Quantum gates using tunneling electron spins of a quantum-dot chain

Quantum gates using tunneling qubits: tunneling of electrons whose spins work as qubits is described by the Hamiltonian using both electron spins and pseudo-spins representing the photon-assisted tunneling. The phase factor during the controlled-NOT operation is also discussed. Preliminary data on a triple quantum dot system realized by closely stacking technique of molecular beam epitaxy are also shown.