class RamseyXY(physical_qubits, backend=None, delays=None, osc_freq=2000000.0)[source]

A sign-sensitive experiment to measure the frequency of a qubit.


This experiment differs from the T2Ramsey since it is sensitive to the sign of the frequency offset from the main transition. This experiment consists of following two circuits:

(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/════════════════════════════════════════╩═

(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/════════════════════════════════════════════╩═

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 \(\Delta\omega\). The Hamiltonian during the Delay instruction is \(H^R = - \frac{1}{2} \Delta\omega\) in the rotating frame, and the propagator will be \(U(\tau) = \exp(-iH^R\tau / \hbar)\) where \(\tau\) is the duration of the delay. By scanning this duration, we can get

\[\begin{split}{\cal E}_x(\tau) = {\rm Re} {\rm Tr}\left( Y U \rho U^\dagger \right) &= - \cos(\Delta\omega\tau) = \sin(\Delta\omega\tau - \frac{\pi}{2}), \\ {\cal E}_y(\tau) = {\rm Re} {\rm Tr}\left( X U \rho U^\dagger \right) &= \sin(\Delta\omega\tau),\end{split}\]

where \(\rho\) is prepared by the first \(\sqrt{\rm X}\) gate. Note that phase difference of these two outcomes \({\cal E}_x, {\cal E}_y\) depends on the sign and the magnitude of the frequency offset \(\Delta\omega\). By contrast, the measured data in the standard Ramsey experiment does not depend on the sign of \(\Delta\omega\), because \(\cos(-\Delta\omega\tau) = \cos(\Delta\omega\tau)\).

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).

Analysis class reference


Experiment options

These options can be set by the set_experiment_options() method.

  • Defined in the class RamseyXY:

    • delays (list)

      Default value: array(0.0, 2e-08, 4e-08, 6.000000000000001e-08, 8e-08, ..., size=51)
      The list of delays that will be scanned in the experiment, in seconds.
    • osc_freq (float)

      Default value: 2000000.0
      A frequency shift in Hz that will be applied by means of a virtual Z rotation to increase the frequency of the measured oscillation.
  • Defined in the class BaseExperiment:

    • max_circuits (Optional[int])

      Default value: None
      The maximum number of circuits per job when running an experiment on a backend.


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()
name experiment components value quality backend run_time chisq
a304c603 @Parameters_RamseyXYAnalysis RamseyXY [Q0] CurveFitResult:\n - fitting method: least_squa... good aer_simulator_from(fake_perth) None None
9bd82df4 freq RamseyXY [Q0] (1.9978+/-0.0015)e+06 good aer_simulator_from(fake_perth) None 0.856306


Create new experiment.

  • physical_qubits (Sequence[int]) – List containing the qubit on which to run the Ramsey XY experiment.

  • backend (Backend | None) – Optional, the backend to run the experiment on.

  • delays (List | None) – The delays to scan, in seconds.

  • osc_freq (float) – the oscillation frequency induced by the user through a virtual Rz rotation. This quantity is given in Hz.


analysis: BaseAnalysis

Return the analysis instance for the experiment


Return the backend for the experiment


Return the options for the experiment.


Return experiment type.


Return the number of qubits for the experiment.


Return the device qubits for the experiment.


Return options values for the experiment run() method.


Return the transpiler options for the run() method.



Create the circuits for the Ramsey XY characterization experiment.


A list of circuits with a variable delay.

Return type:



Return the config dataclass for this experiment

Return type:



Return a copy of the experiment

Return type:


enable_restless(rep_delay=None, override_processor_by_restless=True, suppress_t1_error=False)

Enables a restless experiment by setting the restless run options and the restless data processor.

  • rep_delay (float | None) – The repetition delay. This is the delay between a measurement and the subsequent quantum circuit. Since the backends have dynamic repetition rates, the repetition delay can be set to a small value which is required for restless experiments. Typical values are 1 us or less.

  • override_processor_by_restless (bool) – If False, a data processor that is specified in the analysis options of the experiment is not overridden by the restless data processor. The default is True.

  • suppress_t1_error (bool) – If True, the default is False, then no error will be raised when rep_delay is larger than the T1 times of the qubits. Instead, a warning will be logged as restless measurements may have a large amount of noise.

  • DataProcessorError – If the attribute rep_delay_range is not defined for the backend.

  • DataProcessorError – If a data processor has already been set but override_processor_by_restless is True.

  • DataProcessorError – If the experiment analysis does not have the data_processor option.

  • DataProcessorError – If the rep_delay is equal to or greater than the T1 time of one of the physical qubits in the experiment and the flag ignore_t1_check is False.

classmethod from_config(config)

Initialize an experiment from experiment config

Return type:



Get information about job distribution for the experiment on a specific backend.


backend (Backend) – Optional, the backend for which to get job distribution information. If not specified, the experiment must already have a set backend.


A dictionary containing information about job distribution.

  • ”Total number of circuits in the experiment”: Total number of circuits in the experiment.

  • ”Maximum number of circuits per job”: Maximum number of circuits in one job based on backend and experiment settings.

  • ”Total number of jobs”: Number of jobs needed to run this experiment on the currently set backend.

Return type:



QiskitError – if backend is not specified.

run(backend=None, analysis='default', timeout=None, **run_options)

Run an experiment and perform analysis.

  • backend (Backend | None) – Optional, the backend to run the experiment on. This will override any currently set backends for the single execution.

  • analysis (BaseAnalysis | None) – Optional, a custom analysis instance to use for performing analysis. If None analysis will not be run. If "default" the experiments analysis() instance will be used if it contains one.

  • timeout (float | None) – Time to wait for experiment jobs to finish running before cancelling.

  • run_options – backend runtime options used for circuit execution.


The experiment data object.


QiskitError – If experiment is run with an incompatible existing ExperimentData container.

Return type:



Set the experiment options.


fields – The fields to update the options


AttributeError – If the field passed in is not a supported options


Set options values for the experiment run() method.


fields – The fields to update the options

See also

The Setting options for your experiment guide for code example.


Set the transpiler options for run() method.


fields – The fields to update the options


QiskitError – If initial_layout is one of the fields.

See also

The Setting options for your experiment guide for code example.