Dynamical cooling of nuclear spins in double quantum dots

Abstract

Electrons trapped in quantum dots can exhibit quantum-coherent spin dynamics over longtimescales. These timescales are limited by the coupling of electron spins to the disorderednuclear spin background, which is a major source of noise and dephasing in suchsystems. We propose a scheme for controlling and suppressing fluctuations of nuclearspin polarization in double quantum dots, which uses nuclear spin pumping inthe spin-blockade regime. We show that nuclear spin polarization fluctuationscan be suppressed when electronic levels in the two dots are properly positionednear resonance. The proposed mechanism is analogous to that of optical Dopplercooling. The Overhauser shift due to fluctuations of nuclear polarization bringselectron levels in and out of resonance, creating internal feedback to suppressfluctuations. Estimates indicate that a better than 10-fold reduction of fluctuations ispossible.