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  • richardmitnick 2:16 pm on May 16, 2017 Permalink | Reply
    Tags: , , , , , Quantum entanglement, Tim Maudlin   

    From Quanta: “A Defense of the Reality of Time” Tim Maudlin 

    Quanta Magazine
    Quanta Magazine

    May 16, 2017
    George Musser

    1
    Tim Maudlin. Edwin Tse for Quanta Magazine

    Time isn’t just another dimension, argues Tim Maudlin. To make his case, he’s had to reinvent geometry.

    Physicists and philosophers seem to like nothing more than telling us that everything we thought about the world is wrong. They take a peculiar pleasure in exposing common sense as nonsense. But Tim Maudlin thinks our direct impressions of the world are a better guide to reality than we have been led to believe.

    Not that he thinks they always are. Maudlin, who is a professor at New York University and one of the world’s leading philosophers of physics, made his name studying the strange behavior of “entangled” quantum particles, which display behavior that is as counterintuitive as can be; if anything, he thinks physicists have downplayed how transformative entanglement is.

    2
    Quantum entanglement. ATCA

    At the same time, though, he thinks physicists can be too hasty to claim that our conventional views are misguided, especially when it comes to the nature of time.

    He defends a homey and unfashionable view of time. It has a built-in arrow. It is fundamental rather than derived from some deeper reality. Change is real, as opposed to an illusion or an artifact of perspective. The laws of physics act within time to generate each moment. Mixing mathematics, physics and philosophy, Maudlin bats away the reasons that scientists and philosophers commonly give for denying this folk wisdom.

    The mathematical arguments are the target of his current project, the second volume of New Foundations for Physical Geometry (the first appeared in 2014). Modern physics, he argues, conceptualizes time in essentially the same way as space. Space, as we commonly understand it, has no innate direction — it is isotropic. When we apply spatial intuitions to time, we unwittingly assume that time has no intrinsic direction, either. New Foundations rethinks topology in a way that allows for a clearer distinction between time and space. Conventionally, topology — the first level of geometrical structure — is defined using open sets, which describe the neighborhood of a point in space or time. “Open” means a region has no sharp edge; every point in the set is surrounded by other points in the same set.

    Maudlin proposes instead to base topology on lines. He sees this as closer to our everyday geometrical intuitions, which are formed by thinking about motion. And he finds that, to match the results of standard topology, the lines need to be directed, just as time is. Maudlin’s approach differs from other approaches that extend standard topology to endow geometry with directionality; it is not an extension, but a rethinking that builds in directionality at the ground level.

    Maudlin discussed his ideas with Quanta Magazine in March. Here is a condensed and edited version of the interview.

    Why might one think that time has a direction to it? That seems to go counter to what physicists often say.

    I think that’s a little bit backwards. Go to the man on the street and ask whether time has a direction, whether the future is different from the past, and whether time doesn’t march on toward the future. That’s the natural view. The more interesting view is how the physicists manage to convince themselves that time doesn’t have a direction.
    They would reply that it’s a consequence of Einstein’s special theory of relativity, which holds that time is a fourth dimension.

    This notion that time is just a fourth dimension is highly misleading. In special relativity, the time directions are structurally different from the space directions. In the timelike directions, you have a further distinction into the future and the past, whereas any spacelike direction I can continuously rotate into any other spacelike direction. The two classes of timelike directions can’t be continuously transformed into one another.

    Standard geometry just wasn’t developed for the purpose of doing space-time. It was developed for the purpose of just doing spaces, and spaces have no directedness in them. And then you took this formal tool that you developed for this one purpose and then pushed it to this other purpose.

    When relativity was developed in the early part of the 20th century, did people begin to see this problem?

    I don’t think they saw it as a problem. The development was highly algebraic, and the more algebraic the technique, the further you get from having a geometrical intuition about what you’re doing. So if you develop the standard account of, say, the metric of space-time, and then you ask, “Well, what happens if I start putting negative numbers in this thing?” That’s a perfectly good algebraic question to ask. It’s not so clear what it means geometrically. And people do the same thing now when they say, “Well, what if time had two dimensions?” As a purely algebraic question, I can say that. But if you ask me what could it mean, physically, for time to have two dimensions, I haven’t the vaguest idea. Is it consistent with the nature of time that it be a two-dimensional thing? Because if you think that what time does is order events, then that order is a linear order, and you’re talking about a fundamentally one-dimensional kind of organization.
    And so you are trying to allow for the directionality of time by rethinking geometry. How does that work?

    I really was not starting from physics. I was starting from just trying to understand topology. When you teach, you’re forced to confront your own ignorance. I was trying to explain standard topology to some students when I was teaching a class on space and time, and I realized that I didn’t understand it. I couldn’t see the connection between the technical machinery and the concepts that I was using.

    Suppose I just hand you a bag of points. It doesn’t have a geometry. So I have to add some structure to give it anything that is recognizably geometrical. In the standard approach, I specify which sets of points are open sets. In my approach, I specify which sets of points are lines.

    How does this differ from ordinary geometry taught in high school?

    In this approach that’s based on lines, a very natural thing to do is to put directionality on the lines. It’s very easy to implement at the level of axioms. If you’re doing Euclidean geometry, this isn’t going to occur to you, because your idea in Euclidean geometry is if I have a continuous line from A to B, it’s just as well a continuous line B to A — that there’s no directionality in a Euclidean line.
    From the pure mathematical point of view, why might your approach be preferable?

    In my approach, you put down a linear structure on a set of points. If you put down lines according to my axioms, there’s then a natural definition of an open set, and it generates a topology.

    Another important conceptual advantage is that there’s no problem thinking of a line that’s discrete. People form lines where there are only finitely many people, and you can talk about who’s the next person in line, and who’s the person behind them, and so on. The notion of a line is neutral between it being discrete and being continuous. So you have this general approach.

    Why is this kind of modification important for physics?

    As soon as you start talking about space-time, the idea that time has a directionality is obviously something we begin with. There’s a tremendous difference between the past and the future. And so, as soon as you start to think geometrically of space-time, of something that has temporal characteristics, a natural thought is that you are thinking of something that does now have an intrinsic directionality. And if your basic geometrical objects can have directionality, then you can use them to represent this physical directionality.
    Physicists have other arguments for why time doesn’t have a direction.

    Often one will hear that there’s a time-reversal symmetry in the laws. But the normal way you describe a time-reversal symmetry presupposes there’s a direction of time. Someone will say the following: “According to Newtonian physics, if the glass can fall off the table and smash on the floor, then it’s physically possible for the shards on the floor to be pushed by the concerted effort of the floor, recombine into the glass and jump back up on the table.” That’s true. But notice, both of those descriptions are ones that presuppose there’s a direction of time. That is, they presuppose that there’s a difference between the glass falling and the glass jumping, and there’s a difference between the glass shattering and the glass recombining. And the difference between those two is always which direction is the future, and which direction is the past.

    So I’m certainly not denying that there is this time-reversibility. But the time-reversibility doesn’t imply that there isn’t a direction of time. It just says that for every event that the laws of physics allow, there is a corresponding event in which various things have been reversed, velocities have been reversed and so on. But in both of these cases, you think of them as allowing a process that’s running forward in time.

    Now that raises a puzzle: Why do we often see the one kind of thing and not the other kind of thing? And that’s the puzzle about thermodynamics and entropy and so on.

    If time has a direction, is the thermodynamic arrow of time still a problem?

    The problem there isn’t with the arrow. The problem is with understanding why things started out in a low-entropy state. Once you have that it starts in a low-entropy state, the normal thermodynamic arguments lead you to expect that most of the possible initial states are going to yield an increasing entropy. So the question is, why did things start out so low entropy?

    One choice is that the universe is only finite in time and had an initial state, and then there’s the question: “Can you explain why the initial state was low?” which is a subpart of the question, “Can you explain an initial state at all?” It didn’t come out of anything, so what would it mean to explain it in the first place?

    The other possibility is that there was something before the big bang. If you imagine the big bang is the bubbling-off of this universe from some antecedent proto-universe or from chaotically inflating space-time, then there’s going to be the physics of that bubbling-off, and you would hope the physics of the bubbling-off might imply that the bubbles would be of a certain character.
    Given that we still need to explain the initial low-entropy state, why do we need the internal directedness of time? If time didn’t have a direction, wouldn’t specification of a low-entropy state be enough to give it an effective direction?

    If time didn’t have a direction, it seems to me that would make time into just another spatial dimension, and if all we’ve got all are spatial dimensions, then it seems to me nothing’s happening in the universe. I can imagine a four-dimensional spatial object, but nothing occurs in it. This is the way people often talk about the, quote, “block universe” as being fixed or rigid or unchanging or something like that, because they’re thinking of it like a four-dimensional spatial object. If you had that, then I don’t see how any initial condition put on it — or any boundary condition put on it; you can’t say “initial” anymore — could create time. How can a boundary condition change the fundamental character of a dimension from spatial to temporal?

    Suppose on one boundary there’s low entropy; from that I then explain everything. You might wonder: “But why that boundary? Why not go from the other boundary, where presumably things are at equilibrium?” The peculiar characteristics at this boundary are not low entropy — there’s high entropy there — but that the microstate is one of the very special ones that leads to a long period of decreasing entropy. Now it seems to me that it has the special microstate because it developed from a low-entropy initial state. But now I’m using “initial” and “final,” and I’m appealing to certain causal notions and productive notions to do the explanatory work. If you don’t have a direction of time to distinguish the initial from the final state and to underwrite these causal locutions, I’m not quite sure how the explanations are supposed to go.

    But all of this seems so — what can I say? It seems so remote from the physical world. We’re sitting here and time is going on, and we know what it means to say that time is going on. I don’t know what it means to say that time really doesn’t pass and it’s only in virtue of entropy increasing that it seems to.

    You don’t sound like much of a fan of the block universe.

    There’s a sense in which I believe a certain understanding of the block universe. I believe that the past is equally real as the present, which is equally real as the future. Things that happened in the past were just as real. Pains in the past were pains, and in the future they’ll be real too, and there was one past and there will be one future. So if that’s all it means to believe in a block universe, fine.

    People often say, “I’m forced into believing in a block universe because of relativity.” The block universe, again, is some kind of rigid structure. The totality of concrete physical reality is specifying that four-dimensional structure and what happens everywhere in it. In Newtonian mechanics, this object is foliated by these planes of absolute simultaneity. And in relativity you don’t have that; you have this light-cone structure instead. So it has a different geometrical character. But I don’t see how that different geometrical character gets rid of time or gets rid of temporality.

    The idea that the block universe is static drives me crazy. What is it to say that something is static? It’s to say that as time goes on, it doesn’t change. But it’s not that the block universe is in time; time is in it. When you say it’s static, it somehow suggests that there is no change, nothing really changes, change is an illusion. It blows your mind. Physics has discovered some really strange things about the world, but it has not discovered that change is an illusion.
    What does it mean for time to pass? Is that synonymous with “time has a direction,” or is there something in addition?

    There’s something in addition. For time to pass means for events to be linearly ordered, by earlier and later. The causal structure of the world depends on its temporal structure. The present state of the universe produces the successive states. To understand the later states, you look at the earlier states and not the other way around. Of course, the later states can give you all kinds of information about the earlier states, and, from the later states and the laws of physics, you can infer the earlier states. But you normally wouldn’t say that the later states explain the earlier states. The direction of causation is also the direction of explanation.
    Am I accurate in getting from you that there’s a generation or production going on here — that there’s a machinery that sits grinding away, one moment giving rise to the next, giving rise to the next?

    Well, that’s certainly a deep part of the picture I have. The machinery is exactly the laws of nature. That gives a constraint on the laws of nature — namely, that they should be laws of temporal evolution. They should be laws that tell you, as time goes on, how will new states succeed old ones. The claim would be there are no fundamental laws that are purely spatial and that where you find spatial regularities, they have temporal explanations.

    Does this lead you to a different view of what a law even is?

    It leads me to a different view than the majority view. I think of laws as having a kind of primitive metaphysical status, that laws are not derivative on anything else. It’s, rather, the other way around: Other things are derivative from, produced by, explained by, derived from the laws operating. And there, the word “operating” has this temporal characteristic.
    Why is yours a minority view? Because it seems to me, if you ask most people on the street what the laws of physics do, they would say, “It’s part of a machinery.”

    I often say my philosophical views are just kind of the naïve views you would have if you took a physics class or a cosmology class and you took seriously what you were being told. In a physics class on Newtonian mechanics, they’ll write down some laws and they’ll say, “Here are the laws of Newtonian mechanics.” That’s really the bedrock from which you begin.

    I don’t think I hold really bizarre views. I take “time doesn’t pass” or “the passage of time is an illusion” to be a pretty bizarre view. Not to say it has to be false, but one that should strike you as not what you thought.
    What does this all have to say about whether time is fundamental or emergent?

    I’ve never been able to quite understand what the emergence of time, in its deeper sense, is supposed to be. The laws are usually differential equations in time. They talk about how things evolve. So if there’s no time, then things can’t evolve. How do we understand — and is the emergence a temporal emergence? It’s like, in a certain phase of the universe, there was no time; and then in other phases, there is time, where it seems as though time emerges temporally out of non-time, which then seems incoherent.

    Where do you stop offering analyses? Where do you stop — where is your spade turned, as Wittgenstein would say? And for me, again, the notion of temporality or of time seems like a very good place to think I’ve hit a fundamental feature of the universe that is not explicable in terms of anything else.

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 6:57 am on May 16, 2017 Permalink | Reply
    Tags: , , EPR paradox, , , , Quantum entanglement, Spooky action at a distance   

    From COSMOS: “Using Einstein’s ‘spooky action at a distance’ to hear ripples in spacetime” 

    Cosmos Magazine bloc

    COSMOS

    16 May 2017
    Cathal O’Connell

    1
    The new technique will aid in the detection of gravitational waves caused by colliding black holes. Henze / NASA

    In new work that connects two of Albert Einstein’s ideas in a way he could scarcely have imagined, physicists have proposed a way to improve gravitational wave detectors, using the weirdness of quantum physics.

    The new proposal, published in Nature Physics, could double the sensitivity of future detectors listening out for ripples in spacetime caused by catastrophic collisions across the universe.

    When the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves in late 2015 it was the first direct evidence of the gravitational waves Einstein had predicted a century before.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    Now it another of Einstein’s predictions – one he regarded as a failure – could potentially double the sensitivity of LIGOs successors.

    The story starts with his distaste for quantum theory – or at least for the fundamental fuzziness of all things it seemed to demand.

    Einstein thought the universe would ultimately prove predictable and exact, a clockwork universe rather than one where God “plays dice”. In 1935 he teamed up with Boris Podolsky and Nathan Rosen to publish a paper they thought would be a sort of reductio ad absurdum. They hoped to disprove quantum mechanics by following it to its logical, ridiculous conclusion. Their ‘EPR paradox’ (named for their initials) described the instantaneous influence of one particle on another, what Einstein called “spooky action at a distance” because it seemed at first to be impossible.

    Yet this sally on the root of quantum physics failed, as the EPR effect turned out not to be a paradox after all. Quantum entanglement, as it’s now known, has been repeatedly proven to exist, and features in several proposed quantum technologies, including quantum computation and quantum cryptography.

    2
    Artistic rendering of the generation of an entangled pair of photons by spontaneous parametric down-conversion as a laser beam passes through a nonlinear crystal. Inspired by an image in Dance of the Photons by Anton Zeilinger. However, this depiction is from a different angle, to better show the “figure 8” pattern typical of this process, clearly shows that the pump beam continues across the entire image, and better represents that the photons are entangled.
    Date 31 March 2011
    Source Entirely self-generated using computer graphics applications.
    Author J-Wiki at English Wikipedia

    Now we can add gravity wave detection to the list.

    LIGO works by measuring the minute wobbling of mirrors as a gravitational wave stretches and squashes spacetime around them. It is insanely sensitive – able to detect wobbling down to 10,000th the width of a single proton.

    At this level of sensitivity the quantum nature of light becomes a problem. This means the instrument is limited by the inherent fuzziness of the photons bouncing between its mirrors — this quantum noise washes out weak signals.

    To get around this, physicists plan to use so-called squeezed light to dial down the level of quantum noise near the detector (while increasing it elsewhere).

    The new scheme aids this by adding two new, entangled laser beams to the mix. Because of the ‘spooky’ connection between the two entangled beams, their quantum noise is correlated – detecting one allows the prediction of the other.

    This way, the two beams can be used to probe the main LIGO beam, helping nudge it into a squeezed light state. This reduces the noise to a level that standard quantum theory would deem impossible.

    The authors of the new proposal write that it is “appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the standard quantum limit”.

    Indeed, the proposal could as much as double the sensitivity of future detectors.

    Over the next 30 years, astronomers aim to improve the sensitivity of the detectors, like LIGO, by 30-fold. At that level, we’d be able to hear all black hole mergers in the observable universe.

    ESA/eLISA, the future of gravitational wave research

    However, along with improved sensitivity, the proposed system would also increase the number of photons lost in the detector. Raffaele Flaminio, a physicist at the National Astronomical Observatory of Japan, points out in a perspective piece for Nature Physics [no link], Flaminio that the team need to do more work to understand how this will affect ultimate performance.

    “But the idea of using Einstein’s most famous (mistaken) paradox to improve the sensitivity of gravitational-wave detectors, enabling new tests of his general theory of relativity, is certainly intriguing,” Flaminio writes. “Einstein’s ideas – whether wrong or right – continue to have a strong influence on physics and astronomy.”

    See the full article here .

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  • richardmitnick 2:40 pm on April 9, 2017 Permalink | Reply
    Tags: , NIST Team Proves 'Spooky Action at a Distance' is Really Real, , Quantum entanglement   

    From NIST: “NIST Team Proves ‘Spooky Action at a Distance’ is Really Real” 

    NIST

    March 28, 2017

    1
    US physicists have made a breakthrough in proving that quantum mechanics is indeed “spooky” and that trapped ions can be relied on for the quantum entanglement crucial for building super-fast futuristic computers iStock

    Adding to strong recent demonstrations that particles of light perform what Einstein called “spooky action at a distance,” in which two separated objects can have a connection that exceeds everyday experience, physicists at the National Institute of Standards and Technology (NIST) have confirmed that particles of matter can act really spooky too.

    The NIST team entangled a pair of beryllium ions (charged atoms) in a trap, thus linking their properties, and then separated the pair and performed one of a set of possible manipulations on each ion’s properties before measuring them. Across thousands of runs, the pair’s measurement outcomes in certain cases matched, or in other cases differed, more often than everyday experience would predict. These strong correlations are hallmarks of quantum entanglement.

    What’s more, statistical calculations found the ion pairs displayed a rare high level of spookiness.

    “We are confident that the ions are 67 percent spooky,” said Ting Rei Tan, lead author of a new Physical Review Letters paper about the experiments.

    The experiments were “chained” Bell tests, meaning that they were constructed from a series of possible sets of manipulations on two ions. Unlike earlier experiments, these were enhanced
    Bell tests in which the number of possible manipulations for each ion was chosen randomly from sets of at least two and as many as 15 choices.

    This method produces stronger statistical results than conventional Bell tests (link is external). That’s because as the number of options grows for manipulating each ion, the chance automatically decreases that the ions are behaving by classical, or non-quantum, rules. According to classical rules, all objects must have definite “local” properties and can only influence each other at the speed of light or slower. Bell tests have been long used to show that through quantum physics, objects can break one or both of these rules, demonstrating spooky action.

    Conventional Bell tests produce data that are a mixture of local and spooky action. Perfect chained Bell tests can, in theory, prove there is zero chance of local influence. The NIST results got down to a 33 percent chance of local influence—lower than conventional Bell tests can achieve, although not the lowest ever reported for a chained test, Tan said.

    However, the NIST experiment broke new ground by closing two of three “loopholes” that could undermine the results, the only chained Bell test to do this using three or more options for manipulating material particles. The results are good enough to infer the high quality of the entangled states using minimal assumptions about the experiment—a rare achievement, Tan said.

    Last year, a different group of NIST researchers and collaborators closed all three loopholes in conventional Bell tests with particles of light. The new ion experiments confirm again that spooky action is real.

    “Actually, I believed in quantum mechanics before this experiment,” Tan said with a chuckle. “Our motivation was we were trying to use this experiment to showcase how good our trapped ion quantum computing technology is, and what we can do with it.”

    The researchers used the same ion trap setup as in previous quantum computing experiments. With this apparatus, researchers use electrodes and lasers to perform all the basic steps needed for quantum computing, including preparing and measuring ions’ quantum states; transporting ions between multiple trap zones; and creating stable quantum bits (qubits), qubit rotations, and reliable two-qubit logic operations. All these features were needed to conduct the chained Bell tests. Quantum computers are expected to one day solve problems that are currently intractable such as simulating superconductivity (the flow of electricity without resistance) and breaking today’s most popular data encryption codes.

    In NIST’s chained Bell tests, the number of settings (options for different manipulations before measurement) ranged from two to 15. The manipulations acted on the ions’ internal energy states called “spin up” or “spin down.” The researchers used lasers to rotate the spins of the ions by specific angles before the final measurements.

    Researchers performed several thousand runs for each setting and collected two data sets 6 months apart. The measurements determined the ions’ spin states. There were four possible final results: (1) both ions spin up, (2) first ion spin up and second ion spin down, (3) first ion spin down and second ion spin up, or (4) both ions spin down. Researchers measured the states based on how much the ions fluoresced or scattered light—bright was spin up and dark was spin down.

    The NIST experiment closed the detection and memory loopholes, which might otherwise allow ordinary classical systems to appear spooky.

    The detection loophole is opened if detectors are inefficient and a subset of the data are used to represent the entire data set. The NIST tests closed this loophole because the fluorescence detection was near 100 percent efficient, and the measurement outcomes of every trial in each experiment were recorded and used to calculate results.

    The memory loophole is opened if one assumes that the outcomes of the trials are identically distributed or there are no experimental drifts. Previous chained Bell tests have relied on this assumption, but the NIST test was able to drop it. The NIST team closed the memory loophole by performing thousands of extra trials over many hours with the set of six possible settings, using a randomly chosen setting for each trial and developing a more robust statistical analysis technique.

    The NIST experiments did not close the locality loophole, which is open if it is possible for the choice of settings to be communicated between the ions. To close this loophole, one would need to separate the ions by such a large distance that communication between them would be impossible, even at light speed. In the NIST experiment, the ions had to be positioned close together (at most, 340 micrometers apart) to be entangled and subsequently measured, Tan explained.

    This work was supported by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA) and the Office of Naval Research.

    Paper: T.R. Tan, Y. Wan, S. Erickson, P. Bierhorst, D. Kienzler, S. Glancy, E. Knill, D. Leibfried and D.J. Wineland. 2017. Chained Bell Inequality Experiment With High-Efficiency Measurements. Physical Review Letters. DOI: 10.1103/PhysRevLett.118.130403

    See the full article here.

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    NIST Campus, Gaitherberg, MD, USA

    NIST Mission, Vision, Core Competencies, and Core Values

    NIST’s mission

    To promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.
    NIST’s vision

    NIST will be the world’s leader in creating critical measurement solutions and promoting equitable standards. Our efforts stimulate innovation, foster industrial competitiveness, and improve the quality of life.
    NIST’s core competencies

    Measurement science
    Rigorous traceability
    Development and use of standards

    NIST’s core values

    NIST is an organization with strong values, reflected both in our history and our current work. NIST leadership and staff will uphold these values to ensure a high performing environment that is safe and respectful of all.

    Perseverance: We take the long view, planning the future with scientific knowledge and imagination to ensure continued impact and relevance for our stakeholders.
    Integrity: We are ethical, honest, independent, and provide an objective perspective.
    Inclusivity: We work collaboratively to harness the diversity of people and ideas, both inside and outside of NIST, to attain the best solutions to multidisciplinary challenges.
    Excellence: We apply rigor and critical thinking to achieve world-class results and continuous improvement in everything we do.

     
  • richardmitnick 9:10 am on March 29, 2017 Permalink | Reply
    Tags: , , Quantum entanglement, Quantum memories, SN   

    From SN: “Millions of atoms entangled in record-breaking quantum tests” 

    ScienceNews bloc

    ScienceNews

    March 27, 2017
    Emily Conover

    Two teams report pushing the spooky effect to larger scales than ever before.

    1
    QUANTUM TANGLES Scientists have pushed quantum entanglement to new levels in two experiments. In one study, researchers linked up millions of atoms, and in another, intertwined hundreds of large groups consisting of billions of atoms. VAlex/Shutterstock

    Researchers from Geneva demonstrated quantum entanglement of 16 million atoms, smashing the previous record of about 3,000 entangled atoms (SN Online: 3/25/2015). Meanwhile, scientists from Canada and the United States used a similar technique to entangle over 200 groups of a billion atoms each. The teams published their results online March 14 in a pair of papers posted at arXiv.org.

    Through quantum entanglement, seemingly independent particles become intertwined. Entangled atoms can no longer be considered separate entities, but make sense only as part of a whole — even though the atoms may be far apart. The process typically operates on small scales, hooking up tiny numbers of particles, but the researchers convinced atoms to defy that tendency.

    “It’s a beautiful result,” says atomic physicist Vladan Vuletić of MIT, who was part of the team that previously demonstrated the 3,000-atom entanglement. Quantum effects typically don’t appear at the large scales that humans deal with every day. Instead, particles’ delicate quantum properties are smeared out through interactions with the messy world. But under the right conditions, quantum effects like entanglement can proliferate. “What this work shows us is that there are certain types of quantum mechanical states that are actually quite robust,” Vuletić says.

    Both teams demonstrated entanglement using devices known as “quantum memories.” Consisting of a crystal interspersed with rare-earth ions — exotic elements like neodymium and thulium — the researchers’ quantum memories are designed to absorb a single photon and re-emit it after a short delay. The single photon is collectively absorbed by many rare-earth ions at once, entangling them. After tens of nanoseconds, the quantum memory emits an echo of the original photon: another photon continuing in the same direction as the photon that entered the crystal.

    By studying the echoes from single photons, the scientists quantified how much entanglement occurred in the crystals. The more reliable the timing and direction of the echo, the more extensive the entanglement was. While the U.S.-Canadian team based its measurement on the timing of the emitted photon, the Swiss team focused on the direction of the photon.

    The quantum memories used to entangle the atoms aren’t new technologies. “The experiments are not complicated,” says physicist Erhan Saglamyurek of the University of Alberta in Canada, who was not involved with the research. Instead, the advance is mainly in the theoretical physics the researchers established to quantify the entanglement that was expected to arise inside such quantum memories. This allowed them to actually prove that such large numbers of particles were entangled, Saglamyurek says.

    Scientists from the two research teams declined to comment, as the papers reporting the work are still undergoing peer review by a journal.

    The results don’t have any obvious practical use. Instead, the work grows out of technology that is being developed for its potential applications: Quantum memories could be used in quantum communication networks to allow for storage of quantum information.

    Eventually, physicists hope to push weird quantum effects to larger and larger scales. For quantum entanglement, “it would be a dream if you could make that visible to the naked eye,” says quantum physicist Jakob Reichel of École Normale Supérieure in Paris. The latest results don’t go that far.

    “It’s not a revolution,” Reichel says. But, “I think it helps us [get] a better feeling for entangled states.”

    See the full article here .

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  • richardmitnick 2:41 pm on August 16, 2016 Permalink | Reply
    Tags: , , , Pan Jian-Wei, , Quantum entanglement   

    From Nature- “China’s quantum space pioneer: We need to explore the unknown” 

    Nature Mag
    Nature

    14 January 2016 [Just appeared in social media, probably because of new Chinese spacecraft that went up today.]
    Celeste Biever

    1
    Pan Jian-Wei is leading a satellite project that will probe quantum entanglement. Tengyun Chen

    Physicist Pan Jian-Wei is the architect of the world’s first attempt to set up a quantum communications link between Earth and space — an experiment that is set to begin with the launch of a satellite in June.

    The satellite will test whether the quantum property of entanglement extends over record-breaking distances of more than 1,000 kilometres, by beaming individual entangled photons between space and various ground stations on Earth. It will also test whether it is possible, using entangled photons, to teleport information securely between Earth and space.

    On 8 January, Pan, who works at the University of Science and Technology of China in Hefei, won a major national Chinese science prize (worth 200,000 yuan, or US$30,000) for his contributions to quantum science. He spoke to Nature about why his experiments are necessary and about the changing nature of Chinese space-science missions.

    How are preparations for the launch going?

    We always have two feelings. We feel, “Yes, everything is all right,” and then we are happy and excited. But we have, a couple of times, thought, “Probably our project will collapse and never work.” I think the satellite should be launched on time.
    What technical challenges do you face?

    The satellite will fly so fast (it takes just 90 minutes to orbit Earth) and there will be turbulence and other problems — so the single-photon beam can be seriously affected. Also we have to overcome background noise from sunlight, the Moon and light noise from cities, which are much stronger than our single photon.

    What is the aim of the satellite?

    Our first mission is to see if we can establish quantum key distribution [the encoding and sharing of a secret cryptographic key using the quantum properties of photons] between a ground station in Beijing and the satellite, and between the satellite and Vienna. Then we can see whether it is possible to establish a quantum key between Beijing and Vienna, using the satellite as a relay.

    The second step will be to perform long-distance entanglement distribution, over about 1,000 kilometres. We have technology on the satellite that can produce pairs of entangled photons. We beam one photon of an entangled pair to a station in Delingha, Tibet, and the other to a station in Lijiang or Nanshan. The distance between the two ground stations is about 1,200 kilometres. Previous tests were done on the order of 100 kilometres.

    Does anyone doubt that entanglement happens no matter how far apart two particles are?

    Not too many people doubt quantum mechanics, but if you want to explore new physics, you must push the limit. Sure, in principle, quantum entanglement can exist for any distance. But we want to see if there is some physical limit. People ask whether there is some sort of boundary between the classical world and the quantum world: we hope to build some sort of macroscopic system in which we can show that the quantum phenomena can still exist.

    In future, we also want to see if it is possible to distribute entanglement between Earth and the Moon. We hope to use the Chang’e programme (China’s Moon programme) to send a quantum satellite to one of the gravitationally-stable points [Lagrangian points] in the Earth-Moon system.

    How does entanglement relate to quantum teleportation?

    We will beam one photon from an entangled pair created at a ground station in Ali, Tibet, to the satellite. The quantum state of a third photon in Ali can then be teleported to the particle in space, using the entangled photon in Ali as a conduit.
    The quantum satellite is a basic-science space mission, as is the Dark Matter Particle Explorer (DAMPE), which China launched in December.

    Are basic-research satellites a new trend for China?

    Yes, and my colleagues at the Chinese Academy of Sciences (CAS) and I helped to force things in this direction. In the past, China had only two organizations that could launch satellites: the army and the Ministry of Industry and Information Technology. So scientists had no way to launch a satellite for scientific research. One exception is the Double Star probe, launched in collaboration with the European Space Agency in 2003 to study magnetic storms on Earth.

    What changed?

    We at CAS really worked hard to convince our government that it is important that we have a way to launch science satellites. In 2011, the central government established the Strategic Priority Program on Space Science, which DAMPE and our quantum satellite are part of. This is a very important step.

    I think China has an obligation not just to do something for ourselves — many other countries have been to the Moon, have done manned spaceflight — but to explore something unknown.

    Will scientists also be involved in China’s programme to build a space station, Tiangong?

    The mechanism to make decisions for which projects can go to the space station has been significantly changed. Originally, the army wanted to take over the responsibility, but it was finally agreed that CAS is the right organization.

    We will have a quantum experiment on the space station and it will make our studies easier because we can from time to time upgrade our experiment (unlike on the quantum satellite). We are quite happy with this mechanism. We need only talk to the leaders of CAS — and they are scientists, so you can communicate with them much more easily.

    See the full article here .

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

     
  • richardmitnick 10:52 am on July 13, 2016 Permalink | Reply
    Tags: , Quantum entanglement,   

    From UC Santa Barbara- “Entanglement : Chaos” 

    UC Santa Barbara Name bloc

    July 11, 2016
    Sonia Fernandez

    1
    A quantum qubit array. Photo Credit: Michael Fang/Martinis Lab

    2
    Experimental link between quantum entanglement (left) and classical chaos (right) found using a small quantum computer. Photo Credit: Courtesy Image

    3
    The Google and UCSB researchers, from left to right: Jimmy Chen, John Martinis, Pedram Roushan, Yu Chen, Anthony Megrant and Charles Neill. Photo Credit: Sonia Fernandez

    Using a small quantum system consisting of three superconducting qubits, researchers at UC Santa Barbara and Google have uncovered a link between aspects of classical and quantum physics thought to be unrelated: classical chaos and quantum entanglement. Their findings suggest that it would be possible to use controllable quantum systems to investigate certain fundamental aspects of nature.

    “It’s kind of surprising because chaos is this totally classical concept — there’s no idea of chaos in a quantum system,” Charles Neill, a researcher in the UCSB Department of Physics and lead author of a paper that appears in Nature Physics. “Similarly, there’s no concept of entanglement within classical systems. And yet it turns out that chaos and entanglement are really very strongly and clearly related.”

    Initiated in the 15th century, classical physics generally examines and describes systems larger than atoms and molecules. It consists of hundreds of years’ worth of study including Newton’s laws of motion, electrodynamics, relativity, thermodynamics as well as chaos theory — the field that studies the behavior of highly sensitive and unpredictable systems. One classic example of a chaotic system is the weather, in which a relatively small change in one part of the system is enough to foil predictions — and vacation plans — anywhere on the globe.

    At smaller size and length scales in nature, however, such as those involving atoms and photons and their behaviors, classical physics falls short. In the early 20th century quantum physics emerged, with its seemingly counterintuitive and sometimes controversial science, including the notions of superposition (the theory that a particle can be located in several places at once) and entanglement (particles that are deeply linked behave as such despite physical distance from one another).

    And so began the continuing search for connections between the two fields.

    All systems are fundamentally quantum systems, according Neill, but the means of describing in a quantum sense the chaotic behavior of, say, air molecules in an evacuated room, remains limited.

    Imagine taking a balloon full of air molecules, somehow tagging them so you could see them and then releasing them into a room with no air molecules, noted co-author and UCSB/Google researcher Pedram Roushan. One possible outcome is that the air molecules remain clumped together in a little cloud following the same trajectory around the room. And yet, he continued, as we can probably intuit, the molecules will more likely take off in a variety of velocities and directions, bouncing off walls and interacting with each other, resting after the room is sufficiently saturated with them.

    “The underlying physics is chaos, essentially,” he said. The molecules coming to rest — at least on the macroscopic level — is the result of thermalization, or of reaching equilibrium after they have achieved uniform saturation within the system. But in the infinitesimal world of quantum physics, there is still little to describe that behavior. The mathematics of quantum mechanics, Roushan said, do not allow for the chaos described by Newtonian laws of motion.

    To investigate, the researchers devised an experiment using three quantum bits, the basic computational units of the quantum computer. Unlike classical computer bits, which utilize a binary system of two possible states (e.g., zero/one), a qubit can also use a superposition of both states (zero and one) as a single state. Additionally, multiple qubits can entangle, or link so closely that their measurements will automatically correlate. By manipulating these qubits with electronic pulses, Neill caused them to interact, rotate and evolve in the quantum analog of a highly sensitive classical system.

    The result is a map of entanglement entropy of a qubit that, over time, comes to strongly resemble that of classical dynamics — the regions of entanglement in the quantum map resemble the regions of chaos on the classical map. The islands of low entanglement in the quantum map are located in the places of low chaos on the classical map.

    “There’s a very clear connection between entanglement and chaos in these two pictures,” said Neill. “And, it turns out that thermalization is the thing that connects chaos and entanglement. It turns out that they are actually the driving forces behind thermalization.

    “What we realize is that in almost any quantum system, including on quantum computers, if you just let it evolve and you start to study what happens as a function of time, it’s going to thermalize,” added Neill, referring to the quantum-level equilibration. “And this really ties together the intuition between classical thermalization and chaos and how it occurs in quantum systems that entangle.”

    The study’s findings have fundamental implications for quantum computing. At the level of three qubits, the computation is relatively simple, said Roushan, but as researchers push to build increasingly sophisticated and powerful quantum computers that incorporate more qubits to study highly complex problems that are beyond the ability of classical computing — such as those in the realms of machine learning, artificial intelligence, fluid dynamics or chemistry — a quantum processor optimized for such calculations will be a very powerful tool.

    “It means we can study things that are completely impossible to study right now, once we get to bigger systems,” said Neill.

    See the full article here .

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

     
  • richardmitnick 12:13 pm on June 9, 2016 Permalink | Reply
    Tags: , , Quantum entanglement   

    From MIT Tech Review: “Proof That Quantum Computers Will Change Everything” 

    MIT Technology Review
    MIT Technology Review

    First Demonstration of 10-Photon Quantum Entanglement

    June 9, 2016
    Emerging Technology from the arXiv

    The ability to entangle 10 photons should allow physicists to prove, once and for all, that quantum computers really can do things classical computers cannot.

    Entanglement is the strange phenomenon in which quantum particles become so deeply linked that they share the same existence. Once rare, entangling particles has become routine in labs all over the world.

    Quantum approach to big data. MIT
    Quantum approach to big data. MIT

    Physicists have learned how to create entanglement, transfer it from one particle to another, and even distil it. Indeed, entanglement has become a resource in itself and a crucial one for everything from cryptography and teleportation to computing and simulation.

    But a significant problem remains. To carry out ever more complex and powerful experiments, physicists need to produce entanglement on ever-larger scales by entangling more particles at the same time.

    The current numbers are paltry, though. Photons are the quantum workhorses in most labs and the record for the number of entangled photons is a mere eight, produced at a rate of about nine events per hour.

    Using the same techniques to create a 10-photon count rate would result in only 170 per year, too few even to measure easily. So the prospects of improvement have seemed remote.

    Which is why the work of Xi-Lin Wang and pals at the University of Science and Technology of China in Heifu is impressive. Today, they announce that they’ve produced 10-photon entanglement for the first time, and they’ve done it at a count rate that is three orders of magnitude higher than anything possible until now.

    The biggest bottleneck in entangling photons is the way they are produced. This involves a process called spontaneous parametric down conversion, in which one energetic photon is converted into two photons of lower energy inside a crystal of beta-barium borate. These daughter photons are naturally entangled.

    2
    Experiment setup for generating ten-photon polarization-entangled GHZ, from the science paper

    By zapping the crystal continuously with a laser beam, it is possible to create a stream of entangled photon pairs. However, the rate of down conversion is tiny, just one photon per trillion. So collecting the entangled pairs efficiently is hugely important.

    That’s no easy tasks, not least because the photons come out of the crystal in slightly different directions, neither of which can be easily predicted. Physicists collect the photons from the two points where they are most likely to appear but most of the entangled photons are lost.

    Xi-Lin and co have tackled this problem by reducing the uncertainty in the photon directions. Indeed, they have been able to shape the beams of entangled photons so that they form two separate circular beams, which can be more easily collected.

    In this way, the team has generated entangled photon pairs at the rate of about 10 million per watt of laser power. This is brighter than previous entanglement generators by a factor of about four. It is this improvement that makes 10-photon entanglement possible.

    Their method is to collect five successively generated pairs of entangled photons and pass them into an optical network of four beam splitters. The team then introduces time delays that ensure the photons arrive at the beam splitters simultaneously and so become entangled.

    This creates the 10-photon entangled state, albeit at a rate of about four per hour, which is low but finally measureable for the first time. “We demonstrate, for the first time, genuine and distillable entanglement of 10 single photons,” say Xi-Lin and co.

    That’s impressive work that immediately opens the prospect of a new generation of experiments. The most exciting of these is a technique called boson sampling that physicists hope will prove that quantum computers really are capable of things classical computers are not.

    That’s important because nobody has built a quantum computer more powerful than a pocket calculator (the controversial D-Wave results aside). Neither are they likely to in the near future. So boson sampling is quantum physicists’ greatest hope that will allow them to show off the mind-boggling power of quantum computation for the first time.

    Other things also become possible, such as the quantum teleportation of three degrees of freedom in a single photon and multi-photon experiments over very long distances.

    But it is the possibility of boson sampling that will send a frisson through the quantum physics community.

    Ref: arxiv.org/abs/1605.08547: Experimental Ten-Photon Entanglement

    See the full article here .

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  • richardmitnick 7:54 am on June 3, 2016 Permalink | Reply
    Tags: , , Quantum entanglement   

    From Daily Galaxy: “‘Quantum Entanglement in Space’ – A New Global Satellite-Based Quantum Network” 

    Daily Galaxy
    The Daily Galaxy

    June 02, 2016
    No writer credit found

    1
    Image credit: With thanks to shockingscience.com

    “We are reaching the limits of how precisely we can test quantum theory on Earth,” says Daniel Oi at the University of Strathclyde. Researchers from the National University of Singapore (NUS) and the University of Strathclyde, UK, have become the first to test in orbit technology for satellite-based quantum network nodes. With a network that carries information in the quantum properties of single particles, you can create secure keys for secret messaging and potentially connect powerful quantum computers in the future. But scientists think you will need equipment in space to get global reach.

    They have put a compact device carrying components used in quantum communication and computing into orbit. And it works: the team report* first data in a paper published 31 May 2016 in the journal Physical Review Applied. The team’s device, dubbed SPEQS, creates and measures pairs of light particles, called photons. Results from space show that SPEQS is making pairs of photons with correlated properties — an indicator of performance.

    “This is the first time anyone has tested this kind of quantum technology in space,” said team-leader Alexander Ling, an Assistant Professor at the Centre for Quantum Technologies (CQT) at NUS.

    The team had to be inventive to redesign a delicate, table-top quantum setup to be small and robust enough to fly inside a nanosatellite only the size of a shoebox. The whole satellite weighs just 1.65-kilogramme.

    Making correlated photons is a precursor to creating entangled photons. Described by Einstein as “spooky action at a distance,” entanglement is a connection between quantum particles that lends security to communication and power to computing.

    “Alex and his team are taking entanglement, literally, to a new level. Their experiments will pave the road to secure quantum communication and distributed quantum computation on a global scale,” said Artur Ekert, Director of CQT, invented the idea of using entangled particles for cryptography. He said, I am happy to see that Singapore is one of the world leaders in this area.”

    Local quantum networks already exist. The problem Ling’s team aims to solve is a distance limit. Losses limit quantum signals sent through air at ground level or optical fibre to a few hundred kilometers — but we might ultimately use entangled photons beamed from satellites to connect points on opposite sides of the planet. Although photons from satellites still have to travel through the atmosphere, going top-to-bottom is roughly equivalent to going only 10 kilometres at ground level.

    The group’s first device is a technology pathfinder. It takes photons from a BluRay laser and splits them into two, then measures the pair’s properties, all on board the satellite. To do this it contains a laser diode, crystals, mirrors and photon detectors carefully aligned inside an aluminum block. This sits on top of a 10 centimetres by 10 centimetres printed circuit board packed with control electronics.

    Through a series of pre-launch tests — and one unfortunate incident — the team became more confident that their design could survive a rocket launch and space conditions. The team had a device in the October 2014 Orbital-3 rocket which exploded on the launch pad. The satellite containing that first device was later found on a beach intact and still in working order.

    Even with the success of the more recent mission, a global network is still a few milestones away. The team’s roadmap calls for a series of launches, with the next space-bound SPEQS slated to produce entangled photons. SPEQS stands for Small Photon-Entangling Quantum System.

    With later satellites, the researchers will try sending entangled photons to Earth and to other satellites. The team are working with standard “CubeSat” nanosatellites, which can get relatively cheap rides into space as rocket ballast. Ultimately, completing a global network would mean having a fleet of satellites in orbit and an array of ground stations.

    In the meantime, quantum satellites could also carry out fundamental experiments — for example, testing entanglement over distances bigger than Earth-bound scientists can manage.

    *Science paper:
    Generation and Analysis of Correlated Pairs of Photons aboard a Nanosatellite

    See the full article here .

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  • richardmitnick 7:48 am on May 8, 2016 Permalink | Reply
    Tags: , Quantum entanglement, ,   

    From Ethan Siegel: “Ask Ethan: Can we use quantum entanglement to communicate faster-than-light?” 

    Starts with a Bang

    5.7.16
    Ethan Siegel

    NanoSail-D poses after a successful laboratory deployment test  NASA
    NanoSail-D poses after a successful laboratory deployment test NASA

    Einstein called it spooky, but if we figure it out right, can we learn about distant star systems instantaneously?

    “Trying to understand the way nature works involves a most terrible test of human reasoning ability. It involves subtle trickery, beautiful tightropes of logic on which one has to walk in order not to make a mistake in predicting what will happen.”

    1
    -Richard Feynman

    Earlier this month, billionaire Yuri Milner and astrophysicist Stephen Hawking teamed up to announce the Breakthrough Starshot, an incredibly ambitious plan to send the first human-created spacecraft to other star systems within our galaxy. While a giant laser array could, feasibly, launch a low mass, microchip-sized spaceship towards another star at some ~20% the speed of light, it’s unclear how such an underpowered, small device like that would ever communicate across the vastness of interstellar space. But Olivier Manuel had an idea that he submitted for Ask Ethan:

    It’s a long shot, but could quantum entanglement be used for communication?

    Imagine you have two coins, where each one can turn up either heads or tails. You have one and I have one, and we’re located extremely far away from each other. We each toss them up in the air, catch them, and slap them down on the table. When we reveal the flip, we fully expect that there’s a 50/50 chance that each one of us will uncover a “heads” result and a 50/50 shot we’ll each get a “tails.” In the normal, unentangled Universe, your results and my results are completely independent of one another: if you get a “heads” result, there’s still a 50/50 shot for my coin to either display “heads” or “tails.” But under some circumstances, these results could be entangled, meaning that if we do this experiment and you get a “heads” result, you’ll know with 100% certainty that my coin is displaying “tails,” even before I told you. You’d know it instantaneously, even if we were separated by light years and not even a single second had passed.

    2
    The quantum mechanical Bell test for half-integer spin particles. Image credit: Wikimedia Commons user Maksim, under a c.c.a.-s.a.-3.0 license.

    In quantum physics, we normally entangle not coins but individual particles like electrons or photons, where, for example, each photon can have a spin of either +1 or -1. If you measure the spin of one of them, you instantaneously know the spin of the other, even if it’s halfway across the Universe. Until you measure the spin of either one, they both exist in an indeterminate state; but once you measure even one, you immediately know both. We’ve done an experiment on Earth where we’ve separated two entangled photons by many miles, measuring their spins within nanoseconds of one another. What we find is that if we measure one of them to be +1, we know the other to be -1 at least 10,000 times faster than the speed of light would enable us to communicate.

    A quantum optics setup. Image credit Matthew Broome
    A quantum optics setup. Image credit Matthew Broome

    So now to Olivier’s question: could we use this property — quantum entanglement — to communicate from a distant star system to our own? The answer to that is yes, if you consider making a measurement at a distant location a form of communication. But when you say communicate, typically you want to know something about your destination. You could, for example, keep an entangled particle in an indeterminate state, send it aboard a spacecraft bound for the nearest star, and tell it to look for signs of a rocky planet in that star’s habitable zone. If you see one, make a measurement that forces the particle you have to be in the +1 state, and if you don’t see one, make a measurement that forces the particle you have to be in the -1 state.

    3
    Artist’s impression of a sunset from the world Gliese 667 Cc, in a trinary star system. Image credit: ESO/L. Calçada.

    Therefore, you reason, the particle you have back on Earth will then either be in the -1 state when you measure it, telling you that your spacecraft found a rocky planet in the habitable zone, or it will be in the +1 state, telling you that it didn’t find one. If you know the measurement has been made, you should then be able to make your own measurement, and instantly know the state of the other particle, even if it’s many light years away.

    4
    The wave pattern for electrons passing through a double slit. If you measure “which slit” the electron goes through, you destroy the quantum interference pattern shown here. Image credit: Dr. Tonomura and Belsazar of Wikimedia Commons, under c.c.a.-s.a.-3.0.

    It’s a brilliant plan, but there’s a problem: entanglement only works if you ask a particle, “what state are you in?” If you force an entangled particle into a particular state, you break the entanglement, and the measurement you make on Earth is completely independent of the measurement at the distant star. If you had simply measured the distant particle to be +1 or -1, then your measurement, here on Earth, of either -1 or +1 (respectively) would give you information about the particle located light years away. But by forcing that distant particle to be +1 or -1, that means, no matter the outcome, your particle here on Earth has a 50/50 shot of being +1 or -1, with no bearing on the particle so many light years distant.

    5
    A quantum eraser experiment setup, where two entangled particles are separated and measured. No alterations of one particle at its destination affect the outcome of the other. Image credit: Wikimedia Commons user Patrick Edwin Moran, under c.c.a.-s.a.-3.0.

    This is one of the most confusing things about quantum physics: entanglement can be used to gain information about a component of a system when you know the full state and make a measurement of the other component(s), but not to create-and-send information from one part of an entangled system to the other. As clever of an idea as this is, Olivier, there’s still no faster-than-light communication.

    6
    Quantum teleportation, an effect (erroneously) touted as faster-than-light travel. In reality, no information is being exchanged faster than light. Image credit: American Physical Society, via http://www.csm.ornl.gov/SC99/Qwall.html.

    Quantum entanglement is a wonderful property that we can exploit for any number of purposes, such as for the ultimate lock-and-key security system. But faster-than-light communication? Understanding why that’s not possible requires us to understand this key property of quantum physics: that forcing even part of an entangled system into one state or another doesn’t allow you to gain information about that forcing from measuring the remainder of the system. As Niels Bohr once famously put it:

    If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.

    The Universe plays dice with us all the time, much to Einstein’s chagrin. But even our best attempts to cheat at the game are thwarted by nature itself. If only all referees and umpires were as consistent as the laws of quantum physics!

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 2:36 pm on April 30, 2016 Permalink | Reply
    Tags: , Quantum entanglement, ,   

    From Ethan Siegel: “Can We Use Quantum Entanglement To Communicate Faster-Than-Light?” 

    Starts with a Bang

    4.30.16
    Ethan Siegel

    1
    The concept art of a solar sail (Japan’s IKAROS project) at a distant planet or star system. Image credit: Andrzej Mirecki of Wikimedia Commons, under a c.c.a.-s.a.-3.0 license.

    Earlier this month, billionaire Yuri Milner and astrophysicist Stephen Hawking teamed up to announce the Breakthrough Starshot, an incredibly ambitious plan to send the first human-created spacecraft to other star systems within our galaxy. While a giant laser array could, feasibly, launch a low mass, microchip-sized spaceship towards another star at some ~20% the speed of light, it’s unclear how such an underpowered, small device like that would ever communicate across the vastness of interstellar space. But Olivier Manuel had an idea that he submitted for Ask Ethan:

    It’s a long shot, but could quantum entanglement be used for communication?

    It’s certainly worth considering. Let’s take a look at the idea.

    1
    Two coins: one showing heads and the other showing tails. Image credit: United States Mint, public domain.

    Imagine you have two coins, where each one can turn up either heads or tails. You have one and I have one, and we’re located extremely far away from each other. We each toss them up in the air, catch them, and slap them down on the table. When we reveal the flip, we fully expect that there’s a 50/50 chance that each one of us will uncover a “heads” result and a 50/50 shot we’ll each get a “tails.” In the normal, unentangled Universe, your results and my results are completely independent of one another: if you get a “heads” result, there’s still a 50/50 shot for my coin to either display “heads” or “tails.” But under some circumstances, these results could be entangled, meaning that if we do this experiment and you get a “heads” result, you’ll know with 100% certainty that my coin is displaying “tails,” even before I told you. You’d know it instantaneously, even if we were separated by light years and not even a single second had passed.

    2
    The quantum mechanical Bell test for half-integer spin particles. Image credit: Wikimedia Commons user Maksim, under a c.c.a.-s.a.-3.0 license.

    In quantum physics, we normally entangle not coins but individual particles like electrons or photons, where, for example, each photon can have a spin of either +1 or -1. If you measure the spin of one of them, you instantaneously know the spin of the other, even if it’s halfway across the Universe. Until you measure the spin of either one, they both exist in an indeterminate state; but once you measure even one, you immediately know both. We’ve done an experiment on Earth where we’ve separated two entangled photons by many miles, measuring their spins within nanoseconds of one another. What we find is that if we measure one of them to be +1, we know the other to be -1 at least 10,000 times faster than the speed of light would enable us to communicate.

    3
    By creating two entangled photons from a pre-existing system and separating them by great distances, we can know information about the state of one by measuring the state of the other. Image credit: Melissa Meister, of laser photons through a beam splitter, under c.c.-by-2.0 generic, from https://www.flickr.com/photos/mmeister/3794835939.

    So now to Olivier’s question: could we use this property — quantum entanglement — to communicate from a distant star system to our own? The answer to that is yes, if you consider making a measurement at a distant location a form of communication. But when you say communicate, typically you want to know something about your destination. You could, for example, keep an entangled particle in an indeterminate state, send it aboard a spacecraft bound for the nearest star, and tell it to look for signs of a rocky planet in that star’s habitable zone. If you see one, make a measurement that forces the particle you have to be in the +1 state, and if you don’t see one, make a measurement that forces the particle you have to be in the -1 state.

    4
    Artist’s impression of a sunset from the world Gliese 667 Cc, in a trinary star system. Image credit: ESO/L. Calçada.

    Therefore, you reason, the particle you have back on Earth will then either be in the -1 state when you measure it, telling you that your spacecraft found a rocky planet in the habitable zone, or it will be in the +1 state, telling you that it didn’t find one. If you know the measurement has been made, you should then be able to make your own measurement, and instantly know the state of the other particle, even if it’s many light years away.

    5
    The wave pattern for electrons passing through a double slit. If you measure “which slit” the electron goes through, you destroy the quantum interference pattern shown here. Image credit: Dr. Tonomura and Belsazar of Wikimedia Commons, under c.c.a.-s.a.-3.0.

    It’s a brilliant plan, but there’s a problem: entanglement only works if you ask a particle, “what state are you in?” If you force an entangled particle into a particular state, you break the entanglement, and the measurement you make on Earth is completely independent of the measurement at the distant star. If you had simply measured the distant particle to be +1 or -1, then your measurement, here on Earth, of either -1 or +1 (respectively) would give you information about the particle located light years away. But by forcing that distant particle to be +1 or -1, that means, no matter the outcome, your particle here on Earth has a 50/50 shot of being +1 or -1, with no bearing on the particle so many light years distant.

    6
    A quantum eraser experiment setup, where two entangled particles are separated and measured. No alterations of one particle at its destination affect the outcome of the other. Image credit: Wikimedia Commons user Patrick Edwin Moran, under c.c.a.-s.a.-3.0.

    This is one of the most confusing things about quantum physics: entanglement can be used to gain information about a component of a system when you know the full state and make a measurement of the other component(s), but not to create-and-send information from one part of an entangled system to the other. As clever of an idea as this is, Olivier, there’s still no faster-than-light communication.

    7
    Quantum teleportation, an effect (erroneously) touted as faster-than-light travel. In reality, no information is being exchanged faster than light. Image credit: American Physical Society, via http://www.csm.ornl.gov/SC99/Qwall.html.

    Quantum entanglement is a wonderful property that we can exploit for any number of purposes, such as for the ultimate lock-and-key security system. But faster-than-light communication? Understanding why that’s not possible requires us to understand this key property of quantum physics: that forcing even part of an entangled system into one state or another doesn’t allow you to gain information about that forcing from measuring the remainder of the system. As Niels Bohr once famously put it:

    If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.

    The Universe plays dice with us all the time, much to Einstein’s chagrin. But even our best attempts to cheat at the game are thwarted by nature itself. If only all referees and umpires were as consistent as the laws of quantum physics!

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
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