Source code for pennylane.ops.snapshot

# Copyright 2018-2022 Xanadu Quantum Technologies Inc.

# Licensed under the Apache License, Version 2.0 (the "License");
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This module contains the Snapshot (pseudo) operation that is common to both
cv and qubit computing paradigms in PennyLane.
from pennylane.operation import AnyWires, Operation

# pylint: disable=unused-argument
[docs]class Snapshot(Operation): r""" The Snapshot operation saves the internal simulator state at specific execution steps of a quantum function. As such, it is a pseudo operation with no effect on the quantum state. **Details:** * Number of wires: AllWires * Number of parameters: 0 Args: tag (str or None): An optional custom tag for the snapshot, used to index it in the snapshots dictionary. **Example** .. code-block:: python3 dev = qml.device("default.qubit", wires=2) @qml.qnode(dev, interface=None) def circuit(): qml.Snapshot() qml.Hadamard(wires=0) qml.Snapshot("very_important_state") qml.CNOT(wires=[0, 1]) qml.Snapshot() return qml.expval(qml.PauliX(0)) >>> qml.snapshots(circuit)() {0: array([1., 0., 0., 0.]), 'very_important_state': array([0.70710678, 0. , 0.70710678, 0. ]), 2: array([0.70710678, 0. , 0. , 0.70710678]), 'execution_results': 0.0} .. seealso:: :func:`~.snapshots` """ num_wires = AnyWires num_params = 0 grad_method = None def __init__(self, tag=None): self.tag = tag super().__init__(wires=[])
[docs] def label(self, decimals=None, base_label=None, cache=None): return "|Snap|"
[docs] @staticmethod def compute_decomposition(*params, wires=None, **hyperparameters): return []
def _controlled(self, _): return Snapshot(tag=self.tag)
[docs] def adjoint(self): return Snapshot(tag=self.tag)