Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire

Ensembles of nuclear spins display thermal fluctuations—spin noise—that interfere with nuclear magnetic resonance measurements of samples below a threshold size. Experiments on nanowires show that by monitoring spin noise in real time and applying instantaneously adjusted radiofrequency pulses, spin polarization distributions that are narrower than the thermal distribution can be obtained. Soon after the first measurements of nuclear magnetic resonance in a condensed-matter system, Bloch 1 predicted the presence of statistical fluctuations proportional to 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 , 4 , 5 , 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.