Source code for pennylane.ops.functions.iterative_qpe

# Copyright 2018-2023 Xanadu Quantum Technologies Inc.

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This module contains the qml.iterative_qpe function.

import numpy as np
import pennylane as qml

[docs]def iterative_qpe(base, ancilla, iters): r"""Performs the `iterative quantum phase estimation <>`_ circuit. Given a unitary :math:`U`, this function applies the circuit for iterative quantum phase estimation and returns a list of mid-circuit measurements with qubit reset. Args: base (Operator): the phase estimation unitary, specified as an :class:`~.Operator` ancilla (Union[Wires, int, str]): the wire to be used for the estimation iters (int): the number of measurements to be performed Returns: list[MidMeasureMP]: the list of measurements performed .. seealso:: :class:`~.QuantumPhaseEstimation`, :func:`~.measure` **Example** .. code-block:: python dev = qml.device("default.qubit", shots=5) @qml.qnode(dev) def circuit(): # Initial state qml.X(0) # Iterative QPE measurements = qml.iterative_qpe(qml.RZ(2.0, wires=[0]), ancilla=1, iters=3) return qml.sample(measurements) .. code-block:: pycon >>> print(circuit()) [[0 0 1] [0 0 1] [0 0 1] [1 1 1] [0 0 1]] The output is an array of size ``(number of shots, number of iterations)``. .. code-block:: pycon >>> print(qml.draw(circuit, max_length=150)()) 0: ──X─╭RZ(2.00)⁴─────────────────╭RZ(2.00)²────────────────────────────╭RZ(2.00)¹────────────────────────────────────┤ 1: ──H─╰●──────────H──┤↗│ │0⟩──H─╰●──────────Rϕ(-1.57)──H──┤↗│ │0⟩──H─╰●──────────Rϕ(-1.57)──Rϕ(-0.79)──H──┤↗│ │0⟩─┤ ╚══════════════════════╩══════════════║══════════════════════║══════════╩══════════════║═══════╡ ╭Sample[MCM] ╚══════════════════════╩═════════════════════════║═══════╡ ├Sample[MCM] ╚═══════╡ ╰Sample[MCM] """ measurements = [] for i in range(iters): qml.Hadamard(wires=ancilla) qml.ctrl(qml.pow(base, z=2 ** (iters - i - 1)), control=ancilla) for ind, meas in enumerate(measurements): qml.cond(meas, qml.PhaseShift)(-2.0 * np.pi / 2 ** (ind + 2), wires=ancilla) qml.Hadamard(wires=ancilla) measurements.insert(0, qml.measure(wires=ancilla, reset=True)) return measurements