RZXCalibrationBuilder aligns pulses incorrectly

Environment

• Qiskit Terra version: 0.22.0
• Python version: 3.9.13
• Operating system: Darwin

What is happening?

When using the RZXCalibrationBuilder on the dev branch of qiskit-terra, the resulting pulses are scheduled incorrectly. In particular, pulses cannot simultaneously be played on both the control qubit’s DriveChannel and ControlChannel simultaneous, resulting in a 9999 error on the (actual) backend.

How can we reproduce the issue?

from qiskit import schedule
from qiskit.circuit import QuantumCircuit
from qiskit.transpiler import PassManager
from qiskit.transpiler.passes import RZXCalibrationBuilder
from qiskit.providers.fake_provider import FakeMumbai

qc = QuantumCircuit(2)
qc.rzx(0.7, 0, 1)
qc.draw()

yields

     ┌───────────┐
q_0: ┤0          ├
     │  Rzx(0.7) │
q_1: ┤1          ├
     └───────────┘

Then

backend = FakeMumbai()
inst_sched_map = backend.defaults().instruction_schedule_map
coupling_map = backend.configuration().coupling_map
pm = PassManager(RZXCalibrationBuilder(inst_sched_map, coupling_map))
qc_pulse = pm.run(qc)
schedule(qc_pulse, backend).draw()

Note the top blue pulses should never occur at the same time as the yellow pulses.

What should happen?

Using the current stable version of Terra (0.21.2), the above code yields

Any suggestions?

There is likely a missing pulse.align_sequential() context in rzx_builder.py.

[nkanazawa1989]

Thanks for reporting and testing the PR. I added this (unintentional) fix to the release note.

[nbronn]

Well, this issue should be kept open until that PR is actually merged.

If you say so.