qml.measurements.SampleMeasurement¶

class
SampleMeasurement
(obs=None, wires=None, eigvals=None, id=None)[source]¶ Bases:
pennylane.measurements.measurements.MeasurementProcess
Samplebased measurement process.
Any class inheriting from
SampleMeasurement
should define its ownprocess_samples
method, which should have the following arguments:samples (Sequence[complex]): computational basis samples generated for all wires
wire_order (Wires): wires determining the subspace that
samples
acts on shot_range (tuple[int]): 2tuple of integers specifying the range of samples
to use. If not specified, all samples are used.
 bin_size (int): Divides the shot range into bins of size
bin_size
, and returns the measurement statistic separately over each bin. If not provided, the entire shot range is treated as a single bin.
 bin_size (int): Divides the shot range into bins of size
Example:
Let’s create a measurement that returns the sum of all samples of the given wires.
>>> class MyMeasurement(SampleMeasurement): ... def process_samples(self, samples, wire_order, shot_range=None, bin_size=None): ... return qml.math.sum(samples[..., self.wires])
We can now execute it in a QNode:
>>> dev = qml.device("default.qubit", wires=2, shots=1000) >>> @qml.qnode(dev) ... def circuit(): ... qml.PauliX(0) ... return MyMeasurement(wires=[0]), MyMeasurement(wires=[1]) >>> circuit() tensor([1000, 0], requires_grad=True)
Attributes
Whether or not the MeasurementProcess returns a defined decomposition when calling
expand
.returns an integer hash uniquely representing the measurement process
The Python numeric type of the measurement result.
The wires the measurement process acts on.
Measurement return type.
Whether or not the MeasurementProcess measures in the computational basis.
The wires the measurement process acts on.

has_decomposition
¶ Whether or not the MeasurementProcess returns a defined decomposition when calling
expand
. Type
Bool

hash
¶ returns an integer hash uniquely representing the measurement process
 Type
int

numeric_type
¶ The Python numeric type of the measurement result.
 Returns
The output numeric type;
int
,float
orcomplex
. Return type
type
 Raises
QuantumFunctionError – the return type of the measurement process is unrecognized and cannot deduce the numeric type

raw_wires
¶ The wires the measurement process acts on.
For measurements involving more than one set of wires (such as mutual information), this is a list of the Wires objects. Otherwise, this is the same as
wires()

return_type
¶ Measurement return type.

samples_computational_basis
¶ Whether or not the MeasurementProcess measures in the computational basis.
 Type
Bool

wires
¶ The wires the measurement process acts on.
This is the union of all the Wires objects of the measurement.
Methods
Returns the gates that diagonalize the measured wires such that they are in the eigenbasis of the circuit observables.
eigvals
()Eigenvalues associated with the measurement process.
expand
()Expand the measurement of an observable to a unitary rotation and a measurement in the computational basis.
map_wires
(wire_map)Returns a copy of the current measurement process with its wires changed according to the given wire map.
process_samples
(samples, wire_order[, …])Process the given samples.
queue
([context])Append the measurement process to an annotated queue.
shape
([device])The expected output shape of the MeasurementProcess.
simplify
()Reduce the depth of the observable to the minimum.

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]

eigvals
()¶ Eigenvalues associated with the measurement process.
If the measurement process has an associated observable, the eigenvalues will correspond to this observable. Otherwise, they will be the eigenvalues provided when the measurement process was instantiated.
Note that the eigenvalues are not guaranteed to be in any particular order.
Example:
>>> m = MeasurementProcess(Expectation, obs=qml.PauliX(wires=1)) >>> m.eigvals() array([1, 1])
 Returns
eigvals representation
 Return type
array

expand
()¶ Expand the measurement of an observable to a unitary rotation and a measurement in the computational basis.
 Returns
a quantum tape containing the operations required to diagonalize the observable
 Return type
Example:
Consider a measurement process consisting of the expectation value of an Hermitian observable:
>>> H = np.array([[1, 2], [2, 4]]) >>> obs = qml.Hermitian(H, wires=['a']) >>> m = MeasurementProcess(Expectation, obs=obs)
Expanding this out:
>>> tape = m.expand()
We can see that the resulting tape has the qubit unitary applied, and a measurement process with no observable, but the eigenvalues specified:
>>> print(tape.operations) [QubitUnitary(array([[0.89442719, 0.4472136 ], [ 0.4472136 , 0.89442719]]), wires=['a'])] >>> print(tape.measurements[0].eigvals()) [0. 5.] >>> print(tape.measurements[0].obs) None

map_wires
(wire_map)¶ Returns a copy of the current measurement process with its wires changed according to the given wire map.
 Parameters
wire_map (dict) – dictionary containing the old wires as keys and the new wires as values
 Returns
new measurement process
 Return type

abstract
process_samples
(samples, wire_order, shot_range=None, bin_size=None)[source]¶ Process the given samples.
 Parameters
samples (Sequence[complex]) – computational basis samples generated for all wires
wire_order (Wires) – wires determining the subspace that
samples
acts onshot_range (tuple[int]) – 2tuple of integers specifying the range of samples to use. If not specified, all samples are used.
bin_size (int) – Divides the shot range into bins of size
bin_size
, and returns the measurement statistic separately over each bin. If not provided, the entire shot range is treated as a single bin.

queue
(context=<class 'pennylane.queuing.QueuingManager'>)¶ Append the measurement process to an annotated queue.

shape
(device=None)¶ The expected output shape of the MeasurementProcess.
Note that the output shape is dependent on the device when:
The measurement type is either
ProbabilityMP
,StateMP
(fromstate()
) orSampleMP
;The shot vector was defined in the device.
For example, assuming a device with
shots=None
, expectation values and variances defineshape=(1,)
, whereas probabilities in the qubit model defineshape=(1, 2**num_wires)
wherenum_wires
is the number of wires the measurement acts on.Note that the shapes for vectorvalued measurements such as
ProbabilityMP
andStateMP
are adjusted to the output ofqml.execute
and may have an extra first element that is squeezed when using QNodes. Parameters
device (pennylane.Device) – a PennyLane device to use for determining the shape
 Returns
the output shape
 Return type
tuple
 Raises
QuantumFunctionError – the return type of the measurement process is unrecognized and cannot deduce the numeric type

simplify
()¶ Reduce the depth of the observable to the minimum.
 Returns
A measurement process with a simplified observable.
 Return type