Registration decorator for parametric pulse shapes

[lcapelluto]

What is the expected behavior?

From @eggerdj on PR #3463 which introduces Parametric Pulses:

Is there some way around this structure? I'm thinking of the following scenario:
External party, named ABC, wants to use Qiskit and provide their own pulse shapes. It would be a lot nicer if, a user of ABC, in his application, could do

from ABC.parametric_pulses import ABCPulse

where ABC.parametric_pulses.py contains the parametric pulses defined by ABC, without having to manually register the parametric pulse names in this Enum class. Is something like that possible?

The goal of this feature is to replace manually entering new parametric pulses into the mapper in assemble.

[drewrisinger]

As an end-user looking at doing exactly this, I'd be interested in this functionality. If there is no registration decorator, where would we need to plug into/overwrite this functionality? qiskit.qobj.converters.pulse_instruction.ParametricPulseShapes, AFAICT? https://github.com/Qiskit/qiskit-terra/blob/6dbf9dd06b52e4530747bae0af69d728f011f431/qiskit/qobj/converters/pulse_instruction.py#L31-L40

[taalexander]

Yes, I think you have the right idea. This would likely need to be modified into a registry, that registers standard pulses.

[drewrisinger]

Hacky and haven't fully tested it, but looks like the following also temporarily does the job (not as good as registering)

import qiskit.qobj.converters.pulse_instruction as pulse_converter

class NewParamPulse(ParametricPulse):
    pass

pulse_converter.ParametricPulseShapes.NewParamPulse = NewParamPulse

[taalexander]

This does seem like a good solution 👍.

[drewrisinger]

follow-up. The above ^^ method doesn't work b/c of the enum lookup in qiskit.assembler.assemble_schedules::_assemble_instructions(): https://github.com/Qiskit/qiskit-terra/blob/ff5fede2dadf338e7ba36a3efcbf4df6b0e651aa/qiskit/assembler/assemble_schedules.py#L179-L180
Per https://docs.python.org/3/library/enum.html#programmatic-access-to-enumeration-members-and-their-attributes, looking up an enum this way (by passing the instruction type i.e. value) is only available for native enum members. So the remedy is to create a new replacement enum with your custom value, and then overwrite the ParametricPulseShapes above. However, due to the assemble_schedules() method being compiled at import time due to pervasive use of from ... import ... syntax, a much more hacky temporary solution is required:

class NewParamPulseShapes(enum.Enum):
    gaussian = ...
    new_param_pulse = ...

import qiskit.assembler
qiskit.assembler.assemble_schedules.__globals__["ParametricPulseShapes"] = NewParamPulseShapes
# NOTE: tried this syntax, didn't work
# pulse_converter.ParametricPulseShapes = NewParamPulseshapes

# Verify
print(qiskit.assembler.assemble_schedules.__globals__["ParametricPulseShapes"])
qiskit.assemble(schedule_with_new_param_pulse) # errors if above global replacement doesn't succeed

Hope this helps people in future!

[drewrisinger]

Found a better solution than above. Unfortunately it involves an extra python library, but it's a one-line solution, so...

It uses https://pypi.org/project/aenum/

import aenum
import qiskit.qobj.converters.pulse_instruction as pulse_converter

aenum.extend_enum(pulse_converter.ParametricPulseShapes, "new_pulse_shape", NewParamPulse)

[jwoehr]

Did this requirement get subsumed in Pulse Builder?

[drewrisinger]

@jwoehr, I don't think so. Pulse Builder still doesn't cover e.g. a linear ramp parametric pulse defined as e.g. y = m*t + b. I've been using my workaround to add this functionality.

[jwoehr]

@jwoehr, I don't think so. Pulse Builder still doesn't cover e.g. a linear ramp parametric pulse defined as e.g. y = m*t + b. I've been using my workaround to add this functionality.

Thank you, noting that, @drewrisinger

[jakelishman]

I believe this to have been obsoleted by #7821 and follow-on work. @nkanazawa1989, could you check, and close this issue if so?