Noise-resistant off-resonance π-rotation realized in an NMR system

Abstract

Precise manipulation of qubits (spins) requires strong suppression of noise arising from couplings between qubits and their environment, as well as from driving field fluctuations. We propose a double-pulse sequence and an eighteen-pulse sequence to realize a single spin pi-rotation under off-resonance conditions (instead of conventional on-resonance or near-resonance conditions). It is proved that the latter sequence performs much better than the former in simultaneously suppressing both dephasing and driving field noise. As a proof of principle, we experimentally demonstrate, by implementing both sequences in an NMR spin system with a polarized initial spin state, that the off-resonance pi-rotation fidelity reaches as high as 0.9992 +/- 0.0008 for the double-pulse sequence and 0.9997 +/- 0.0006 for the eighteen-pulse sequence. In addition, the noise-tolerance range of the eighteen-pulse sequence is about 20 percent of the driving field strength, approximately three times wider than that of the double-pulse sequence. Besides its potential application in the NMR community, our proposal provides an alternative practical way to accurately control qubits by suppressing the coexisting transversal and longitudinal noises.