Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath

Ajoy, Ashok and Alvarez, Gonzalo A and Suter, Dieter (2011) Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath. In: Physical Review A, 83 (3).

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Abstract

Maintaining quantum coherence is a crucial requirement for quantum computation; hence protecting quantum systems against their irreversible corruption due to environmental noise is an important open problem. Dynamical decoupling (DD) is an effective method for reducing decoherence with a low control overhead. It also plays an important role in quantum metrology, where, for instance, it is employed in multiparameter estimation. While a sequence of equidistant control pulses the Carr-Purcell-Meiboom-Gill (CPMG) sequence] has been ubiquitously used for decoupling, Uhrig recently proposed that a nonequidistant pulse sequence the Uhrig dynamic decoupling (UDD) sequence] may enhance DD performance, especially for systems where the spectral density of the environment has a sharp frequency cutoff. On the other hand, equidistant sequences outperform UDD for soft cutoffs. The relative advantage provided by UDD for intermediate regimes is not clear. In this paper, we analyze the relative DD performance in this regime experimentally, using solid-state nuclear magnetic resonance. Our system qubits are C-13 nuclear spins and the environment consists of a H-1 nuclear spin bath whose spectral density is close to a normal (Gaussian) distribution. We find that in the presence of such a bath, the CPMG sequence outperforms the UDD sequence. An analogy between dynamical decoupling and interference effects in optics provides an intuitive explanation as to why the CPMG sequence performs better than any nonequidistant DD sequence in the presence of this kind of environmental noise.

Item Type:	Journal Article
Publication:	Physical Review A
Publisher:	The American Physical Society
Additional Information:	Copyright of this article belongs to The American Physical Society.
Department/Centre:	Division of Chemical Sciences > NMR Research Centre (Formerly Sophisticated Instruments Facility)
Date Deposited:	29 Mar 2011 08:12
Last Modified:	29 Mar 2011 08:12
URI:	http://eprints.iisc.ac.in/id/eprint/36339

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