The effect of dynamical decoupling in the case of a single fluctuator coupled to a qubit

We consider the role of dynamical decoupling in the case of a single classical fluctuator coupled to a qubit which is operated in a pure dephasing regime. We study the effect of various pulse sequences on the decoherence time for both weakly and strongly coupled fluctuators described by random telegraph noise (RTN). For a strongly coupled two-level system, the application of multiple pulses leads to a large enhancement of qubit coherence time. By theoretically comparing various dynamic decoupling schemes, we conclude that the Car-Purcell-Meiblum-Gill (CPMG) pulse sequence, well-known in NMR spectroscopy and recently discussed in the context of electron spin qubits in semiconductors [1], is the most optimal coherence-restoring scheme for the single fluctuator problem of relevance to superconducting qubits. We also find that for a large number of applied pulses the Gaussian approximation for the noise reproduces the exact results even in the strongly coupled regime. \newline [1] W. M. Witzel and S. Das Sarma, Phys. Rev. Lett. 98, 077601 (2007).