Bloch sphere model for understanding quantum computers

To learn the basics of quantum computers, it is necessary to understand qubits and quantum logic gates. At first, it is a little difficult to envision their properties and actions.

A qubit is a vector in three-dimensional space, but that vector actually connects the origin and the spherical surface of a sphere with a radius of 1. A spherical surface is a two-dimensional space. Therefore, the state vector of a qubit is represented by two variables, amplitude θ and phase φ.

It would be nice to display it with computer graphics and understand it, but it is still easier to understand by creating a physical sphere and touching it.

Now we have created four Bloch sphere models to represent the state vector of the qubit. It is shown in the figure below. The functions of Pauli X gate and Hadamard gate can also be imagined.