edoc: No conditions. Results ordered -Date Deposited. 2024-06-23T05:21:42ZEPrintshttps://edoc.unibas.ch/images/uni-logo.jpghttps://edoc.unibas.ch/2014-12-05T09:45:24Z2018-08-03T14:13:36Zhttps://edoc.unibas.ch/id/eprint/34878This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/348782014-12-05T09:45:24ZBoundary between the thermal and statistical polarization regimes in a nuclear spin ensembleAs the number of spins in an ensemble is reduced, the statistical fluctuations in its polarization eventually exceed the mean thermal polarization. This transition has now been surpassed in a number of recent nuclear magnetic resonance experiments, which achieve nanometer-scale detection volumes. Here, we measure nanometer-scale ensembles of nuclear spins in a KPF6 sample using magnetic resonance force microscopy. In particular, we investigate the transition between regimes dominated by thermal and statistical nuclear polarization. The ratio between the two types of polarization provides a measure of the number of spins in the detected ensemble. B. E. HerzogD. CadedduF. XueP. PeddibhotlaM. Poggio2013-10-25T08:33:13Z2018-08-03T13:35:26Zhttps://edoc.unibas.ch/id/eprint/29583This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/295832013-10-25T08:33:13ZHarnessing nuclear spin polarization fluctuations in a semiconductor nanowireSoon after the first measurements of nuclear magnetic resonance in a condensed-matter system, Bloch1 predicted the presence of statistical fluctuations proportional to in the polarization of an ensemble of N spins. Such spin noise2 has recently emerged as a critical ingredient for nanometre-scale magnetic resonance imaging3,4,5,6. 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. P. PeddbhotlaF. XueH. I. T. HaugeS. AssaliE. P. A. M. BakkersM. Poggio2013-07-16T09:18:55Z2018-01-22T15:51:44Zhttps://edoc.unibas.ch/id/eprint/27821This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/278212013-07-16T09:18:55ZMagnetic resonance force microscopy : harnessing nuclear spin fluctuationsOver the past few years, a wide variety of nuclear spin preparation techniques using hyperfine interaction-mediated dynamics have been developed in systems including gate-defined double quantum dots, self-assembled single quantum dots and nitrogen-vacancy centers in diamond. Here, we present a novel approach to nuclear spin state preparation by harnessing the naturally occuring stochastic fluctuations in nanoscale ensembles of nuclear spins in a semiconductor nanowire. Taking advantage of the excellent sensitivity of magnetic resonance force microscopy (MRFM) to monitor the statistical polarization fluctuations in samples containing very few nuclear spins, we develop real-time spin manipulation protocols that allow us to measure and control the spin fluctuations in the rotating frame. We focus on phosphorus and hydrogen nuclear spins associated with an InP and a GaP nanowire and their hydrogen-containing adsorbate layers. The weak magnetic moments of these spins can be detected with high spatial resolution using the outstanding sensitivty of MRFM. Recently, MRFM has been used to image the proton spin density in a tobacco mosaic virus with a sensitivity reaching up to 100 net polarized spins. We describe how MRFM together with real-time radio frequency (RF) control techniques can also be used for the hyperpolarization, narrowing and storage of nuclear spin fluctuations and discuss how such nuclear spin states could potentially be harnessed for applications in magnetic resonance and quantum information processing. In addition to presenting the experimental results on nuclear spin order, the theory of nuclear spin resonance and nanomechanical resonators is briefy discussed. The physical concepts explained provide the necessary background for the understanding of our MRFM experiments. The MRFM experimental apparatus, both sample-on- cantilever and magnet-on-cantilever, is also presented in considerable detail. Phani Kumar Peddibhotla2013-03-01T11:12:54Z2018-07-27T14:48:45Zhttps://edoc.unibas.ch/id/eprint/25178This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/251782013-03-01T11:12:54ZFeedback cooling of cantilever motion using a quantum point contact transducerWe use a quantum point contact (QPC) as a displacement transducer to measure and control the low-temperature thermal motion of a nearby micromechanical cantilever. The QPC is included in an active feedback loop designed to cool the cantilever's fundamental mechanical mode, achieving a squashing of the QPC noise at high gain. The minimum achieved effective mode temperature of 0.2 K and the displacement resolution of 10−11 m/Hz⎯⎯⎯⎯⎯√ are limited by the performance of the QPC as a one-dimensional conductor and by the cantilever-QPC capacitive coupling. M. MontinaroA. MehlinH. S. SolankiP. PeddibhotlaS. MackD. D. AwschalomM. Poggio2013-02-01T08:44:51Z2018-07-27T14:43:17Zhttps://edoc.unibas.ch/id/eprint/24410This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/244102013-02-01T08:44:51ZMeasurement of statistical nuclear spin polarization in a nanoscale GaAs sampleWe measure the statistical polarization of quadrupolar nuclear spins in a submicrometer (0.6μm3) particle of GaAs using magnetic resonance force microscopy. The crystalline sample is cut out of a GaAs wafer and attached to a micromechanical cantilever force sensor using a focused ion beam technique. Nuclear magnetic resonance is demonstrated on ensembles containing less than 5×108 nuclear spins and occupying a volume of around (300nm)3 in GaAs with reduced volumes possible in future experiments. We discuss how the further reduction of this detection volume will bring the spin ensembles into a regime where random spin fluctuations, rather than Boltzmann polarization, dominate their dynamics. The detection of statistical polarization in GaAs therefore represents an important first step toward 3D magnetic resonance imaging of III-V structures on the nanometer scale. F. XueD. P. WeberP. PeddibhotlaM. Poggio2013-02-01T08:44:49Z2018-07-27T14:38:27Zhttps://edoc.unibas.ch/id/eprint/24406This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/244062013-02-01T08:44:49ZA geometry for optimizing nanoscale magnetic resonance force microscopyWe implement magnetic resonance force microscopy (MRFM) in an experimental geometry, where the long axis of the cantilever is normal to both the external magnetic field and the rf microwire source. Measurements are made of the statistical polarization of H1 in polystyrene with negligible magnetic dissipation, gradients greater than 105 T/m within 100 nm of the magnetic tip, and rotating rf magnetic fields over 12 mT at 115 MHz. This geometry could facilitate the application of nanometer-scale MRFM to nuclear species with low gyromagnetic ratios and samples with broadened resonances, such as In spins in quantum dots. F. XueP. PeddibhotlaM. MontinaroD. P. WeberM. Poggio