Superconducting memory bit reaches an estimated 5× physics limit at −269°C

Physicists at the Hebrew University of Jerusalem estimate that a single superconducting vortex can store and erase a bit using about five times the energy set by Landauer’s limit. The device, however, works at −269°C, and the estimate does not include the energy used for cooling.

Published in Nature Communications on September 24 and described by the university on October 11, the study used a 55-nanometer niobium film patterned into a 10-micrometer-wide strip and cooled to 4.2 kelvin. The team positioned individual vortices between two nearby resting places, representing zero and one, then measured energy dissipated as an alternating current moved them. The estimated near-limit result applies to a bit operated at 150 kHz; the researchers inferred erasure costs from continuous-motion measurements and numerical analysis.

The result drew mixed peer reviews. One reviewer opposed the final version, arguing that force, displacement and work were inferred rather than directly measured. The authors said scanning drift limited static imaging to about 20 nanometers and that changing temperature also changes the pinning landscape.

Speed and data retention are further limits. The estimate is for 150 kHz, or one operation every 6.7 microseconds, while superconducting logic chips were clocked at 6 GHz more than a decade ago. At 4.2 kelvin, the two wells used for the result let vortices hop spontaneously about 3,000 to 7,000 times per second. The study does not show a near-limit well that also holds data for long.