Light and matter merge in quantum coupling

August 22, 2016, Rice University
A method created at Rice University closes the gap between light and matter and may help advance technologies like quantum computers and communications. The lab designed and built a high-quality cavity to contain an ultrathin layer of gallium arsenide. By tuning the material with a magnetic field to resonate with a certain state of light in the cavity, they prompted the formation of polaritons that act in a collective manner. Credit: Qi Zhang/Rice University

Where light and matter intersect, the world illuminates. Where light and matter interact so strongly that they become one, they illuminate a world of new physics, according to Rice University scientists.

Rice physicists are closing in on a way to create a new state in which all the electrons in a material act as one by manipulating them with and a magnetic field. The effect made possible by a custom-built, finely tuned cavity for terahertz radiation shows one of the strongest light-matter coupling phenomena ever observed.

The work by Rice physicist Junichiro Kono and his colleagues is described in Nature Physics. It could help advance technologies like quantum computers and communications by revealing new phenomena to those who study cavity quantum electrodynamics and , Kono said.

Condensed matter in the general sense is anything solid or liquid, but condensed matter physicists study forms that are much more esoteric, like Bose-Einstein condensates. A Rice team was one of the first to make a Bose-Einstein condensate in 1995 when it prompted atoms to form a gas at ultracold temperatures in which all the atoms lose their individual identities and behave as a single unit.

The Kono team is working toward something similar, but with electrons that are strongly coupled, or "dressed," with light. Qi Zhang, a former graduate student in Kono's group and lead author of the paper, designed and constructed an extremely high-quality cavity to contain an ultrathin layer of gallium arsenide, a material they've used to study superfluorescence. By tuning the material with a magnetic field to resonate with a certain state of light in the cavity, they prompted the formation of polaritons that act in a collective manner.

Xinwei Li. Credit: Jeff Fitlow/Rice University

"This is a nonlinear optical study of a two-dimensional electronic material," said Zhang, who based his Ph.D. thesis on the work. "When you use light to probe a material's electronic structure, you're usually looking for light absorption or reflection or scattering to see what's happening in the material. That light is just a weak probe and the process is called linear optics.

"Nonlinear optics means light does something to the material," he said. "Light is not a small perturbation anymore; it couples strongly with the material. As you change the coupling strength, things change in the material. What we're doing is the extreme case of nonlinear optics, where the light and matter are coupled so strongly that we don't have light and matter anymore. We have something in between, called a polariton."

The researchers employed a parameter known as vacuum Rabi splitting to measure the strength of the light-matter coupling. "In more than 99 percent of previous studies of light-matter coupling in cavities, this value is a negligibly small fraction of the of the light used," said Xinwei Li, a co-author and graduate student in Kono's group. "In our study, vacuum Rabi splitting is as large as 10 percent of the photon energy. That puts us in the so-called ultrastrong coupling regime.

"This is an important regime because, eventually, if the vacuum Rabi splitting becomes larger than the photon energy, the matter goes into a new ground state. That means we can induce a phase transition, which is an important element in condensed matter physics," he said.

Rice University graduate student Xinwei Li, with physicist Junichiro Kono, prepares a sample for a cavity quantum electrodynamics experiment. They are part of a team probing the boundaries of light-matter interactions as they bridge traditional condensed matter physics and cavity-based quantum optics. Credit: Jeff Fitlow/Rice University

Phase transitions are transitions between states of matter, like ice to water to vapor. The specific transition Kono's team is looking for is the superradiant phase transition in which the polaritons go into an ordered state with macroscopic coherence.

Kono said the amount of terahertz light put into the cavity is very weak. "What we depend on is the vacuum fluctuation. Vacuum, in a classical sense, is an empty space. There's nothing. But in a quantum sense, a vacuum is full of fluctuating photons, having so-called zero-point energy. These vacuum photons are actually what we are using to resonantly excite electrons in our cavity.

"This general subject is what's known as (QED)," Kono said. "In cavity QED, the cavity enhances the light so that matter in the cavity resonantly interacts with the vacuum field. What is unique about solid-state cavity QED is that the light typically interacts with this huge number of electrons, which behave like a single gigantic atom."

He said solid-state cavity QED is also key for applications that involve quantum information processing, like quantum computers. "The light-matter interface is important because that's where so-called light-matter entanglement occurs. That way, the quantum information of matter can be transferred to light and light can be sent somewhere.

"For improving the utility of QED in quantum information, the stronger the light-matter coupling, the better, and it has to use a scalable, solid-state system instead of atomic or molecular systems," he said. "That's what we've achieved here."

The high-quality gallium arsenide materials used in the study were synthesized via molecular beam epitaxy by John Reno of Sandia National Laboratories and John Watson and Michael Manfra of Purdue University, all co-authors of the paper. Weil Pan of Sandia National Laboratories and Rice Minhan Lou, who participated in sample preparation and transport and terahertz measurements, are also co-authors.

Zhang is now the Alexei Abrikosov Postdoctoral Fellow at Argonne National Laboratory. Kono is a Rice professor of electrical and computer engineering, of physics and astronomy and of materials science and nanoengineering. Li received a "Best First-Year Research Award" from Rice's Department of Electrical and Computer Engineering for his work on the project.

Explore further: Bridging the gap between the quantum and classical worlds

More information: Qi Zhang et al, Collective non-perturbative coupling of 2D electrons with high-quality-factor terahertz cavity photons, Nature Physics (2016). DOI: 10.1038/nphys3850

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17 comments

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Steelwolf
3 / 5 (2) Aug 22, 2016
This is along the way towards being able to build any sort of matter we want by setting together the correct numbers and energies of photons within a specific area and allow it to nucleate into whatever species and flavor of particle we desire.
Whydening Gyre
3 / 5 (2) Aug 22, 2016
interesting possibility...
You are talking star trek kinda stuff, aren't you...
Steelwolf
3 / 5 (2) Aug 23, 2016
That IS where tech is taking us, fairly quickly, especially if you include the some 6K patents that have been covered up for "National (Profit) Security"
Stevepidge
1 / 5 (3) Aug 24, 2016
How can you seek to combine that which is separate into a whole? How can the "separate" forces of the universe be unified? This is flawed thinking. This hypothesis of separate forces is rooted in a deep seated psychological assumption that this reality is made of indiscriminate separate entities "particles". In other words it reeks of absolute individualism and thus like a magnetic monopole. It is an AFFRONT to man who is just as much a part of nature as anything else. This monopole philosophy is one of would be kings and gods.
Spaced out Engineer
1 / 5 (1) Aug 25, 2016
Stevepidge

We may have found monopoles in the lab. Guth may have created a universe that seeding off and we are protected from it by nothing.

We solved the physics problem of using light gold colliders to make matter.

Don't tell Nature what to do. It's fine if you wish to guide the hearts of man, but it is.
Stevepidge
1 / 5 (1) Aug 25, 2016
Stevepidge

We may have found monopoles in the lab. Guth may have created a universe that seeding off and we are protected from it by nothing.

We solved the physics problem of using light gold colliders to make matter.

Don't tell Nature what to do. It's fine if you wish to guide the hearts of man, but it is.


Here you go again, separating man and nature. You can't help it.
Stevepidge
1 / 5 (1) Aug 26, 2016
Stevepidge

We may have found monopoles in the lab. Guth may have created a universe that seeding off and we are protected from it by nothing.

We solved the physics problem of using light gold colliders to make matter.

Don't tell Nature what to do. It's fine if you wish to guide the hearts of man, but it is.


As far as the turn light into matter thing. It is not creation, it's energizing waveforms such that they gain enough energy to change their frequency to materialize.
Whydening Gyre
1 / 5 (1) Aug 27, 2016
As far as the turn light into matter thing. It is not creation, it's energizing waveforms such that they gain enough energy to change their frequency to materialize.

Will that change be up or down?
Phys1
not rated yet Aug 27, 2016
Right.
OMG.
Stevepidge
1 / 5 (1) Aug 27, 2016
As far as the turn light into matter thing. It is not creation, it's energizing waveforms such that they gain enough energy to change their frequency to materialize.

Will that change be up or down?

Are we dead or alive?
why your query? Does it matter? How would you know?
Tell me where is up in space? I expect more from you. You know who you are.
Whydening Gyre
1 / 5 (1) Aug 27, 2016
As far as the turn light into matter thing. It is not creation, it's energizing waveforms such that they gain enough energy to change their frequency to materialize.

Will that change be up or down?

Are we dead or alive?
why your query? Does it matter? How would you know?
Tell me where is up in space? I expect more from you. You know who you are.

Simply wondering if you think the frequency change is up or down...
Stevepidge
1 / 5 (1) Aug 27, 2016
As far as the turn light into matter thing. It is not creation, it's energizing waveforms such that they gain enough energy to change their frequency to materialize.

Will that change be up or down?

Are we dead or alive?
why your query? Does it matter? How would you know?
Tell me where is up in space? I expect more from you. You know who you are.

Simply wondering if you think the frequency change is up or down...

I don't know.
tinitus
Aug 28, 2016
This comment has been removed by a moderator.
swordsman
not rated yet Aug 29, 2016
These investigators are misinterpreting the data. The light field does not bend due to the magnetic field, but rather due to the fields of the nearby molecules reacting and adding another active field factor. When the electromagnetic field is strong in the near field, the material electrons react and move in other directions (spiralling)>
EnsignFlandry
not rated yet Aug 29, 2016
How can you seek to combine that which is separate into a whole? How can the "separate" forces of the universe be unified? This is flawed thinking. This hypothesis of separate forces is rooted in a deep seated psychological assumption that this reality is made of indiscriminate separate entities "particles". In other words it reeks of absolute individualism and thus like a magnetic monopole. It is an AFFRONT to man who is just as much a part of nature as anything else. This monopole philosophy is one of would be kings and gods.


You can unify separate forces by increased temperature. The electromagnetic and weak nuclear forces unify to become one electroweak force at high enough temperature. Whatever absolute individualism is, affronting man is irrelevant.
Stevepidge
not rated yet Aug 30, 2016
Man IS the universe and the universe is man. In other words, life is something the whole universe is doing just as a wave is something the whole ocean is doing.
Spaced out Engineer
1 / 5 (1) Aug 30, 2016
Man is not the universe. That is idealism and not physics. Even the math becomes unclear if the momentum of process becomes an application of a lower level metaphor to a higher level abstraction.

We know some processes are not imaginable given how neurons fire. And yet Bayesianism can encapsulate the methods of science.

I am not saying that we may not be able to project feedbacks or feed forward aspects to virtual fields or particles, but rather transactionally we are waves.

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