New instrument measures flow of supercurrents, data has applications in quantum computing – News Physics and Quantum Computing

Jigang Wang offered a quick overview of a new type of microscope that can help researchers understand, and ultimately develop, the inner workings of quantum computing.

Wang, a professor of physics and astronomy at Iowa State University, also affiliated with the US Department of Energy’s Ames National Laboratory, described how the instrument works at extreme scales of space, of time and energy – billionths of a meter, quadrillionths of a second and trillions of electromagnetic waves per second.

Wang pointed out and explained the control systems, the laser source, the maze of mirrors that form an optical path for pulsed light at billions of cycles per second, the superconducting magnet that surrounds the sample space, the force microscope Bespoke atomic, the bright yellow cryostat that lowers the temperature of the sample to the temperature of liquid helium, approximately -450 degrees Fahrenheit.

Wang calls the instrument a near-field scanning magneto-terahertz cryogenic optical microscope. (It’s cm-SNOM for short.) It’s based at the Ames National Laboratory Sensitive Instrument Facility, just northwest of the Iowa State campus.

It took five years and $2 million — $1.3 million from the WM Keck Foundation of Los Angeles and $700,000 from Iowa State and Ames National Laboratory — to build the instrument. He has been collecting data and contributing to experiments for less than a year.

“Nobody has it,” Wang said of the extreme-scale nanoscope. “It’s the first in the world. »

It can focus down to about 20 nanometers, or 20 billionths of a meter, while operating below liquid helium temperatures and in strong Tesla magnetic fields. That’s small enough to get a read on the superconducting properties of materials in those extreme environments.

Superconductors are materials that conduct electricity — electrons — without resistance or heat, usually at very cold temperatures. Superconducting materials have many uses, including medical applications such as MRI scans and as magnetic racetracks for charged subatomic particles accelerating around accelerators such as the Large Hadron Collider.

Now, superconducting materials are being considered for quantum computing, the emerging generation of computing power based on the mechanics and energies at the atomic and subatomic scales of the quantum world. Superconducting quantum bits, or qubits, are at the heart of the new technology. One strategy to control supercurrent fluxes in qubits is to use strong pulses of light waves.

“Superconducting technology is a major goal for quantum computing,” Wang said. “So we need to understand and characterize superconductivity and how it is controlled by light. »

And that’s what the cm-SNOM instrument does. As described in a research paper just published by the journal Nature Physics and a preprint article published on the arXiv website (see sidebars), Wang and a team of researchers are taking the first ensemble mean measurements of supercurrent flux in terahertz iron-based superconductors. (trillion waves per second) energy scales and the first cm-SNOM action to detect terahertz supercurrent tunneling in a copper-based high-temperature cuprate superconductor.

“This is a new way to measure the response of superconductivity under light wave pulses,” Wang said. “We are using our tools to provide a new view of this nanoscale quantum state during terahertz cycles. »

Ilias Perakis, professor and chair of physics at the University of Alabama at Birmingham, a collaborator on this project who developed the theoretical understanding of light-controlled superconductivity, said: “By analyzing new sets of experimental data , we can develop advanced tomography methods to observe quantum entangled states in light-controlled superconductors. »

The researchers’ paper reports that “the interactions capable of driving” these supercurrents “are still poorly understood, in part due to the lack of measurements.”

Now that these measurements are occurring at the ensemble level, Wang envisions the next steps to measure the existence of supercurrents using cm-SNOM at simultaneous nanometer and terahertz scales. With support from the Superconducting Quantum Materials and Systems Center run by the US Department of Energy’s Fermi National Accelerator Laboratory in Illinois, his group is looking for ways to make the new instrument even more precise. Could measurements go so far as to accurately visualize supercurrent tunneling at single Josephson junctions, the movement of electrons through a barrier separating two superconductors?

“We really need to measure up to this level to have an impact on optimizing qubits for quantum computers,” he said. “It’s a big goal. And now it’s just a small step in that direction. It’s one step at a time. »

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New instrument measures flow of supercurrents, data has applications in quantum computing – News Physics and Quantum Computing


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