Quantum Devices

Quantum computers use quantum bits, or qubits-based electron/nuclear spin, which have been proven to process certain types of problems and information more effectively than a conventional digital computer. We have developed a novel nuclear magnetic resonance device system for the quantum manipulation of nuclear spins in a semiconductor channel. The operational mechanism of the device can be clarified as follow. It is known that semiconductor as GaAs has a zero-spin polarization at fermi level (Ef); numbers of up and down electron spins are equal. On the other hand, some ferromagnetic materials as half-metallic Heusler alloy (CoMnSi) are completely spin polarized at Ef. and are considered as a highly-spin source. Therefore, we use the advantage of ferromagnetic materials to polarize the electron spins in the deep width of a GaAs layer in the spin-transistors; by injecting a spin-polarized current from CoMnSi to a GaAs channel, a process called electrical spin injection of electron spins (1). By achieving high spin injection efficiency of electron spins, one can transfer the spin polarization to the nuclear spins as well through the hyperfine interaction between them, a process called dynamic nuclear spin polarization (2). Once the nuclear spins become spin polarized and well-aligned toward a certain direction, up or down spin states, we manipulate their spin state by application of radio frequency and nuclear magnetic resonance effect (4). We therefore perform Rabi oscillation and spin echo measurements, which are the basic units of realizing the quantum bits in quantum computing devices. The observed signals can be recorded by a back process to the injection one via the other ferromagnetic detecting electrodes, a process called electrical spin detection (5). The main advantage of our devices was achieving a long coherence time (320 μS) for data & signal processing.