General Codes
In general, a quantum code for a quantum channel is a subspace, where is the state Hilbert space, such that there exists another quantum channel with

where is the orthogonal projection onto . Here is known as the correction operation.
Read more about this topic: Quantum Error Correction
Famous quotes containing the words general and/or codes:
“Of what use, however, is a general certainty that an insect will not walk with his head hindmost, when what you need to know is the play of inward stimulus that sends him hither and thither in a network of possible paths?”
—George Eliot [Mary Ann (or Marian)
“We must trust infinitely to the beneficent necessity which shines through all laws. Human nature expresses itself in them as characteristically as in statues, or songs, or railroads, and an abstract of the codes of nations would be an abstract of the common conscience.”
—Ralph Waldo Emerson (18031882)