The More You Know: Qubit

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 $|1\rangle$ , $|0\rangle$ but also in any superposition of these two. That is, the state $|\psi\rangle$ of a Qubit will be of the form

$|\psi\rangle=\alpha|0\rangle + \beta|1\rangle$ ,

where $\alpha$ and $\beta$ are complex number satisfying

$|\alpha|^2+|\beta|^2=1$ .

The states $|1\rangle$ and $|0\rangle$ form the so-called computational basis $\{|1\rangle,|0\rangle\}$ . Then, as a mathematical concept, a Qubit is a vector normalized to length 1 in a $2D$ 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.

Go to the Dictionary of Quantum Information and Quantum Computation.

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.

About marcocerezo

I'm Marco Cerezo, I have a Ph.D in Physics and I'm currently a Postdoctoral Research Associate at Los Alamos National Laboratory in New Mexico, USA. My main fields of study are Quantum Information, Quantum Computing and Condensed Matter. Currently I'm working to develop novel quantum algorithms which can be useful in near-term quantum devices.

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