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A qubit (comes from: quantum bit) is the quantum mechanical version of a bit, and has two basic states, ket 0 and ket 1. You write it as

|0⟩  and  |1⟩



That looks a lot like the numbers 0 and 1, which you can store in a bit. A bit has a value of 0 or 1 but not both values simultaneously.

A qubit is a unit of quantum information. Superposition enables multiple qubits to express different strings. So can e.g. four qubits have the value 1010 as well as the value 1101.

In a quantum byte (8 qubits) you can store 256 strings, which you then can read out again separately due to their entanglement.



A graphical representation of a qubit results in a Bloch sphere.


Besides the states {|0⟩, |1⟩}, general states of the type {|ψ⟩} are also possible. A qubit can be presented as a linear combination of the two basic states

|ψ⟩ = α |0⟩ + β |1⟩

where α and β are complex probability amplitudes. The probability that a qubit has status |0⟩ t is |α|2 and that it has status |1⟩ is |β|2, because

|α|2 + |β|2 = 1



The Dutch physicisr Leo Kouwenhoven uses the majorana particle to make a qubit. Warning: The article on this subject in the science journal Nature was withdrawn in 2021.

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