, a Columbia University theoretical physicist and mathematician, has made it his mission to illuminate the wonders of the universe for non-scientists. Photo by Greg Kessler/World Science Festival

    Harvard Overseer and Columbia physicist Brian Greene seeks wider audience for the wonders of science.

    He is the founder of the World Science Festival, the author of numerous best-selling books, including the Pulitzer Prize finalist “The Elegant Universe,” and an expert at explaining knotty concepts. Now he’s back at Harvard. On Sept. 19, Brian Greene ’84, Harvard Overseer and Columbia University theoretical physicist and mathematician, will explore shifting ideas of space, time, and reality in a talk at the Radcliffe Institute for Advanced Study. The Gazette caught up with Greene to ask him about his years at Harvard, his passion for science, and how he defines superstring theory in a tweet.

    GAZETTE: Where did your initial interest in math and physics come from?

    GREENE: When I was a kid growing up in Manhattan I was deeply fascinated with mathematics, and at a young age my dad taught me the basics of arithmetic. I was captivated from then on by the ability to use a few simple rules to undertake calculations that no one had ever done before. Now, most of these calculations weren’t ever done because they weren’t interesting, but for a kid to be able to do something new is deeply thrilling. Later on, when I learned in high school and most forcefully when I got to college at Harvard that math isn’t merely a game but it’s something that can help you understand what happens out there in the real universe, then I was kind of hooked for life.

    GAZETTE: Were there any classes or professors that had a big impact on you at Harvard?

    GREENE: Oh, huge. Howard Georgi was my freshman physics professor, and he had a deep impact on my love of the subject. There’s now a mathematician who wasn’t at Harvard when I was an undergrad but whom I worked with extensively as a graduate student and then he moved to Harvard, Shing-Tung Yau in the Mathematics Department. He had a deep impact on me. The Harvard faculty had quite a formative impact on me across the years.

    GAZETTE: I know you are famous for being able to explain awesome scientific concepts. In the age of social media, can you define superstring theory in a tweet?

    GREENE: Superstring theory is our best attempt to realize Einstein’s dream of the unified theory. #unification.

    GAZETTE: So break that down for me, and this doesn’t have to be in a tweet format. What is the unified theory of physics and why is it so important?

    GREENE: Einstein envisioned that there might be a master law of physics, perhaps captured by a single mathematical equation that would be so powerful that in principle it could describe every physical process in the universe — the big stuff, the small stuff, and everything in between. And he believed it so deeply that he pursued it relentlessly for the last 30 years of his life. On various occasions Einstein announced that he had the unified theory, always, however, to have to retract that sometime later when he realized that his latest proposal didn’t quite work. In the end it was a very frustrating experience for him. And when he died, that dream of unification died with him. But about 10 or 15 years later some scientist stumbled upon a new approach — this approach called superstring theory — and over the course of decades realized that this may in fact be the unified theory that Einstein was looking for. And that’s what we have been developing ever since.

    GAZETTE: What has been the main focus of your work for the last several years?

    GREENE: I have been working on issues of cosmology, origins of the universe. I’ve been working on the possibility of a multiverse — that we might live in a reality that comprises more than one universe. I’ve been working on some strange features of quantum mechanics called quantum entanglement, where distant objects can somehow act as though they are sitting right next to each other. Again this is a discovery that sort of goes back to Einstein himself, so things in that domain have been my main focus of late.

    GAZETTE: Tell me more about multiple universes.

    GREENE: Well, it’s a curious idea because for most people the word universe means everything: all that there is. But developments over the past couple of decades have convinced many of us that there is at least a possibility that what we have long thought to be everything is actually perhaps just a small part of a much bigger reality. And that bigger reality might have other realms that would rightly be called universes of their own, and if that’s the case then the grand picture of reality involves a whole collection of universes, and that’s why we no longer use the word universe to describe all there is … we speak of “multi” — there are multiverses because of this multiplicity of universes.

    GAZETTE: Is there current or future research that you could see really changing the nature of how we see the universe?

    GREENE: My own feeling, and it’s shared by colleagues, is that the next breakthrough will come when we deeply understand the fundamental ingredients of space and time themselves. And this is an open question. Just like matter is made up of atoms and molecules, could it be that space and time are themselves made up of more fundamental constituents? In fact, this is what I will be talking about at Radcliffe, recent work that at least hints at an answer to what the ingredients of space and time might actually be.

    GAZETTE: What has inspired you to work to make science understandable?

    GREENE: My view of science is not that it’s merely an effort to unearth the basic laws of physics, but I view it more as a very human undertaking to see how we fit into the grand scheme of things and to answer the questions that have been asked since the time we could ask questions: Where did we come from? What are we made of? How did the universe come to be? What is time? What will happen in the distant future? All these questions I think speak deeply to who we are as a species, and for the vast majority of people to be cut off from the most up-to-date thinking on these deep questions because they don’t speak mathematics, they don’t have a graduate degree in physics, I think that’s tragic. So for decades now I’ve felt that part of my charge is to bring these ideas to a wider audience, to make them available to anyone who has a curiosity and a little bit of stick-to-itiveness to push through some deep, difficult, but ultimately gratifying ideas.

    GAZETTE: If you weren’t a physicist what would you be?

    GREENE: Well, if I was starting out today I think I would probably go into neuroscience. I like to think of the big questions. Where did the universe come from? Where did life come from? And where does mind come from? And for those I think the time is really ripe to understand the nature of intelligence and thought. I think there are going to be great, great breakthroughs in that area in the next couple of decades.

    GAZETTE: Favorite physicist?

    GREENE: There’s nobody who compares with Isaac Newton in terms of the leap that he pushed humanity through from the way we understood the world before he began to think about it until after he existed.

    GAZETTE: What is your take on Voyager?

    GREENE: The “Star Trek” version or the real version?

    GAZETTE: The real version.

    GREENE: I think it’s a great symbol of who we are as a species. We are explorers. We are deeply committed to understanding the universe, and to envision these little spacecraft that have left the solar system and they are floating out there in the great unknown as harbingers, if you will, of human life back on the planet is a deeply moving picture and one that really captures who we are.

    See the full article here .

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    Harvard University campus
    Harvard is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

     
  • richardmitnick 11:57 am on September 5, 2017 Permalink | Reply
    Tags: "Minuscule jitters may hint at quantum collapse mechanism, , , Quantum Mechanics, ,   

    From Science News: “Minuscule jitters may hint at quantum collapse mechanism” 

    ScienceNews bloc

    ScienceNews

    September 1, 2017
    Emily Conover

    Data match prediction for wave function theory, but more experiments are needed.

    1
    A tiny, shimmying cantilever wiggles a bit more than expected in a new experiment. The excess jiggling of the miniature, diving board–like structure might hint at why the strange rules of quantum mechanics don’t apply in the familiar, “classical” world. But that potential hint is still a long shot: Other sources of vibration are yet to be fully ruled out, so more experiments are needed.

    Quantum particles can occupy more than one place at the same time, a condition known as a superposition (SN: 11/20/10, p. 15). Only once a particle’s position is measured does its location become definite. In quantum terminology, the particle’s wave function, which characterizes the spreading of the particle, collapses to a single location (SN Online: 5/26/14).

    In contrast, larger objects are always found in one place. “We never see a table or chair in a quantum superposition,” says theoretical physicist Angelo Bassi of the University of Trieste in Italy, a coauthor of the study, to appear in Physical Review Letters. But standard quantum mechanics doesn’t fully explain why large objects don’t exist in superpositions, or how and why wave functions collapse.

    Extensions to standard quantum theory can alleviate these conundrums by assuming that wave functions collapse spontaneously, at random intervals. For larger objects, that collapse happens more quickly, meaning that on human scales objects don’t show up in two places at once.

    Now, scientists have tested one such theory by looking for one of its predictions: a minuscule jitter, or “noise,” imparted by the random nature of wave function collapse. The scientists looked for this jitter in a miniature cantilever, half a millimeter long. After cooling the cantilever and isolating it to reduce external sources of vibration, the researchers found that an unexplained trembling still remained.

    In 2007, physicist Stephen Adler of the Institute for Advanced Study in Princeton, N.J., predicted that the level of jitter from wave function collapse would be large enough to spot in experiments like this one. The new measurement is consistent with Adler’s prediction. “That’s the interesting fact, that the noise matches these predictions,” says study coauthor Andrea Vinante, formerly of the Institute for Photonics and Nanotechnologies in Trento, Italy. But, he says, he wouldn’t bet on the source being wave function collapse. “It is much more likely that it’s some not very well understood effect in the experiment.” In future experiments, the scientists plan to change the design of the cantilever to attempt to isolate the vibration’s source.

    The result follows similar tests performed with the LISA Pathfinder spacecraft, which was built as a test-bed for gravitational wave detection techniques. Two different studies found no excess jiggling Physical Review D] of free-falling weights [Physical Review D] within the spacecraft. But the new cantilever experiment tests for wave function collapse occurring at different rate and length scales than those previous studies.

    ESA/LISA Pathfinder

    Two different studies found no excess jiggling of free-falling weights within the spacecraft. But the new cantilever experiment tests for wave function collapse occurring at different rate and length scales than those previous studies.

    Theories that include spontaneous wave function collapse are not yet accepted by most physicists. But interest in them has recently become more widespread, says physicist David Vitali of the University of Camerino in Italy, “sparked by the fact that technological advances now make fundamental tests of quantum mechanics much easier to conceive.” Focusing on a simple system like the cantilever is the right approach, says Vitali, who was not involved with the research. Still, “a lot of things can go wrong or can be not fully controlled.”

    To conclude that wave function collapse is the cause of the excess vibrations, every other possible source will have to be ruled out. So, Adler says, “it’s going to take a lot of confirmation to check that this is a real effect.”

    See the full article here .

    Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

    Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

    Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

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  • richardmitnick 11:03 am on July 31, 2017 Permalink | Reply
    Tags: , Nanocrystals, , , Quantum Mechanics, , Superlattices,   

    From SLAC: “Scientists Watch ‘Artificial Atoms’ Assemble into Perfect Lattices with Many Uses” 


    SLAC Lab

    July 31, 2017
    Written by Glennda Chui

    Press Office Contact:
    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    1
    An illustration shows nanocrystals assembling into an ordered ‘superlattice’ – a process that a SLAC/Stanford team was able to observe in real time with X-rays from the Stanford Synchrotron Radiation Lightsource (SSRL). They discovered that this assembly takes just a few seconds when carried out in hot solutions. The results open the door for rapid self-assembly of nanocrystal building blocks into complex structures with applications in optoelectronics, solar cells, catalysis and magnetic materials. (Greg Stewart/SLAC National Accelerator Laboratory.)

    SLAC/SSRL

    Some of the world’s tiniest crystals are known as “artificial atoms” because they can organize themselves into structures that look like molecules, including “superlattices” that are potential building blocks for novel materials.

    Now scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have made the first observation of these nanocrystals rapidly forming superlattices while they are themselves still growing. What they learn will help scientists fine-tune the assembly process and adapt it to make new types of materials for things like magnetic storage, solar cells, optoelectronics and catalysts that speed chemical reactions.

    The key to making it work was the serendipitous discovery that superlattices can form superfast – in seconds rather than the usual hours or days – during the routine synthesis of nanocrystals. The scientists used a powerful beam of X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) to observe the growth of nanocrystals and the rapid formation of superlattices in real time.

    A paper describing the research, which was done in collaboration with scientists at the DOE’s Argonne National Laboratory, was published today in Nature.

    2
    A lab in the Stanford Chemical Engineering Department where nanocrystals are grown. Experiments at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) were able to observe the simultaneous growth of nanocrystals and superlattices for the first time. (Dawn Harmer/SLAC National Accelerator Laboratory.)

    “The idea is to see if we can get an independent understanding of how these superlattices grow so we can make them more uniform and control their properties,” said Chris Tassone, a staff scientist at SSRL who led the study with Matteo Cargnello, assistant professor of chemical engineering at Stanford.

    Tiny Crystals with Outsized Properties

    Scientists have been making nanocrystals in the lab since the 1980s. Because of their tiny size –they’re billionths of a meter wide and contain just 100 to 10,000 atoms apiece — they are governed by the laws of quantum mechanics, and this gives them interesting properties that can be changed by varying their size, shape and composition. For instance, spherical nanocrystals known as quantum dots, which are made of semiconducting materials, glow in colors that depend on their size; they are used in biological imaging and most recently in high-definition TV displays.

    In the early 1990s, researchers started using nanocrystals to build superlattices, which have the ordered structure of regular crystals, but with small particles in place of individual atoms. These, too, are expected to have unusual properties that are more than the sum of their parts.

    But until now, superlattices have been grown slowly at low temperatures, sometimes in a matter of days.

    That changed in February 2016, when Stanford postdoctoral researcher Liheng Wu serendipitously discovered that the process can occur much faster than scientists had thought.

    3
    The experimental set-up at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) where scientists used an X-ray beam to observe superlattices forming during the synthesis of nanocrystals for the first time. The vessel where the reactions took place is at bottom center, wrapped in gold heating tape that boosted the temperature inside to more than 230 degrees Celsius. (Liheng Wu/Stanford University.)

    ‘Something Weird Is Happening’

    He was trying to make nanocrystals of palladium – a silvery metal that’s used to promote chemical reactions in catalytic converters and many industrial processes – by heating a solution containing palladium atoms to more than 230 degrees Celsius. The goal was to understand how these tiny particles form, so their size and other properties could be more easily adjusted.

    The team added small windows to a reaction chamber about the size of a tangerine so they could shine an SSRL X-ray beam through it and watch what was happening in real time.

    “It’s kind of like cooking,” Cargnello explained. “The reaction chamber is like a pan. We add a solvent, which is like the frying oil; the main ingredients for the nanocrystals, such as palladium; and condiments, which in this case are surfactant compounds that tune the reaction conditions so you can control the size and composition of the particles. Once you add everything to the pan, you heat it up and fry your stuff.”

    Wu and Stanford graduate student Joshua Willis expected to see the characteristic pattern made by X-rays scattering off the tiny particles. They saw a completely different pattern instead.

    “So something weird is happening,” they texted their adviser.

    The something weird was that the palladium nanocrystals were assembling into superlattices.

    4
    Members of the nanocrystal research team, from left: Assistant Professor Jian Qin, postdoctoral researcher Liheng Wu and Assistant Professor Matteo Cargnello, all of Stanford; SLAC staff scientist Chris Tassone; and Stanford graduate student Joshua Willis. (Dawn Harmer/SLAC National Accelerator Laboratory)

    A Balance of Forces

    At this point, “The challenge was to understand what brings the particles together and attracts them to each other but not too strongly, so they have room to wiggle around and settle into an ordered position,” said Jian Qin, an assistant professor of chemical engineering at Stanford who performed theoretical calculations to better understand the self-assembly process.

    Once the nanocrystals form, what seems to be happening is that they acquire a sort of hairy coating of surfactant molecules. The nanocrystals glom together, attracted by weak forces between their cores, and then a finely tuned balance of attractive and repulsive forces between the dangling surfactant molecules holds them in just the right configuration for the superlattice to grow.

    To the scientists’ surprise, the individual nanocrystals then kept on growing, along with the superlattices, until all the chemical ingredients in the solution were used up, and this unexpected added growth made the material swell. The researchers said they think this occurs in a wide range of nanocrystal systems, but had never been seen because there was no way to observe it in real time before the team’s experiments at SSRL.

    “Once we understood this system, we realized this process may be more general than we initially thought,” Wu said. “We have demonstrated that it’s not only limited to metals, but it can also be extended to semiconducting materials and very likely to a much larger set of materials.”

    The team has been doing follow-up experiments to find out more about how the superlattices grow and how they can tweak the size, composition and properties of the finished product.

    Ian Salmon McKay, a graduate student in chemical engineering at Stanford, and Benjamin T. Diroll, a postdoctoral researcher at Argonne National Laboratory’s Center for Nanoscale Materials (CNM), also contributed to the work.

    SSRL and CNM are DOE Office of Science User Facilities. The research was funded by the DOE Office of Science and by a Laboratory Directed Research and Development grant from SLAC.

    See the full article here .

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
    i1

     
  • richardmitnick 4:46 pm on July 15, 2017 Permalink | Reply
    Tags: , , Laser communication to the orbit, , , , Quantum cryptography, Quantum Mechanics   

    From Max Planck Gesellschaft: “Quantum communication with a satellite” 

    Max Planck Gesellschaft

    July 10, 2017
    Prof. Dr. Gerd Leuchs
    Max Planck Institute for the Science of Light, Erlangen
    Phone:+49 9131 7133-100
    Fax:+49 9131 7133-109
    gerd.leuchs@mpl.mpg.de

    What started out as exotic research in physics laboratories could soon change the global communication of sensitive data: quantum cryptography. Interest in this technique has grown rapidly over the last two years or so. The most recent work in this field, which a team headed by Christoph Marquardt and Gerd Leuchs at the Max Planck Institute for the Science of Light in Erlangen is now presenting, is set to heighten the interest of telecommunications companies, banks and governmental institutions even further. This is due to the fact that the physicists collaborating with the company Tesat-Spacecom and the German Aerospace Center have now created one precondition for using quantum cryptography to communicate over large distances as well without any risk of interception. They measured the quantum states of light signals which were transmitted from a geostationary communication satellite 38,000 kilometres away from Earth. The physicists are therefore confident that a global interception-proof communications network based on established satellite technology could be set up within only a few years.

    1
    More versatile than originally thought: A part of the Alphasat I-XL was actually developed to demonstrate data transmission between the Earth observation satellites of the European Copernicus project and Earth, but has now helped a group including researchers from the Max Planck Institute for the Science of Light to test the measurement of quantum states after they have been transmitted over a distance of 38,000 kilometres.© ESA.

    Sensitive data from banks, state institutions or the health sector, for example, must not fall into unauthorized hands. Although modern encryption techniques are far advanced, they can be cracked in many cases if significant, commensurate efforts are expended. And conventional encryption methods would hardly represent a challenge for the quantum computers of the future. While scientists used to think that the realization of such a computer was still a very long way off, considerable progress in the recent past has now raised physicists’ hopes. “A quantum computer could then also crack the data being stored today,” as Christoph Marquardt, leader of a research group at the Max Planck Institute for the Science of Light, states. “And this is why we are harnessing quantum cryptography now in order to develop a secure data transfer method.”

    Quantum mechanics protects a key against spies

    In quantum cryptography, two parties exchange a secret key, which can be used to encrypt messages. Unlike established public key encryption methods, this method cannot be cracked as long as the key does not fall into the wrong hands. In order to prevent this from happening, the two parties send each other keys in the form of quantum states in laser pulses. The laws of quantum mechanics protect a key from spies here, because any eavesdropping attempt will inevitably leave traces in the signals, which sender and recipient will detect immediately. This is because reading quantum information equates to a measurement on the light pulse, which inevitably changes the quantum state of the light.

    In the laboratory and over short distances quantum key distribution already works rather well via optical fibres that are used in optical telecommunications technology. Over large distances the weak and sensitive quantum signals need to be refreshed, which is difficult for reasons similar to those determining the fact that that laser pulses cannot be intercepted unnoticed. Christoph Marquardt and his colleagues are therefore relying on the transmission of quantum states via the atmosphere, between Earth and satellites to be precise, to set up a global communications network that is protected by quantum cryptography.

    2
    Laser communication to the orbit: The infrared image shows the ground station for the communication with the Alphasat I-XL satellite 38,000 kilometres away. The receiver sends an infrared laser beam in the direction of the orbit so that the satellite can find it. Since the beam is scattered by a higher atmospheric layer, it appears as a larger spot. © Imran Khan, MPI for the Science of Light.

    In their current publication [Optica], the researchers showed that this can largely be based on existing technology. Using a measuring device on the Canarian island Teneriffe, they detected the quantum properties of laser pulses which the Alphasat I-XL communications satellite had transmitted to Earth. The satellite circles Earth on a geostationary orbit and therefore appears to stand still in the sky. The satellite, which was launched in 2013, carries laser communication equipment belonging to the European Space Agency ESA. The company Tesat-Spacecom, headquartered in Backnang near Stuttgart, developed the technology in collaboration with the German Aerospace Center as part of the European Copernicus project for Earth observation, which is funded by the German Federal Ministry for Economic Affairs and Energy.


    ESA Sentinels (Copernicus)

    While Alphasat I-XL was never intended for quantum communication, “we found out at some stage, however, that the data transmission of the satellite worked according to the same principle as that of our laboratory experiments,” explains Marquardt, “which is by modulating the amplitude and phase of the light waves.” The amplitude is a measure for the intensity of the light waves and the mutual shift of two waves can be determined with the aid of the phase.

    The laser beam is 800 metres wide after travelling 38,000 kilometres

    For conventional data transmission, the modulation of the amplitude, for example, is made particularly large. This makes it easier to read out in the receiver and guarantees a clear signal. Marquardt and his colleagues were striving to achieve the exact opposite, however: in order to get down to the quantum level with the laser pulses, they have to greatly reduce the amplitude.

    The signal, which is therefore already extremely weak, is attenuated a great deal more as it is being transmitted to Earth. The largest loss occurs due to the widening of the laser beam. After 38,000 kilometres, it has a diameter of 800 metres at the ground, while the diameter of the mirror in the receiving station is a mere 27 centimetres. Further receiving mirrors, which uninvited listeners could use to eavesdrop on the communication, could easily be accommodated in a beam which is widened to such an extent. The quantum cryptography procedure, however, takes this into account. In a simple picture it exploits the fact that a photon – which is what the signals of quantum communication employ – can only be measured once completely: either with the measuring apparatus of the lawful recipient or the eavesdropping device of the spy. The exaction location of where a photon is registered within the beam diameter, however, is still left to chance.

    The experiment carried out at the beginning of 2016 was successful despite the greatly attenuated signal, because the scientists found out that the properties of the signals received on the ground came very close to the limit of quantum noise. The noise of laser light is the term physicists use to describe variations in the detected photons. Some of this irregularity is caused by the inadequacies of the transmitting and receiving equipment or turbulences in the atmosphere, and can therefore be avoided in principle. Other variations result from the laws of quantum physics – more precisely the uncertainty principle – according to which amplitude and phase of the light cannot be specified simultaneously to any arbitrary level of accuracy.

    Quantum cryptography can use established satellite technology

    Since the transmission with the aid of the Tesat system already renders the quantum properties of the light pulses measurable, this technique can be used as the basis on which to develop satellite-based quantum cryptography. “We were particularly impressed by this because the satellite had not been designed for quantum communication,” as Marquardt explains.

    Together with their colleagues from Tesat and other partners, the Erlangen physicists now want to develop a new satellite specifically customized for the needs of quantum cryptography. Since they can largely build on tested and tried technology, the development should take much less time than a completely new development. Their main task is to develop a board computer designed for quantum communication and to render the quantum mechanical random number generator space-proof, which supplies the cryptographic key.

    Consequently, quantum cryptography, which started out as an exotic playground for physicists, became quite close to practical application. The race for the first operational secure system is in full swing. Countries such as Japan, Canada, the USA and China in particular are funneling a lot of money into this research. “The conditions for our research have changed completely,” explains Marquardt. “At the outset, we attempted to whet industry’s appetite for such a method, today they are coming to us without prompting and asking for practicable solutions.” These could become reality in the next five to ten years.

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    The Max Planck Society is Germany’s most successful research organization. Since its establishment in 1948, no fewer than 18 Nobel laureates have emerged from the ranks of its scientists, putting it on a par with the best and most prestigious research institutions worldwide. The more than 15,000 publications each year in internationally renowned scientific journals are proof of the outstanding research work conducted at Max Planck Institutes – and many of those articles are among the most-cited publications in the relevant field.

    What is the basis of this success? The scientific attractiveness of the Max Planck Society is based on its understanding of research: Max Planck Institutes are built up solely around the world’s leading researchers. They themselves define their research subjects and are given the best working conditions, as well as free reign in selecting their staff. This is the core of the Harnack principle, which dates back to Adolph von Harnack, the first president of the Kaiser Wilhelm Society, which was established in 1911. This principle has been successfully applied for nearly one hundred years. The Max Planck Society continues the tradition of its predecessor institution with this structural principle of the person-centered research organization.

    The currently 83 Max Planck Institutes and facilities conduct basic research in the service of the general public in the natural sciences, life sciences, social sciences, and the humanities. Max Planck Institutes focus on research fields that are particularly innovative, or that are especially demanding in terms of funding or time requirements. And their research spectrum is continually evolving: new institutes are established to find answers to seminal, forward-looking scientific questions, while others are closed when, for example, their research field has been widely established at universities. This continuous renewal preserves the scope the Max Planck Society needs to react quickly to pioneering scientific developments.

     
  • richardmitnick 10:40 am on July 3, 2017 Permalink | Reply
    Tags: Larry Zamick, Lattice dynamics, Max Born, Quantum Mechanics, Vigyan Prasar Science Portal, Warner Heisenberg   

    Provided by Larry Zamick, Physics, Rutgers University: “Max Born Founder of Lattice Dynamics” 

    From Vigyan Prasar Science Portal

    1
    Max Born

    “I am now convinced that theoretical physics is actual philosophy.”

    “The problem of physics is how the actual phenomena, as observed with the help of our sense organs aided by instruments, can be reduced to simple notions which are suited for precise measurement and used for the formulation of quantitative laws.”

    Max Born in his Experiments and Theory in Physics

    Max Born was a pioneer in developing quantum mechanics. The term “quantum mechanics” was introduced by Born. Born’s initial research interests were lattice dynamics and how atoms in solids one held together and vibrate. The Born-Haber cycle, a cycle of theoretical reactions and changes, allows calculation of the lattice energy of ionic crystals. In 1926, immediately after his student Warner Heisenberg had formulated his first laws of a new quantum theory of atoms. Born collaborated with him to develop the mathematical formulation that would adequately describe it. It was Born who first showed that the solution of Schroendinger’s quantum mechanical wave equation has a statistical meaning of physical significance. Born’s interpretation of the wave equation has proved to be of great importance in the new quantum theory. Born reformulated the first law of thermodynamics. Born produced a very precise definition of quantity of heat and thus provide the most satisfactory mathematical interpretation of the first law of thermodynamics.

    Commenting on Born’s scientific contributions, the winner of 1977 Nobel Prize for Physics, Sir Neville Francis Mott (1905-1996) wrote: “As the founder of lattice dynamics, that is, the theory of how atoms in solids stick together and vibrate, Max Born is one of the pre-eminent physicists of this century. His celebrated work on cohesion in ionic crystals formed the bridge between the physicist’s and chemist’s ways of studying crystals. For the physicists, lattice energies of the crystals were of central interest and for the chemists, heats of reaction. Born showed that the ionization potentials of the atoms could be used to compare the chemical and physical concepts. This was a landmark.”

    Max Born was born on December 11, 1882 at Breslau, Germany (now Worclaw, Poland). His father Gustav Born was a professor of embryology at the University of Breslau and his mother Margarete Born (nee Kaufmann) came from a Silesian family of industrialists. It was from his mother that Born inherited his love for music. Born’s mother died when he was four years old. In his childhood, Born badly suffered from bad colds and asthma and which continued to afflict him throughout his life. Because of his bad health, he was taught by private tutor for a year in home and then after spending two years in a preparatory school, he joined the Wilhelm’s Gymnasium in Breslau. At the Gymnasium, Born studied a wide range of subjects including mathematics, physics, history, modern languages, Latin, Greek, and German. At the School, Born did not display any sign of a gifted child. He was more interested in humanities than in science subjects.

    In 1901, Born joined the University of Breslau. Following his father’s advice, Born did not specialize in any particular subject. He took a wide range of subjects including mathematics, astronomy, physics, chemistry, logic, philosophy, and zoology. At the Breslau University, Born became interested in mathematics and the credit for this goes to his teachers Rosanes and London. Rosanes, a student of Leopold Kronecker (1823-91), who developed algebraic number theory and invented the Kronecker delta, gave brilliant lectures on analytical geometry. It was Rosanes, who introduced Born the ideas of group theory and matrix calculus, which were later used successfully by Born to solve physical problems. London’s lectures on definite integrals and on analytical mechanics were clear and lucid. The resultant effect of the teachings of Rosanes and London was that Born was drawn towards mathematics. He was helped by some of his classmates to develop interest in science. One of his classmates named Lachmann awakened his interest in astronomy. His other classmate Otto Toeplitz introduced the lives and works of some of the greatest mathematicians like Euler, Lagrange, Cauchy and Riemann to Born. Toeplitz had learnt these from his father, who was a schoolmaster and mathematician. In his later life Born acknowledged his debt to Otto Toeplitz ‘for the first introduction to these pathfinders in mathematical science’.

    In those days it was a common practice for a German student to move from university to university. And Born was no exception. In 1902 Born went to the University of Heidelberg and then in 1903 he went to the University of Zurich. It was at Zurich that Born attended his first course on advanced mathematics given by Adolf Hurwitz (1859-1919). After coming back to Breslau University, he was told by his classmates Toeplitz and Hellinger of the great teachers of mathematics, Christian Felix Klein (1849-1925), the founder of modern geometry unifying Euclidean and non-Euclidean geometry; David Hilbert (1862-1943), who originated the concept of Hilbert Space; and Hermann Minkowski (1864-1909), who developed the mathematics that played a crucial role in Einstein’s formulation of theory of relativity at the University of Gottingen. So Born went to the University of Gottingen to attend lectures by these great scientists. At the Gottingen University, Born served as an Assistant to David Hilbert. He attended lectures by Klein and Carl Runge (1856-1927) on elasticity and a seminar on electrodynamics by Hilbert and Minkowski. Klein was annoyed with Born because of Born’s irregular attendance at his lectures. Born then attended Schwarzschild’s astronomy lectures. During his student days at the Gottingen University, he had the opportunity to go for walks in the woods with Hilbert and Minkowski. During these walks, all matters of fascinating subjects were discussed in addition to mathematics including problems pertaining to philosophy, politics and social. Born was also interacting with non-mathematicians like Courant, Schmidt and Caratheodory.

    Born earned his PhD in physics from the University of Gottingen in 1907. He then undertook compulsory military service. However, he did not have to complete the standard one year period because he suffered from asthma. Even his brief stint with the military made him loath all things military. After serving in the military Born visited Caius College, Cambridge for six months to study under Larmor and J. J. Thomson (1908-1909). He came back to Breslau and worked there with the physicists Lummer and Pringsheim. Around this time he was fascinated by Einstein’s work on relativity. Born’s work on combining ideas of Einstein and Minkowski led to an invitation to Gottingen in 1909, by Minkowski as his assistant. However, Minkowski died within weeks after Born’s coming to Gottingen. In 1912, Born joined the faculty of the Gottingen University and he started with working with Theodore von Karman (1881-1963), who discovered Karman vortices.

    In 1915 Born was appointed as Professor (extraordinarius) at the Berlin University to assist Max Plunck. At the time Albert Einstein was also at the Berlin University. However, soon he had to join the Army. He was attached to a scientific office of the Army, where he worked on the theory of sound ranging. He could also manage to find time to work on the theory of crystals, which led to publication his first book entitled “Dynamics of Crystal Lattices” summarizing a series of investigations that Born had initiated at Gottingen.

    In 1919, after the conclusion of the First World War, Born was appointed Professor at the University of Frankfurt-on-Main, where a laboratory was put at his disposal.. Here Born’s assistant was Otto Stern, the first of Stern’s well-known experiments, which were awarded with a Nobel Prize originated there.

    In 1921, Born came back to the University of Gottingen as Professor of Physics, where he stayed for 12 years, interrupted only by a visit to USA in 1925. Among his collaborators at Gottingen were Pauli, Heisenberg, Jordan, Fermi, Dirac, Hund, Weisskopf, Oppenheimer, Joseph Mayer and Maria Goeppert- Mayer. During his stay Born’s most important contributions to physics were made. He published a modernized version of his book on crystals. Assisted by his students he undertook numerous investigations on crystal lattices, followed by a series of studies on quantum theory. He collaborated with Heisenberg and Jordan to develop further the principles of quantum mechanics discovered by Heisenberg. He also undertook his own studies on the statistical interpretation of quantum mechanics. Born proposed that what Schrodinger had described with his wave equation, not the electron itself, but the probability of finding the electron in any given location. Consider you are bombarding a barrier with electrons, when some will go through and some will bounce off. Born figured out that a single electron has, say 55 percent chance of going through the barrier, and a 45 percent chance of bouncing back. Because electrons cannot readily divide, Schrodinger’s quantum mechanical wave equation could not have describing the electron itself, what it was describing was its probable location. Born’s interpretation was hailed by Leon Lederman, as “the single most dramatic and major change in our world view since Newton”. However, at the beginning Born’s interpretation was not liked either by Schrodinger, the propounder of the wave equation or many other physicists including Einstein. Born corresponded with Einstein on the subject and the Born-Einstein letters were published in 1971. Born’s proposition of probability meant that the determinism of Newton’s classical physics was no more valid. There is no predetermined way in which absolute prediction can be made, as in classical physics. Everything depends on probability. A similar idea is embodied in the uncertainty principle of Werner Heisenberg. But Bohr, Sommerfeld, Heisenberg and many others took Born’s ideas seriously and they continued the exciting work of trying to get all pieces to fit.

    Born introduced a useful technique, known as the Born Approximation, for solving problems concerning the scattering of atomic particles. Born and J. Robert Oppenheimer introduced a widely used simplification of the calculations dealing with electronic structures of molecules. This work known as “Born-Oppenheimer theory of molecules deals with interatomic forces.”

    In 1933, like many other scientists of Jewish origin, Born was forced to leave Germany. He went to England and became Stokes lecturer at the University of Cambridge. He worked there for three years. During these years he mostly worked in the field of nonliniear electrodynamics, which he developed with Infeld.

    During the winter of 1935-1936, Born spent six months at Bangalore at the invitation of C. V. Raman. Commenting on his coming to Bangalore and subsequent events, Born said: “ As I had no other job, I was willing to accept Raman’s offer namely, a permanent position at his institute, if he could obtain the consent of the Council. Then he insisted on my attending the next faculty meeting which had to decide on bringing my appointment before the Council.

    The English professor Aston (who had joined around the same time) went up and spoke in a most unpleasant way against Raman’s motion declaring that a second rank foreigner driven out from his own his country was not good enough for them. I was so shaken that, when I returned home, I simply cried.”

    Born was elected to the Tait Chair of natural philosophy at the University of Edinburgh in 1936. He became a British subject in 1936. One of Born’s research students described Born’s days at Edinburgh: “When Born arrived in the morning he first used to make the round of his research students, asking them whether they had any progress to report, and giving them advice, sometimes presenting them with sheets of elaborate calculations concerning their problems which he had himself done the day before…The rest of the morning was spent by Born in delivering his lectures to undergraduate honours students, attending to departmental business, and doing research work of his own. Most of the latter, however he used to carry out at home in the afternoons and evenings.”

    After his retirement in 1953 Born went back to his native country and settled in Gottingen. In 1954 he was awarded the Nobel Prize in Physics “for his fundamental research in quantum mechanics, especially for his statistical interpretation of the wavefunction.” He shared the Prize with Walther Wilhelm Georg Franz Bothe (1891-1957).

    Born was awarded Fellowships of many scientific academies—Gottingen, Moscow, Berlin, Bangalore, Bucharest, Edinburgh, London, Lima, Dublin, Copenhagen, Stockholm, Washington, and Boston. He was awarded honorary doctorates from a number of universities including Bristol, Bordeaux, Oxford, Freidburg/Breisgau, Edinburgh, Oslo, and Brussels. He received the Stokes Medal of Cambridge, the Max Planck Medal of the German Physical Society, the Hughes Medal of the Royal Society of London. He was also awarded the MacDougall-Brisbane Prize, the Gunning-Victoria Jubilee Prize of the Royal Society, Edinburgh and the Grand Cross of Merit with Star of the order of Merit of the German Federal Republic.
    During his post-retirement life in Bad Pyrmomt, a town neer Gottingen, Born wrote many articles and books on philosophy of science and the impact of science on human affairs particularly the responsibility of scientists for the use of nuclear energy in war and peace. He was totally against the use contemporary scientific knowledge of nuclear energy for warfare. He took the initiative in 1955 to get a statement on this subject signed by a gathering of Nobel Laureates. Born is buried in Gottingen, where he died on January 05, 1970. His tombstone displays his fundamental equation of matrix mechanics that is pq-qp = (h/ 2??i.

    References , [Sorry no lnks provided.]

    Born. Max. My Life: Reflections of a Nobel Laureate. London: Taylor & Francis, 1978.

    A Dictionary of Scientists. Oxford: Oxford University Press, 1999.

    The Cambridge Dictionary of Scientists (Second Edition). Cambridge: Cambridge University Press, 2002.

    Parthasarathy, R. Paths of Innovators in Science, Engineering & Technology. Chennai: East West Books (Madras) Pvt. Ltd., 2000.

    Spangenburg, Ray and Diane K. Moser. The History of Science: From 1895 to 1945. Hyderabad: Universities Press (India) Ltd., 1999.

    Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. Cambridge: Cambridge University Press, 2004.

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  • richardmitnick 4:01 pm on July 1, 2017 Permalink | Reply
    Tags: , , , Quantum Mechanics, Van der Waals interactions repulsive in confinement   

    From phys.org: “Researchers refute textbook knowledge in molecular interactions” 

    physdotorg
    phys.org

    June 29, 2017

    1
    Repulsive ground state interaction E rep (solid lines) and the sum of repulsion and London attraction (E att) energy (broken lines) for argon and methane dimers on a perfectly reflecting surface. Credit: arXiv:1610.09275 [cond-mat.mes-hall]

    Van der Waals interactions between molecules are among the most important forces in biology, physics, and chemistry, as they determine the properties and physical behavior of many materials. For a long time, it was considered that these interactions between molecules are always attractive. Now, for the first time, Mainak Sadhukhan and Alexandre Tkatchenko from the Physics and Materials Science Research Unit at the University of Luxembourg found that in many rather common situations in nature the van der Waals force between two molecules becomes repulsive. This might lead to a paradigm shift in molecular interactions.

    “The textbooks so far assumed that the forces are solely attractive. For us, the interesting question is whether you can also make them repulsive,” Prof Tkatchenko explains. “Until recently, there was no evidence in scientific literature that van der Waals forces could also be repelling.” Now, the researchers have shown in their paper, published in the renowned scientific journal Physical Review Letters, that the forces are, in fact, repulsive when they take place under confinement.

    The ubiquitous van der Waals force was first explained by the German-American physicist Fritz London in 1930. Using quantum mechanics, he proved the purely attractive nature of the van der Waals force for any two molecules interacting in free space. “However, in nature molecules in most cases interact in confined spaces, such as cells, membranes, nanotubes, etc. In is this particular situation, van der Waals forces become repulsive at large distances between molecules,” says Prof Tkatchenko.

    Mainak Sadhukhan, the co-author of the study, developed a novel quantum-mechanical method that enabled them to model van der Waals forces in confinement. “We could rationalize many previous experimental results that remained unexplained until now. Our new theory allows, for the first time, for an interpretation of many interesting phenomena observed for molecules under confinement,” Mainak Sadhukhan says.

    The discovery could have many potential implications for the delivery of pharmaceutical molecules in cells, water desalination and transport, and self-assembly of molecular layers in photovoltaic devices.

    Prof Tkatchenko’s research group is working on methods that model the properties of a wide range of intermolecular interactions. Only in 2016, they found that the true nature of these van der Wals forces differs from conventional wisdom in chemistry and biology, as they have to be treated as coupling between waves rather than as mutual attraction (or repulsion) between particles.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 11:23 am on July 1, 2017 Permalink | Reply
    Tags: Entanglement and quantum interference, IBM Q experience, Now an interface based on the popular programming language Python, , Quantum Mechanics, , Supercomputers still rule   

    From SA: “Quantum Computing Becomes More Accessible” 

    Scientific American

    Scientific American

    June 26, 2017
    Dario Gil

    1
    Credit: World Economic Forum

    Quantum computing has captured imaginations for almost 50 years. The reason is simple: it offers a path to solving problems that could never be answered with classical machines. Examples include simulating chemistry exactly to develop new molecules and materials and solving complex optimization problems, which seek the best solution from among many possible alternatives. Every industry has a need for optimization, which is one reason this technology has so much disruptive potential.

    Until recently, access to nascent quantum computers was restricted to specialists in a few labs around the world. But progress over the past several years has enabled the construction of the world’s first prototype systems that can finally test out ideas, algorithms and other techniques that until now were strictly theoretical.

    Quantum computers tackle problems by harnessing the power of quantum mechanics. Rather than considering each possible solution one at a time, as a classical machine would, they behave in ways that cannot be explained with classical analogies. They start out in a quantum superposition of all possible solutions, and then they use entanglement and quantum interference to home in on the correct answer—processes that we do not observe in our everyday lives. The promise they offer, however, comes at the cost of them being difficult to build. A popular design requires superconducting materials (kept 100 times colder than outer space), exquisite control over delicate quantum states and shielding for the processor to keep out even a single stray ray of light.

    Existing machines are still too small to fully solve problems more complex than supercomputers can handle today. Nevertheless, tremendous progress has been made. Algorithms have been developed that will run faster on a quantum machine. Techniques now exist that prolong coherence (the lifetime of quantum information) in superconducting quantum bits by a factor of more than 100 compared with 10 years ago. We can now measure the most important kinds of quantum errors. And in 2016 IBM provided the public access to the first quantum computer in the cloud—the IBM Q experience—with a graphical interface for programming it and now an interface based on the popular programming language Python. Opening this system to the world has fueled innovations that are vital for this technology to progress, and to date more than 20 academic papers have been published using this tool. The field is expanding dramatically. Academic research groups and more than 50 start-ups and large corporations worldwide are focused on making quantum computing a reality.

    With these technological advancements and a machine at anyone’s fingertips, now is the time for getting “quantum ready.” People can begin to figure out what they would do if machines existed today that could solve new problems. And many quantum computing guides are available online to help them get started.

    There are still many obstacles. Coherence times must improve, quantum error rates must decrease, and eventually, we must mitigate or correct the errors that do occur. Researchers will continue to drive innovations in both the hardware and software. Investigators disagree, however, over which criteria should determine when quantum computing has achieved technological maturity. Some have proposed a standard defined by the ability to perform a scientific measurement so obscure that it is not easily explained to a general audience. I and others disagree, arguing that quantum computing will not have emerged as a technology until it can solve problems that have commercial, intellectual and societal importance. The good news is, that day is finally within our sights.

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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
  • richardmitnick 7:36 pm on June 26, 2017 Permalink | Reply
    Tags: , Electromagnetic radiation [light], Hyperbolic metamaterials (HMMs), Molecular beam epitaxy, Nanoresonators, , , , , Quantum Mechanics   

    From Notre Dame: “Notre Dame Researchers Open Path to New Generation of Optical Devices” 

    Notre Dame bloc

    Notre Dame University

    COLLEGE of ENGINEERING

    OFFICE of the PROVOST
    College of Engineering

    June 22, 2017
    Nina Welding

    1
    Sub-diffraction Confinement in All-semiconductor Hyperbolic Metamaterial Resonators was co-authored by graduate students Kaijun Feng and Galen Harden and Deborah L. Sivco, engineer-in-residence at MIRTHE+ Photonics Sensing Center, Princeton Univ.

    Cameras, telescopes and microscopes are everyday examples of optical devices that measure and manipulate electromagnetic radiation [light]. Being able to control the light in such devices provides the user with more information through a much better “picture” of what is occurring through the lens. The more information one can glean, the better the next generation of devices can become. Similarly, controlling light on small scales could lead to improved optical sources for applications that span health, homeland security and industry. This is what a team of researchers, led by Anthony Hoffman, assistant professor of electrical engineering and researcher in the University’s Center for Nano Science and Technology (NDnano), has been pursuing. Their findings were recently published in the June 19 issue of ACS Photonics.

    In fact, the team has fabricated and characterized sub-diffraction mid-infrared resonators using all-semiconductor hyperbolic metamaterials (HMMs) that confine light to extremely small volumes — thousands of times smaller than common materials.

    2
    The scanning electron microscope image here shows an array of 0.47 μm wide resonators with a 2.5 μm pitch. No image credit.

    HMMs combine the properties of metals, which are excellent conductors, and dielectrics, which are insulators, to realize artificial optical materials with properties that are very difficult, even impossible, to find naturally. These unusual properties may elucidate the quantum mechanical interactions between light and matter at the nanoscale while giving researchers a powerful tool to control and engineer these light-matter interactions for new optical devices and materials.

    Hoffman’s team engineered these desired properties in the HMMs by growing them via molecular beam epitaxy using III-V semiconductor materials routinely used for high-performance optoelectronic devices, such as lasers and detectors. Layers of Si-doped InGaAs and intrinsic AlInAs were placed on top of one another, with a single layer being 50 nm thick. The total thickness of the HMM was 1μm, about 100 times smaller than the width of a human hair.

    The nanoresonators were produced by Kaijun Feng, graduate student in the Department of Electrical Engineering, using state-of-the-art fabrication equipment in Notre Dame’s Nanofabrication Facility. The devices were then characterized in Hoffman’s laboratory using a variety of spectroscopic techniques.

    “What is particularly exciting about this work,” says Hoffman, “is that we have found a way to squeeze light into small volumes using a mature semiconductor technology. In addition to being able to employ these nanoresonators to generate mid-infrared light, we believe that these new sources could have significant application in the mid-infrared portion of the spectrum, which is used for optical sensing across areas such as medicine, environmental monitoring, industrial process control and defense. We are also excited about the possibility of utilizing these nanoresonators to study interactions between light and matter that previously have not been possible.”

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    Notre Dame Campus

    The University of Notre Dame du Lac (or simply Notre Dame /ˌnoʊtərˈdeɪm/ NOH-tər-DAYM) is a Catholic research university located near South Bend, Indiana, in the United States. In French, Notre Dame du Lac means “Our Lady of the Lake” and refers to the university’s patron saint, the Virgin Mary.

    The school was founded by Father Edward Sorin, CSC, who was also its first president. Today, many Holy Cross priests continue to work for the university, including as its president. It was established as an all-male institution on November 26, 1842, on land donated by the Bishop of Vincennes. The university first enrolled women undergraduates in 1972. As of 2013 about 48 percent of the student body was female.[6] Notre Dame’s Catholic character is reflected in its explicit commitment to the Catholic faith, numerous ministries funded by the school, and the architecture around campus. The university is consistently ranked one of the top universities in the United States and as a major global university.

    The university today is organized into five colleges and one professional school, and its graduate program has 15 master’s and 26 doctoral degree programs.[7][8] Over 80% of the university’s 8,000 undergraduates live on campus in one of 29 single-sex residence halls, each of which fields teams for more than a dozen intramural sports, and the university counts approximately 120,000 alumni.[9]

    The university is globally recognized for its Notre Dame School of Architecture, a faculty that teaches (pre-modernist) traditional and classical architecture and urban planning (e.g. following the principles of New Urbanism and New Classical Architecture).[10] It also awards the renowned annual Driehaus Architecture Prize.

     
  • richardmitnick 1:27 pm on June 18, 2017 Permalink | Reply
    Tags: , China has taken the leadership in quantum communication, China Shatters 'Spooky Action at a Distance' Record, For now the system remains mostly a proof of concept, Global quantum communication is possible and will be achieved in the near future, , Preps for Quantum Internet, , Quantum Mechanics,   

    From SA: “China Shatters ‘Spooky Action at a Distance’ Record, Preps for Quantum Internet” 

    Scientific American

    Scientific American

    June 15, 2017
    Lee Billings

    1
    Credit: Alfred Pasieka Getty Images

    In a landmark study, a team of Chinese scientists using an experimental satellite has tested quantum entanglement over unprecedented distances, beaming entangled pairs of photons to three ground stations across China—each separated by more than 1,200 kilometers. The test verifies a mysterious and long-held tenet of quantum theory, and firmly establishes China as the front-runner in a burgeoning “quantum space race” to create a secure, quantum-based global communications network—that is, a potentially unhackable “quantum internet” that would be of immense geopolitical importance. The findings were published Thursday in Science.

    “China has taken the leadership in quantum communication,” says Nicolas Gisin, a physicist at the University of Geneva who was not involved in the study. “This demonstrates that global quantum communication is possible and will be achieved in the near future.”

    The concept of quantum communications is considered the gold standard for security, in part because any compromising surveillance leaves its imprint on the transmission. Conventional encrypted messages require secret keys to decrypt, but those keys are vulnerable to eavesdropping as they are sent out into the ether. In quantum communications, however, these keys can be encoded in various quantum states of entangled photons—such as their polarization—and these states will be unavoidably altered if a message is intercepted by eavesdroppers. Ground-based quantum communications typically send entangled photon pairs via fiber-optic cables or open air. But collisions with ordinary atoms along the way disrupt the photons’ delicate quantum states, limiting transmission distances to a few hundred kilometers. Sophisticated devices called “quantum repeaters”—equipped with “quantum memory” modules—could in principle be daisy-chained together to receive, store and retransmit the quantum keys across longer distances, but this task is so complex and difficult that such systems remain largely theoretical.

    “A quantum repeater has to receive photons from two different places, then store them in quantum memory, then interfere them directly with each other” before sending further signals along a network, says Paul Kwiat, a physicist at the University of Illinois in Urbana–Champaign who is unaffiliated with the Chinese team. “But in order to do all that, you have to know you’ve stored them without actually measuring them.” The situation, Kwiat says, is a bit like knowing what you have received in the mail without looking in your mailbox or opening the package inside. “You can shake the package—but that’s difficult to do if what you’re receiving is just photons. You want to make sure you’ve received them but you don’t want to absorb them. In principle it’s possible—no question—but it’s very hard to do.”

    To form a globe-girdling secure quantum communications network, then, the only available solution is to beam quantum keys through the vacuum of space then distribute them across tens to hundreds of kilometers using ground-based nodes. Launched into low Earth orbit in 2016 and named after an ancient Chinese philosopher, the 600-kilogram “Micius” satellite is China’s premiere effort to do just that, and is only the first of a fleet the nation plans as part of its $100-million Quantum Experiments at Space Scale (QUESS) program.

    Micius carries in its heart an assemblage of crystals and lasers that generates entangled photon pairs then splits and transmits them on separate beams to ground stations in its line-of-sight on Earth. For the latest test, the three receiving stations were located in the cities of Delingha and Ürümqi—both on the Tibetan Plateau—as well as in the city of Lijiang in China’s far southwest. At 1,203 kilometers, the geographical distance between Delingha and Lijiang is the record-setting stretch over which the entangled photon pairs were transmitted.

    For now the system remains mostly a proof of concept, because the current reported data transmission rate between Micius and its receiving stations is too low to sustain practical quantum communications. Of the roughly six million entangled pairs that Micius’s crystalline core produced during each second of transmission, only about one pair per second reached the ground-based detectors after the beams weakened as they passed through Earth’s atmosphere and each receiving station’s light-gathering telescopes. Team leader Jian-Wei Pan—a physicist at the University of Science and Technology of China in Hefei who has pushed and planned for the experiment since 2003—compares the feat with detecting a single photon from a lone match struck by someone standing on the moon. Even so, he says, Micius’s transmission of entangled photon pairs is “a trillion times more efficient than using the best telecommunication fibers. … We have done something that was absolutely impossible without the satellite.” Within the next five years, Pan says, QUESS will launch more practical quantum communications satellites.

    Although Pan and his team plan for Micius and its nascent network of sister satellites to eventually distribute quantum keys, their initial demonstration instead aimed to achieve a simpler task: proving Einstein wrong.

    Einstein famously derided as “spooky action at a distance” one of the most bizarre elements of quantum theory—the way that measuring one member of an entangled pair of particles seems to instantaneously change the state of its counterpart, even if that counterpart particle is on the other side of the galaxy. This was abhorrent to Einstein, because it suggests information might be transmitted between the particles faster than light, breaking the universal speed limit set by his theory of special relativity. Instead, he and others posited, perhaps the entangled particles somehow shared “hidden variables” that are inaccessible to experiment but would determine the particles’ subsequent behavior when measured. In 1964 the physicist John Bell devised a way to test Einstein’s idea, calculating a limit that physicists could statistically measure for how much hidden variables could possibly correlate with the behavior of entangled particles. If experiments showed this limit to be exceeded, then Einstein’s idea of hidden variables would be incorrect.

    Ever since the 1970s “Bell tests” by physicists across ever-larger swaths of spacetime have shown that Einstein was indeed mistaken, and that entangled particles do in fact surpass Bell’s strict limits. The most definitive test arguably occurred in the Netherlands in 2015, when a team at Delft University of Technology closed several potential “loopholes” that had plagued past experiments and offered slim-but-significant opportunities for the influence of hidden variables to slip through. That test, though, involved separating entangled particles by scarcely more than a kilometer. With Micius’s transmission of entangled photons between widely separated ground stations, Pan’s team has now performed a Bell test at distances a thousand times greater. Just as before, their results confirm that Einstein was wrong. The quantum realm remains a spooky place—although no one yet understands why.

    “Of course, no one who accepts quantum mechanics could possibly doubt that entanglement can be created over that distance—or over any distance—but it’s still nice to see it made concrete,” says Scott Aaronson, a physicist at The University of Texas at Austin. “Nothing we knew suggested this goal was unachievable. The significance of this news is not that it was unexpected or that it overturns anything previously believed, but simply that it’s a satisfying culmination of years of hard work.”

    That work largely began in the 1990s when Pan, leader of the Chinese team, was a graduate student in the lab of the physicist Anton Zeilinger at the University of Innsbruck in Austria. Zeilinger was Pan’s PhD adviser, and they collaborated closely to test and further develop ideas for quantum communication. Pan returned to China to start his own lab in 2001, and Zeilinger started one as well at the Austrian Academy of Sciences in Vienna. For the next seven years they would compete fiercely to break records for transmitting entangled photon pairs across ever-wider gaps, and in ever-more extreme conditions, in ground-based experiments. All the while each man lobbied his respective nation’s space agency to green-light a satellite that could be used to test the technique from space. But Zeilinger’s proposals perished in a bureaucratic swamp at the European Space Agency whereas Pan’s were quickly embraced by the China National Space Administration. Ultimately, Zeilinger chose to collaborate again with his old pupil rather than compete against him; today the Austrian Academy of Sciences is a partner in QUESS, and the project has plans to use Micius to perform an intercontinental quantum key distribution experiment between ground stations in Vienna and Beijing.

    “I am happy that the Micius works so well,” Zeilinger says. “But one has to realize that it is a missed opportunity for Europe and others, too.”

    For years now, other researchers and institutions have been scrambling to catch up, pushing governments for more funding for further experiments on the ground and in space—and many of them see Micius’s success as the catalytic event they have been waiting for. “This is a major milestone, because if we are ever to have a quantum internet in the future, we will need to send entanglement over these sorts of long distances,” says Thomas Jennewein, a physicist at the University of Waterloo in Canada who was not involved with the study. “This research is groundbreaking for all of us in the community—everyone can point to it and say, ‘see, it does work!’”

    Jennewein and his collaborators are pursuing a space-based approach from the ground up, partnering with the Canadian Space Agency to plan a smaller, simpler satellite that could launch as soon as five years from now to act as a “universal receiver” and redistribute entangled photons beamed up from ground stations. At the National University of Singapore, an international collaboration led by the physicist Alexander Ling has already launched cheap shoe box–size CubeSats to create, study and perhaps even transmit photon pairs that are “correlated”—a situation just shy of full entanglement. And in the U.S., Kwiat at the University of Illinois is using NASA funding to develop a device that could someday test quantum communications using “hyperentanglement” (the simultaneous entanglement of photon pairs in multiple ways) onboard the International Space Station.

    Perhaps most significantly, a team led by Gerd Leuchs and Christoph Marquardt at the Max Planck Institute for the Science of Light in Germany is developing quantum communications protocols for commercially available laser systems already in space onboard the European Copernicus and SpaceDataHighway satellites. Using one of these systems, the team successfully encoded and sent simple quantum states to ground stations using photons beamed from a satellite in geostationary orbit, some 38,000 kilometers above Earth. This approach, Marquardt explains, does not rely on entanglement and is very different from that of QUESS—but it could, with minimal upgrades, nonetheless be used to distribute quantum keys for secure communications in as little as five years. Their results appear in Optica.

    “Our purpose is really to find a shortcut into making things like quantum key distribution with satellites economically viable and employable, pretty fast and soon,” Marquardt says. “[Engineers] invested 20 years of hard work making these systems, so it’s easier to upgrade them than to design everything from scratch. … It is a very good advantage if you can rely on something that is already qualified in space, because space qualification is very complicated. It usually takes five to 10 years just to develop that.”

    Marquardt and others suspect, however, that this field could be much further advanced than has been publicly acknowledged, with developments possibly hidden behind veils of official secrecy in the U.S. and elsewhere. It may be that the era of quantum communication is already upon us. “Some colleague of mine made the joke, ‘the silence of the U.S. is very loud,’” Marquardt says. “They had some very good groups concerning free-space satellites and quantum key distribution at Los Alamos [National Laboratory] and other places, and suddenly they stopped publishing. So we always say there are two reasons that they stopped publishing: either it didn’t work, or it worked really well!”

    See the full article here .

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