Southwest Quantum Information and Technology

Optimal digital dynamical decoupling for general decoherence via Walsh modulation

Presenting Author: Haoyu Qi, Louisiana State
Contributing Author(s): Jonathan Dowling and Lorenza Viola

We provide a general framework for constructing digital dynamical decoupling sequences based on Walsh modulation, applicable to arbitrary qubit decoherence scenarios. Building on the equivalence between the Walsh formalism and the recently introduced concatenated-projection approach, we identify a family of optimal Walsh sequences which can be exponentially more efficient, in terms of the required total pulse number for fixed cancellation order, than known sequences based on concatenated design. Optimal sequences for a given cancellation order are highly non-unique, their performance depending sensitively on the control path. We provide an analytical upper bound to the achievable decoupling error, and argue how suitable path-optimized sequences within the optimal Walsh family can substantially outperform concatenated decoupling, while respecting realistic timing constraints. We validate these conclusions by numerically computing the average fidelity in a toy model capturing the essential feature of hyperfine-induced decoherence in a quantum dot.

(Session 9a : Friday from 4:45pm - 5:15pm)