qml.add_noise¶
-
add_noise
(tape, noise_model, level=None)[source]¶ Insert operations according to a provided noise model.
Circuits passed through this quantum transform will be updated to apply the insertion-based
NoiseModel
, which contains a mapping{BooleanFn: Callable}
from conditions to the corresponding noise gates. Each condition in the noise model will be evaluated on the operations contained within the given circuit. For conditions that evaluate toTrue
, the noisy gates contained within theCallable
will be inserted after the operation under consideration.- Parameters
tape (QNode or QuantumTape or Callable or pennylane.devices.Device) – the input circuit or device to be transformed.
noise_model (NoiseModel) – noise model according to which noise has to be inserted.
level (None, str, int, slice) –
An indication of which stage in the transform program the noise model should be applied to. Only relevant when transforming a
QNode
. More details on the following permissible values can be found in theget_transform_program()
-None
: expands the tape to have noAdjoint
andTemplates
.str
: acceptable keys are"top"
,"user"
,"device"
, and"gradient"
.int
: how many transforms to include, starting from the front of the program.slice
: a slice to select out components of the transform program.
- Returns
Transformed circuit as described in
qml.transform
.- Return type
qnode (QNode) or quantum function (Callable) or tuple[List[QuantumTape], function] or device (pennylane.devices.Device)
- Raises
ValueError – argument
noise_model
is not a valid noise model.
Note
For a given
model_map
within aNoiseModel
, if multiple conditionals in themodel_map
evaluate toTrue
for an operation, then the noise operations defined via their respective noisy quantum functions will be added in the same order in which the conditionals appear in themodel_map
.Example:
The following QNode can be transformed to add noise to the circuit:
from functools import partial dev = qml.device("default.mixed", wires=2) fcond1 = qml.noise.op_eq(qml.RX) & qml.noise.wires_in([0, 1]) noise1 = qml.noise.partial_wires(qml.PhaseDamping, 0.4) fcond2 = qml.noise.op_in([qml.RX, qml.RZ]) def noise2(op, **kwargs): qml.ThermalRelaxationError(op.parameters[0] * 0.5, kwargs["t1"], kwargs["t2"], 0.6, op.wires) noise_model = qml.NoiseModel({fcond1: noise1, fcond2: noise2}, t1=2.0, t2=0.2) @partial(qml.transforms.add_noise, noise_model=noise_model) @qml.qnode(dev) def circuit(w, x, y, z): qml.RX(w, wires=0) qml.RY(x, wires=1) qml.CNOT(wires=[0, 1]) qml.RY(y, wires=0) qml.RX(z, wires=1) return qml.expval(qml.Z(0) @ qml.Z(1))
Executions of this circuit will differ from the noise-free value:
>>> circuit(0.9, 0.4, 0.5, 0.6) array(0.544053) >>> print(qml.draw(circuit)(0.9, 0.4, 0.5, 0.6)) 0: ──RX(0.90)──PhaseDamping(0.40)──ThermalRelaxationError(0.45,2.00,0.20,0.60)─╭●──RY(0.50) 1: ──RY(0.40)──────────────────────────────────────────────────────────────────╰X──RX(0.60) ───────────────────────────────────────────────────────────────────┤ ╭<Z@Z> ───PhaseDamping(0.40)──ThermalRelaxationError(0.30,2.00,0.20,0.60)─┤ ╰<Z@Z>
Tranform Levels
When transforming an already constructed
QNode
, theadd_noise
transform will be added at the end of the “user” transforms by default, i.e., after all the transforms that have been manually applied to the QNode up to that point.dev = qml.device("default.mixed", wires=2) @qml.metric_tensor @qml.transforms.undo_swaps @qml.transforms.merge_rotations @qml.transforms.cancel_inverses @qml.qnode(dev) def circuit(w, x, y, z): qml.RX(w, wires=0) qml.RY(x, wires=1) qml.CNOT(wires=[0, 1]) qml.RY(y, wires=0) qml.RX(z, wires=1) return qml.expval(qml.Z(0) @ qml.Z(1)) noisy_circuit = qml.transforms.add_noise(circuit, noise_model)
>>> qml.workflow.get_transform_program(circuit) TransformProgram(cancel_inverses, merge_rotations, undo_swaps, _expand_metric_tensor, batch_transform, expand_fn, metric_tensor)
>>> qml.workflow.get_transform_program(noisy_circuit) TransformProgram(cancel_inverses, merge_rotations, undo_swaps, _expand_metric_tensor, add_noise, batch_transform, expand_fn, metric_tensor)
However, one can request to insert the
add_noise
transform at any specific point in the transform program. By specifying thelevel
keyword argument while transforming aQNode
, this transform can be added at a designated level within the transform program, as determined using theget_transform_program
. For example, specifyingNone
will add it at the end, ensuring that the tape is expanded to have noAdjoint
andTemplates
:>>> qml.transforms.add_noise(circuit, noise_model, level=None).transform_program TransformProgram(cancel_inverses, merge_rotations, undo_swaps, _expand_metric_tensor, batch_transform, expand_fn, add_noise, metric_tensor)
Other acceptable values for
level
are"top"
,"user"
,"device"
, and"gradient"
. Among these, “top” will allow addition to an empty transform program, “user” will allow addition at the end of user-specified transforms, “device” will allow addition at the end of device-specific transforms, and “gradient” will allow addition at the end of transforms that expand trainable operations. For example:>>> qml.transforms.add_noise(circuit, noise_model, level="top").transform_program TransformProgram(add_noise)
>>> qml.transforms.add_noise(circuit, noise_model, level="user").transform_program TransformProgram(cancel_inverses, merge_rotations, undo_swaps, _expand_metric_tensor, add_noise, metric_tensor)
>>> qml.transforms.add_noise(circuit, noise_model, level="device").transform_program TransformProgram(cancel_inverses, merge_rotations, undo_swaps, _expand_metric_tensor, batch_transform, expand_fn, add_noise, metric_tensor)
Finally, more precise control over the insertion of the transform can be achieved by specifying an integer or slice for indexing when extracting the transform program. For example, one can do:
>>> qml.transforms.add_noise(circuit, noise_model, level=2).transform_program TransformProgram(cancel_inverses, merge_rotations, add_noise)
>>> qml.transforms.add_noise(circuit, noise_model, level=slice(1,3)).transform_program TransformProgram(merge_rotations, undo_swaps, add_noise)