qml.tape.QuantumTape¶

class
QuantumTape
(ops=None, measurements=None, shots=None, trainable_params=None, _update=True)[source]¶ Bases:
pennylane.tape.qscript.QuantumScript
,pennylane.queuing.AnnotatedQueue
A quantum tape recorder, that records and stores variational quantum programs.
 Parameters
ops (Iterable[Operator]) – An iterable of the operations to be performed
measurements (Iterable[MeasurementProcess]) – All the measurements to be performed
prep (Iterable[Operator]) – Arguments to specify state preparations to perform at the start of the circuit. These should go at the beginning of
ops
instead.
 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 tape is only an intermediary step.
Example
Tapes can be constructed by directly providing operations and measurements:
>>> ops = [qml.BasisState([1,0], wires=0), qml.S(0), qml.T(1)] >>> measurements = [qml.state()] >>> tape = qml.tape.QuantumTape(ops, measurements) >>> tape.circuit [BasisState([1, 0], wires=[0]), S(wires=[0]), T(wires=[1]), state(wires=[])]
They can also be populated into a recording tape via queuing.
with qml.tape.QuantumTape() as tape: qml.RX(0.432, wires=0) qml.RY(0.543, wires=0) qml.CNOT(wires=[0, 'a']) qml.RX(0.133, wires='a') qml.expval(qml.Z(0))
A
QuantumTape
can also be constructed directly from anAnnotatedQueue
:with qml.queuing.AnnotatedQueue() as q: qml.RX(0.432, wires=0) qml.RY(0.543, wires=0) qml.CNOT(wires=[0, 'a']) qml.RX(0.133, wires='a') qml.expval(qml.Z(0)) tape = qml.tape.QuantumTape.from_queue(q)
Once constructed, the tape may act as a quantum circuit and information about the quantum circuit can be queried:
>>> list(tape) [RX(0.432, wires=[0]), RY(0.543, wires=[0]), CNOT(wires=[0, 'a']), RX(0.133, wires=['a']), expval(Z(0))] >>> tape.operations [RX(0.432, wires=[0]), RY(0.543, wires=[0]), CNOT(wires=[0, 'a']), RX(0.133, wires=['a'])] >>> tape.observables [expval(Z(0))] >>> tape.get_parameters() [0.432, 0.543, 0.133] >>> tape.wires <Wires = [0, 'a']> >>> tape.num_params 3
The existing circuit is overriden upon exiting a recording context.
Iterating over the quantum circuit can be done by iterating over the tape object:
>>> for op in tape: ... print(op) RX(0.432, wires=[0]) RY(0.543, wires=[0]) CNOT(wires=[0, 'a']) RX(0.133, wires=['a']) expval(Z(0))
Tapes can also as sequences and support indexing and the
len
function:>>> tape[0] RX(0.432, wires=[0]) >>> len(tape) 5
The
CircuitGraph
can also be accessed:>>> tape.graph <pennylane.circuit_graph.CircuitGraph object at 0x7fcc0433a690>
Once constructed, the quantum tape can be executed directly on a supported device via the
execute()
function:>>> dev = qml.device("default.qubit", wires=[0, 'a']) >>> qml.execute([tape], dev, gradient_fn=None) [array([0.77750694])]
A new tape can be created by passing new parameters along with the indices to be updated to
bind_new_parameters()
:>>> new_tape = tape.bind_new_parameters(params=[0.56], indices=[0]) >>> tape.get_parameters() [0.432, 0.543, 0.133] >>> new_tape.get_parameters() [0.56, 0.543, 0.133]
To prevent the tape from being queued use
stop_recording()
.with qml.tape.QuantumTape() as tape1: with qml.QueuingManager.stop_recording(): with qml.tape.QuantumTape() as tape2: qml.RX(0.123, wires=0)
Here, tape2 records the RX gate, but tape1 doesn’t record tape2.
>>> tape1.operations [] >>> tape2.operations [RX(0.123, wires=[0])]
This is useful for when you want to transform a tape first before applying it.
Attributes
The batch size of the quantum script inferred from the batch sizes of the used operations for parameter broadcasting.
Returns the underlying quantum circuit as a list of operations and measurements.
Alias to
get_parameters()
andset_parameters()
for backwards compatibilities with operations.Returns the gates that diagonalize the measured wires such that they are in the eigenbasis of the circuit observables.
Returns a directed acyclic graph representation of the recorded quantum circuit:
returns an integer hash uniquely representing the quantum script
automatic differentiation interface used by the quantum script (if any)
Returns the measurements on the quantum script.
Returns the number of trainable parameters on the quantum script.
Returns the index of the first operator that is not an StatePrepBase operator.
Returns the expected numeric type of the quantum script result by inspecting its measurements.
Returns the observables on the quantum script.
Returns the wires that the tape operations act on.
Returns the state preparations and operations on the quantum script.
The (inferred) output dimension of the quantum script.
Returns a list of objects in the annotated queue
Determines if any of the measurements are in the computational basis.
Returns a
Shots
object containing information about the number and batches of shotsResource information about a quantum circuit.
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 midcircuit measurements andThe
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()
andset_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

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.

queue
¶ Returns a list of objects in the annotated queue

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 methodget_parameters()
.Note
For devices that support native backpropagation (such as
default.qubit.tf
anddefault.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]
Methods
adjoint
()Create a quantum script that is the adjoint of this one.
append
(obj, **kwargs)Append
obj
into the queue withkwargs
metadata.bind_new_parameters
(params, indices)Create a new tape with updated parameters.
clear
()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.
fromkeys
([value])Create a new ordered dictionary with keys from iterable and values set to value.
get
(key[, default])Return the value for key if key is in the dictionary, else default.
get_info
(obj)Retrieve the metadata for
obj
.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.
items
()keys
()Map a circuit’s wires such that they are in a standard order.
move_to_end
(key[, last])Move an existing element to the end (or beginning if last is false).
pop
(k[,d])value.
popitem
([last])Remove and return a (key, value) pair from the dictionary.
remove
(obj)Remove
obj
from the queue.setdefault
(key[, default])Insert key with a value of default if key is not in the dictionary.
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.
update
([E, ]**F)If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k]
update_info
(obj, **kwargs)Update
obj
’s metadata withkwargs
if it exists in the queue.values
()
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

append
(obj, **kwargs)¶ Append
obj
into the queue withkwargs
metadata.

bind_new_parameters
(params, indices)¶ 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
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]

clear
() → None. Remove all items from od.¶

copy
(copy_operations=False)¶ 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

draw
(wire_order=None, show_all_wires=False, decimals=None, max_length=100, show_matrices=True)¶ 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)¶ 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)¶ Construct a QuantumScript from an AnnotatedQueue.

fromkeys
(value=None)¶ Create a new ordered dictionary with keys from iterable and values set to value.

get
(key, default=None, /)¶ Return the value for key if key is in the dictionary, else default.

get_info
(obj)¶ Retrieve the metadata for
obj
. Raises aQueuingError
if obj is not in the queue.

get_operation
(idx)¶ 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)¶ 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 toFalse
to instead return all parameters:>>> qscript.get_parameters(trainable_only=False) [0.432, 0.543, 0.133]

items
() → a setlike object providing a view on D’s items¶

keys
() → a setlike object providing a view on D’s keys¶

map_to_standard_wires
()¶ 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
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 wiremapping 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

move_to_end
(key, last=True)¶ Move an existing element to the end (or beginning if last is false).
Raise KeyError if the element does not exist.

pop
(k[, d]) → v, remove specified key and return the corresponding¶ value. If key is not found, d is returned if given, otherwise KeyError is raised.

popitem
(last=True)¶ Remove and return a (key, value) pair from the dictionary.
Pairs are returned in LIFO order if last is true or FIFO order if false.

remove
(obj)¶ Remove
obj
from the queue. Passes silently if the object is not in the queue.

setdefault
(key, default=None)¶ Insert key with a value of default if key is not in the dictionary.
Return the value for key if key is in the dictionary, else default.

shape
(device)¶ 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)¶ 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 settingmeasure_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 userspecified 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

update
([E, ]**F) → None. Update D from dict/iterable E and F.¶ If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k]

update_info
(obj, **kwargs)¶ Update
obj
’s metadata withkwargs
if it exists in the queue.

values
() → an object providing a view on D’s values¶