qml.measurements.MeasurementProcess¶
- class MeasurementProcess(obs=None, wires=None, eigvals=None, id=None)[source]¶
Bases:
abc.ABC
Represents a measurement process occurring at the end of a quantum variational circuit.
- Parameters
obs (Union[Operator, MeasurementValue, Sequence[MeasurementValue]]) – The observable that is to be measured as part of the measurement process. Not all measurement processes require observables (for example
Probability
); this argument is optional.wires (Wires) – The wires the measurement process applies to. This can only be specified if an observable was not provided.
eigvals (array) – A flat array representing the eigenvalues of the measurement. This can only be specified if an observable was not provided.
id (str) – custom label given to a measurement instance, can be useful for some applications where the instance has to be identified
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.
queue
([context])Append the measurement process to an annotated queue.
shape
([shots, num_device_wires])Calculate the shape of the result object tensor.
simplify
()Reduce the depth of the observable to the minimum.
- diagonalizing_gates()[source]¶
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()[source]¶
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.X(1)) >>> m.eigvals() array([1, -1])
- Returns
eigvals representation
- Return type
array
- expand()[source]¶
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)[source]¶
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
- queue(context=<class 'pennylane.queuing.QueuingManager'>)[source]¶
Append the measurement process to an annotated queue.
- shape(shots=None, num_device_wires=0)[source]¶
Calculate the shape of the result object tensor.
- Parameters
shots (Optional[int]) – the number of shots used execute the circuit.
None
indicates an analytic simulation. Shot vectors are handled by calling this method multiple times.num_device_wires (int) – The number of wires that will be used if the measurement is broadcasted across all available wires (
len(mp.wires) == 0
). If the device itself doesn’t provide a number of wires, the number of tape wires will be provided here instead:
- Returns
An arbitrary length tuple of ints. May be an empty tuple.
- Return type
tuple[int,…]
>>> qml.probs(wires=(0,1)).shape() (4,) >>> qml.sample(wires=(0,1)).shape(shots=50) (50, 2) >>> qml.state().shape(num_device_wires=4) (16,) >>> qml.expval(qml.Z(0)).shape() ()