Physicists use light waves to accelerate supercurrents, enable ultrafast quantum computing

Jigang Wang and his collaborators have demonstrated light-induced acceleration of supercurrents, which could enable practical applications of quantum mechanics such as computing, sensing and communicating. Larger image. Image courtesy of Jigang Wang.

https://www.news.iastate.edu/news/2019/07/01/supercurrents

AMES, Iowa – Jigang Wang patiently explained his latest discovery in quantum control that could lead to superfast computing based on quantum mechanics: He mentioned light-induced superconductivity without energy gap. He brought up forbidden supercurrent quantum beats. And he mentioned terahertz-speed symmetry breaking.

Then he backed up and clarified all that. After all, the quantum world of matter and energy at terahertz and nanometer scales – trillions of cycles per second and billionths of meters – is still a mystery to most of us.

“I like to study quantum control of superconductivity exceeding the gigahertz, or billions of cycles per second, bottleneck in current state-of-the-art quantum computation applications,” said Wang, a professor of physics and astronomy at Iowa State University whose research has been supported by the Army Research Office. “We’re using terahertz light as a control knob to accelerate supercurrents.”

Superconductivity is the movement of electricity through certain materials without resistance. It typically occurs at very, very cold temperatures. Think -400 Fahrenheit for “high-temperature” superconductors.

Terahertz light is light at very, very high frequencies. Think trillions of cycles per second. It’s essentially extremely strong and powerful microwave bursts firing at very short time frames.

Wang and a team of researchers demonstrated such light can be used to control some of the essential quantum properties of superconducting states, including macroscopic supercurrent flowing, broken symmetry and accessing certain very high frequency quantum oscillations thought to be forbidden by symmetry.

It all sounds esoteric and strange. But it could have very practical applications.

“Light-induced supercurrents chart a path forward for electromagnetic design of emergent materials properties and collective coherent oscillations for quantum engineering applications,” Wang and several co-authors wrote in a research paper just published online by the journal Nature Photonics.

In other words, the discovery could help physicists “create crazy-fast quantum computers by nudging supercurrents,” Wang wrote in a summary of the research team’s findings.

Finding ways to control, access and manipulate the special characteristics of the quantum world and connect them to real-world problems is a major scientific push these days. The National Science Foundation has included the “Quantum Leap” in its “10 big ideas” for future research and development.

“By exploiting interactions of these quantum systems, next-generation technologies for sensing, computing, modeling and communicating will be more accurate and efficient,” says a summary of the science foundation’s support of quantum studies. “To reach these capabilities, researchers need understanding of quantum mechanics to observe, manipulate and control the behavior of particles and energy at dimensions at least a million times smaller than the width of a human hair.”

Wang and his collaborators – Xu Yang, Chirag Vaswani and Liang Luo from Iowa State, responsible for terahertz instrumentation and experiments; Chris Sundahl, Jong-Hoon Kang and Chang-Beom Eom from the University of Wisconsin-Madison, responsible for high-quality superconducting materials and their characterizations; Martin Mootz and Ilias E. Perakis from the University of Alabama at Birmingham, responsible for model building and theoretical simulations – are advancing the quantum frontier by finding new macroscopic supercurrent flowing states and developing quantum controls for switching and modulating them.

A summary of the research team’s study says experimental data obtained from a terahertz spectroscopy instrument indicates terahertz light-wave tuning of supercurrents is a universal tool “and is key for pushing quantum functionalities to reach their ultimate limits in many cross-cutting disciplines” such as those mentioned by the science foundation.

And so, the researchers wrote, “We believe that it is fair to say that the present study opens a new arena of light-wave superconducting electronics via terahertz quantum control for many years to come.”

Physicists use terahertz flashes to uncover new state of matter hidden by superconductivity

Jigang Wang of Iowa State and the Ames Laboratory led experiments that switched on a hidden state of matter in a superconductive alloy. Larger photo. Photo by Christopher Gannon.

https://www.news.iastate.edu/news/2018/06/04/terahertzflashes

AMES, Iowa – Using the physics equivalent of the strobe photography that captures every twitch of a cheetah in full sprint, researchers have used ultrafast spectroscopy to visualize electrons interacting as a hidden state of matter in a superconductive alloy.

It takes intense, single-cycle pulses of photons – flashes – hitting the cooled alloy at terahertz speed – trillions of cycles per second – to switch on this hidden state of matter by modifying quantum interactions down at the atomic and subatomic levels.

And then it takes a second terahertz light to trigger an ultrafast camera to take images of the state of matter that, when fully understood and tuned, could one day have implications for faster, heat-free, quantum computing, information storage and communication.

The discovery of this new switching scheme and hidden quantum phase was full of conceptual and technical challenges.

To find new, emergent electron states of matter beyond solids, liquids and gases, today’s condensed matter physicists can no longer fully rely on traditional, slow, thermodynamic tuning methods such as changing temperatures, pressures, chemical compositions or magnetic fields, said Jigang Wang, an Iowa State University professor of physics and astronomy and a faculty scientist at the U.S. Department of Energy’s Ames Laboratory.

“The grand, open question of what state is hidden underneath superconductivity is universal, but poorly understood,” Wang said. “Some hidden states appear to be inaccessible with any thermodynamic tuning methods.”

The new quantum switching scheme developed by the researchers (they call it terahertz light-quantum-tuning) uses short pulses of trillionths of a second at terahertz frequency to selectively bombard, without heating, superconducting niobium-tin, which at ultracold temperatures can conduct electricity without resistance. The flashes suddenly switch the model compound to a hidden state of matter.

The scientific journal Nature Materials has just published a paper describing the discovery. Wang is corresponding author. Leading authors are Xu Yang and Chirag Vaswani, Iowa State graduate students in physics and astronomy. (See sidebar for other co-authors.)

In most cases, exotic states of matter such as the one described in this research paper are unstable and short-lived. In this case, the state of matter is metastable, meaning it doesn’t decay to a stable state for an order of magnitude longer than other, more typical transient states of matter.

The fast speed of the switch to a hidden quantum state likely has something to do with that.

“Here, the quantum quench (change) is so fast, the system is trapped in a strange ‘plateau’ and doesn’t know how to go back,” Wang said. “With this fast-quench, yet non-thermal system, there’s no normal place to go.”

A remaining challenge for the researchers is to figure out how to control and further stabilize the hidden state and determine if it is suitable for quantum logic operations, Wang said. That could allow researchers to harness the hidden state for practical functions such as quantum computing and for fundamental tests of bizarre quantum mechanics.

It all starts with the researchers’ discovery of a new quantum switching scheme that gives them access to new and hidden states of matter.

Said Wang: “We are creating and controlling a new quantum matter that can’t be achieved by any other means.”

Physicists use terahertz flashes to uncover new state of matter hidden by superconductivity

https://www.news.iastate.edu/news/2018/06/04/terahertzflashes

Jigang Wang of Iowa State and the Ames Laboratory led experiments that switched on a hidden state of matter in a superconductive alloy. Larger photo. Photo by Christopher Gannon.

AMES, Iowa – Using the physics equivalent of the strobe photography that captures every twitch of a cheetah in full sprint, researchers have used ultrafast spectroscopy to visualize electrons interacting as a hidden state of matter in a superconductive alloy.

It takes intense, single-cycle pulses of photons – flashes – hitting the cooled alloy at terahertz speed – trillions of cycles per second – to switch on this hidden state of matter by modifying quantum interactions down at the atomic and subatomic levels.

And then it takes a second terahertz light to trigger an ultrafast camera to take images of the state of matter that, when fully understood and tuned, could one day have implications for faster, heat-free, quantum computing, information storage and communication.

The discovery of this new switching scheme and hidden quantum phase was full of conceptual and technical challenges.

To find new, emergent electron states of matter beyond solids, liquids and gases, today’s condensed matter physicists can no longer fully rely on traditional, slow, thermodynamic tuning methods such as changing temperatures, pressures, chemical compositions or magnetic fields, said Jigang Wang, an Iowa State University professor of physics and astronomy and a faculty scientist at the U.S. Department of Energy’s Ames Laboratory.

“The grand, open question of what state is hidden underneath superconductivity is universal, but poorly understood,” Wang said. “Some hidden states appear to be inaccessible with any thermodynamic tuning methods.”

The new quantum switching scheme developed by the researchers (they call it terahertz light-quantum-tuning) uses short pulses of trillionths of a second at terahertz frequency to selectively bombard, without heating, superconducting niobium-tin, which at ultracold temperatures can conduct electricity without resistance. The flashes suddenly switch the model compound to a hidden state of matter.

The scientific journal Nature Materials has just published a paper describing the discovery. Wang is corresponding author. Leading authors are Xu Yang and Chirag Vaswani, Iowa State graduate students in physics and astronomy. (See sidebar for other co-authors.)

In most cases, exotic states of matter such as the one described in this research paper are unstable and short-lived. In this case, the state of matter is metastable, meaning it doesn’t decay to a stable state for an order of magnitude longer than other, more typical transient states of matter.

The fast speed of the switch to a hidden quantum state likely has something to do with that.

“Here, the quantum quench (change) is so fast, the system is trapped in a strange ‘plateau’ and doesn’t know how to go back,” Wang said. “With this fast-quench, yet non-thermal system, there’s no normal place to go.”

A remaining challenge for the researchers is to figure out how to control and further stabilize the hidden state and determine if it is suitable for quantum logic operations, Wang said. That could allow researchers to harness the hidden state for practical functions such as quantum computing and for fundamental tests of bizarre quantum mechanics.

It all starts with the researchers’ discovery of a new quantum switching scheme that gives them access to new and hidden states of matter.

Said Wang: “We are creating and controlling a new quantum matter that can’t be achieved by any other means.”