# cirq.depolarize

Returns a DepolarizingChannel with given probability of error.

### Used in the notebooks

Used in the tutorials

This channel applies one of 4n disjoint possibilities: nothing (the identity channel) or one of the 4n - 1 pauli gates. The disjoint probabilities of the non-identity Pauli gates are all the same, p / (4**n - 1), and the identity is done with probability 1 - p. The supplied probability must be a valid probability or else this constructor will raise a ValueError.

This channel evolves a density matrix via

$$\rho \rightarrow (1 - p) \rho + p / (4**n - 1) \sum _i P_i \rho P_i$$


where $$P_i$$ are the $$4^n - 1$$ Pauli gates (excluding the identity).

p The probability that one of the Pauli gates is applied. Each of the Pauli gates is applied independently with probability p / (4**n - 1).
n_qubits The number of qubits.

ValueError if p is not a valid probability.

[{ "type": "thumb-down", "id": "missingTheInformationINeed", "label":"Missing the information I need" },{ "type": "thumb-down", "id": "tooComplicatedTooManySteps", "label":"Too complicated / too many steps" },{ "type": "thumb-down", "id": "outOfDate", "label":"Out of date" },{ "type": "thumb-down", "id": "samplesCodeIssue", "label":"Samples / code issue" },{ "type": "thumb-down", "id": "otherDown", "label":"Other" }]
[{ "type": "thumb-up", "id": "easyToUnderstand", "label":"Easy to understand" },{ "type": "thumb-up", "id": "solvedMyProblem", "label":"Solved my problem" },{ "type": "thumb-up", "id": "otherUp", "label":"Other" }]