New nanoscope investigates superconductivity at smallest scales

Jigang Wang, a professor of physics and astronomy at Iowa State University, offered a quick walk-around a new sort of microscope that can help researchers understand, and ultimately develop, the inner workings of quantum computing.

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

He pointed out and explained the control systems, the laser source, the maze of mirrors that make an optical path for light pulsing at trillions of cycles per second, the superconducting magnet that surrounds the sample space, the custom-made atomic force microscope, and the bright yellow cryostat that lowers sample temperatures down to the temperature of liquid helium, about -450°F.

Wang calls the instrument a Cryogenic Magneto-Terahertz Scanning Near-field Optical Microscope. (cm-SNOM). It’s based at the Ames National Laboratory’s Sensitive Instrument Facility just northwest of Iowa State’s campus.

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

“No one has it,” Wang said of this extreme-scale nanoscope. “It’s the first in the world.”

The nanoscope can focus down to about 20nm, 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 these extreme environments.

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

Superconducting materials are also being considered for quantum computing, the emerging generation of computing power that’s based on the mechanics and energies at the quantum world’s atomic and subatomic scales. Superconducting quantum bits, or qubits, are the heart of the new technology. One strategy to control supercurrent flows in qubits is to use strong light-wave pulses.

“Superconducting technology is a major focus for quantum computing,” Wang said. “So, we need to understand and characterize superconductivity and how it’s controlled with light.”

And that’s what the cm-SNOM instrument is doing. In a paper in Nature Physics and a preprint paper posted to the arXiv website, Wang and his team report taking the first ensemble average measurements of supercurrent flow in iron-based superconductors at terahertz (trillions of waves per second) energy scales. They have also taken the first cm-SNOM action to detect terahertz supercurrent tunneling in a high-temperature, copper-based, cuprate superconductor.

“This is a new way to measure the response of superconductivity under light-wave pulses,” explained Wang. “We’re using our tools to offer a new view of this quantum state at nanometer-length scales during terahertz cycles.”

“By analyzing the new experimental datasets, we can develop advanced tomography methods for observing quantum entangled states in superconductors controlled by light,” said Ilias Perakis, a professor of physics at the University of Alabama at Birmingham and a collaborator on this project, who has developed the theoretical understanding of light-controlled superconductivity.

In the Nature Physics paper, they researchers say that “the interactions able to drive” these supercurrents “are still poorly understood, partially due to the lack of measurements.”

Now that those measurements are happening at the ensemble level, Wang is looking ahead to the next steps, which include using the cm-SNOM to measure supercurrent existence at simultaneous nanometer and terahertz scales. With support from the Superconducting Quantum Materials and Systems Center led by the US Department of Energy’s Fermi National Accelerator Laboratory in Illinois, his group is also searching for ways to make the new instrument even more precise.

Potentially, the measurements could become precise enough to visualize supercurrent tunneling at single Josephson junctions, which means the movement of electrons across a barrier separating two superconductors.

“We really need to measure down to that level to impact the optimization of qubits for quantum computers,” Wang said. “That’s a big goal. And this is now only a small step in that direction. It’s one step at a time.”

This story is adapted from material from Iowa State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.