Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot

TL;DR

This paper reports the first experimental observation of motional narrowing in the optical spectrum of semiconductor quantum dots, revealing a counterintuitive dependence on power and temperature that differs from traditional NMR behavior.

Contribution

It demonstrates motional narrowing in quantum dots' optical response and uncovers its unusual dependence on power and temperature, expanding understanding of decoherence in quantum systems.

Findings

Motional narrowing observed in quantum dot optical spectra.

Narrowing occurs when decreasing power or temperature, opposite to NMR expectations.

Implications for quantum information processing and decoherence control.

Abstract

Motional narrowing refers to the striking phenomenon where the resonance line of a system coupled to a reservoir becomes narrower when increasing the reservoir fluctuation. A textbook example is found in nuclear magnetic resonance, where the fluctuating local magnetic fields created by randomly oriented nuclear spins are averaged when the motion of the nuclei is thermally activated. The existence of a motional narrowing effect in the optical response of semiconductor quantum dots remains so far unexplored. This effect may be important in this instance since the decoherence dynamics is a central issue for the implementation of quantum information processing based on quantum dots. Here we report on the experimental evidence of motional narrowing in the optical spectrum of a semiconductor quantum dot broadened by the spectral diffusion phenomenon. Surprisingly, motional narrowing is achieved when decreasing incident power or temperature, in contrast with the standard phenomenology observed for nuclear magnetic resonance.