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Bit (binary)
Nat (base e)
Ban (decimal)
Qubit (quantum)

In quantum computing, a qubit (pronounced /ˈkjuːbɪt/) or quantum bit is a unit of quantum information —the quantum analogue of the classical bit —with additional dimensions associated to the quantum properties of a physical atom. The physical construction of a quantum computer is itself an arrangement of entangled[clarification needed] atoms, and the qubit represents[clarification needed] both the state memory and the state of entanglement in a system. A quantum computation is performed by initializing a system of qubits with a quantum algorithm —"initialization" here referring to some advanced physical process that puts the system into an entangled state.[citation needed]

The qubit is described by a quantum state in a two-state quantum-mechanical system, which is formally equivalent to a two-dimensional vector space over the complex numbers. One example of a two-state quantum system is the polarization of a single photon: here the two states are vertical polarisation and horizontal polarisation. In a classical system, a bit would have to be in one state or the other, but quantum mechanics allows the qubit to be in a superposition of both states at the same time, a property which is fundamental to quantum computing.


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