Bang-Bang Control of a Qubit Coupled to a Quantum Critical Spin Bath

We analytically and numerically study the effects of pulsed control on the decoherence of a qubit coupled to a quantum spin bath. When theenvironment is critical, decoherence is faster and we show that thecontrol is relatively more effective. Two coupling models areinvestigated, namely a qubit coupled to a bath via a single link and aspin star model, yielding results that are similar and consistent.