---
title: noise (latest version)
description: API reference for qiskit_mitigation.noise in the latest version of qiskit-mitigation
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-mitigation/noise
---

# Noise

`qiskit_mitigation.noise`

Functionality for specifying and transforming quantum noise.

### create\_postselected\_noise\_mask

`create_postselected_noise_mask(noisy_circuit, noise_maps, detectors)`

[GitHub](https://github.com/Qiskit/qiskit-mitigation/tree/stable/0.1/qiskit_mitigation/noise.py#L47-L108)

Identify generators in `noise_maps` that anticommute with one or more `detectors`.

Each detector, given as a Pauli operator at the end of `noisy_circuit` is evolved backward through the circuit. At each [`InjectNoise`](https://qiskit.github.io/samplomatic/api/auto/samplomatic.InjectNoise.html#samplomatic.InjectNoise "(in samplomatic)") site, a generator that anticommutes with some evolved detector gets scale `0`; a surviving generator gets `1`.

**Parameters**

- **noisy\_circuit** ([*QuantumCircuit*](/docs/api/qiskit/qiskit.circuit.QuantumCircuit)) – A circuit of box instructions. Box instructions may contain Clifford instructions, and any non-Clifford instructions they contain must commute with all `detectors`. `InjectNoise` annotations should be used to denote noisy layers in the circuit, and each `InjectNoise` reference ID should be a key in `noise_maps`.
- **detectors** ([*PauliList*](/docs/api/qiskit/qiskit.quantum_info.PauliList)  *|*[*Sequence*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Sequence)*\[*[*Pauli*](/docs/api/qiskit/qiskit.quantum_info.Pauli)  *|*[*str*](https://docs.python.org/3/builtins/stdtypes.html#str)*]*) – Pauli detectors defined at the end of `noisy_circuit` on all qubits.
- **noise\_maps** ([*dict*](https://docs.python.org/3/builtins/stdtypes.html#dict)*\[*[*str*](https://docs.python.org/3/builtins/stdtypes.html#str)*,* [*PauliLindbladMap*](/docs/api/qiskit/qiskit.quantum_info.PauliLindbladMap)*]*) – A mapping from each unique `InjectNoise` reference ID to the Pauli-Lindblad noise associated with that circuit layer.

**Returns**

- A `dict` mapping each noisy box’s `InjectNoise.modifier_ref` to a `0`/`1` array aligned with that box’s `noise_maps` generators, ready to use as samplomatic `local_scales`
- The sampling cost $\gamma^2 = e^{(4 \sum \lambda \cdot \text{mask})}$ of inverting only the surviving generators with PEC.

**Return type**

[tuple](https://docs.python.org/3/builtins/stdtypes.html#tuple)\[[dict](https://docs.python.org/3/builtins/stdtypes.html#dict)\[[str](https://docs.python.org/3/builtins/stdtypes.html#str), [*ndarray*](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.html#numpy.ndarray)], [float](https://docs.python.org/3/builtins/functions.html#float)]