Source code for qiskit_experiments.library.characterization.ramsey_xy

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# (C) Copyright IBM 2021.
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# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
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"""Ramsey XY frequency characterization experiment."""
from typing import List, Optional, Sequence

import numpy as np
from qiskit.circuit import QuantumCircuit, Parameter
from qiskit.providers.backend import Backend
from qiskit.qobj.utils import MeasLevel

from qiskit_experiments.framework import BaseExperiment, Options, BackendTiming
from qiskit_experiments.framework.restless_mixin import RestlessMixin
from qiskit_experiments.library.characterization.analysis import RamseyXYAnalysis


[docs] class RamseyXY(BaseExperiment, RestlessMixin): r"""A sign-sensitive experiment to measure the frequency of a qubit. # section: overview This experiment differs from the :class:`~qiskit_experiments.characterization.\ t2ramsey.T2Ramsey` since it is sensitive to the sign of the frequency offset from the main transition. This experiment consists of following two circuits: .. parsed-literal:: (Ramsey X) The second pulse rotates by pi-half around the X axis ┌────┐┌─────────────┐┌───────┐┌────┐ ░ ┌─┐ q_0: ┤ √X ├┤ Delay(τ[s]) ├┤ Rz(θ) ├┤ √X ├─░─┤M├ └────┘└─────────────┘└───────┘└────┘ ░ └╥┘ measure: 1/════════════════════════════════════════╩═ 0 (Ramsey Y) The second pulse rotates by pi-half around the Y axis ┌────┐┌─────────────┐┌───────────┐┌────┐ ░ ┌─┐ q_0: ┤ √X ├┤ Delay(τ[s]) ├┤ Rz(θ-π/2) ├┤ √X ├─░─┤M├ └────┘└─────────────┘└───────────┘└────┘ ░ └╥┘ measure: 1/════════════════════════════════════════════╩═ 0 The first and second circuits measure the expectation value along the -Y and X axes, respectively. This experiment therefore tracks the dynamics of the Bloch vector around the equator. The drive frequency of the control electronics defines a reference frame, which differs from the true qubit frequency by :math:`\Delta\omega`. The Hamiltonian during the ``Delay`` instruction is :math:`H^R = - \frac{1}{2} \Delta\omega` in the rotating frame, and the propagator will be :math:`U(\tau) = \exp(-iH^R\tau / \hbar)` where :math:`\tau` is the duration of the delay. By scanning this duration, we can get .. math:: {\cal E}_x(\tau) = {\rm Re} {\rm Tr}\left( Y U \rho U^\dagger \right) &= - \cos(\Delta\omega\tau) = \sin(\Delta\omega\tau - \frac{\pi}{2}), \\ {\cal E}_y(\tau) = {\rm Re} {\rm Tr}\left( X U \rho U^\dagger \right) &= \sin(\Delta\omega\tau), where :math:`\rho` is prepared by the first :math:`\sqrt{\rm X}` gate. Note that phase difference of these two outcomes :math:`{\cal E}_x, {\cal E}_y` depends on the sign and the magnitude of the frequency offset :math:`\Delta\omega`. By contrast, the measured data in the standard Ramsey experiment does not depend on the sign of :math:`\Delta\omega`, because :math:`\cos(-\Delta\omega\tau) = \cos(\Delta\omega\tau)`. The experiment also allows users to add a small frequency offset to better resolve any oscillations. This is implemented by a virtual Z rotation in the circuits. In the circuit above it appears as the delay-dependent angle θ(τ). # section: analysis_ref :class:`RamseyXYAnalysis` # section: example .. jupyter-execute:: :hide-code: # backend from qiskit_aer import AerSimulator from qiskit_ibm_runtime.fake_provider import FakePerth backend = AerSimulator.from_backend(FakePerth()) .. jupyter-execute:: import numpy as np from qiskit_experiments.library.characterization import RamseyXY delays = np.linspace(0, 10.e-7, 101) exp = RamseyXY((0,), backend=backend, delays=delays, osc_freq=2.0e6) exp_data = exp.run().block_for_results() display(exp_data.figure(0)) exp_data.analysis_results(dataframe=True) """ @classmethod def _default_experiment_options(cls) -> Options: """Default values for the Ramsey XY experiment. Experiment Options: delays (list): The list of delays that will be scanned in the experiment, in seconds. osc_freq (float): A frequency shift in Hz that will be applied by means of a virtual Z rotation to increase the frequency of the measured oscillation. """ options = super()._default_experiment_options() options.delays = np.linspace(0, 1.0e-6, 51) options.osc_freq = 2e6 return options def __init__( self, physical_qubits: Sequence[int], backend: Optional[Backend] = None, delays: Optional[List] = None, osc_freq: float = 2e6, ): """Create new experiment. Args: physical_qubits: List containing the qubit on which to run the Ramsey XY experiment. backend: Optional, the backend to run the experiment on. delays: The delays to scan, in seconds. osc_freq: the oscillation frequency induced by the user through a virtual Rz rotation. This quantity is given in Hz. """ super().__init__(physical_qubits, analysis=RamseyXYAnalysis(), backend=backend) if delays is None: delays = self.experiment_options.delays self.set_experiment_options(delays=delays, osc_freq=osc_freq) def _pre_circuit(self) -> QuantumCircuit: """Return a preparation circuit. This method can be overridden by subclasses e.g. to run on transitions other than the 0 <-> 1 transition. """ return QuantumCircuit(1)
[docs] def circuits(self) -> List[QuantumCircuit]: """Create the circuits for the Ramsey XY characterization experiment. Returns: A list of circuits with a variable delay. """ timing = BackendTiming(self.backend) p_delay = Parameter("delay") rotation_angle = 2 * np.pi * self.experiment_options.osc_freq * p_delay if timing.delay_unit == "dt": rotation_angle = rotation_angle * timing.dt # Create the X and Y circuits. ram_x = self._pre_circuit() ram_x.sx(0) ram_x.delay(p_delay, 0, timing.delay_unit) ram_x.rz(rotation_angle, 0) ram_x.sx(0) ram_x.measure_active() ram_y = self._pre_circuit() ram_y.sx(0) ram_y.delay(p_delay, 0, timing.delay_unit) ram_y.rz(rotation_angle - np.pi / 2, 0) ram_y.sx(0) ram_y.measure_active() circs = [] for delay in self.experiment_options.delays: delay_dt = timing.round_delay(time=delay) delay_sec = timing.delay_time(time=delay) assigned_x = ram_x.assign_parameters({p_delay: delay_dt}, inplace=False) assigned_x.metadata = { "series": "X", "xval": delay_sec, } assigned_y = ram_y.assign_parameters({p_delay: delay_dt}, inplace=False) assigned_y.metadata = { "series": "Y", "xval": delay_sec, } circs.extend([assigned_x, assigned_y]) return circs
def _finalize(self): # Set initial guess for sinusoidal offset when meas level is 2. # This returns probability P1 thus offset=0.5 is obvious. # This guarantees reasonable fit especially when data contains only less than half cycle. meas_level = self.run_options.get("meas_level", MeasLevel.CLASSIFIED) if meas_level == MeasLevel.CLASSIFIED: init_guess = self.analysis.options.get("p0", {}) if "base" not in init_guess: init_guess["base"] = 0.5 self.analysis.set_options(p0=init_guess) def _metadata(self): metadata = super()._metadata() # Store measurement level and meas return if they have been # set for the experiment for run_opt in ["meas_level", "meas_return"]: if hasattr(self.run_options, run_opt): metadata[run_opt] = getattr(self.run_options, run_opt) return metadata