Dynamic nuclear polarization using a single pair of electrons

TL;DR

This paper demonstrates dynamic nuclear polarization in a GaAs double quantum dot system using a single pair of electrons, revealing a novel dependence on nuclear Larmor precession and effective nuclear cooling.

Contribution

It introduces a method for nuclear polarization using a single electron pair without reservoir exchange, highlighting a new pulsing protocol aligned with nuclear precession.

Findings

Polarization builds up at the singlet-triplet degeneracy point.

Maximum efficiency occurs when the duty cycle matches nuclear Larmor precession.

Nuclear polarization results in cooling of the nuclear spin system.

Abstract

We observe dynamic nuclear polarization in a GaAs double dot system using two electrons that are never exchanged with the reservoir. By periodically bringing the system to the mixing point where the singlet and the triplet T+ states are degenerate, we observe that an excess polarization is built up. Surprisingly, the pumping procedure is most effective when the total duty cycle equals a multiple of the Larmor precession time of the Ga and As nuclei. The induced polarization corresponds to cooling of the underlying nuclear system. The dependence on the dwell time at the mixing point is found to be non-monotonic.