DANIEL LIDAR
(USC)
   
QUANTUM KRISPY KREME SEMINAR:
COMBINING DYNAMICAL DECOUPLING WITH
FAULT-TOLERANT QUANTUM ERROR CORRECTION


This talk will be a not very technical presentation of the very technical paper by the title above (arXiv:0911.3202, joint work with Hui Ng and John Preskill), whose abstract reads as follows:We study how dynamical decoupling (DD) pulse sequences can improve the reliability of quantum computers. We prove upper bounds on the accuracy of DD-protected quantum gates and derive sufficient conditions for DD-protected gates to outperform unprotected gates. Under suitable conditions, fault-tolerant quantum circuits constructed from DD-protected gates can tolerate stronger noise, and have a lower overhead cost, than fault-tolerant circuits constructed from unprotected gates. Our accuracy estimates depend on the dynamics of the bath that couples to the quantum computer, and can be expressed either in terms of the operator norm of the bath’s Hamiltonian or in terms of the power spectrum of bath correlations; we explain in particular how the performance of recursively generated concatenated pulse sequences can be analyzed from either viewpoint. Our results apply to Hamiltonian noise models with limited spatial correlations.