Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire

Soon after the first measurements of nuclear magnetic resonance in a condensed-matter system, Bloch(1) predicted the presence of statistical fluctuations proportional to 1/root N in the polarization of an ensemble of N spins. Such spin noise(2) has recently emerged as a critical ingredient for nanometre-scale magnetic resonance imaging(3-6). This prominence is a consequence of present magnetic resonance imaging resolutions having reached less than (100 nm)(3), a size scale at which statistical spin fluctuations begin to dominate the polarization dynamics. Here, we demonstrate a technique that creates spin order in nanometre-scale ensembles of nuclear spins by harnessing these fluctuations to produce polarizations both larger and narrower than the thermal distribution. This method may provide a route to enhancing the weak magnetic signals produced by nanometre-scale volumes of nuclear spins or a way of initializing the nuclear hyperfine field of electron-spin qubits in the solid state.