Free induction decay of a superposition stored in a quantum dot

TL;DR

This paper investigates the free evolution of a superposition in a quantum dot, demonstrating hyperfine interaction effects analogous to NMR free induction decay, with implications for quantum information storage and entangled photon emission.

Contribution

It introduces a method to observe and model free induction decay in quantum dots by controlling the fine-structure splitting with an electric field.

Findings

Hyperfine interactions cause polarization decay in quantum dot superpositions.

Controlling the FSS reduces polarization decay, improving superposition stability.

Numerical models agree well with experimental results.

Abstract

We study the free evolution of a superposition initialized with high fidelity in the neutral-exciton state of a quantum dot. Readout of the state at later times is achieved by polarized photon detection, averaged over a large number of cycles. By controlling the fine-structure splitting (FSS) of the dot with a dc electric field, we show a reduction in the degree of polarization of the signal when the splitting is minimized. In analogy with the "free induction decay" observed in nuclear magnetic resonance, we attribute this to hyperfine interactions with nuclei in the semiconductor. We numerically model this effect and find good agreement with experimental studies. Our findings have implications for storage of superpositions in solid-state systems and for entangled photon pair emission protocols that require a small value of the FSS.