Nuclear State Preparation via Landau-Zener-Stueckelberg transitions in Double Quantum Dots

TL;DR

This paper models a nuclear-state preparation method in double quantum dots using Landau-Zener-Stueckelberg transitions, which enhances electron spin coherence by nuclear-state narrowing, supported by simulations up to 200 nuclear spins.

Contribution

It introduces a theoretical model for nuclear-state preparation that explains experimental observations and predicts stronger effects with larger nuclear spin systems.

Findings

Weak nuclear polarization minimally affects electron coherence.

Partial adiabaticity during slow sweeps causes nuclear-state narrowing.

Simulation shows increased effect with more nuclear spins.

Abstract

We theoretically model a nuclear-state preparation scheme that increases the coherence time of a two-spin qubit in a double quantum dot. The two-electron system is tuned repeatedly across a singlet-triplet level-anticrossing with alternating slow and rapid sweeps of an external bias voltage. Using a Landau-Zener-Stueckelberg model, we find that in addition to a small nuclear polarization that weakly affects the electron spin coherence, the slow sweeps are only partially adiabatic and lead to a weak nuclear spin measurement and a nuclear-state narrowing which prolongs the electron spin coherence. This resolves some open problems brought up by a recent experiment [D. J. Reilly et al., Science 321, 817 (2008).]. Based on our description of the weak measurement, we simulate a system with up to n=200 nuclear spins per dot. Scaling in n indicates a stronger effect for larger n.