qiskit.providers.aer.noise.NoiseModel

class NoiseModel(basis_gates=None)

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Noise model class for Qiskit Aer simulators.

This class is used to represent noise model for the QasmSimulator . It can be used to construct custom noise models for simulator, or to automatically generate a basic device noise model for an IBMQ backend. See the noise module documentation for additional information.

Example: Basic device noise model

An approximate NoiseModel can be generated automatically from the properties of real device backends from the IBMQ provider using the from_backend() method.

from qiskit import IBMQ, Aer
from qiskit.providers.aer.noise import NoiseModel
 
provider = IBMQ.load_account()
backend = provider.get_backend('ibmq_vigo')
noise_model = NoiseModel.from_backend(backend)
print(noise_model)

Example: Custom noise model

Custom noise models can be used by adding QuantumError to circuit gate, reset or measure instructions, and ReadoutError to measure instructions.

import qiskit.providers.aer.noise as noise
 
# Error probabilities
prob_1 = 0.001  # 1-qubit gate
prob_2 = 0.01   # 2-qubit gate
 
# Depolarizing quantum errors
error_1 = noise.depolarizing_error(prob_1, 1)
error_2 = noise.depolarizing_error(prob_2, 2)
 
# Add errors to noise model
noise_model = noise.NoiseModel()
noise_model.add_all_qubit_quantum_error(error_1, ['u1', 'u2', 'u3'])
noise_model.add_all_qubit_quantum_error(error_2, ['cx'])
print(noise_model)

Initialize an empty noise model.

Parameters

basis_gates (list[str] or None) - Specify an initial basis_gates for the noise model. If None a default value of [‘id’, ‘u3’, ‘cx’] is used (Default: None).

Additional Information: Errors added to the noise model will have their instruction appended to the noise model basis_gates if the instruction is in the QasmSimulator basis_gates. If the instruction is not in the QasmSimulator basis_gates it is assumed to be a label for a standard gate, and that gate should be added to the NoiseModel basis_gates either using the init method, or the add_basis_gates() method.

init

__init__(basis_gates=None)

Initialize an empty noise model.

Parameters

basis_gates (list[str] or None) - Specify an initial basis_gates for the noise model. If None a default value of [‘id’, ‘u3’, ‘cx’] is used (Default: None).

Additional Information: Errors added to the noise model will have their instruction appended to the noise model basis_gates if the instruction is in the QasmSimulator basis_gates. If the instruction is not in the QasmSimulator basis_gates it is assumed to be a label for a standard gate, and that gate should be added to the NoiseModel basis_gates either using the init method, or the add_basis_gates() method.

Methods


`__init__`([basis_gates])	Initialize an empty noise model.
`add_all_qubit_quantum_error`(error, instructions)	Add a quantum error to the noise model that applies to all qubits.
`add_all_qubit_readout_error`(error[, warnings])	Add a single-qubit readout error that applies measure on all qubits.
`add_basis_gates`(instructions[, warnings])	Add additional gates to the noise model basis_gates.
`add_nonlocal_quantum_error`(error, …[, …])	Add a non-local quantum error to the noise model.
`add_quantum_error`(error, instructions, qubits)	Add a quantum error to the noise model.
`add_readout_error`(error, qubits[, warnings])	Add a readout error to the noise model.
`from_backend`(backend[, gate_error, …])	Return a noise model derived from a devices backend properties.
`from_dict`(noise_dict)	Load NoiseModel from a dictionary.
`is_ideal`()	Return True if the noise model has no noise terms.
`reset`()	Reset the noise model.
`set_x90_single_qubit_gates`(instructions)	Declares X90 based gates for noise model.
`to_dict`([serializable])	Return the noise model as a dictionary.

Attributes


`basis_gates`	Return basis_gates for compiling to the noise model.
`noise_instructions`	Return the set of noisy instructions for this noise model.
`noise_qubits`	Return the set of noisy qubits for this noise model.

add_all_qubit_quantum_error

add_all_qubit_quantum_error(error, instructions, warnings=True)

Add a quantum error to the noise model that applies to all qubits.

Parameters

error (QuantumError) – the quantum error object.
**(str or list[str] **or (instructions) – Instruction or list[Instruction]): the instructions error applies to.
warnings (bool) – Display warning if appending to an instruction that already has an error (Default: True).

Raises

NoiseError - if the input parameters are invalid.

Additional Information:

If the error object is ideal it will not be added to the model.

add_all_qubit_readout_error

add_all_qubit_readout_error(error, warnings=True)

Add a single-qubit readout error that applies measure on all qubits.

Parameters

error (ReadoutError) – the quantum error object.
warnings (bool) – Display warning if appending to an instruction that already has an error (Default: True)

Raises

NoiseError - if the input parameters are invalid.

Additional Information:

If the error object is ideal it will not be added to the model.

add_basis_gates

add_basis_gates(instructions, warnings=True)

Add additional gates to the noise model basis_gates.

This should be used to add any gates that are identified by a custom gate label in the noise model.

Parameters

**(list[str] **or (instructions) – list[Instruction]): the instructions error applies to.
warnings (bool) – display warning if instruction is not in QasmSimulator basis_gates (Default: True).

add_nonlocal_quantum_error

add_nonlocal_quantum_error(error, instructions, qubits, noise_qubits, warnings=True)

Add a non-local quantum error to the noise model.

Parameters

error (QuantumError) – the quantum error object.
**(str or list[str] **or (instructions) – Instruction or list[Instruction]): the instructions error applies to.
qubits (list[int]) – qubits instruction error applies to.
noise_qubits (list[int]) – Specify the exact qubits the error should be applied to if different to the instruction qubits.
warnings (bool) – Display warning if appending to an instruction that already has an error (Default: True).

Raises

NoiseError - if the input parameters are invalid.

Additional Information:

If the error object is ideal it will not be added to the model.

add_quantum_error

add_quantum_error(error, instructions, qubits, warnings=True)

Add a quantum error to the noise model.

Parameters

error (QuantumError) – the quantum error object.
**(str or list[str] **or (instructions) – Instruction or list[Instruction]): the instructions error applies to.
qubits (list[int]) – qubits instruction error applies to.
warnings (bool) – Display warning if appending to an instruction that already has an error (Default: True).

Raises

NoiseError - if the input parameters are invalid.

Additional Information:

If the error object is ideal it will not be added to the model.

add_readout_error

add_readout_error(error, qubits, warnings=True)

Add a readout error to the noise model.

Parameters

error (ReadoutError) – the quantum error object.
qubits (list[int]) – qubits instruction error applies to.
warnings (bool) – Display warning if appending to an instruction that already has an error [Default: True]

Raises

NoiseError - if the input parameters are invalid.

Additional Information:

If the error object is ideal it will not be added to the model.

basis_gates

Return basis_gates for compiling to the noise model.

from_backend

classmethod from_backend(backend, gate_error=True, readout_error=True, thermal_relaxation=True, temperature=0, gate_lengths=None, gate_length_units='ns', standard_gates=True, warnings=True)

Return a noise model derived from a devices backend properties.

This function generates a noise model based on:

1 and 2 qubit gate errors consisting of a depolarizing_error() followed by a thermal_relaxation_error().
Single qubit ReadoutError on all measurements.

T_1

Additional Information

The noise model includes the following errors:

$If readout_error=True include single qubit readout errors on measurements.$
If gate_error=True and thermal_relaxation=True include:
- Single-qubit gate errors consisting of a depolarizing_error() followed by a thermal_relaxation_error() for the qubit the gate acts on.
- Two-qubit gate errors consisting of a 2-qubit depolarizing_error() followed by single qubit thermal_relaxation_error() on each qubit participating in the gate.
If gate_error=True is True and thermal_relaxation=False:
- An N-qubit depolarizing_error() on each N-qubit gate.
$If gate_error=False and thermal_relaxation=True include single-qubit thermal_relaxation_errors() on each qubits participating in a multi-qubit gate.$

For best practice in simulating a backend make sure that the circuit is compiled using the set of basis gates in the noise module by setting basis_gates=noise_model.basis_gates and using the device coupling map with coupling_map=backend.configuration().coupling_map

Specifying custom gate times

T_1

If a custom gate is specified that already exists in the backend properties, the gate_lengths value will override the gate time value from the backend properties. If non-default values are used gate_lengths should be a list

Parameters

backend (Backend orBackendProperties) – backend properties.
gate_error (bool) – Include depolarizing gate errors (Default: True).
readout_error (Bool) – Include readout errors in model (Default: True).
thermal_relaxation (Bool) – Include thermal relaxation errors (Default: True).
temperature (double) – qubit temperature in milli-Kelvin (mK) for thermal relaxation errors (Default: 0).
gate_lengths (list) – Custom gate times for thermal relaxation errors. Used to extend or override the gate times in the backend properties (Default: None))
gate_length_units (str) – Time units for gate length values in gate_lengths. Can be ‘ns’, ‘ms’, ‘us’, or ‘s’ (Default: ‘ns’).
standard_gates (bool) – If true return errors as standard qobj gates. If false return as unitary qobj instructions (Default: True)
warnings (bool) – Display warnings (Default: True).

Returns

An approximate noise model for the device backend.

Return type

NoiseModel

Raises

NoiseError - If the input backend is not valid.

from_dict

static from_dict(noise_dict)

Load NoiseModel from a dictionary.

Parameters

noise_dict (dict) - A serialized noise model.

Returns

the noise model.

Return type

NoiseModel

Raises

NoiseError - if dict cannot be converted to NoiseModel.

is_ideal

is_ideal()

Return True if the noise model has no noise terms.

noise_instructions

Return the set of noisy instructions for this noise model.

noise_qubits

Return the set of noisy qubits for this noise model.

reset

reset()

Reset the noise model.

set_x90_single_qubit_gates

set_x90_single_qubit_gates(instructions)

Declares X90 based gates for noise model.

Parameters

**(list [str] ** or (instructions) - list[Instruction]): the instructions error applies to.

Raises

NoiseError - if the input instructions are not valid.

to_dict

to_dict(serializable=False)

Return the noise model as a dictionary.

Parameters

serializable (bool) - if True, return a dict containing only types that can be serializable by the stdlib json module.

Returns

a dictionary for a noise model.

Return type

dict

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