  We have developed semiconductor point contact devices in which nuclear spins
in a nanoscale region are coherently controlled by all-electrical methods.
Different from the standard nuclear-magnetic resonance technique, the
longitudinal magnetization of nuclear spins is directly detected by measuring
resistance, resulting in ultra-sensitive detection of the microscopic quantity
of nuclear spins. All possible coherent oscillations have been successfully
demonstrated between two levels from four nuclear spin states of I = 3/2
nuclei. Quantum information processing is discussed based on two fictitious
qubits of an I = 3/2 system and methods are described for performing arbitrary
logical gates both on one and two qubits. A scheme for quantum state tomography
based on Mz-detection is also proposed. As the starting point of quantum
manipulations, we have experimentally prepared the effective pure states for
the I = 3/2 nuclear spin system.
