Classical Control of a Quantum System

G. Huang

Siao Xie, Shanping Yu, Zairong Xi

The classical noise is unavoided in the real world. In what way classical part impact quantum dynamics and whether classical part impact controllability of quantum system have become problems. To figure out these two problems, we focus on a specific hybrid system which is both quasi-free and Markov. Because of its quasi-free property, the hybrid system comprising an open quantum system and a classical stochastic process possesses a distinct transformation formula that determines its dynamical semigroup. All these discussions are described by Weyl operators which also constitue the observable space. The controllability of reduced quantum system is first discussed, given its likely Lindblad form. The drift term is consisted of both classical information and quantum information. By adding classical control term in drift term, the controllability is analyzed using LARC(Lie Algebra Rank Condition). We discover that the reduced quantum system is fully controllable under certain controls. When we take classical information as a control, the reduced quantum system is fully controllable without external input. And the same conclusions hold in hybrid system.

P. Zoller, J. I. Cirac, S. M. Girvin +1 more

Gerard J Milburn

We find the conditions for one quantum system to function as a classical controller of another quantum system: the controller must be an open system and rapidly diagonalized in the diagonal basis of the controller variable that is coupled to the controlled system. This causes decoherence in the controlled system that can be made small if the rate of diagonalization is fast. We give a detailed example based on the quantum optomechanical control of a mechanical resonator. The resulting equations are structurally similar to recently proposed models for consistently combining quantum and classical stochastic dynamics.

Emanuel-Cristian Boghiu, Jesús Clemente-Gallardo, Jorge Alberto Jover-Galtier +1 more

The notion of hybrid quantum-classical control system was introduced as a control dynamical system which combined classical and quantum degrees of freedom. Classical and quantum objects were combined within a geometrical description of both types of systems. We also considered the notion of hybrid quantum-classical controllability by means of the usual definitions of geometric control theory, and we discussed how the different concepts associated to quantum controllability are lost in the hybrid context because of the nonlinearity of the dynamics. We also considered several examples of physically relevant problems, such as the spin-boson model or the notion of hybrid spline.

Manoj Kumar