Nuclear Feedback in a Single Electron-Charged Quantum Dot under Pulsed Optical Control

TL;DR

This paper demonstrates a feedback process between nuclear spins and a single electron spin in a quantum dot, revealing complex behaviors and enabling dynamic tuning of electron spin properties through optical control.

Contribution

It introduces a mathematical model capturing the feedback dynamics and experimentally confirms novel phenomena like hysteresis and non-sinusoidal spin fringes in a quantum dot system.

Findings

Observation of hysteretic sawtooth pattern in spin decay

Detection of hysteresis during laser frequency scans

Identification of non-sinusoidal fringes in spin echo signals

Abstract

Electron spins in quantum dots under coherent control exhibit a number of novel feedback processes. Here, we present experimental and theoretical evidence of a feedback process between nuclear spins and a single electron spin in a single charged InAs quantum dot, controlled by the coherently modified probability of exciting a trion state. We present a mathematical model describing competition between optical nuclear pumping and nuclear spin-diffusion inside the quantum dot. The model correctly postdicts the observation of a hysteretic sawtooth pattern in the free-induction-decay of the single electron spin, hysteresis while scanning a narrowband laser through the quantum dot's optical resonance frequency, and non-sinusoidal fringes in the spin echo. Both the coherent electron-spin rotations, implemented with off-resonant ultrafast laser pulses, and the resonant narrow-band optical pumping for spin initialization interspersed between ultrafast pulses, play a role in the observed behavior. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.