'Remarkably close to the minimum permitted by physics': this superconducting memory bit runs at an estimated 5x the limit, but at -269°C the fridge shrinks its claimed million-fold edge over today’s chips considerably

Hebrew University physicists estimate a single superconducting vortex can act as a memory bit at about five times Landauer's limit, at 4.2 kelvin The fivefold figure is a simulation-based estimate anchored to continuous-drive measurements, not a measured erasure, however The release's million-fold e

<![CDATA[ <article> <ul><li><strong>Hebrew University physicists estimate a single superconducting vortex can act as a memory bit at about five times Landauer's limit, at 4.2 kelvin</strong></li><li><strong>The fivefold figure is a simulation-based estimate anchored to continuous-drive measurements, not a measured erasure, however</strong></li><li><strong>The release's million-fold edge over conventional computers disregards refrigeration costs</strong></li></ul><p>Every time a computer erases a bit, it pays an energy toll that physics will not waive; IBM physicist Rolf Landauer pinned down the minimum in 1961: kT ln 2, a figure that scales with temperature and works out to about 2.9 zeptojoules at room temperature.</p><p>No real chip comes close, making that gap a favorite target as computing's electricity bill keeps climbing.</p><p>Physicists at the Hebrew University of Jerusalem now say they have come within about five times of that floor using a single superconducting vortex, a nanoscale whirlpool of electrical current.</p><h2 id="storing-a-bit-in-a-whirlpool-might-be-a-slightly-controversial-play">Storing a bit in a whirlpool might be a slightly controversial play</h2><p>The work, <a href="https://www.nature.com/articles/s41467-026-77988-x" target="_blank" rel="nofollow">published in <em>Nature Communications</em></a> on September 24 and <a href="https://www.eurekalert.org/news-releases/1147538" target="_blank" rel="nofollow">publicized in a university release</a> on October 11, is a clever measurement, but it has limitations: the device works only at liquid-helium temperatures, and one of the paper's three peer reviewers has opposed the final version.</p><p>In a thin superconducting film, a magnetic field can punch through in tiny tubes, each ringed by circulating current and carrying one quantum of flux, and these vortices snag on defects.</p><p>The team, led by Yonathan Anahory, used a 55-nanometer niobium film patterned into a strip 10 micrometers wide and cooled to 4.2 kelvin. Sweeping a steady current through the strip nudged individual vortices into spots where the film's natural disorder offers two neighboring resting places only a few nanometers apart. The positioning matters here, acting effectively as a store of value: left or right becomes zero or one.</p><p>They then rocked each vortex with an alternating current and tracked it with a SQUID-on-tip microscope, a magnetic sensor built onto a tapered glass probe. The part of the motion that lags behind the push reveals how much energy is lost each cycle.</p><p>Anahory said the result puts the bit at roughly five times Landauer's limit, <a href="https://www.eurekalert.org/news-releases/1147538" target="_blank" rel="nofollow">“bringing it remarkably close to the minimum permitted by physics.”</a> The release covers the energy as measured for the actual test, not the cooling aspect, which could significantly reduce the efficiency story here.</p><p>The paper adds another caveat here: Its abstract concedes that <a href="https://www.nature.com/articles/s41467-026-77988-x" target="_blank" rel="nofollow">“our experimental method requires a steady sinusoidal drive incompatible with Landauer’s erasure protocol”</a> and attributes the near-limit figure to numerical analysis.</p><p>The lab measured dissipation while vortices were wiggled back and forth continuously; the cost of a true erasure, forcing a bit of unknown value into a known state, was estimated with simulations anchored to that data. The fivefold number is the authors' estimate for a working bit driven at 150 kHz, spelled out in their replies to reviewers.</p><p>This has, however, spurred a peer review fight, also published by Nature Communications, which lists the unusually blunt <a href="https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs41467-026-77988-x/MediaObjects/41467_2026_77988_MOESM2_ESM.pdf" target="_blank" rel="nofollow">referee reports</a> alongside the paper.</p><p>Reviewer #2 rejected the first draft, said the second could run only with extra experiments, and recommended against the final version, opening with <a href="https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs41467-026-77988-x/MediaObjects/41467_2026_77988_MOESM2_ESM.pdf" target="_blank" rel="nofollow">“Authors write that they measure work. It is not true.”</a> The reviewer argued that force, displacement, and work were estimated or inferred rather than observed, and asked for two sanity checks: show the vortex being pushed into one well and staying there, and show its spontaneous hopping changing with temperature, as thermal activation predicts.</p><p>The authors declined both, citing scanning drift that limits static imaging to about 20 nanometers and noting that changing temperature also reshapes the pinning landscape.</p><p>Reviewer #3 backed publication, calling the work original and sound and warning that the extra experiments could delay it indefinitely. Reviewer #1 judged the technique ill-suited to erasure at useful speeds and encouraged a more modest title. </p><h2 id="speed-is-the-tradeoff">Speed is the tradeoff</h2><p>Not only is the cost of cooling unaccounted for, with real-world refrigeration costs not being factored in, but the bigger problem is also speed. Landauer's limit is only reachable if you take your time, and <a href="https://arxiv.org/abs/2006.03242" target="_blank" rel="nofollow">work by Proesmans, Ehrich, and Bechhoefer</a> shows that the extra cost of erasure rises as operations speed up.</p><p>The Hebrew University estimate applies at 150 kHz, or essentially one operation every 6.7 microseconds, while superconducting logic chips were <a href="https://www.technologyreview.com/s/423405/superconducting-niobium-chip-smashes-silicon-power-consumption-standards/" target="_blank">clocked at 6 GHz</a> more than a decade ago.</p><p>Going slower does not help either. By the authors' own noise data, the two wells central to the near-limit result let the vortex hop on its own roughly 3,000 to 7,000 times a second at 4.2 K.</p><p>The authors argue that this is fine as long as operations run much faster than the hopping. But it means the most efficient wells hold information for well under a millisecond, and the paper does not show a single well that is both near the limit and able to keep data for long.</p><p>The tradeoff, therefore, is one between speed, cost, and durability, and given that the use case is data storage, it is a tough call to make. Vortex memory <a href="https://www.nature.com/articles/s41467-023-40654-7" target="_blank" rel="nofollow">is not entirely new</a>; the Hebrew University contribution is energy accounting, and its claim to a first is narrow, though it uses a single vortex.</p><p>The Hebrew University team has produced a careful, somewhat contested estimate of how cheaply a single vortex can be shuffled between two spots, and a reminder that sitting close to the physical limit and being efficient at the wall socket are very different things.</p><div class="block__comparison"><h3></h3><div class="comparisons"><div class="comparison"><h4></h4><ul></ul></div><div class="comparison"><h4></h4><ul></ul></div></div></div> </article> ]]>