Two-laser dynamic nuclear polarization with semiconductor electrons: Feedback, suppressed fluctuations, and bistability near two-photon resonance

Abstract

We present how optical coherent population trapping (CPT) of the spin of localized semiconductor electrons stabilizes the surrounding nuclear spin bath via the hyperfine interaction, resulting in a state which is more ordered than the thermal equilibrium state. We find distinct control regimes for different signs of laser detuning and examine the transition from an unpolarized, narrowed state to a polarized state possessing a bistability. The narrowing of the state yields slower electron spin dephasing and self-improving CPT. Our analysis is relevant for a variety of solid state systems where hyperfine-induced dephasing is a limitation for using electron spin coherence. arXiv:1409.7576v2 [cond-mat.mes-hall]

Direct high-resolution resonant Raman scattering measurements of dynamic nuclear spin polarization states of an InAs quantum dot

“…We show directly that negative and positive feedback loops acting on the OH field are associated with dynamic optical excitation of the |x− and |x+ electron spin states, respectively. With unprecedented spectral resolution, our experimental findings confirm and expand upon previous theoretical work [14,15,40] showing that these nonlinear feedback loops in the electron-trion system can be manipulated by optical excitation in order to tune the NSP in a single QD down to the sub-100 nuclear spin level.…”

“…The implications of these findings regarding the OH field distributions are significant. First, instability points have been predicted theoretically to result from the nonlinear feedback loop between the OH field acting on the electron and the electron polarization and/or trion populations acting on the nuclei, which are tuned by the scanning excitation laser; these instability points can correspond to points of increased OH field distribution width [14,15,40]. At these points, there is an amplification, or increase, of the fluctuations of the OH field; we have confirmed these predictions here experimentally in the case of dynamic optical excitation (scanning the excitation laser) of the |x+ electron spin state.…”

Improving a Solid-State Qubit through an Engineered Mesoscopic Environment

“…In contrast to other systems, the polarisation of this isolated mesoscopic ensemble can persist for hours [13]. Coupling the electronic energy shifts to the optical pumping rate closes a feedback loop [14][15][16][17] that allows for selection of the degree of nuclear spin polarisation.A spectrally sharp version of such stabilizing feedback is achieved through coherent population trapping (CPT), when driving the Λ system formed by the two electron spin states and an excited trion state of a negatively charged QD [6,18,19], as depicted in Fig. 1a.…”

“…A spectrally sharp version of such stabilizing feedback is achieved through coherent population trapping (CPT), when driving the Λ system formed by the two electron spin states and an excited trion state of a negatively charged QD [6,18,19], as depicted in Fig. 1a.…”

“…2b-f). This model captures the effect of CPT on the electron spin polarisation, which in turn affects the average nuclear spin polarisation, causing an evolution of P (δ n ) under the Fokker-Planck formalism [18,23,31]. The feedback on the probability distribution is governed by the time derivative of the Overhauser field,…”