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---
title: ReadoutError
description: API reference for qiskit.providers.aer.noise.ReadoutError
in_page_toc_min_heading_level: 1
python_api_type: class
python_api_name: qiskit.providers.aer.noise.ReadoutError
---
# qiskit.providers.aer.noise.ReadoutError
<Class id="qiskit.providers.aer.noise.ReadoutError" isDedicatedPage={true} github="https://github.com/qiskit/qiskit-aer/tree/stable/0.8/qiskit/providers/aer/noise/errors/readout_error.py" signature="ReadoutError(probabilities, atol=1e-08)" modifiers="class">
Readout error class for Qiskit Aer noise model.
Create a readout error for a noise model.
For an N-qubit readout error probabilities are entered as vectors:
```python
probabilities[m] = [P(0|m), P(1|m), ..., P(2 ** N - 1|m)]
```
where `P(n|m)` is the probability of recording a noisy measurement outcome as `n` given the true ideal measurement outcome was `m`, where `n` and `m` are integer representations of bit-strings.
**Example: 1-qubit**
```python
probabilities[0] = [P("0"|"0"), P("1"|"0")]
probabilities[1] = [P("0"|"1"), P("1"|"1")]
```
**Example: 2-qubit**
```python
probabilities[0] = [P("00"|"00"), P("01"|"00"), P("10"|"00"), P("11"|"00")]
probabilities[1] = [P("00"|"01"), P("01"|"01"), P("10"|"01"), P("11"|"01")]
probabilities[2] = [P("00"|"10"), P("01"|"10"), P("10"|"10"), P("11"|"10")]
probabilities[3] = [P("00"|"11"), P("01"|"11"), P("10"|"11"), P("11"|"11")]
```
**Parameters**
* **probabilities** (*matrix*) – List of outcome assignment probabilities.
* **atol** (*double*) – Threshold for checking probabilities are normalized (Default: 1e-8).
### \_\_init\_\_
<Function id="qiskit.providers.aer.noise.ReadoutError.__init__" signature="__init__(probabilities, atol=1e-08)">
Create a readout error for a noise model.
For an N-qubit readout error probabilities are entered as vectors:
```python
probabilities[m] = [P(0|m), P(1|m), ..., P(2 ** N - 1|m)]
```
where `P(n|m)` is the probability of recording a noisy measurement outcome as `n` given the true ideal measurement outcome was `m`, where `n` and `m` are integer representations of bit-strings.
**Example: 1-qubit**
```python
probabilities[0] = [P("0"|"0"), P("1"|"0")]
probabilities[1] = [P("0"|"1"), P("1"|"1")]
```
**Example: 2-qubit**
```python
probabilities[0] = [P("00"|"00"), P("01"|"00"), P("10"|"00"), P("11"|"00")]
probabilities[1] = [P("00"|"01"), P("01"|"01"), P("10"|"01"), P("11"|"01")]
probabilities[2] = [P("00"|"10"), P("01"|"10"), P("10"|"10"), P("11"|"10")]
probabilities[3] = [P("00"|"11"), P("01"|"11"), P("10"|"11"), P("11"|"11")]
```
**Parameters**
* **probabilities** (*matrix*) – List of outcome assignment probabilities.
* **atol** (*double*) – Threshold for checking probabilities are normalized (Default: 1e-8).
</Function>
## Methods
| | |
| ------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------- |
| [`__init__`](#qiskit.providers.aer.noise.ReadoutError.__init__ "qiskit.providers.aer.noise.ReadoutError.__init__")(probabilities\[, atol]) | Create a readout error for a noise model. |
| [`compose`](#qiskit.providers.aer.noise.ReadoutError.compose "qiskit.providers.aer.noise.ReadoutError.compose")(other\[, front]) | Return the composition readout error other \* self. |
| [`copy`](#qiskit.providers.aer.noise.ReadoutError.copy "qiskit.providers.aer.noise.ReadoutError.copy")() | Make a copy of current ReadoutError. |
| [`dot`](#qiskit.providers.aer.noise.ReadoutError.dot "qiskit.providers.aer.noise.ReadoutError.dot")(other) | Return the composition readout error self \* other. |
| [`expand`](#qiskit.providers.aer.noise.ReadoutError.expand "qiskit.providers.aer.noise.ReadoutError.expand")(other) | Return the tensor product readout error self ⊗ other. |
| [`ideal`](#qiskit.providers.aer.noise.ReadoutError.ideal "qiskit.providers.aer.noise.ReadoutError.ideal")() | Return True if current error object is an identity |
| [`power`](#qiskit.providers.aer.noise.ReadoutError.power "qiskit.providers.aer.noise.ReadoutError.power")(n) | Return the compose of the readout error with itself n times. |
| [`set_atol`](#qiskit.providers.aer.noise.ReadoutError.set_atol "qiskit.providers.aer.noise.ReadoutError.set_atol")(value) | Set the class default absolute tolerance parameter for float comparisons. |
| [`set_rtol`](#qiskit.providers.aer.noise.ReadoutError.set_rtol "qiskit.providers.aer.noise.ReadoutError.set_rtol")(value) | Set the class default relative tolerance parameter for float comparisons. |
| [`tensor`](#qiskit.providers.aer.noise.ReadoutError.tensor "qiskit.providers.aer.noise.ReadoutError.tensor")(other) | Return the tensor product readout error self ⊗ other. |
| [`to_dict`](#qiskit.providers.aer.noise.ReadoutError.to_dict "qiskit.providers.aer.noise.ReadoutError.to_dict")() | Return the current error as a dictionary. |
| [`to_instruction`](#qiskit.providers.aer.noise.ReadoutError.to_instruction "qiskit.providers.aer.noise.ReadoutError.to_instruction")() | Convert the ReadoutError to a circuit Instruction. |
## Attributes
| | |
| ------------------------------------------------------------------------------------------------------------------------------------------ | --------------------------------------------------------------- |
| [`atol`](#qiskit.providers.aer.noise.ReadoutError.atol "qiskit.providers.aer.noise.ReadoutError.atol") | The default absolute tolerance parameter for float comparisons. |
| [`number_of_qubits`](#qiskit.providers.aer.noise.ReadoutError.number_of_qubits "qiskit.providers.aer.noise.ReadoutError.number_of_qubits") | Return the number of qubits for the error. |
| [`probabilities`](#qiskit.providers.aer.noise.ReadoutError.probabilities "qiskit.providers.aer.noise.ReadoutError.probabilities") | Return the readout error probabilities matrix. |
| [`rtol`](#qiskit.providers.aer.noise.ReadoutError.rtol "qiskit.providers.aer.noise.ReadoutError.rtol") | The relative tolerance parameter for float comparisons. |
### atol
<Attribute id="qiskit.providers.aer.noise.ReadoutError.atol">
The default absolute tolerance parameter for float comparisons.
</Attribute>
### compose
<Function id="qiskit.providers.aer.noise.ReadoutError.compose" signature="compose(other, front=False)">
Return the composition readout error other \* self.
Note that for front=True this is equivalent to the [`ReadoutError.dot()`](#qiskit.providers.aer.noise.ReadoutError.dot "qiskit.providers.aer.noise.ReadoutError.dot") method.
**Parameters**
* **other** ([*ReadoutError*](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")) – a readout error.
* **front** (*bool*) – If True return the reverse order composation self \* other instead \[default: False].
**Returns**
The composition readout error.
**Return type**
[ReadoutError](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")
**Raises**
* **NoiseError** – if other is not a ReadoutError or has incompatible
* **dimensions.** –
</Function>
### copy
<Function id="qiskit.providers.aer.noise.ReadoutError.copy" signature="copy()">
Make a copy of current ReadoutError.
</Function>
### dot
<Function id="qiskit.providers.aer.noise.ReadoutError.dot" signature="dot(other)">
Return the composition readout error self \* other.
**Parameters**
**other** ([*ReadoutError*](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")) – a readout error.
**Returns**
The composition readout error.
**Return type**
[ReadoutError](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")
**Raises**
* **NoiseError** – if other is not a ReadoutError or has incompatible
* **dimensions.** –
</Function>
### expand
<Function id="qiskit.providers.aer.noise.ReadoutError.expand" signature="expand(other)">
Return the tensor product readout error self ⊗ other.
**Parameters**
**other** ([*ReadoutError*](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")) – a readout error.
**Returns**
the tensor product readout error other ⊗ self.
**Return type**
[ReadoutError](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")
**Raises**
**NoiseError** – if other is not a ReadoutError.
</Function>
### ideal
<Function id="qiskit.providers.aer.noise.ReadoutError.ideal" signature="ideal()">
Return True if current error object is an identity
</Function>
### number\_of\_qubits
<Attribute id="qiskit.providers.aer.noise.ReadoutError.number_of_qubits">
Return the number of qubits for the error.
</Attribute>
### power
<Function id="qiskit.providers.aer.noise.ReadoutError.power" signature="power(n)">
Return the compose of the readout error with itself n times.
**Parameters**
**n** (*int*) – the number of times to compose with self (n>0).
**Returns**
the n-times composition channel.
**Return type**
[ReadoutError](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")
**Raises**
**NoiseError** – if the power is not a positive integer.
</Function>
### probabilities
<Attribute id="qiskit.providers.aer.noise.ReadoutError.probabilities">
Return the readout error probabilities matrix.
</Attribute>
### rtol
<Attribute id="qiskit.providers.aer.noise.ReadoutError.rtol">
The relative tolerance parameter for float comparisons.
</Attribute>
### set\_atol
<Function id="qiskit.providers.aer.noise.ReadoutError.set_atol" signature="set_atol(value)" modifiers="classmethod">
Set the class default absolute tolerance parameter for float comparisons.
</Function>
### set\_rtol
<Function id="qiskit.providers.aer.noise.ReadoutError.set_rtol" signature="set_rtol(value)" modifiers="classmethod">
Set the class default relative tolerance parameter for float comparisons.
</Function>
### tensor
<Function id="qiskit.providers.aer.noise.ReadoutError.tensor" signature="tensor(other)">
Return the tensor product readout error self ⊗ other.
**Parameters**
**other** ([*ReadoutError*](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")) – a readout error.
**Returns**
the tensor product readout error self ⊗ other.
**Return type**
[ReadoutError](#qiskit.providers.aer.noise.ReadoutError "qiskit.providers.aer.noise.ReadoutError")
**Raises**
**NoiseError** – if other is not a ReadoutError.
</Function>
### to\_dict
<Function id="qiskit.providers.aer.noise.ReadoutError.to_dict" signature="to_dict()">
Return the current error as a dictionary.
</Function>
### to\_instruction
<Function id="qiskit.providers.aer.noise.ReadoutError.to_instruction" signature="to_instruction()">
Convert the ReadoutError to a circuit Instruction.
</Function>
</Class>
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