Logically and Physically Reversible Natural Computing: A Tutorial

This year marks the 40

th

anniversary of Charles Bennett’s seminal paper on reversible computing. Bennett’s contribution is remembered as one of the first to demonstrate how any deterministic computation can be simulated by a logically reversible Turing machine. Perhaps less remembered is that the same paper suggests the use of nucleic acids to realise physical reversibility. In context, Bennett’s foresight predates Leonard Adleman’s famous experiments to solve instances of the Hamiltonian path problem using strands of DNA — a landmark date for the field of natural computing — by more than twenty years. The ensuing time has seen active research in both reversible computing and natural computing that has been, for the most part, unrelated. Encouraged by new, experimentally viable DNA computing models, there is a resurgent interest in logically reversible computing by the natural computing community. We survey these recent results, and their underlying ideas, which demonstrate the potential for logically and physically reversible computation using nucleic acids.