Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire

TL;DR

This paper demonstrates a technique to harness and control nuclear spin polarization fluctuations in nanowire ensembles, enabling enhanced and narrowed spin polarization for improved nanoMRI and quantum information applications.

Contribution

The authors introduce a method to create and control spin order by exploiting statistical fluctuations in nanometer-scale nuclear spin ensembles, surpassing natural thermal polarization limits.

Findings

Achieved real-time monitoring and control of spin fluctuations.

Extended storage of polarization fluctuations.

Potential for enhanced nanoMRI signals and quantum initialization.

Abstract

Soon after the first measurements of nuclear magnetic resonance (NMR) in a condensed matter system, Bloch predicted the presence of statistical fluctuations proportional to $1/\sqrt{N}$ in the polarization of an ensemble of $N$ spins. First observed by Sleator et al., so-called "spin noise" has recently emerged as a critical ingredient in nanometer-scale magnetic resonance imaging (nanoMRI). This prominence is a direct result of MRI resolution improving to better than 100 nm^3, a size-scale in which statistical spin fluctuations begin to dominate the polarization dynamics. We demonstrate a technique that creates spin order in nanometer-scale ensembles of nuclear spins by harnessing these fluctuations to produce polarizations both larger and narrower than the natural thermal distribution. We focus on ensembles containing ~10^6 phosphorus and hydrogen spins associated with single InP and GaP nanowires (NWs) and their hydrogen-containing adsorbate layers. We monitor, control, and capture fluctuations in the ensemble's spin polarization in real-time and store them for extended periods. This selective capture of large polarization fluctuations may provide a route for enhancing the weak magnetic signals produced by nanometer-scale volumes of nuclear spins. The scheme may also prove useful for initializing the nuclear hyperfine field of electron spin qubits in the solid-state.