Initial resets being removed by transpiler

[nonhermitian]

Information

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

What is the current behavior?

This circuit

has becomes

after transpilation (levels 1,2,3) on a backend with reset support.

print(backend.configuration().basis_gates)

['id', 'rz', 'sx', 'x', 'cx', 'ecr', 'reset']

This means that I do not get correct answers using init_qubits=False.

Steps to reproduce the problem

What is the expected behavior?

Suggested solutions

[1ucian0]

Is there a backend property that indicates that the backend start in ground state? We could do the transpilation process depending on that.

[nonhermitian]

If one sets init_qubits=False in execute then the backend does not initialize qubits. This is a Qobj thing not a transpile thing, so perhaps the correct thing to do is to remove reset only when they are not supported on the device. Indeed, a reset at the beginning will not do much to a state if initialized anyway.