Support new-style Bit in Pauli convertor from QuantumCircuit (#10757) (…

…#10760)

* Do not use Bit.index in quantum_info/operators/symplectic/pauli.py

* bugfix

* Fix cross-reference

---------

Co-authored-by: Jake Lishman <jake@binhbar.com>
(cherry picked from commit 89ea58b)

Co-authored-by: Luciano Bello <bel@zurich.ibm.com>

qiskit/quantum_info/operators/symplectic/pauli.py

@@ -157,7 +157,12 @@ class initialization (``Pauli('-iXYZ')``). A ``Pauli`` object can be
     _CANONICAL_PHASE_LABEL = {"": 0, "-i": 1, "-": 2, "i": 3}
 
     def __init__(
-        self, data: str | tuple | Pauli | ScalarOp | None = None, x=None, *, z=None, label=None
+        self,
+        data: str | tuple | Pauli | ScalarOp | QuantumCircuit | None = None,
+        x=None,
+        *,
+        z=None,
+        label=None,
     ):
         """Initialize the Pauli.
 
@@ -712,7 +717,7 @@ def _from_circuit(cls, instr):
             if not isinstance(inner.operation, (Barrier, Delay)):
                 next_instr = BasePauli(*cls._from_circuit(inner.operation))
                 if next_instr is not None:
-                    qargs = [tup.index for tup in inner.qubits]
+                    qargs = [instr.find_bit(tup).index for tup in inner.qubits]
                     ret = ret.compose(next_instr, qargs=qargs)
         return ret._z, ret._x, ret._phase
 

releasenotes/notes/fix_pauli_new_style_bit-0704933127b4debe.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The class :class:`.Pauli` now support creation from :class:`.QuantumCircuit`
+    that use new-style :class:`.Bit`.

test/python/quantum_info/operators/symplectic/test_pauli.py

@@ -23,6 +23,7 @@
 from ddt import ddt, data, unpack
 
 from qiskit import QuantumCircuit
+from qiskit.circuit import Qubit
 from qiskit.exceptions import QiskitError
 from qiskit.circuit.library import (
     IGate,
@@ -484,6 +485,15 @@ def test_zero_qubit_pauli_construction(self, label, phase):
         test = Pauli(label)
         self.assertEqual(expected, test)
 
+    def test_circuit_with_bit(self):
+        """Test new-style Bit support when converting from QuantumCircuit"""
+        circ = QuantumCircuit([Qubit()])
+        circ.x(0)
+        value = Pauli(circ)
+        target = Pauli("X")
+
+        self.assertEqual(value, target)
+
 
 if __name__ == "__main__":
     unittest.main()