Reversible computing

Reversible computing is any model of computation where the computational process, to some extent, is time-reversible. In a model of computation that uses deterministic transitions from one state of the abstract machine to another, a necessary condition for reversibility is that the relation of the mapping from states to their successors must be one-to-one. Reversible computing is a form of unconventional computing.

Due to the unitarity of quantum mechanics, quantum circuits are reversible, as long as they do not "collapse" the quantum states on which they operate.