DYNAMICAL SUPPRESSION OF DECOHERENCE IN 2-STATE QUANTUM-SYSTEMS

The dynamics of a decohering two-level system driven by a suitable con trol Hamiltonian is studied. The control procedure is implemented as a sequence of radio-frequency pulses that repetitively flip the state o f the system, a technique that can be termed quantum ''bang-bang'' con trol after its classical analog. Decoherence introduced by the system' s interaction with a quantum environment is shown to be washed out com pletely in the limit of continuous flipping and greatly suppressed pro vided the interval between the pulses is made comparable to the correl ation time of the environment. The model suggests a strategy to fight against decoherence that complements existing quantum error-correction techniques. [S1050-2947(98)07169-1].