Exotic Physics Phenomenon Involving Time Reversal Observed for First Time

Images showing interference patterns (top) and a Wilson loop (bottom) were produced by the researchers to confirm the presence of non-Abelian gauge fields created in the research. Image courtesy of researchers

Observation of the predicted non-Abelian Aharonov-Bohm Effect may offer step toward fault-tolerant quantum computers.

An exotic physical phenomenon, involving optical waves, synthetic magnetic fields, and time reversal, has been directly observed for the first time, following decades of attempts. The new finding could lead to realizations of what are known as topological phases, and eventually to advances toward fault-tolerant quantum computers, the researchers say.

The new finding involves the non-Abelian Aharonov-Bohm Effect and is published in the journal Science by MIT graduate student Yi Yang, MIT visiting scholar Chao Peng (a professor at Peking University), MIT graduate student Di Zhu, Professor Hrvoje Buljan at University of Zagreb in Croatia, Francis Wright Davis Professor of Physics John Joannopoulos at MIT, Professor Bo Zhen at the University of Pennsylvania, and MIT professor of physics Marin Soljačić.

The finding relates to gauge fields, which describe transformations that particles undergo. Gauge fields fall into two classes, known as Abelian and non-Abelian. The Aharonov-Bohm Effect, named after the theorists who predicted it in 1959, confirmed that gauge fields — beyond being a pure mathematical aid — have physical consequences.

But the observations only worked in Abelian systems, or those in which gauge fields are commutative — that is, they take place the same way both forward and backward in time.  In 1975, Tai-Tsun Wu and Chen-Ning Yang generalized the effect to the non-Abelian regime as a thought experiment. Nevertheless, it remained unclear whether it would even be possible to ever observe the effect in a non-Abelian system. Physicists lacked ways of creating the effect in the lab, and also lacked ways of detecting the effect even if it could be produced. Now, both of those puzzles have been solved, and the observations carried out successfully.

The effect has to do with one of the strange and counterintuitive aspects of modern physics, the fact that virtually all fundamental physical phenomena are time-invariant. That means that the details of the way particles and forces interact can run either forward or backward in time, and a movie of how the events unfold can be run in either direction, so there’s no way to tell which is the real version. But a few exotic phenomena violate this time symmetry.

Creating the Abelian version of the Aharonov-Bohm effects requires breaking the time-reversal symmetry, a challenging task in itself, Soljačić says. But to achieve the non-Abelian version of the effect requires breaking this time-reversal multiple times, and in different ways, making it an even greater challenge.

To produce the effect, the researchers use photon polarization. Then, they produced two different kinds of time-reversal breaking. They used fiber optics to produce two types of gauge fields that affected the geometric phases of the optical waves, first by sending them through a crystal biased by powerful magnetic fields, and second by modulating them with time-varying electrical signals, both of which break the time-reversal symmetry. They were then able to produce interference patterns that revealed the differences in how the light was affected when sent through the fiber-optic system in opposite directions, clockwise or counterclockwise. Without the breaking of time-reversal invariance, the beams should have been identical, but instead, their interference patterns revealed specific sets of differences as predicted, demonstrating the details of the elusive effect.

The original, Abelian version of the Aharonov-Bohm effect “has been observed with a series of experimental efforts, but the non-Abelian effect has not been observed until now,” Yang says. The finding “allows us to do many things,” he says, opening the door to a wide variety of potential experiments, including classical and quantum physical regimes, to explore variations of the effect.

The experimental approach devised by this team “might inspire the realization of exotic topological phases in quantum simulations using photons, polaritons, quantum gases, and superconducting qubits,” Soljačić says. For photonics itself, this could be useful in a variety of optoelectronic applications, he says. In addition, the non-Abelian gauge fields that the group was able to synthesize produced a non-Abelian Berry phase, and “combined with interactions, it may potentially one day serve as a platform for fault-tolerant topological quantum computation,” he says.

At this point, the experiment is primarily of interest for fundamental physics research, with the aim of gaining a better understanding of some basic underpinnings of modern physical theory. The many possible practical applications “will require additional breakthroughs going forward,” Soljačić says.

For one thing, for quantum computation, the experiment would need to be scaled up from one single device to likely a whole lattice of them. And instead of the beams of laser light used in their experiment, it would require working with a source of single individual photons. But even in its present form, the system could be used to explore questions in topological physics, which is a very active area of current research, Soljačić says.

“The non-Abelian Berry phase is a theoretical gem that is the doorway to understanding many intriguing ideas in contemporary physics,” says Ashvin Vishwanath, a professor of physics at Harvard University, who was not associated with this work. “I am glad to see it getting the experimental attention it deserves in the current work, which reports a well-controlled and characterized realization. I expect this work to stimulate progress both directly as a building block for more complex architectures, and also indirectly in inspiring other realizations.”

Reference: “Synthesis and observation of non-Abelian gauge fields in real space” by Yi Yang, Chao Peng, Di Zhu, Hrvoje Buljan, John D. Joannopoulos, Bo Zhen, and Marin Soljačić, Science.
DOI: 10.1126/science.aay3183

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Comments ( 19 )
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  • Daniel Izzo

    Can anyone point in the direction of the universe where the Big Bang occurred?
    Is it possible people created a Higgs muon that started motion in the universe? If motion first started on earth, it would explain why the cosmic red shift points to the earth at the center of the universe, maybe because motion first started here? see: ” The red shift hypothesis for quasars: Is the earth the center of the universe? – Astrophysics and Space Science August 1976. “ The recently generated Higgs boson muon experiment at LHC in Cern in 2012 ..the Higgs muon may have decayed faster than the speed of light as predicted.
    Could people have started motion in the universe by generating a particle that allegedly went faster than the speed of light ? (with a 10 Billion Dollar man made machine that is colder than the 3 kelvin universe vs the LHC at 2 kelvin and creating a particle that goes back into time – 15 billion + years ago, ) when there was no motion – just motionless static gravity fields and that particle started motion, (gravitational) instability, the microwave background was then formed as a result of the instability, that created dust particles and matter in the universe ?

    Was this the time the universe started to fall (expand) into another static gravity field past the microwave background ?

    When was the last time the universe was at 2 kelvin ?

  • Neil Byrne

    Eh,yeah?

  • Anon

    Daniel, bro you are not even wrong.

    • Anon

      If the universe was never in motion how in the hell would someone build a machine to set it in motion and how in the hell would 15 billion years even be relevant in a place that had no motion since it would be identical on any timeline into infinity. I am being really generous here in assuming the fantasy that the universe was generated as it is at the point of this impossible experiment.

      • Matthew Kucera

        I was just reading something called quantum time where they say an event can be the cause and effect of another event. It’s possible the universe is cyclical and nothing is the cause of anything but everything is the cause of everything.

  • Jimbo Jones

    Daniel and Anon…Ah, yet who is to say it is the same universe? One which is generated by such an event, and matures until life repeats the experiment. Boom! New universe. Right or wrong; I like the way you guys are thinkin’.

  • Rabbit Whole

    I predict the coming of many YouTube videos trying to explain what they actually did and why they think it reversed time, and how time reversal can be imperfect. Also I predict that many including myself will have trouble wrapping our heads around the notion of these various forms of time travel.

  • M

    From the available 6 comments i can see it is a mostly trolling site, not targeting serious science.

    • Not M

      Yeah, those dudes from MIT are too busy with sports and women to do any real science.

  • HMM

    Did anyone notice how the graph looks like a face with googly eyes and an open mouth?

    • Jasper

      LOL!

  • Hermes

    The big bang happened in different places at different time points in time. In not a singular event.
    Even though time seems to be moving from our point of view, it is a fixed state into itself. Everything is happening at once. This is how infinity works. Since everything that can be created will be created in an infinite plane, this idea of a reality where we have created ourselves from etherial future thought and projected to the past is plausible thus possible, but likely could only happen once.

  • Vertex

    Daniel, there is no spatial point where the big bang happened. That point lies in time, not space. You can think of the fabric of space as the surface of a balloon, and the big bang was the point in time where you started to inflate it. To your observation of red shift, everything is moving away from one another. You can use the balloon example once again to visualize this. Think of that balloon again, put a bunch of dots all on its surface (symbolizing galaxies). Now, continue to blow that balloon up. Every dot moves away from one another. No matter what dot you use as a reference point, as the balloon expands it will look as though everything is expanding away from that one dot. If you go over to the Andromeda Galaxy it will look like it’s the epicenter, when in reality nothing is.

  • Eric

    I think the problem is that at the quantum level the atom, and the astrophysical theory of the universe, are mathematical concepts and as such cannot be converted to a physical model that the enthusiast can understand.

  • Mintas Lanxor

    And, when quantum computers are finally designed, they will, among other things, help hackers to better syphon money out of people’s and institutions’ bank accounts, or disable the digital infrastructure of whole nations or continents, or help rogue governments interfere with foreign elections more effectively, or speed up the transition to AI with all its unknown dangers.

  • Mark

    Are you controling the dynamic Plank engines of space with polarization when light is directed in a laser beam then photons seem to have a influence on the fabric of space, a reverse polarization with antiphotons would then travel backward in time..

    • Mark

      Then are they describing a way to make antiphotons..

  • Thirdmusket

    It was sound that started the motions of the universe. A singularity isn’t nothing. It’s an incredibly dense something and it was alone. No work space to grow into… Ever hear about a pistol shrimp? It strikes so fast that it literally tears molecules apart under water…pulling apart the h2o and creating a bubble with a vacuum in it… The sound of which comes in behind the motion and as it cuts through the bubble, creating a small spark of light. Sonoluminescence. This is not quite understood by science …but if singularities are packed together in an unstable way… Then God saying “Let there be light” into that singularity bubble… Starts the universe. Now… In order to keep things balanced. We are cycled through our own black hole at the center of the Galaxy… Gravity is much faster than light. Hawking radiation is dark energy is gravity. It pushes …it doesn’t pull so much… Also Gravity-time and space-matter seem more likely than “space time”… Because there is an obvious effect that happens when matter reaches speeds of light… Time seems to slow. On a train going lightspeed.. you get up and walk forward…time slows so that you cannot surpass this “constant” …but if light can’t escape …if shit gets ripped apart so terribly bad that it leaves a bit of information behind (Hawking radiation) that sounds like gravity done effected the constant in a major way. If it were a constant then why doesn’t information going into a black hole seem more like walking down an up escalator? It should cancel out as it approaches its own speed out… To counter… Black holes cycle matter and space through the use of gravity and time … Multiverses are time verses where backwards is normal… Or humans live 125 years or 5000 years but ultimately at the same pace of life. You think slower…move slower… Calculate time slower . Die at 75 years old but it took 5000 years to do it.

  • Bill Mutschler

    Dan, the answer is in the balloon analogy down below. Another analogy is that of baking dough with raisins or chocolate chips…as the dough cooks and expands, these chips get farther apart. How does this relate? As the Big Bang was the beginning of time and had rapid inflation, my take on it is that -everywhere- is the center of the universe. From any given point, there is expansion. We lack the means to ‘step outside’ for an objective/external view of space-time. It also relates to one of three possible geometries of spacetime; closed, open, or flat.