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Quantum Mechanics
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What is a qubit (quantum bit)?
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from https://www.techtarget.com/whatis/definition/qubit
A qubit (short for quantum bit) is the basic unit of information in quantum computing and counterpart to the bit (binary digit) in classical computing. A qubit plays a similar role as a bit, in terms of storing information, but it behaves much differently because of the quantum properties on which it's based.
In a quantum computer, a number of elemental particles such as electrons or photons can be used (in practice, success has also been achieved with ions), with either their charge or polarization acting as a representation of 0 and/or 1. Each of these particles is known as a qubit; the nature and behavior of these particles (as expressed in quantum theory) form the basis of quantum computing. Two of the most relevant aspects of quantum physics are the principles of superposition and entanglement.
from https://learn.microsoft.com/en-us/azure/quantum/concepts-the-qubit
Just as bits are the fundamental object of information in classical computing, qubits (quantum bits) are the fundamental object of information in quantum computing. To understand this correspondence, this article looks at the simplest example: a single qubit.
While a bit, or binary digit, can have a value either 0 or 1, a qubit can have a value that is either 0, 1 or a quantum superposition of 0 and 1
The state of a single qubit can be described by a two-dimensional column vector of unit norm, that is, the magnitude squared of its entries must sum to 1. This vector, called the quantum state vector, holds all the information needed to describe the one-qubit quantum system just as a single bit holds all of the information needed to describe the state of a binary variable.
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