Note

This is the documentation for the current state of the development branch of Qiskit Experiments. The documentation or APIs here can change prior to being released.

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.

Initialization

Create new experiment.

Parameters:

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

• backend (Optional[Backend]) – Optional, the backend to run the experiment on.

• delays (Optional[List]) – 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

RamseyXY.analysis	Return the analysis instance for the experiment
RamseyXY.backend	Return the backend for the experiment
RamseyXY.experiment_options	Return the options for the experiment.
RamseyXY.experiment_type	Return experiment type.
RamseyXY.num_qubits	Return the number of qubits for the experiment.
RamseyXY.physical_qubits	Return the device qubits for the experiment.
RamseyXY.run_options	Return options values for the experiment run() method.
RamseyXY.transpile_options	Return the transpiler options for the run() method.

Methods

RamseyXY.circuits()	Create the circuits for the Ramsey XY characterization experiment.
RamseyXY.config()	Return the config dataclass for this experiment
RamseyXY.copy()	Return a copy of the experiment
RamseyXY.enable_restless([rep_delay, ...])	Enables a restless experiment by setting the restless run options and the restless data processor.
RamseyXY.from_config(config)	Initialize an experiment from experiment config
RamseyXY.run([backend, analysis, timeout])	Run an experiment and perform analysis.
RamseyXY.set_experiment_options(**fields)	Set the experiment options.
RamseyXY.set_run_options(**fields)	Set options values for the experiment run() method.
RamseyXY.set_transpile_options(**fields)	Set the transpiler options for run() method.