RamseyXY

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

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

Overview

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

$$\begin{array}{rl}{\mathcal{E}}_x(\tau )=\mathrm{R}\mathrm{e}\mathrm{T}\mathrm{r}\left(YU\rho U^{†}\right)& =-\cos (\mathrm{\Delta }\omega \tau )=\sin (\mathrm{\Delta }\omega \tau -\frac{\pi }{2}),\\ {\mathcal{E}}_y(\tau )=\mathrm{R}\mathrm{e}\mathrm{T}\mathrm{r}\left(XU\rho U^{†}\right)& =\sin (\mathrm{\Delta }\omega \tau ),\end{array}$$

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

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

RamseyXYAnalysis

Experiment options

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

Options

• 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.

Example

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)

	name	experiment	components	value	quality	backend	run_time	chisq
06a2b334	freq	RamseyXY	[Q0]	2099264.5824970957+/-nan	good	T2Hahn_simulator	None	0.998714

Initialization

Create new experiment.

Parameters:

• 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.

Attributes

analysis

Return the analysis instance for the experiment

backend

Return the backend for the experiment

experiment_options

Return the options for the experiment.

experiment_type

Return experiment type.

num_qubits

Return the number of qubits for the experiment.

physical_qubits

Return the device qubits for the experiment.

run_options

Return options values for the experiment run() method.

transpile_options

Return the transpiler options for the run() method.

Methods

circuits()

Create the circuits for the Ramsey XY characterization experiment.

Returns:

A list of circuits with a variable delay.

Return type:

List[QuantumCircuit]

config()

Return the config dataclass for this experiment

Return type:

ExperimentConfig

copy()

Return a copy of the experiment

Return type:

BaseExperiment

classmethod from_config(config)

Initialize an experiment from experiment config

Return type:

BaseExperiment

job_info(backend=None)

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

Parameters:

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

Returns:

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:

dict

Raises:

QiskitError – if backend is not specified.

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

Run an experiment and perform analysis.

Parameters:

• backend (Backend | None) – Optional, the backend to run on. Will override existing backend settings.

• sampler (BaseSamplerV2 | None) – Optional, the sampler to run the experiment on. If None then a sampler will be invoked from previously set backend

• 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.

• backend_run (bool | None) – Use backend run (temp option for testing)

• run_options – backend runtime options used for circuit execution.

Returns:

The experiment data object.

Raises:

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

Return type:

ExperimentData

set_experiment_options(**fields)

Set the experiment options.

Parameters:

fields – The fields to update the options

Raises:

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

set_run_options(**fields)

Set options values for the experiment run() method.

Parameters:

fields – The fields to update the options

See also

The Setting options for your experiment guide for code example.

set_transpile_options(**fields)

Set the transpiler options for run() method.

Parameters:

fields – The fields to update the options

Raises:

QiskitError – If initial_layout is one of the fields.

See also

The Setting options for your experiment guide for code example.