Quantum simulation with natural decoherence

A quantum system may be efficiently simulated by a quantum information processor as suggested by Feynman and developed by Lloyd, Wiesner, and Zalka. Within the limits of the experimental implementation, simulation permits the design and control of the kinematic and dynamic parameters of a quantum system. Extension to the inclusion of the effects of decoherence, if approached from a full quantum-mechanical treatment of the system and the environment, or from a semiclassical fluctuating field treatment (Langevin), requires the difficult access to dynamics on the time scale of the environment correlation time. Alternatively, a quantum-statistical approach may be taken which exploits the natural decoherence of the experimental system, and requires a more modest control of the dynamics. This is illustrated for quantum simulations of a four-level quantum system by a two-spin NMR ensemble quantum information processor.