Controllability and Noise in Large Quantum Systems

13:00 23-01-2014

Holon Institute of Technology, Faculty of Sciences
Controllability and Noise in Large Quantum Systems
Dr. Shimshon Kallush, Ort Braude

23.1.14 | Thursday | 13:00 | Dr. Shimshon Kallush | Building 8 Room 424

A closed quantum system is defined as completely controllable if an arbitrary unitary transformation can be executed using the available controls. In practice, control field are a source of unavoidable noise. Can one design control fields such that the effect of noise is negligible on the time-scale of the transformation? Complete controllability in practice requires that the effect of noise can be suppressed for an arbitrary transformation.
The present study considers a paradigm of control, where the Lie-algebraic structure of the control Hamiltonian is fixed, while the size of the system increases, determined by the dimension of the Hilbert space representation of the algebra. We show that in general, for large quantum systems, generic noise in the controls dominates for a typical class of target transformations, i.e., complete controllability is destroyed by the noise. One exception to this case is classical-like transitions where the controlled state remains close to a generalized coherent state throughout the whole dynamics.