Control of electron spin decoherence caused by electron-nuclear spin dynamics in a quantum dot

TL;DR

This paper investigates how to control electron spin decoherence in a quantum dot caused by interactions with nuclear spins, using quantum dynamics solutions and pulse sequences to achieve high-fidelity coherence preservation.

Contribution

It introduces a novel geometric mapping of nuclear bath dynamics and demonstrates control schemes, including quantum disentanglement and concatenated pulse sequences, to mitigate decoherence.

Findings

Partial coherence recovery via $ au$-pulse at $ au$ and $ au ightarrow ext{sqrt}(2) au$

Disentanglement through bath evolution control differs from traditional spin-echo

Concatenated pulse sequences can eliminate decoherence with high precision

Abstract

Control of electron spin decoherence in contact with a mesoscopic bath of many interacting nuclear spins in an InAs quantum dot is studied by solving the coupled quantum dynamics. The nuclear spin bath, because of its bifurcated evolution predicated on the electron spin up or down state, measures the which-state information of the electron spin and hence diminishes its coherence. The many-body dynamics of nuclear spin bath is solved with a pair-correlation approximation. In the relevant timescale, nuclear pair-wise flip-flops, as elementary excitations in the mesoscopic bath, can be mapped into the precession of non-interacting pseudo-spins. Such mapping provides a geometrical picture for understanding the decoherence and for devising control schemes. A close examination of nuclear bath dynamics reveals a wealth of phenomena and new possibilities of controlling the electron spin decoherence. For example, when the electron spin is flipped by a $\pi$-pulse at $\tau$, its coherence will partially recover at $\sqrt{2}\tau$ as a consequence of quantum disentanglement from the mesoscopic bath. In contrast to the re-focusing of inhomogeneously broadened phases by conventional spin-echoes, the disentanglement is realized through shepherding quantum evolution of the bath state via control of the quantum object. A concatenated construction of pulse sequences can eliminate the decoherence with arbitrary accuracy, with the nuclear-nuclear spin interaction strength acting as the controlling small parameter.