In quantum mechanics, a qubit is a two-level quantum system. These two quantum state could be spin up and spin down, herein denoted by the 0 and 1 kets. The quantum mechanical state can be in a superposition of 0 and 1. The Bloch sphere is a geometrical representation of the quantum state of a qubit. It is a unit sphere with the north pole representing the 0 state and the south pole representing the 1 state. The Bloch sphere provides a powerful visualization of the state of a qubit and is a powerful tool for understanding quantum mechanics and quantum computing. In this video, we will discuss the Bloch sphere representation and show how it can be used to visualize the state of a qubit and to perform calculations. 

In this video, we will investigate the Bloch sphere. This is a geometrical representation of a quantum state in a two-level system, named after the Swiss physicist Felix Bloch. Being a two-level system means that we can have two basis states, so this is for example what a single qubit represents, which is in a superposition of 0 and 1. Another example could be a spin-1/2 particle, which is in a superposition of spin-up and spin-down.