Controlling open quantum systems: Tools, achievements, and limitations.

Abstract

The advent of quantum devices, which exploit the two essential elements of quantum 
physics, coherence and entanglement, has sparked renewed interest in the control of 
open quantum systems. Successful implementations face the challenge of preserving 
relevant nonclassical features at the level of device operation. A major obstacle is 
decoherence, which is caused by interaction with the environment. Optimal control 
theory is a tool that can be used to identify control strategies in the presence of 
decoherence. Here we review recent advances in optimal control methodology that allow 
typical tasks in device operation for open quantum systems to be tackled and discuss 
examples of relaxation-optimized dynamics. Optimal control theory is also a useful 
tool to exploit the environment for control. We discuss examples and point out 
possible future extensions.