Bra–ket notation or Dirac notation is a notation for linear algebra and linear operators on complex vector spaces together with their dual spaces both in the finite- and infinite-dimensional cases. It is specifically designed to ease the types of calculations that frequently arise in quantum mechanics. It is now of ubiquitous usage in that subject. Bra–ket notation was created by Paul Dirac in his paper, "A New Notation for Quantum Mechanics" from 1939. The name comes from the English word brack...
