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.
Quantum circuit
For quantum circuits a similar composition of qubit gates can be defined. That is, associated to any "classical assemblage" as above, we can produce a reversible quantum circuit when in place of "f" we have an "n"-qubit gate "U" and in place of "g" we have an "m"-qubit gate "W". See illustration below: