Source code for pennylane.pauli.grouping.optimize_measurements

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The main function for measurement reduction, ``optimize_measurements`` returns the partitions and
corresponding necessary circuit post-rotations for a given list of Pauli words.

from pennylane.pauli.utils import diagonalize_qwc_groupings
from .group_observables import group_observables

[docs]def optimize_measurements(observables, coefficients=None, grouping="qwc", colouring_method="rlf"): """Partitions then diagonalizes a list of Pauli words, facilitating simultaneous measurement of all observables within a partition. The input list of observables are partitioned into mutually qubit-wise commuting (QWC) or mutually commuting partitions by approximately solving minimum clique cover on a graph where each observable represents a vertex. The unitaries which diagonalize the partitions are then found. See `arXiv:1907.03358 <>`_ and `arXiv:1907.09386 <>`_ for technical details of the QWC and fully-commuting measurement-partitioning approaches respectively. Args: observables (list[Observable]): a list of Pauli words (Pauli operation instances and Tensor instances thereof) coefficients (list[float]): a list of float coefficients, for instance the weights of the Pauli words comprising a Hamiltonian grouping (str): the binary symmetric relation to use for operator partitioning colouring_method (str): the graph-colouring heuristic to use in obtaining the operator partitions Returns: tuple: * list[callable]: a list of the post-rotation templates, one for each partition * list[list[Observable]]: A list of the obtained groupings. Each grouping is itself a list of Pauli words diagonal in the measurement basis. * list[list[float]]: A list of coefficient groupings. Each coefficient grouping is itself a list of the partitions corresponding coefficients. Only output if coefficients are specified. **Example** >>> obs = [qml.PauliY(0), qml.PauliX(0) @ qml.PauliX(1), qml.PauliZ(1)] >>> coeffs = [1.43, 4.21, 0.97] >>> rotations, groupings, grouped_coeffs = optimize_measurements(obs, coeffs, 'qwc', 'rlf') >>> print(rotations) [[RY(-1.5707963267948966, wires=[0]), RY(-1.5707963267948966, wires=[1])], [RX(1.5707963267948966, wires=[0])]] >>> print(groupings) [[PauliZ(wires=[0]) @ PauliZ(wires=[1])], [PauliZ(wires=[0]), PauliZ(wires=[1])]] >>> print(grouped_coeffs) [[4.21], [1.43, 0.97]] """ if coefficients is None: grouped_obs = group_observables( observables, grouping_type=grouping, method=colouring_method ) else: grouped_obs, grouped_coeffs = group_observables( observables, coefficients, grouping_type=grouping, method=colouring_method ) if grouping.lower() == "qwc": ( post_rotations, diagonalized_groupings, ) = diagonalize_qwc_groupings(grouped_obs) else: raise NotImplementedError( f"Measurement reduction by '{grouping.lower()}' grouping not implemented." ) if coefficients is None: return post_rotations, diagonalized_groupings return post_rotations, diagonalized_groupings, grouped_coeffs