Keyword | CPC | PCC | Volume | Score | Length of keyword |
---|---|---|---|---|---|

density matrix theory and applications | 1.18 | 0.7 | 1695 | 29 | 38 |

density | 1.3 | 0.4 | 1174 | 51 | 7 |

matrix | 1.88 | 0.3 | 5723 | 61 | 6 |

theory | 0.14 | 0.5 | 3775 | 50 | 6 |

and | 0.77 | 0.4 | 9618 | 98 | 3 |

applications | 1.34 | 0.5 | 4274 | 48 | 12 |

e In quantum mechanics, a density matrix is a matrix that describes the quantum state of a physical system. It allows for the calculation of the probabilities of the outcomes of any measurement performed upon this system, using the Born rule.

Some specific examples where density matrices are especially helpful and common are as follows: Statistical mechanics uses density matrices, most prominently to express the idea that a system is prepared at a nonzero temperature. Constructing a density matrix using a canonical ensemble gives a result of the form is the system's Hamiltonian.

The formalism of density operators and matrices was introduced in 1927 by John von Neumann and independently, but less systematically, by Lev Landau and later in 1946 by Felix Bloch. Von Neumann introduced the density matrix in order to develop both quantum statistical mechanics and a theory of quantum measurements.

The density matrix is the quantum-mechanical analogue to a phase-space probability measure (probability distribution of position and momentum) in classical statistical mechanics. Mixed states arise in situations where the experimenter does not know which particular states are being manipulated.