We propose a formalism for describing two-strand systems of a DNA type by means of soliton von Neumann equations, and illustrate how it works on a simple example exactly solvably by a Darboux transformation. The main idea behind the construction is the link between solutions of von Neumann equations and entangled states of systems consisting of two subsystems evolving in time in opposite directions. Such a time evolution has analogies in realistic DNA where the polymerazes move on leading and lagging strands in opposite directions.
Two-Strand Systems and Mutually Time-Reflected Turing MachinesAccording to Adleman [1] the process of DNA replication may be analyzed in terms of Turing machines: One strand plays a role of an instruction tape, a polymeraze is the read/write head, and the second strand contains the results of instructions. At a molecular level each strand is a sequence of molecules. In simple models one can represent sequences of molecules in a strand as chains of two-level systems (bits) in a state |ψ(t) = B1...Bn ψ(t) B1...Bn |B 1 . . . B n , B j = 0, 1. Thinking of the motion of the head in terms of a dynamics, one can write |ψ(t) = U (t, 0)|ψ(0) , where 0 ≤ t ≤ T . The final time T is the time of arrival of the head at the end of the strand, and U (t 1 , t 2 ) is a unitary operator which, in principle, may be different for different initial states of the system (this type of evolution occurs for nonlinear Schrödinger equations). A two-strand system can be represented by an entangled state