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Superconductivity is an advantageous property observed in some materials, which entails an electrical resistance of zero at extremely low temperatures. Superconductors, materials that exhibit this property, have proved to be highly promising for the development of various electronic components for both classical and quantum technologies.

Researchers at Massachusetts Institute of Technology (MIT), University of California–Riverside and SEEQC Inc. recently introduced a new system comprised of four superconducting diodes (SDs), which are electronic devices that allow electric current to flow in only one direction and are made of superconducting materials.

Their superconducting diode bridge, introduced in a paper in Nature Electronics, was found to perform remarkably well at cryogenic temperatures, achieving rectification efficiencies as high as 42% ± 5%.

"Our recent work on superconducting diodes inspired us to advance toward addressing technology needs," Dr. Josep Ingla-Aynes, Dr. Jagadeesh S. Moodera and Dr. Oleg A. Mukhanov, main authors of the paper, told Â鶹ÒùÔº. "Since our SDs were already highly efficient, reproducible and scalable, we decided to exploit them for applications. We thus explored useful circuits that could be made with such SDs."

Dr. Ingla-Aynes and Dr. Moodera discussed their plans for developing circuits made of SDs with Dr. Mukhanov, co-author of the new paper and a pioneer in the development of superconducting devices for both classical and quantum computers. During their discussion with Dr. Mukhanov, they learned that converting AC currents into DC currents at cryogenic temperatures is a requirement of all cryogenic circuitry and would be necessary to upscale DC-biased superconducting logic systems.

"We thus set ourselves to make full-wave superconducting rectifiers capable of performing this for efficient power delivery," explained the main authors of the paper. "The SD bridges we developed are patterned into ultrathin film layers fabricated by ultra-high vacuum evaporation techniques to achieve optimal quality.

"These films have two important layers: a superconductor and a ferromagnetic insulator. After patterning the layers for micrometer-sized devices using standard nanofabrication techniques, the ferromagnetic insulator creates stray fields at the edges that help make our superconducting diodes work efficiently."

As the key goal of their paper was to develop a full-wave rectifier circuit, the researchers first had to boost the performance of their SDs. To do this, they designed the diodes with asymmetric edges and applied a tiny out-of-plane magnetic field to them.

"This approach resulted in a bridge made of four near-identical and highly efficient SDs that are all patterned on the same superconducting film, including the superconducting strips used as electrodes, something crucial for enhancing its efficiency," said the authors.

"The unique advantage of our SD rectifier circuit design is that it allows for placing four highly efficient superconducting diodes in a full-wave rectifier circuit, something that was not possible before. We have shown its operation for input current up to high frequencies."

Following their improved diode design, the researchers created a highly efficient SD rectifier circuit. In an initial test, this circuit was able to efficiently convert AC currents into DC signals at liquid helium temperatures (e.g., those attained using closed-cycle refrigeration techniques).

"Our work has direct applications for powering the DC-biased superconducting logic and quantum circuits and thus readily enables their scaled-up operation, thereby has the most relevant practical application," explained the authors.

"Such circuits are also used in controlling quantum computers; the introduction of on-chip rectifiers should help increase miniaturization, reducing power consumption and electromagnetic noise for signal coherence of such systems."

This recent work by Dr. Ingla-Aynes, Dr. Moodera, Dr. Mukhanov and their colleagues could open new possibilities for the future advancement of a wide range of quantum technologies. The SD bridge and the rectifier circuit they developed could soon be improved further and integrated in various quantum devices, including quantum computers and sophisticated quantum detectors used to search for dark matter.

"We now want to bring the efficient operation of SDs and rectifiers down to zero magnetic field," added the authors. "This would be an important step toward the integration with superconducting circuits. SDs and Josephson junctions integrated in one circuit will enable new functionalities and reduce overall power consumption of data processing and storage. There are other relevant critical ideas that we are pursuing, as well."

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