Physicists observe behavior of quantum materials in curved space

June 13, 2016, University of Chicago
These false-color images represent the quantum Hall state that UChicago physicists created by shining infrared laser light at specially configured mirrors. Achieving this state with light instead of matter was an important step in developing computing and other applications from quantum phenomena. Credit: Nathan Schine, Albert Ryou, Andrey Gromov, Ariel Sommer, and Jonathan Simon

Light and matter are typically viewed as distinct entities that follow their own, unique rules. Matter has mass and typically exhibits interactions with other matter, while light is massless and does not interact with itself. Yet, wave-particle duality tells us that matter and light both act sometimes like particles, and sometimes like waves.

Harnessing the shared wave nature of light and matter, researchers at the University of Chicago, led by Jonathan Simon, the Neubauer Family Assistant Professor of Physics, have used light to explore some of the most intriguing questions in the quantum mechanics of materials. The topic encompasses complex and non-intuitive phenomena that are often difficult to explain in non-technical language, but which carry important implications to specialists in the field.

In work published online this week in the journal Nature, Simon's group presents new experimental observations of a quantum Hall material near a singularity of curvature in space.

Quantum effects give rise to some of the most useful and promising properties of materials: They define standard units of measurement, give rise to superconductivity and describe quantum computers. The quantum Hall materials are one prominent example in which are trapped in non-conducting circular orbits except at the edges of the material. There, electrons exhibit quantized resistance-free electrical conduction that is immune to disorder such as material impurities or surface defects.

Furthermore, electrons in quantum Hall materials do not transmit sound waves but instead have particle-like excitations, some of which are unlike any other particles ever discovered. Some of these materials also exhibit simultaneous quantum entanglement between millions of electrons, meaning that the electrons are so interconnected, the state of one instantly influences the state of all others. This combination of properties makes quantum Hall materials a promising platform for future quantum computation.

Researchers worldwide have spent the past 35 years delving into the mysteries of quantum Hall materials, but always in the same fundamental way. They use superconducting magnets to make very powerful magnetic fields and refrigerators to cool electronic samples to thousandths of a degree above absolute zero.

Trapping light...

In a new approach, Simon and his team demonstrated the creation of a quantum Hall material made up of light. "Using really good mirrors that are pointed at each other, we can trap light for a long time while it bounces back and forth many thousands of times between the mirrors," explained graduate student Nathan Schine.

In the UChicago experiment, photons travel back and forth between mirrors, while their side-to-side motion mimics the behavior of massive particles like electrons. To emulate a strong , the researchers created a non-planar arrangement of four mirrors that makes the light twist as it completes a round trip. The twisting motion causes the photons to move like charged particles in a magnetic field, even though there is no actual magnet present.

"We make the photons spin, which leads to a force that has the same effect as a magnetic field," explained Schine. While the light is trapped, it behaves like the electrons in a quantum Hall material.

First, Simon's group demonstrated that they had a quantum Hall material of light. To do so, they shined infrared laser light at the mirrors. By varying the laser's frequency, Simon's team could map out precisely at which frequencies the laser was transmitted through the mirrors. These transmission frequencies, along with camera images of the transmitted light, gave a telltale signature of a quantum Hall state.

Next, the researchers took advantage of the precise control that advanced optical systems provide to place the photons in curved space, which has not been possible so far with electrons. In particular, they made the photons behave as if they resided on the surface of a cone.

...near a singularity

"We created a cone for light, much like you might do by cutting a wedge of paper and taping the edges together," said postdoctoral fellow Ariel Sommer, also a co-author of the paper. "In this case, we imposed a three-fold symmetry on our light, which essentially divides the plane into three wedges and forces the light to repeat itself on each wedge."

The tip of a cone has infinite curvature—the singularity—so the researchers were able to study the effect of strong spatial curvature in a quantum Hall material. They observed that photons accumulated at the cone tip, confirming a previously untested theory of the quantum Hall effect in curved space.

Despite 20 years of interest, this is the first time an experiment has observed the behavior of quantum materials in curved space. "We are beginning to make our photons interact with each other," said Schine. "This opens up many possibilities, such as making crystalline or exotic quantum liquid states of . We can then see how they respond to spatial curvature."

The researchers say this could be useful for characterizing a certain type of quantum computer that is built of quantum Hall materials.

"While quantum Hall materials were discovered in the '80s, they continue to reveal their fascinating secrets to this day," said Simon. "The final frontier is exploring the interplay of these beautiful materials with the curvature of space. That is what we've begun to explore with our ."

Explore further: The quantum spin Hall effect is a fundamental property of light

More information: Nathan Schine et al. Synthetic Landau levels for photons, Nature (2016). DOI: 10.1038/nature17943

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Steve 200mph Cruiz
4.2 / 5 (5) Jun 13, 2016
Normally I try not to be this guy,
But I've had this idea for years that the force of gravity is an illusion created by the impact of mass on space time. There is no graviton.

The slowing of time relative to the outside observer causes particles to appear closer together. If a particle can be at any place, they are more likely to be where time is moving by the fastest, IE: in a gravitational field.

Da Schneib
3.9 / 5 (7) Jun 14, 2016
It's OK, we all speculate sometimes. The important thing is to make sure your speculations don't conflict with known facts.

I'll go along for a bit, but I've got a couple things for you to think about:

Actually it's energy that has an impact on spacetime. At least that's what GRT says. It's just that it takes c² more energy to have the same impact as a given amount of mass. I don't see why this affects whether there are gravitons or not.

Is there a possibility you got your signs reversed, and you meant to say that if a particle can be any place it's more likely to be at a place where time is moving *slower*? And by the way, that doesn't throw your speculation out; time *does* move slower in a gravity field according to an observer outside it. This is an interesting observation, BTW; good speculation.
torbjorn_b_g_larsson
3.7 / 5 (6) Jun 14, 2016
If we look away from the low energy effects of general relativity, one can claim - as is often done - that curvature puts up an 'illusory' force. I.e. created by curvature, which may act due to energy densities instead of mass densities.

However, the low energy behavior makes the force and - putatively - the graviton existence unavoidable. Gravity can be approximated by a quantum particle field same as all the other fundamental forces. (Gravity, strong, electroweak, Higgs). That is why we - arguably - have a valid Core Theory of just fields, not just a valid semiclassical GR + quantum fields theory, at low energies. [ http://www.prepos...-shirts/ ]

Nice experiment in the article though!
trevor_white
1 / 5 (1) Jun 14, 2016
Not being quite serious for the moment, just an observation for those of you who played Doom but this type of Quantum hall effect couple with some of the recent papers that have appeared here could very well allow the design and manufacture of a BFG. The single minded pursuit of computer application for these technologies may be missing some interesting opportunities.
Da Schneib
4.2 / 5 (5) Jun 14, 2016
To really get what you were saying, @torbjorn, I had to follow to this article: http://www.prepos...fective/

I found it very interesting and it does explain why there have to be gravitons.
ursiny33
1 / 5 (1) Jun 14, 2016
The biggest problem in charged particle physics. Is mans closed conceptual vision of the electron and positron single level a quantum constructions, and their magnetic relationships to each other ,to build mass with each other magnetically that an single level electron can be magnetically attached to a positron and become a two level electron with a dominant charge of negative by its quantum mass, compared to size of the magnetically connected positron and you can't even measure its minority charge in that construction, a two level negative dominant electron mass, it can also field chain together with this construction with the electrons, but that's not all that a single level positron can magnetically attache to both sides of a single level electron to construct a three level magnetically positive dominant position whose positive dominant charge is larger then the single level electron between those positrons in quantum mass ,those are building blocks
ursiny33
1 / 5 (1) Jun 14, 2016
That the particle magnetic construction phase between your known charged particles and their ability to become building blocks for photons neutrons and protons
ursiny33
1 / 5 (1) Jun 14, 2016
When you shoot lasers at heavy atoms and you see electrons and positrons coming out of that kinetic collisions your not producing new particles your decoupling those particle with kinetic collisions from it constructed mass of two level and three level electrons that make up the constructed equal charged mass of a photon, or in neutron kinetic collisions you see electrons coming out but identified proton is just a three level positive electron construction not a proton , in those kinetic collisions
ursiny33
1 / 5 (1) Jun 14, 2016
Those two level and three level magnetically bound electrons , decay outside of negatively charged induction environments ,but that just means they return to their individual quantum parts and state unassembled in in the higher electrical state
ursiny33
1 / 5 (1) Jun 14, 2016
The positron is not the anti matter particle of an electron,its a quantum construction matter particle that magnetically works with single level negative electrons to build mass in the electron world
ursiny33
1 / 5 (1) Jun 14, 2016
Particle physics must consider that their assumption of a singularity charged particle of negative or positive does not exist in the quantum dimension of matter only dominant mass charge with both charges present in its construction a minor charge and a minor quantum mass charge ,is the only flavor just like all the hydrogen atom based constructions have major and minor charges in their constructions
ursiny33
1 / 5 (1) Jun 14, 2016
That even on the quantum particle chart that those particles classified negative have a minor positive charge. ,those classified positive have a minor negative charge and those classified neutral have equal charges, that a charge particle can't exist out side the laws of magnetics in charges
Steve 200mph Cruiz
5 / 5 (4) Jun 14, 2016
Da Schneib,
Doesn't time go by faster within a gravity field? I thought people who went to space aged slower than people on earth.
The dice rolls aren't frozen in time, they are happening faster and faster the more energy there is (mass and energy are the same thing)

And you and Torbjorn are right, gravitons have to exist, even without the hard core physics, the fact is gravity waves are a real thing, which means a carrier particle.
big_hairy_jimbo
5 / 5 (2) Jun 14, 2016
@ursiny33 I thought the currency here was Energy and that Energy is converted into a particle following probabilities. This would mean that your idea of it already containing an electron and positron incorrect. You are talking as if that will ALWAYS occur, when I thought quantum mechanics dealt with probabilities.
Da Schneib
3.7 / 5 (3) Jun 15, 2016
Da Schneib,
Doesn't time go by faster within a gravity field? I thought people who went to space aged slower than people on earth.
The dice rolls aren't frozen in time, they are happening faster and faster the more energy there is (mass and energy are the same thing)
No, I went and double checked and you have it backwards (which is easy to do). The stronger the field, the more dilation. https://en.wikipe...dilation

And you and Torbjorn are right, gravitons have to exist, even without the hard core physics, the fact is gravity waves are a real thing, which means a carrier particle.
Yes, that's correct. A good additional point.
nikola_milovic_378
Jun 17, 2016
This comment has been removed by a moderator.
nikola_milovic_378
Jun 17, 2016
This comment has been removed by a moderator.
nikola_milovic_378
Jun 17, 2016
This comment has been removed by a moderator.
antialias_physorg
5 / 5 (2) Jun 17, 2016
To really get what you were saying, @torbjorn, I had to follow to this article: http://www.prepos...fective/

I found it very interesting and it does explain why there have to be gravitons.

Holy smokes, that is a great link. Thanks!

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