Bloch Sphere and Single-Qubit Arbitrary Unitary Gate

In this chapter, we will first introduce the Bloch sphere and discuss its physical meaning for the electron spin qubit case. After that, we will introduce the single-qubit arbitrary unitary gate, \(\boldsymbol {U_{\theta ,\phi ,\lambda }}\) . This will be very useful to understand the quantum phase estimation (QPE) to be introduced in the next chapter.