Dynamical control of electron spin coherence in a quantum dot

TL;DR

This paper demonstrates that optimized dynamical decoupling protocols can significantly extend electron spin coherence in quantum dots by creating a stable decoherence-free subspace, even with slower control rates than previously expected.

Contribution

It introduces a concatenated periodic protocol that outperforms traditional methods in suppressing decoherence in quantum dot electron spins.

Findings

Optimal control achieved with concatenated periodic protocol.

Coherence saturation indicates a stable decoherence-free subspace.

Control rates slower than the bath's spectral cutoff are effective.

Abstract

We investigate the performance of dynamical decoupling methods at suppressing electron spin decoherence from a low-temperature nuclear spin reservoir in a quantum dot. The controlled dynamics is studied through exact numerical simulation, with emphasis on realistic pulse delays and long-time limit. Our results show that optimal performance for this system is attained by a periodic protocol exploiting concatenated design, with control rates substantially slower than expected from the upper spectral cutoff of the bath. For a known initial electron spin state, coherence can saturate at long times, signaling the creation of a stable ``spin-locked'' decoherence-free subspace. Analytical insight on saturation is obtained for a simple echo protocol, in good agreement with numerical results.