Erase a bit as cheaply as possible

1 · Say what the limit sets

Beginner

What does Landauer's limit, k_B T ln 2, set?

The smallest possible size of a bit The top speed of a memory The minimum heat to erase a bit

According to the authors, a vortex takes about 4 nanoseconds to move from one hollow to the other.

Intermediate

At most, how many switches per second does that allow?

25 MHz 250 MHz 4 GHz

At low frequency, the measured work per cycle falls below Landauer's limit.

Expert

Why is that not a violation of the limit?

A steady back-and-forth is not an erasure The limit does not apply to superconductors The measurement is too imprecise to tell

Expert

Why not build a memory in this slow regime, where the work is so low?

The force needed becomes too large there The vortex hops on its own and loses its bit The current heats the film above 4.2 K

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