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The general definition of a qubit as the quantum state of a two-level quantum system.In quantum computing, a qubit (/ ˈ k juː b ɪ t /) or quantum bit is a basic unit of quantum information—the quantum version of the classic binary bit physically realized with a two-state device.
[1] [2] A logical qubit is a physical or abstract qubit that performs as specified in a quantum algorithm or quantum circuit [3] subject to unitary transformations, has a long enough coherence time to be usable by quantum logic gates (c.f. propagation delay for classical logic gates). [1] [4] [5]
The purpose of quantum computing focuses on building an information theory with the features of quantum mechanics: instead of encoding a binary unit of information (), which can be switched to 1 or 0, a quantum binary unit of information (qubit) can simultaneously turn to be 0 and 1 at the same time, thanks to the phenomenon called superposition.
Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10 −6 metre).
The kayser (K) is a unit of wavenumber equal to 1 cm −1 (100 m −1). The gal (Gal) is a unit of acceleration equal to 1 cm/s 2. [3] The dyne (dyn) is a unit of force equal to 1 g⋅cm⋅s −2 (10 μN). [3] The barye (Ba) is a unit of pressure equal to 1 dyn⋅cm −2 (100 mPa). The erg (erg) is a unit of energy equal to 1 dyn⋅cm (100 nJ). [3]
This may seem to be "setting the constants c, G, etc., to 1" if the correspondence of the quantities is thought of as equality. For this reason, Planck or other natural units should be employed with care. Referring to "G = c = 1", Paul S. Wesson wrote that, "Mathematically it is an acceptable trick which saves labour. Physically it represents a ...
By moving the measurement to the end, the 2-qubit controlled-X and -Z gates need to be applied, which requires both qubits to be near (i.e. at a distance where 2-qubit quantum effects can be controlled), and thus limits the distance of the teleportion. While logically equivalent, deferring the measurement have physical implications.
1 ebit + 2 bits 1 qubit (i.e. quantum teleportation), where ⩾ {\displaystyle \geqslant } indicates "can do the job of". These principles were formulated around 1993 by Charles H. Bennett .