Write a Pulse Schedule Transformation that reduces all pulse channels to a single Waveform

What is the expected enhancement?

As noted in this Slack conversation there is a desire to be able to reduce all PulseChannels in a Schedule/ScheduleBlock into a single waveform. This means compressing all Play/ShiftPhase/SetPhase/ShiftFrequency/SetFrequency instructions into a single Waveform and also recursively unrolling internally Calls.

It should be noted that there is likely relevant routines in the plotter which does similar transformations.

This could be added as a new transform module here.

[nkanazawa1989]

This is what the plotter calls https://github.com/Qiskit/qiskit-terra/blob/75e06dc915f764ea4e5c1a57097e980e9d01b119/qiskit/pulse/transforms/base_transforms.py#L25-L28 (flattening Call and other high-level transformations are done by this pass)

The target_qobj_transform is called here https://github.com/Qiskit/qiskit-terra/blob/75e06dc915f764ea4e5c1a57097e980e9d01b119/qiskit/visualization/pulse_v2/core.py#L254

Actually, ShiftFrequency and SetFrequency do affect the waveform. Indeed, a waveform needs to get phase factor (exp(i f_d t)) associated with its frame to be played. The frame is rotating at the frequency f which is defined by the backend.defaults().qubit_freq_est, otherwise updated by the SetFrequency and ShiftFrequency. This phase factor is usually computed by the backend control electronics (either by a software or hardware), but the pulse plotter is missing to emulate this behavior. I guess @taalexander needs this option also on the front end.

Usually we don’t need to compute the frame on front end, however, if we need a custom frame such as qudit, we need to compute it. This is the relevant WIP PR: #5977. Apart from this, such frame computation might be necessary for the pulse simulator (it usually uses a rotating frame Hamiltonian to avoid fine dt step, and waveform in the lab frame is not necessary), or necessary for pulse plotter to understand how the waveform look like on the actual hardware.

Here, you need to add multiple transform passes that

• convert ParametricPulses into Waveform
• apply phase shift, set phase instruction to the waveform
• apply frequency shift, set frequency instruction to update frame associated with channels, then get phase factor at t
• optionally apply carrier wave (emulating the mixer)

Then you can create new transform that generates low-level waveform data.

[snsunx]

Hi @1ucian0, sorry I got busy with some other stuff and haven’t been working on this. I unassigned myself and please feel free to assign this issue to others.