| Abstract: | Abstract (if needed): There is a strong interest in optimal manipulation of single quantum systems by external controls. Traps are controls which are optimal only locally but not globally and if they would exist, they would be important obstacles for the search for globally optimal controls in numerical and laboratory experiments. For this reason the analysis of traps has attracted a great interest in recent years. However, despite of the intensive studies no examples of trap-free quantum systems have been known. In this talk we will show that controlled two-level quantum systems are generally free of traps. This finding provides the first known class of trap-free quantum systems. As examples, such important task as unconstrained manipulation of the transition probability in the Landau-Zener system and fundamental problems of state preparation and gate generation for qubits---two-level quantum systems forming a basic building block for quantum computation---are shown to be trap-free.
Reference: A.N. Pechen and N.B. Ilin, Trap-free manipulation in the Landau-Zener system, Phys. Rev. A 86, 052117 (2012). |
