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Qubit
This article is about the quantum computing unit.
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Unsolved problem in physics:
Is it possible to have three-dimensional, self-correcting, quantum memory?
(more unsolved problems in physics)
In quantum computing, a qubit or quantum bit (sometimes qbit) is the basic unit of quantum information — the quantum version of the classical binary bit physically realized with a two-state device.
A qubit is a two-state (or two-level) quantum-mechanical system, one of the simplest quantum systems
displaying the weirdness of quantum mechanics. Examples include: the
spin of the electron in which the two levels can be taken as spin up and spin down; or the polarization of a single photon in which the two states can be taken to be the vertical polarization and the horizontal polarization.
In a classical system, a bit would have to be in one state or the other. However, quantum mechanics allows the qubit to be in a coherent superposition of both states/levels at the same time, a property that is fundamental to quantum mechanics and thus quantum computing.
Origin of the name
The coining of the term “qubit” is attributed to Benjamin Schumacher.[1] In the acknowledgments of his 1995 paper, Schumacher states that the term qubit was invented in jest during a conversation with William Wootters.
The paper describes a way of compressing states emitted by a quantum source of information so that they require fewer physical resources to store. This procedure is now known as Schumacher
compression.Bit versus qubit
A binary digit, characterized as 0 and 1, is used to represent information in classical computers. A binary digit can represent up to one bit of Shannon information, where a bit is the basic unit of information. However, in this article, the word bit is synonymous with binary digit.
In classical computer technologies, a processed bit is implemented by one of two levels of low DC voltage, and whilst switching from one of these two levels to the other, a so-called
forbidden zone must be passed as fast as possible, as electrical voltage cannot change from one level to another instantaneously.
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