Practice question · Multiple choice
Landauer's principle sets a minimum energy for erasing a bit and none for computing with one. Why is erasure the operation that costs?
Hints
- Before erasure the bit could be 0 or 1; afterwards it is definitely 0. What happened to the number of possible states?
- Ask where entropy goes when it decreases inside a system.
Show the answer
A. Because erasure is logically irreversible, so entropy must be paid
Why
Two states collapsing to one lowers the memory's entropy, and the second law requires an equal increase elsewhere, kT ln 2 per bit, released as heat. Reversible operations destroy no information and carry no such floor, which is the basis of reversible computing and why quantum gates are unitary.
Practise Information, Signals, and the Physics of Computing
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