Towards optimized suppression of dephasing in systems subject to pulse timing constraints

TL;DR

This paper compares dynamical decoupling protocols for qubit coherence preservation under pulse timing constraints, providing analytical insights and proposing simple modifications to improve performance in realistic quantum dot systems.

Contribution

It introduces a new representation of controlled qubit evolution and demonstrates how simple protocol modifications outperform complex schemes under practical timing limitations.

Findings

High-level decoupling schemes offer limited advantage under timing constraints.

Modified periodic echo protocols significantly improve coherence preservation.

Analytical expressions describe decoherence behavior in different environments.

Abstract

We investigate the effectiveness of different dynamical decoupling protocols for storage of a single qubit in the presence of a purely dephasing bosonic bath, with emphasis on comparing quantum coherence preservation under uniform vs. non-uniform delay times between pulses. In the limit of instantaneous bit-flip pulses, this is accomplished by establishing a new representation of the controlled qubit evolution, where the resulting decoherence behaviour is directly expressed in terms of the free evolution. Simple analytical expressions are given to approximate the long- and short- term coherence behaviour for both ohmic and supra-ohmic environments. We focus on systems with physical constraints on achievable time delays, with emphasis on pure dephasing of excitonic qubits in quantum dots. Our analysis shows that little advantage of high-level decoupling schemes based on concatenated or optimal design is to be expected if operational constraints prevent pulses to be applied sufficiently fast. In such constrained scenarios, we demonstrate how simple modifications of repeated periodic echo protocols can offer significantly improved coherence preservation in realistic parameter regimes.