Controlling open quantum systems using fast transitions

Unitary control and decoherence appear to be irreconcilable in quantum mechanics. When a quantum system interacts with an environment, control strategies usually fail due to decoherence. In this article we implement a time-optimal unitary control protocol suitable for quantum open systems. The method is based on successive diabatic and sudden switch transitions in the avoided crossings of the energy spectra of closed systems. We show that the speed of this control protocol meets the fundamental bounds imposed by the quantum speed limit, thus making this scheme ideal for application where decoherence needs to be avoided. We show that this method can achieve complex control strategies with high accuracy in quantum open systems.