Algorithmic cooling
A qubit (or quantum bit) is a unit of information that can be in a superposition of two states, denoted as formula_1 and formula_2. The general superposition can be written as formula_3where formula_4 and formula_5. If one measures the state of the qubit in the orthonormal basis composed of formula_1 and formula_2, one gets the result formula_1 with probability formula_9 and the result formula_2 with probability formula_11.
Qubit field theory
In many ordinary quantum field theories, constraining one observable to a fixed value results in the uncertainty of the other observable being infinite (c.f. uncertainty principle), and as a consequence there is potentially an infinite amount of information involved. In the situation of the standard position-momentum commutation (where the uncertainty principle is most commonly cited), this implies that a fixed, finite, volume of space has an infinite capacity to store information. However, Bekenstein's bound hints that the information storage capacity ought to be finite. Qubit field theory seeks to resolve this issue by removing the commutation restriction, allowing the capacity to store information to be finite; hence the name qubit, which derives from quantum-bit or quantised-bit.