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We demonstrate initialization of nuclear spin qubits using a resistively-detected nuclear magnetic resonance (NMR) device. In our device, nuclear spins are dynamically polarized in a sub-micron scale region defined by split gates. The population of each nuclear spin state is estimated from a resistively-detected NMR spectrum combined with numerical analysis. By applying radio frequency pulses to the polarized nuclear spins, we create two-qubit effective pure states, which is a crucial step toward NMR quantum computation. We also demonstrate simple logic gate operations such as controlled-NOT and SWAP gates in this two-qubit system. The obtained spectra are consistent with numerically calculated ones. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We study the nuclear quadrupolar interaction using a resistively-detected NMR device. The nuclear spins are dynamically polarized in a sub-micron scale region defined by split gates. In pulsed NMR spectra for 69Ga and 75As nuclei, three distinct peaks are observed. The peak splitting depends on the electric quadrupolar coupling constant EQ. By comparing the spectra of both nuclei, we find that the relative peak intensity is opposite, which is independent of the condition for the dynamic nuclear spin polarization. This result indicates that the electric-field gradient in EQ has opposite sign at 69Ga and 75As nuclear site. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Manipulations of electron spin and nuclear spin have been studied in AlGaAs/GaAs semiconductor nanosystems. Non-local manipulation of electron spins has been realized by using the correlation effect between localized and mobile electron spins in a quantum dot- quantum wire coupled system. Interaction between electron and nuclear spins was exploited to achieve a coherent control of nuclear spins in a semiconductor point contact device. Using this device, we have demonstrated a fully coherent manipulation of any two states among the four spin levels of Ga and As nuclei. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The scattering of carriers in a two-dimensional electron gas (2DEG) in a series of novel GaAs/ n-AlGaAs heterojunctions is studied for the case where InAlAs anti-dots are embedded near the channel. Mobilities μ are measured as functions of the electron concentrations N e and are compared with theoretical models which take into account the shape and distribution of anti-dots. In samples with low dot densities, mobilities are well explained in terms of the scattering by anti-dots with a random distribution. In contrast, in samples with dense and overlapping dots and a thick wetting layer, a roughness-like potential with Gaussian-type correlation is shown to account for the data. Influences of growth conditions and the alloy composition on the diameter and the density of InAlAs dots are also discussed.