Fredkin gate (Edward Fredkin) and Toffoli gate (Tommaso Toffoli) are reversible circuits that preserve information {reversible computing}.
If first switch is at 1, second switch NOTs second input bit {controlled NOT gate}. If first switch is at 0, second switch transfers same second input bit. First input bit always transfers. Passing two-bit signals through controlled NOT gates twice restores two-bit signals, allowing reversible computing.
Erasing information releases energy {Landauer's principle} {Landauer principle}.
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Date Modified: 2022.0225