A Qubit, or quantum bit is the fundamental unit of quantum information, it is a mathematical concept satisfying particular properties. The Qubit is the quantum counterpart of the classical bit.
A classical bit can be in one of two different states: 0 or 1, whereas a Qubit can be in the quantum states , but also in any superposition of these two. That is, the state of a Qubit will be of the form
where and are complex number satisfying
The states and form the so-called computational basis . Then, as a mathematical concept, a Qubit is a vector normalized to length 1 in a complex vector field.
Just as it’s classical analogue, a Qubit can have many physical realizations: The polarization of a photon, the spin of an electron or a nucleus, the localization of a charge, among other two-state quantum systems.
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The More You Know: Qubit by Marco Vinicio Sebastian Cerezo de la Roca is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.