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.