In 2023, nearly 4.4 percent (176 terawatt-hours) of total energy usage in the United States was consumed by data centers that are vital for managing substantial amounts of data. Out of that 176 TWh, roughly 100 TWh (57 percent) was allocated to CPU and GPU devices. Energy demands have surged significantly over the last ten years and are projected to keep increasing, highlighting the necessity of developing energy-efficient computing solutions.
Superconducting electronics have emerged as a promising alternative for both classical and quantum computing, though fully harnessing their potential for high-performance computing necessitates a considerable reduction in the interconnections between standard temperature electronics and low-temperature superconducting circuits. To create systems that are not only larger but also more efficient, substituting conventional components like semiconductors with their superconducting equivalents could prove extremely advantageous. This is a challenge that has engaged MIT Plasma Science and Fusion Center senior research scientist Jagadeesh Moodera and his team, who recently reported a significant advancement in a Nature Electronics article titled, “Efficient superconducting diodes and rectifiers for quantum circuitry.”
Moodera was addressing a persistent challenge. One of the core ongoing requirements is the need for efficient conversion of AC currents into DC currents on a chip while functioning at the extremely cold cryogenic temperatures essential for superconductors to operate effectively. For instance, in superconducting “energy-efficient rapid single flux quantum” (ERSFQ) circuits, the AC-to-DC dilemma restricts ERSFQ scalability and inhibits their integration into larger, more complex circuits. To tackle this issue, Moodera and his team devised superconducting diode (SD)-based superconducting rectifiers—devices capable of converting AC to DC on the same chip. These rectifiers would facilitate the efficient provision of the DC current needed to power superconducting classical and quantum processors.
Quantum computer circuits can only function at temperatures nearing 0 kelvins (absolute zero), and the manner in which power is supplied must be meticulously regulated to minimize the interference effects introduced by excess heat or electromagnetic noise. Most unwanted noise and heat stem from the wires that link cold quantum chips to room-temperature electronics. By employing superconducting rectifiers to transform AC currents into DC within a cryogenic environment, the number of wires is reduced, thereby decreasing heat and noise and allowing for larger, more stable quantum systems.
In a 2023 experiment, Moodera and his colleagues developed SDs constructed from very thin layers of superconducting material that exhibit nonreciprocal (or unidirectional) current flow and could represent the superconducting equivalent of conventional semiconductors. Although SDs have received considerable attention, especially since 2020, prior research has primarily centered on individual SDs for proof of concept. The 2023 paper from the team detailed their development of a technique that allows for scaling SDs for wider application.
Now, by creating a diode bridge circuit, they demonstrated the successful integration of four SDs and achieved AC-to-DC rectification at cryogenic temperatures.
The new methodology described in their latest Nature Electronics publication will significantly reduce thermal and electromagnetic noise transmission from the ambient environment into cryogenic circuitry, enabling cleaner operation. Additionally, the SDs could potentially function as isolators/circulators, aiding in the insulation of qubit signals from external disruptions. The successful integration of multiple SDs into the inaugural integrated SD circuit marks a pivotal advancement toward realizing superconducting computing as a commercial reality.
“Our work paves the way for the emergence of highly energy-efficient, practical superconductivity-based supercomputers in the coming years,” asserts Moodera. “Moreover, we anticipate that our research will bolster qubit stability while advancing the quantum computing initiative, bringing its realization nearer.” Considering the multiple advantageous roles these components could fulfill, Moodera and his team are already progressing toward the incorporation of such devices into actual superconducting logic circuits, including in dark matter detection circuits that are crucial for experiments at CERN and LUX-ZEPLIN at the Berkeley National Lab.
This research was partially supported by MIT Lincoln Laboratory’s Advanced Concepts Committee, the U.S. National Science Foundation, U.S. Army Research Office, and U.S. Air Force Office of Scientific Research.