What is Quantum Computing? (Part 1)

In the classical computing, information is stored and processed in term of bits. A bit has 2 states: 0 or 1.

In the Quantum Computing (QC), information is stored and processed in Quantum Bit called “Qubit”. A qubit can be 1 or 0, However, because of the quantum property, a qubit can also be a superposition of states, which is represented as the linear combination of states. Therefore, a qubit has infinite number of states.

In QC, we use linear algebra to represent and process the qubit. By definition, a qubit is a state vector in the 2-Dimenional complex Hibert space.

For visualization, the state vector can be viewed as a vector that begins at the origin and terminates on the surface of the unit sphere, called the Bloch Sphere.

Any operation on the state vector will result another vector in the Bloch sphere, i.e. moving the vector around the Bloch sphere.

For example, applying NOT operation to the state |0>, we will have |1>, which is a flip on the direction from the upward antipode to the downward antipode.

The superposition of |0> and |1> = (|0>+|1>)/sqrt(2), can be represented as the vector along the horizontal X-axis.