Sampled-data design for robust decoherence control of a single qubit

This paper presents a sampled-data approach for the robust decoherence control of a single qubit. The required robustness is defined using a sliding mode domain and the control law is designed offline and then utilized online with a single qubit having bounded uncertainties. Two classes of uncertainties are considered involving the system Hamiltonian and the coupling strength of the system-environment interaction. Three cases are analyzed in detail including amplitude damping decoherence, phase damping decoherence and depolarizing decoherence. Sampling periods are specifically designed for these cases to guarantee the required robustness. A sufficient condition is presented for guiding the design of unitary control for the case with amplitude damping decoherence. The proposed approach has potential applications in quantum error-correction and in constructing robust quantum gates.