qml.tape.QuantumScript

class QuantumScript(ops=None, measurements=None, shots=None, trainable_params=None, _update=True)[source]

Bases: object

The operations and measurements that represent instructions for execution on a quantum device.

Parameters
  • ops (Iterable[Operator]) – An iterable of the operations to be performed

  • measurements (Iterable[MeasurementProcess]) – All the measurements to be performed

Keyword Arguments
  • shots (None, int, Sequence[int], Shots) – Number and/or batches of shots for execution. Note that this property is still experimental and under development.

  • trainable_params (None, Sequence[int]) – the indices for which parameters are trainable

  • _update=True (bool) – Whether or not to set various properties on initialization. Setting _update=False reduces computations if the script is only an intermediary step.

Example:

from pennylane.tape import QuantumScript

ops = [qml.BasisState(np.array([1,1]), wires=(0,"a")),
       qml.RX(0.432, 0),
       qml.RY(0.543, 0),
       qml.CNOT((0,"a")),
       qml.RX(0.133, "a")]

qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])
>>> list(qscript)
[BasisState(array([1, 1]), wires=[0, "a"]),
RX(0.432, wires=[0]),
RY(0.543, wires=[0]),
CNOT(wires=[0, 'a']),
RX(0.133, wires=['a']),
expval(Z(0))]
>>> qscript.operations
[BasisState(array([1, 1]), wires=[0, "a"]),
RX(0.432, wires=[0]),
RY(0.543, wires=[0]),
CNOT(wires=[0, 'a']),
RX(0.133, wires=['a'])]
>>> qscript.measurements
[expval(Z(0))]

Iterating over the quantum script can be done by:

>>> for op in qscript:
...     print(op)
BasisState(array([1, 1]), wires=[0, "a"])
RX(0.432, wires=[0])
RY(0.543, wires=[0])
CNOT(wires=[0, 'a'])
RX(0.133, wires=['a'])
expval(Z(0))'

Quantum scripts also support indexing and length determination:

>>> qscript[0]
BasisState(array([1, 1]), wires=[0, "a"])
>>> len(qscript)
6

Once constructed, the script can be executed directly on a quantum device using the execute() function:

>>> dev = qml.device('default.qubit', wires=(0,'a'))
>>> qml.execute([qscript], dev, gradient_fn=None)
[array([-0.77750694])]

Quantum scripts can also store information about the number and batches of executions by setting the shots keyword argument. This information is internally stored in a pennylane.measurements.Shots object:

>>> s_vec = [1, 1, 2, 2, 2]
>>> qscript = QuantumScript([qml.Hadamard(0)], [qml.expval(qml.Z(0))], shots=s_vec)
>>> qscript.shots.shot_vector
(ShotCopies(1 shots x 2), ShotCopies(2 shots x 3))

ops and measurements are converted to lists upon initialization, so those arguments accept any iterable object:

>>> qscript = QuantumScript((qml.X(i) for i in range(3)))
>>> qscript.circuit
[X(0), X(1), X(2)]

batch_size

The batch size of the quantum script inferred from the batch sizes of the used operations for parameter broadcasting.

circuit

Returns the underlying quantum circuit as a list of operations and measurements.

data

Alias to get_parameters() and set_parameters() for backwards compatibilities with operations.

diagonalizing_gates

Returns the gates that diagonalize the measured wires such that they are in the eigenbasis of the circuit observables.

graph

Returns a directed acyclic graph representation of the recorded quantum circuit:

hash

returns an integer hash uniquely representing the quantum script

interface

automatic differentiation interface used by the quantum script (if any)

measurements

Returns the measurements on the quantum script.

num_params

Returns the number of trainable parameters on the quantum script.

num_preps

Returns the index of the first operator that is not an StatePrepBase operator.

numeric_type

Returns the expected numeric type of the quantum script result by inspecting its measurements.

observables

Returns the observables on the quantum script.

op_wires

Returns the wires that the tape operations act on.

operations

Returns the state preparations and operations on the quantum script.

output_dim

The (inferred) output dimension of the quantum script.

samples_computational_basis

Determines if any of the measurements are in the computational basis.

shots

Returns a Shots object containing information about the number and batches of shots

specs

Resource information about a quantum circuit.

trainable_params

Store or return a list containing the indices of parameters that support differentiability.

batch_size

The batch size of the quantum script inferred from the batch sizes of the used operations for parameter broadcasting.

See also

batch_size for details.

Returns

The batch size of the quantum script if present, else None.

Return type

int or None

circuit

Returns the underlying quantum circuit as a list of operations and measurements.

The circuit is created with the assumptions that:

  • The operations attribute contains quantum operations and mid-circuit measurements and

  • The measurements attribute contains terminal measurements.

Note that the resulting list could contain MeasurementProcess objects that some devices may not support.

Returns

the quantum circuit containing quantum operations and measurements

Return type

list[Operator, MeasurementProcess]

data

Alias to get_parameters() and set_parameters() for backwards compatibilities with operations.

diagonalizing_gates

Returns the gates that diagonalize the measured wires such that they are in the eigenbasis of the circuit observables.

Returns

the operations that diagonalize the observables

Return type

List[Operation]

graph

Returns a directed acyclic graph representation of the recorded quantum circuit:

>>> ops = [qml.StatePrep([0, 1], 0), qml.RX(0.432, 0)]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])
>>> qscript.graph
<pennylane.circuit_graph.CircuitGraph object at 0x7fcc0433a690>

Note that the circuit graph is only constructed once, on first call to this property, and cached for future use.

Returns

the circuit graph object

Return type

CircuitGraph

hash

returns an integer hash uniquely representing the quantum script

Type

int

interface

automatic differentiation interface used by the quantum script (if any)

Type

str, None

measurements

Returns the measurements on the quantum script.

Returns

list of measurement processes

Return type

list[MeasurementProcess]

Example

>>> ops = [qml.StatePrep([0, 1], 0), qml.RX(0.432, 0)]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])
>>> qscript.measurements
[expval(Z(0))]
num_params

Returns the number of trainable parameters on the quantum script.

num_preps

Returns the index of the first operator that is not an StatePrepBase operator.

numeric_type

Returns the expected numeric type of the quantum script result by inspecting its measurements.

Returns

The numeric type corresponding to the result type of the quantum script, or a tuple of such types if the script contains multiple measurements

Return type

Union[type, Tuple[type]]

Example:

>>> dev = qml.device('default.qubit', wires=2)
>>> qs = QuantumScript(measurements=[qml.state()])
>>> qs.numeric_type
complex
observables

Returns the observables on the quantum script.

Returns

list of observables

Return type

list[MeasurementProcess, Observable]]

Example

>>> ops = [qml.StatePrep([0, 1], 0), qml.RX(0.432, 0)]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])
>>> qscript.observables
[expval(Z(0))]
op_wires

Returns the wires that the tape operations act on.

operations

Returns the state preparations and operations on the quantum script.

Returns

quantum operations

Return type

list[Operator]

>>> ops = [qml.StatePrep([0, 1], 0), qml.RX(0.432, 0)]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])
>>> qscript.operations
[StatePrep([0, 1], wires=[0]), RX(0.432, wires=[0])]
output_dim

The (inferred) output dimension of the quantum script.

samples_computational_basis

Determines if any of the measurements are in the computational basis.

shots

Returns a Shots object containing information about the number and batches of shots

Returns

Object with shot information

Return type

Shots

specs

Resource information about a quantum circuit.

Returns

dictionaries that contain quantum script specifications

Return type

dict[str, Union[defaultdict,int]]

Example
>>> ops = [qml.Hadamard(0), qml.RX(0.26, 1), qml.CNOT((1,0)),
...         qml.Rot(1.8, -2.7, 0.2, 0), qml.Hadamard(1), qml.CNOT((0, 1))]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0) @ qml.Z(1))])

Asking for the specs produces a dictionary of useful information about the circuit:

>>> qscript.specs['num_observables']
1
>>> qscript.specs['gate_sizes']
defaultdict(<class 'int'>, {1: 4, 2: 2})
>>> print(qscript.specs['resources'])
wires: 2
gates: 6
depth: 4
shots: Shots(total=None)
gate_types:
{'Hadamard': 2, 'RX': 1, 'CNOT': 2, 'Rot': 1}
gate_sizes:
{1: 4, 2: 2}
trainable_params

Store or return a list containing the indices of parameters that support differentiability. The indices provided match the order of appearence in the quantum circuit.

Setting this property can help reduce the number of quantum evaluations needed to compute the Jacobian; parameters not marked as trainable will be automatically excluded from the Jacobian computation.

The number of trainable parameters determines the number of parameters passed to set_parameters(), and changes the default output size of method get_parameters().

Note

For devices that support native backpropagation (such as default.qubit.tf and default.qubit.autograd), this property contains no relevant information when using backpropagation to compute gradients.

Example

>>> ops = [qml.RX(0.432, 0), qml.RY(0.543, 0),
...        qml.CNOT((0,"a")), qml.RX(0.133, "a")]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])
>>> qscript.trainable_params
[0, 1, 2]
>>> qscript.trainable_params = [0] # set only the first parameter as trainable
>>> qscript.get_parameters()
[0.432]

adjoint()

Create a quantum script that is the adjoint of this one.

bind_new_parameters(params, indices)

Create a new tape with updated parameters.

copy([copy_operations])

Returns a shallow copy of the quantum script.

draw([wire_order, show_all_wires, decimals, …])

Draw the quantum script as a circuit diagram.

expand([depth, stop_at, expand_measurements])

Expand all operations to a specific depth.

from_queue(queue[, shots])

Construct a QuantumScript from an AnnotatedQueue.

get_operation(idx)

Returns the trainable operation, the operation index and the corresponding operation argument index, for a specified trainable parameter index.

get_parameters([trainable_only, operations_only])

Return the parameters incident on the quantum script operations.

map_to_standard_wires()

Map a circuit’s wires such that they are in a standard order.

shape(device)

Produces the output shape of the quantum script by inspecting its measurements and the device used for execution.

to_openqasm([wires, rotations, measure_all, …])

Serialize the circuit as an OpenQASM 2.0 program.

adjoint()[source]

Create a quantum script that is the adjoint of this one.

Adjointed quantum scripts are the conjugated and transposed version of the original script. Adjointed ops are equivalent to the inverted operation for unitary gates.

Returns

the adjointed script

Return type

QuantumScript

bind_new_parameters(params, indices)[source]

Create a new tape with updated parameters.

This function takes a list of new parameters as input, and returns a new QuantumScript containing the new parameters at the provided indices, with the parameters at all other indices remaining the same.

Parameters
  • params (Sequence[TensorLike]) – New parameters to create the tape with. This must have the same length as indices.

  • indices (Sequence[int]) – The parameter indices to update with the given parameters. The index of a parameter is defined as its index in tape.get_parameters().

Returns

New tape with updated parameters

Return type

tape.QuantumScript

Example

>>> ops = [qml.RX(0.432, 0), qml.RY(0.543, 0),
...        qml.CNOT((0,"a")), qml.RX(0.133, "a")]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])

A new tape can be created by passing new parameters along with the indices to be updated. To modify all parameters in the above qscript:

>>> new_qscript = qscript.bind_new_parameters([0.1, 0.2, 0.3], [0, 1, 2])
>>> new_qscript.get_parameters()
[0.1, 0.2, 0.3]

The original qscript remains unchanged:

>>> qscript.get_parameters()
[0.432, 0.543, 0.133]

A subset of parameters can be modified as well, defined by the parameter indices:

>>> newer_qscript = new_qscript.bind_new_parameters([-0.1, 0.5], [0, 2])
>>> newer_qscript.get_parameters()
[-0.1, 0.2, 0.5]
copy(copy_operations=False)[source]

Returns a shallow copy of the quantum script.

Parameters

copy_operations (bool) – If True, the operations are also shallow copied. Otherwise, if False, the copied operations will simply be references to the original operations; changing the parameters of one script will likewise change the parameters of all copies.

Returns

a shallow copy of the quantum script

Return type

QuantumScript

draw(wire_order=None, show_all_wires=False, decimals=None, max_length=100, show_matrices=True)[source]

Draw the quantum script as a circuit diagram. See tape_text() for more information.

Parameters
  • wire_order (Sequence[Any]) – the order (from top to bottom) to print the wires of the circuit

  • show_all_wires (bool) – If True, all wires, including empty wires, are printed.

  • decimals (int) – How many decimal points to include when formatting operation parameters. Default None will omit parameters from operation labels.

  • max_length (Int) – Maximum length of a individual line. After this length, the diagram will begin anew beneath the previous lines.

  • show_matrices=True (bool) – show matrix valued parameters below all circuit diagrams

Returns

the circuit representation of the quantum script

Return type

str

expand(depth=1, stop_at=None, expand_measurements=False)[source]

Expand all operations to a specific depth.

Parameters
  • depth (int) – the depth the script should be expanded

  • stop_at (Callable) – A function which accepts a queue object, and returns True if this object should not be expanded. If not provided, all objects that support expansion will be expanded.

  • expand_measurements (bool) – If True, measurements will be expanded to basis rotations and computational basis measurements.

Example

Consider the following nested quantum script:

>>> nested_script = QuantumScript([qml.Rot(0.543, 0.1, 0.4, wires=0)])
>>> ops = [
        qml.BasisState(np.array([1, 1]), wires=[0, 'a']),
        nested_script,
        qml.CNOT(wires=[0, 'a']), qml.RY(0.2, wires='a'),
    ]
>>> measurements = [qml.probs(wires=0), qml.probs(wires='a')]
>>> qscript = QuantumScript(ops, measurements)

The nested structure is preserved:

>>> qscript.operations
[BasisState(tensor([1, 1], requires_grad=True), wires=[0, 'a']),
<QuantumScript: wires=[0], params=3>,
CNOT(wires=[0, 'a']),
RY(0.2, wires=['a'])]

Calling .expand will return a script with all nested scripts expanded, resulting in a single script of quantum operations:

>>> new_qscript = qscript.expand(depth=2)
>>> new_qscript.operations
[X(0),
X('a'),
RZ(0.543, wires=[0]),
RY(0.1, wires=[0]),
RZ(0.4, wires=[0]),
CNOT(wires=[0, 'a']),
RY(0.2, wires=['a'])]
classmethod from_queue(queue, shots=None)[source]

Construct a QuantumScript from an AnnotatedQueue.

get_operation(idx)[source]

Returns the trainable operation, the operation index and the corresponding operation argument index, for a specified trainable parameter index.

Parameters

idx (int) – the trainable parameter index

Returns

tuple containing the corresponding operation, operation index and an integer representing the argument index, for the provided trainable parameter.

Return type

tuple[Operation, int, int]

get_parameters(trainable_only=True, operations_only=False, **kwargs)[source]

Return the parameters incident on the quantum script operations.

The returned parameters are provided in order of appearance on the quantum script.

Parameters
  • trainable_only (bool) – if True, returns only trainable parameters

  • operations_only (bool) – if True, returns only the parameters of the operations excluding parameters to observables of measurements

Example

>>> ops = [qml.RX(0.432, 0), qml.RY(0.543, 0),
...        qml.CNOT((0,"a")), qml.RX(0.133, "a")]
>>> qscript = QuantumScript(ops, [qml.expval(qml.Z(0))])

By default, all parameters are trainable and will be returned:

>>> qscript.get_parameters()
[0.432, 0.543, 0.133]

Setting the trainable parameter indices will result in only the specified parameters being returned:

>>> qscript.trainable_params = [1] # set the second parameter as trainable
>>> qscript.get_parameters()
[0.543]

The trainable_only argument can be set to False to instead return all parameters:

>>> qscript.get_parameters(trainable_only=False)
[0.432, 0.543, 0.133]
map_to_standard_wires()[source]

Map a circuit’s wires such that they are in a standard order. If no mapping is required, the unmodified circuit is returned.

Returns

The circuit with wires in the standard order

Return type

QuantumScript

The standard order is defined by the operator wires being increasing integers starting at zero, to match array indices. If there are any measurement wires that are not in any operations, those will be mapped to higher values.

Example:

>>> circuit = qml.tape.QuantumScript([qml.X("a")], [qml.expval(qml.Z("b"))])
>>> circuit.map_to_standard_wires().circuit
[X(0), expval(Z(1))]

If any measured wires are not in any operations, they will be mapped last:

>>> circuit = qml.tape.QuantumScript([qml.X(1)], [qml.probs(wires=[0, 1])])
>>> circuit.map_to_standard_wires().circuit
[X(0), probs(wires=[1, 0])]

If no wire-mapping is needed, then the returned circuit is the inputted circuit:

>>> circuit = qml.tape.QuantumScript([qml.X(0)], [qml.expval(qml.Z(1))])
>>> circuit.map_to_standard_wires() is circuit
True
shape(device)[source]

Produces the output shape of the quantum script by inspecting its measurements and the device used for execution.

Note

The computed shape is not stored because the output shape may be dependent on the device used for execution.

Parameters

device (pennylane.Device) – the device that will be used for the script execution

Returns

the output shape(s) of the quantum script result

Return type

Union[tuple[int], tuple[tuple[int]]]

Examples

>>> dev = qml.device('default.qubit', wires=2)
>>> qs = QuantumScript(measurements=[qml.state()])
>>> qs.shape(dev)
(4,)
>>> m = [qml.state(), qml.expval(qml.Z(0)), qml.probs((0,1))]
>>> qs = QuantumScript(measurements=m)
>>> qs.shape(dev)
((4,), (), (4,))
to_openqasm(wires=None, rotations=True, measure_all=True, precision=None)[source]

Serialize the circuit as an OpenQASM 2.0 program.

Measurements are assumed to be performed on all qubits in the computational basis. An optional rotations argument can be provided so that output of the OpenQASM circuit is diagonal in the eigenbasis of the quantum script’s observables. The measurement outputs can be restricted to only those specified in the script by setting measure_all=False.

Note

The serialized OpenQASM program assumes that gate definitions in qelib1.inc are available.

Parameters
  • wires (Wires or None) – the wires to use when serializing the circuit

  • rotations (bool) – in addition to serializing user-specified operations, also include the gates that diagonalize the measured wires such that they are in the eigenbasis of the circuit observables.

  • measure_all (bool) – whether to perform a computational basis measurement on all qubits or just those specified in the script

  • precision (int) – decimal digits to display for parameters

Returns

OpenQASM serialization of the circuit

Return type

str