optimize_single_qubit_gates does not preserve layout

[JMuff22]

When using the function optimize_single_qubit_gates on an already transpiled circuit (as per the docs), the layout provided to the transpiler is not preserved. The means that an additional transpiler pass is needed after running optimize_single_qubit_gates.

Reproducible example

from qiskit import QuantumCircuit
from qiskit import transpile
from iqm.qiskit_iqm import IQMFakeAdonis
from iqm.qiskit_iqm.iqm_transpilation import optimize_single_qubit_gates

qc = QuantumCircuit(3)
qc.h(0)
qc.cx(0, 1)
qc.cx(0, 2)
qc.measure_all()

print(qc.draw(output='text'))

backend = IQMFakeAdonis()
transpiled_circuit = transpile(qc, backend=backend)

print()
print(transpiled_circuit.draw(output='text'))

qc_optimized = optimize_single_qubit_gates(transpiled_circuit)

print()
print(qc_optimized.draw(output='text', idle_wires=False))

Gives

        ┌───┐           ░ ┌─┐      
   q_0: ┤ H ├──■────■───░─┤M├──────
        └───┘┌─┴─┐  │   ░ └╥┘┌─┐   
   q_1: ─────┤ X ├──┼───░──╫─┤M├───
             └───┘┌─┴─┐ ░  ║ └╥┘┌─┐
   q_2: ──────────┤ X ├─░──╫──╫─┤M├
                  └───┘ ░  ║  ║ └╥┘
meas: 3/═══════════════════╩══╩══╩═
                           0  1  2 
layout=None

global phase: π/2
               ┌────────────┐┌────────┐   ┌────────────┐  ┌────────┐             ░    ┌─┐   
      q_1 -> 0 ┤ R(π/2,π/2) ├┤ R(π,0) ├─■─┤ R(π/2,π/2) ├──┤ R(π,0) ├─────────────░────┤M├───
               └────────────┘└────────┘ │ └────────────┘  └────────┘             ░    └╥┘   
ancilla_0 -> 1 ─────────────────────────┼──────────────────────────────────────────────╫────
               ┌────────────┐┌────────┐ │                                        ░ ┌─┐ ║    
      q_0 -> 2 ┤ R(π/2,π/2) ├┤ R(π,0) ├─■───────■────────────────────────────────░─┤M├─╫────
               └────────────┘└────────┘         │                                ░ └╥┘ ║    
ancilla_1 -> 3 ─────────────────────────────────┼───────────────────────────────────╫──╫────
               ┌────────────┐┌────────┐         │       ┌────────────┐┌────────┐ ░  ║  ║ ┌─┐
      q_2 -> 4 ┤ R(π/2,π/2) ├┤ R(π,0) ├─────────■───────┤ R(π/2,π/2) ├┤ R(π,0) ├─░──╫──╫─┤M├
               └────────────┘└────────┘                 └────────────┘└────────┘ ░  ║  ║ └╥┘
       meas: 3/═════════════════════════════════════════════════════════════════════╩══╩══╩═
                                                                                    0  1  2 

global phase: 3π/2
        ┌─────────────┐   ┌─────────────┐                ░    ┌─┐   
   q_0: ┤ R(π/2,3π/2) ├─■─┤ R(π/2,5π/2) ├────────────────░────┤M├───
        ├─────────────┤ │ └─────────────┘                ░ ┌─┐└╥┘   
   q_2: ┤ R(π/2,3π/2) ├─■────────■───────────────────────░─┤M├─╫────
        ├─────────────┤          │       ┌─────────────┐ ░ └╥┘ ║ ┌─┐
   q_4: ┤ R(π/2,3π/2) ├──────────■───────┤ R(π/2,5π/2) ├─░──╫──╫─┤M├
        └─────────────┘                  └─────────────┘ ░  ║  ║ └╥┘
meas: 3/════════════════════════════════════════════════════╩══╩══╩═
                                                            0  1  2 

The also applies when providing a layout to the transpiler e.g with initial_layout.

[Aerylia]

This bug has been made obsolete with the integration of the IQMOptimizeSingleQubitGates pass into the native Qiskit transpiler logic in the form of a transpiler plugin. Additionally, the transpile_to_IQM function has made the optimize_single_qubit_gates function obsolete and will be deprecated with version 16.0.

Tests cases for this bug have been created and the issue should be resolved with #116

[JMuff22]

This bug has been made obsolete with the integration of the IQMOptimizeSingleQubitGates pass into the native Qiskit transpiler logic in the form of a transpiler plugin. Additionally, the transpile_to_IQM function has made the optimize_single_qubit_gates function obsolete and will be deprecated with version 16.0.

Tests cases for this bug have been created and the issue should be resolved with #116

Thanks @Aerylia !!