Transpiler removes resets at beginning of circuits unless level=0

Information

• Qiskit Terra version: latest
• Python version:
• Operating system:

What is the current behavior?

qc = QuantumCircuit(5, 4)
qc.reset(range(5))
qc.x(4)
qc.h(range(5))
qc.cx(range(4), 4)
qc.draw()
qc.h(range(4))
qc.barrier()
qc.measure(range(4), range(4))
qc.draw('mpl')

becomes:

backend = FakeCasablanca()
trans_qc = transpile(qc, backend)
trans_qc.draw('mpl')

Steps to reproduce the problem

Run above at optimization levels 1->3.

What is the expected behavior?

If the user explicitly puts resets at the beginning of a circuit they should remain there. This is important as the unconditional reset done by default on IBM Quantum systems is not perfect, leading to state prep errors. Adding a reset at the beginning of a circuit greatly suppresses these errors and is needed to get high-fidelity results.

Suggested solutions

Do not remove resets at the beginning of circuits. i.e. do not run this RemoveResetInZeroState

[taalexander]

I can confirm that this is still an open issue, especially for our QASM3 support which currently does not initialize the qubits by default.

[ajavadia]

let’s just remove the RemoveResetInZeroState pass. It’s kind of pointless I think. I think what it’s doing is valid but don’t see much use for it.