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  • richardmitnick 3:12 pm on October 17, 2014 Permalink | Reply
    Tags: , , , Perimeter Institute,   

    From Perimeter: “The Last Gasp of a Black Hole” 

    Perimeter Institute
    Perimeter Institute

    October 17, 2014
    No Writer Credit

    New research from Perimeter shows that two of the strangest features of quantum mechanicsentanglement and negative energy – might be two faces of one coin.

    Quantum mechanics is, notoriously, weird. Take entanglement: when two or more particles are entangled, their states are linked together, no matter how far apart they go.

    If the idea makes your classical mind twitch, you’re in good company. At the heart of everything, according to quantum mechanics, nature has a certain amount of irreducible jitter. Even nothing – the vacuum of space – can jitter, or as physicists say, fluctuate. When it does, a particle and its anti-particle can pop into existence.

    For example, an electron and an anti-electron (these are called positrons) might pop into existence out of the vacuum. We know that they each have a spin of one half, which might be either up or down. We also know that these particles were created from nothing and so, to balance the books, the total spin must add up to zero. Finally, we know that the spin of either particle is not determined until it is measured.

    So suppose the electron and the positron fly apart a few metres or a few light years, and then a physicist comes by to measure the spin of, say, the electron. She discovers that the electron is spin up, and in that moment, the electron becomes spin up. Meanwhile, a few metres or a few light years away, the positron becomes spin down. Instantly. That is the strangeness of quantum entanglement.

    Negative energy is less well known than entanglement, but no less weird. It begins with the idea – perhaps already implied by the positron and electron popping out of nowhere – that empty space is not empty. It is filled with quantum fields, and the energy of those fields can fluctuate a little bit.

    In fact, the energy of these fields can dip under the zero mark, albeit briefly. When that happens, a small region of space can, for a short span of time, weigh less than nothing – or at least less than the vacuum. It’s a little bit like finding dry land below sea level.

    Despite their air of strangeness, entanglement and negative energy are both well-explored topics. But now, new research, published as a Rapid Communication in Physical Review D, is hinting that these two strange phenomena may be linked in a surprising way.

    The work was done by Perimeter postdoctoral fellow Matteo Smerlak and former postdoc Eugenio Bianchi (now on the faculty at Penn State and a Visiting Fellow at Perimeter). “Negative energy and entanglement are two of the most striking features of quantum mechanics,” says Smerlak. “Now, we think they might be two sides of the same coin.”

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    Perimeter Postdoctoral Researcher Matteo Smerlak

    man
    Perimeter Visiting Fellow Eugenio Bianchi

    Specifically, the researchers proved mathematically that any external influence that changes the entanglement of a system in its vacuum state must also produce some amount of negative energy. The reverse, they say, is also true: negative energy densities can never be produced without entanglement being directly affected.

    At the moment, the result only applies to certain quantum fields in two dimensions – to light pulses travelling up and down a thin cable, for instance. And it is with light that the Perimeter researchers hope that their new idea can be directly tested.

    “Some quantum states which have negative energy are known, and one of them is called a ‘squeezed state,’ and they can be produced in the lab, by optical devices called squeezers,” says Smerlak. The squeezers manipulate light to produce an observable pattern of negative energy.

    Remember that Smerlak and Bianchi’s basic argument is that if an external influence affects vacuum entanglement, it will also release some negative energy. In a quantum optics setup, the squeezers are the external influence.

    Experimentalists should be able to look for the correlation between the entanglement patterns and the negative energy densities which this new research predicts. If these results hold up – always a big if in brand new work – and if they can make the difficult leap from two dimensions to the real world, then there will be startling implications for black holes.

    Like optical squeezers, black holes also produce changes in entanglement and energy density. They do this by separating entangled pairs of particles and preferentially selecting the ones with negative energy.

    Remember that the vacuum is full of pairs of particles and antiparticles blinking into existence. Under normal circumstances, they blink out again just as quickly, as the particle and the antiparticle annihilate each other. But just at a black hole’s event horizon, it sometimes happens that one of the particles is sucked in, while the other escapes. The small stream of escaping particles is known as Hawking radiation.

    By emitting such radiation, black holes slowly give up their energy and mass, and eventually disappear. Black hole evaporation, as the process is known, is a hot topic in physics. This new research has the potential to change the way we think about it.

    “In the late stages of the evaporation of a black hole, the energy released from the black hole will turn negative,” says Smerlak. And if a black hole releases negative energy, then its total energy goes up, not down. “It means that the black hole will shrink and shrink and shrink – for zillions of years – but in the end, it will release its negative energy in a gasp before dying. Its mass will briefly go up.”

    Call it the last gasp of a black hole.

    See the full article here.

    About Perimeter

    Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

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  • richardmitnick 7:35 pm on August 7, 2014 Permalink | Reply
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    From Perimeter Institute: “The Black Hole at the Birth of the Universe” 

    Perimeter Institute
    Perimeter Institute

    August 7, 2014
    Colin Hunter

    The big bang poses a big question: if it was indeed the cataclysm that blasted our universe into existence 13.7 billion years ago, what sparked it?

    Three Perimeter Institute researchers have a new idea about what might have come before the big bang. It’s a bit perplexing, but it is grounded in sound mathematics, testable, and enticing enough to earn the cover story in Scientific American, called The Black Hole at the Beginning of Time.

    What we perceive as the big bang, they argue, could be the three-dimensional “mirage” of a collapsing star in a universe profoundly different than our own.

    “Cosmology’s greatest challenge is understanding the big bang itself,” write Perimeter Institute Associate Faculty member Niayesh Afshordi, Affiliate Faculty member and University of Waterloo professor Robert Mann, and PhD student Razieh Pourhasan.

    Conventional understanding holds that the big bang began with a singularity – an unfathomably hot and dense phenomenon of spacetime where the standard laws of physics break down. Singularities are bizarre, and our understanding of them is limited.

    “For all physicists know, dragons could have come flying out of the singularity,” Afshordi says in an interview with Nature.

    The problem, as the authors see it, is that the big bang hypothesis has our relatively comprehensible, uniform, and predictable universe arising from the physics-destroying insanity of a singularity. It seems unlikely.

    So perhaps something else happened. Perhaps our universe was never singular in the first place.

    Their suggestion: our known universe could be the three-dimensional “wrapping” around a four-dimensional black hole’s event horizon. In this scenario, our universe burst into being when a star in a four-dimensional universe collapsed into a black hole.

    In our three-dimensional universe, black holes have two-dimensional event horizons – that is, they are surrounded by a two-dimensional boundary that marks the “point of no return.” In the case of a four-dimensional universe, a black hole would have a three-dimensional event horizon.

    In their proposed scenario, our universe was never inside the singularity; rather, it came into being outside an event horizon, protected from the singularity. It originated as – and remains – just one feature in the imploded wreck of a four-dimensional star.

    The researchers emphasize that this idea, though it may sound “absurd,” is grounded firmly in the best modern mathematics describing space and time. Specifically, they’ve used the tools of holography to “turn the big bang into a cosmic mirage.” Along the way, their model appears to address long-standing cosmological puzzles and – crucially – produce testable predictions.

    Of course, our intuition tends to recoil at the idea that everything and everyone we know emerged from the event horizon of a single four-dimensional black hole. We have no concept of what a four-dimensional universe might look like. We don’t know how a four-dimensional “parent” universe itself came to be.

    But our fallible human intuitions, the researchers argue, evolved in a three-dimensional world that may only reveal shadows of reality.

    They draw a parallel to Plato’s allegory of the cave, in which prisoners spend their lives seeing only the flickering shadows cast by a fire on a cavern wall.

    “Their shackles have prevented them from perceiving the true world, a realm with one additional dimension,” they write. “Plato’s prisoners didn’t understand the powers behind the sun, just as we don’t understand the four-dimensional bulk universe. But at least they knew where to look for answers.”

    See the full article here.

    About Perimeter

    Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

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  • richardmitnick 7:01 am on July 4, 2014 Permalink | Reply
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    From The Perimeter Institute: “From Pencil Marks To Quantum Computers” 

    Perimeter Institute
    Perimeter Institute

    July 3, 2014
    Erin Bow

    Pick up a pencil. Make a mark on a piece of paper. Congratulations: you are doing cutting-edge condensed matter physics. You might even be making the first mark on the road to quantum computers, according to new Perimeter research.

    Introducing graphene

    One of the hottest materials in condensed matter research today is graphene.

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    Graphene is an atomic-scale honeycomb lattice made of carbon atoms.

    Graphene had an unlikely start: it began with researchers messing around with pencil marks on paper. Pencil “lead” is actually made of graphite, which is a soft crystal lattice made of nothing but carbon atoms. When pencils deposit that graphite on paper, the lattice is laid down in thin sheets. By pulling that lattice apart into thinner sheets – originally using Scotch tape – researchers discovered that they could make flakes of crystal just one atom thick.

    The name for this atom-scale chicken wire is graphene. Those folks with the Scotch tape, Andre Geim and Konstantin Novoselov, won the 2010 Nobel Prize for discovering it. “As a material, it is completely new – not only the thinnest ever but also the strongest,” wrote the Nobel committee. “As a conductor of electricity, it performs as well as copper. As a conductor of heat, it outperforms all other known materials. It is almost completely transparent, yet so dense that not even helium, the smallest gas atom, can pass through it.”

    Developing a theoretical model of graphene

    Graphene is not just a practical wonder – it’s also a wonderland for theorists. Confined to the two-dimensional surface of the graphene, the electrons behave strangely. All kinds of new phenomena can be seen, and new ideas can be tested. Testing new ideas in graphene is exactly what Perimeter researchers Zlatko Papić and Dmitry (Dima) Abanin set out to do.

    p
    Perimeter postdoctoral researcher Zlatko Papić

    abannin
    Perimeter Faculty member Dmitry Abanin

    “Dima and I started working on graphene a very long time ago,” says Papić. “We first met in 2009 at a conference in Sweden. I was a grad student and Dima was in the first year of his postdoc, I think.”

    The two young scientists got to talking about what new physics they might be able to observe in the strange new material when it is exposed to a strong magnetic field.

    “We decided we wanted to model the material,” says Papić. They’ve been working on their theoretical model of graphene, on and off, ever since. The two are now both at Perimeter Institute, where Papić is a postdoctoral researcher and Abanin is a faculty member. They are both cross-appointed with the Institute for Quantum Computing (IQC) at the University of Waterloo.

    In January 2014, they published a paper in Physical Review Letters presenting new ideas about how to induce a strange but interesting state in graphene – one where it appears as if particles inside it have a fraction of an electron’s charge.

    It’s called the fractional quantum Hall effect (FQHE), and it’s head turning. Like the speed of light or Planck’s constant, the charge of the electron is a fixed point in the disorienting quantum universe.

    Every system in the universe carries whole multiples of a single electron’s charge. When the FQHE was first discovered in the 1980s, condensed matter physicists quickly worked out that the fractionally charged “particles” inside their semiconductors were actually quasiparticles – that is, emergent collective behaviours of the system that imitate particles.

    Graphene is an ideal material in which to study the FQHE. “Because it’s just one atom thick, you have direct access to the surface,” says Papić. “In semiconductors, where FQHE was first observed, the gas of electrons that create this effect are buried deep inside the material. They’re hard to access and manipulate. But with graphene you can imagine manipulating these states much more easily.”

    In the January paper, Abanin and Papić reported novel types of FQHE states that could arise in bilayer graphene – that is, in two sheets of graphene laid one on top of another – when it is placed in a strong perpendicular magnetic field. In an earlier work from 2012, they argued that applying an electric field across the surface of bilayer graphene could offer a unique experimental knob to induce transitions between FQHE states. Combining the two effects, they argued, would be an ideal way to look at special FQHE states and the transitions between them.

    Experimental tests

    Two experimental groups – one in Geneva, involving Abanin, and one at Columbia, involving both Abanin and Papić – have since put the electric field + magnetic field method to good use. The paper by the Columbia group appears in the July 4 issue of Science. A third group, led by Amir Yacoby of Harvard, is doing closely related work.

    “We often work hand-in-hand with experimentalists,” says Papić. “One of the reasons I like condensed matter is that often even the most sophisticated, cutting-edge theory stands a good chance of being quickly checked with experiment.”

    Inside both the magnetic and electric field, the electrical resistance of the graphene demonstrates the strange behaviour characteristic of the FQHE. Instead of resistance that varies in a smooth curve with voltage, resistance jumps suddenly from one level to another, and then plateaus – a kind of staircase of resistance. Each stair step is a different state of matter, defined by the complex quantum tangle of charges, spins, and other properties inside the graphene.

    “The number of states is quite rich,” says Papić. “We’re very interested in bilayer graphene because of the number of states we are detecting and because we have these mechanisms – like tuning the electric field – to study how these states are interrelated, and what happens when the material changes from one state to another.”

    For the moment, researchers are particularly interested in the stair steps whose “height” is described by a fraction with an even denominator. That’s because the quasiparticles in that state are expected to have an unusual property.

    There are two kinds of particles in our three-dimensional world: fermions (such as electrons), where two identical particles can’t occupy one state, and bosons (such as photons), where two identical particles actually want to occupy one state. In three dimensions, fermions are fermions and bosons are bosons, and never the twain shall meet.

    But a sheet of graphene doesn’t have three dimensions – it has two. It’s effectively a tiny two-dimensional universe, and in that universe, new phenomena can occur. For one thing, fermions and bosons can meet halfway – becoming anyons, which can be anywhere in between fermions and bosons. The quasiparticles in these special stair-step states are expected to be anyons.

    In particular, the researchers are hoping these quasiparticles will be non-Abelian anyons, as their theory indicates they should be. That would be exciting because non-Abelian anyons can be used in the making of qubits.

    Graphene qubits?

    Qubits are to quantum computers what bits are to ordinary computers: both a basic unit of information and the basic piece of equipment that stores that information. Because of their quantum complexity, qubits are more powerful than ordinary bits and their power grows exponentially as more of them are added. A quantum computer of only a hundred qubits can tackle certain problems beyond the reach of even the best non-quantum supercomputers. Or, it could, if someone could find a way to build stable qubits.

    The drive to make qubits is part of the reason why graphene is a hot research area in general, and why even-denominator FQHE states – with their special anyons – are sought after in particular.

    “A state with some number of these anyons can be used to represent a qubit,” says Papić. “Our theory says they should be there and the experiments seem to bear that out – certainly the even-denominator FQHE states seem to be there, at least according to the Geneva experiments.”

    That’s still a step away from experimental proof that those even-denominator stair-step states actually contain non-Abelian anyons. More work remains, but Papić is optimistic: “It might be easier to prove in graphene than it would be in semiconductors. Everything is happening right at the surface.”

    It’s still early, but it looks as if bilayer graphene may be the magic material that allows this kind of qubit to be built. That would be a major mark on the unlikely line between pencil lead and quantum computers.

    See the full article here.

    About Perimeter

    Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

     
  • richardmitnick 2:46 pm on August 23, 2013 Permalink | Reply
    Tags: , Perimeter Institute,   

    From Perimeter Institute: “The Case of the Shrinking Proton” 

    Perimeter Institute
    Perimeter Institute

    August 23, 2013

    “Perimeter researchers Itay Yavin and Maxim Pospelov have posited a new force of nature to explain the seeming shrinking of the proton.

    How big is the proton? For decades, this was a settled question. Then, in 2010, a new and better technique produced a new answer – one that contradicted decades of careful measurements. Two Perimeter researchers have an intriguing new suspect in the case of the shrinking proton: a new force of nature.

    Before 2010, the size of the proton was so well defined and agreed upon that it joined the speed of light and the charge of the electron on the list of known quantities. But then, an international team of more than 30 researchers, led by Randolf Pohl and working at the Paul Scherrer Institute in Switzerland, announced a new measurement of the proton radius. Whereas the old measurement was 0.8768 femtometres, the new one was 0.841 femtometres. Although the difference was only a quadrillionth of an inch, the relative shift was huge – far larger than can be explained by experimental uncertainty.

    So what happened? Theorists such as Perimeter Faculty members Itay Yavin and Maxim Pospelov have an intriguing idea – one that posits a new force of nature.

    See the full article here.

    About Perimeter

    Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

     
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