In the previous chapter, we implemented a physical system to perform a phase-shift gate of arbitrary phase for an electron spin qubit. It is constructed by placing the electron spin qubit in a constant external magnetic field in the vertical direction, \(\vec {B}=-B_0\hat {z}\) with \(B_0>0\) . This is a field pointing downward in the real 3D space. It causes Larmor precession of the qubit on the Bloch sphere rotating clockwise looking from the top. In this chapter, we will further apply a small oscillating magnetic field in the \(\hat {x}\) direction to enable the rotation of the qubit about the \(y-axis\) . This is called Rabi oscillation. With this tool, we will be able to rotate a spin qubit from and to any point on the Bloch sphere and thus implement an arbitrary 1-qubit gate.