StarkRamseyXY¶

class StarkRamseyXY(physical_qubits, backend=None, **experiment_options)[source]¶

A sign-sensitive experiment to measure the frequency of a qubit under a pulsed Stark tone.

Overview

This experiment is a variant of RamseyXY with a pulsed Stark tone and consists of the following two circuits:

(Ramsey X)  The pulse before measurement rotates by pi-half around the X axis

         ┌────┐┌────────┐┌───┐┌───────────────┐┌────────┐┌────┐┌─┐
      q: ┤ √X ├┤ StarkV ├┤ X ├┤ StarkU(delay) ├┤ Rz(-π) ├┤ √X ├┤M├
         └────┘└────────┘└───┘└───────────────┘└────────┘└────┘└╥┘
    c: 1/═══════════════════════════════════════════════════════╩═
                                                                0

(Ramsey Y) The pulse before measurement rotates by pi-half around the Y axis

         ┌────┐┌────────┐┌───┐┌───────────────┐┌───────────┐┌────┐┌─┐
      q: ┤ √X ├┤ StarkV ├┤ X ├┤ StarkU(delay) ├┤ Rz(-3π/2) ├┤ √X ├┤M├
         └────┘└────────┘└───┘└───────────────┘└───────────┘└────┘└╥┘
    c: 1/══════════════════════════════════════════════════════════╩═
                                                                   0

In principle, the sequence is a variant of RamseyXY circuit. However, the delay in between √X gates is replaced with an off-resonant drive. This off-resonant drive shifts the qubit frequency due to the Stark effect and causes it to accumulate phase during the Ramsey sequence. This frequency shift is a function of the offset of the Stark tone frequency from the qubit frequency and of the magnitude of the tone.

Note that the Stark tone pulse (StarkU) takes the form of a flat-topped Gaussian envelope. The magnitude of the pulse varies in time during its rising and falling edges. It is difficult to characterize the net phase accumulation of the qubit during the edges of the pulse when the frequency shift is varying with the pulse amplitude. In order to simplify the analysis, an additional pulse (StarkV) involving only the edges of StarkU is added to the sequence. The sign of the phase accumulation is inverted for StarkV relative to that of StarkU by inserting an X gate in between the two pulses.

This technique allows the experiment to accumulate only the net phase during the flat-top part of the StarkU pulse with constant magnitude.

User manual

AC Stark Effect

Analysis class reference

qiskit_experiments.library.characterization.RamseyXYAnalysis

Experiment options

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

Options

Defined in the class StarkRamseyXY:
- stark_amp (float)
  
  Default value: 0.0
  
  A single float parameter to represent the magnitude of Stark tone and the sign of expected Stark shift. See Stark tone implementation in Qiskit for details.
- stark_channel (PulseChannel)
  
  Default value: None
  
  Pulse channel to apply Stark tones. If not provided, the same channel with the qubit drive is used. See Stark tone channel for details.
- stark_freq_offset (float)
  
  Default value: 80000000.0
  
  Offset of Stark tone frequency from the qubit frequency. This offset should be sufficiently large so that the Stark pulse does not Rabi drive the qubit. See Stark tone frequency for details.
- stark_sigma (float)
  
  Default value: 1.5e-08
  
  Gaussian sigma of the rising and falling edges of the Stark tone, in seconds.
- stark_risefall (float)
  
  Default value: 2
  
  Ratio of sigma to the duration of the rising and falling edges of the Stark tone.
- min_freq (float)
  
  Default value: 5000000.0
  
  Minimum frequency that this experiment is guaranteed to resolve. Note that fitter algorithm RamseyXYAnalysis of this experiment is still capable of fitting experiment data with lower frequency.
- max_freq (float)
  
  Default value: 100000000.0
  
  Maximum frequency that this experiment can resolve.
- delays (list[float])
  
  Default value: None
  
  The list of delays if set that will be scanned in the experiment. If not set, then evenly spaced delays with interval computed from min_freq and max_freq are used. See StarkRamseyXY.delays() for details.
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.