Quantum Computing.
environment. However it is possible to model a classical computer with a quantum computer in a totally reversible fashion. The Toffoli gate or C2NOT gate is able to do this. U_T = |000⟩⟨000| + |001⟩⟨001| + |010⟩⟨010| + |011⟩⟨011| + |100⟩⟨100| + |101⟩⟨101| + |111⟩⟨110|+ |110⟩⟨111| It acts on 3