Remove deprecated Bit.index and Bit.register usage. (#569)

Address deprecation warnings raised by Qiskit/qiskit#6069 .

qiskit/ignis/verification/accreditation/qotp.py

@@ -152,6 +152,9 @@ def QOTP_fromlayers(layers, rng):
     qotp_circ = QuantumCircuit(qregs, cregs)
     temp_circ = QuantumCircuit(qregs, cregs)
 
+    bit_indices = {bit: index
+                   for index, bit in enumerate(qotp_circ.qubits)}
+
     # initial z gates after prep
     paulizs = rng.randint(2, size=len(qregs))
     for qind, q in enumerate(qregs):
@@ -180,7 +183,8 @@ def QOTP_fromlayers(layers, rng):
         qotp_circ.barrier()
         twoqindices = []
         for _, qsub, _ in gates2q:
-            twoqindices.append([qsub[0].index, qsub[1].index])
+            twoqindices.append([bit_indices[qsub[0]],
+                                bit_indices[qsub[1]]])
         # update Paulis
         for inds in twoqindices:
             if twoqubitgate == 'cx':

qiskit/ignis/verification/randomized_benchmarking/circuits.py

@@ -664,9 +664,11 @@ def replace_q_indices(circuit, q_nums, qr):
     """
 
     new_circuit = QuantumCircuit(qr)
+    bit_indices = {bit: index
+                   for index, bit in enumerate(circuit.qubits)}
     for instr, qargs, cargs in circuit.data:
         new_qargs = [
-            qr[q_nums[x]] for x in [arg.index for arg in qargs]]
+            qr[q_nums[x]] for x in [bit_indices[arg] for arg in qargs]]
         new_op = copy.deepcopy((instr, new_qargs, cargs))
         new_circuit.data.append(new_op)
 

qiskit/ignis/verification/randomized_benchmarking/dihedral.py

@@ -743,8 +743,10 @@ def conjugate(self):
         circ = self.to_instruction()
         new_circ = QuantumCircuit(self.num_qubits)
         qargs = list(range(self.num_qubits))
+        bit_indices = {bit: index
+                       for index, bit in enumerate(circ.definition.qubits)}
         for instr, qregs, _ in circ.definition:
-            new_qubits = [qargs[tup.index] for tup in qregs]
+            new_qubits = [qargs[bit_indices[tup]] for tup in qregs]
             if instr.name == 'u1':
                 params = 2 * np.pi - instr.params[0]
                 instr.params[0] = params
@@ -878,9 +880,13 @@ def append_circuit(elem, circuit, qargs=None):
         raise QiskitError('{} instruction definition is {}; expected QuantumCircuit'.format(
             gate.name, type(gate.definition)))
 
+    flat_instr = gate.definition
+    bit_indices = {bit: index
+                   for index, bit in enumerate(flat_instr.qubits)}
+
     for instr, qregs, _ in gate.definition:
         # Get the integer position of the flat register
-        new_qubits = [qargs[tup.index] for tup in qregs]
+        new_qubits = [qargs[bit_indices[tup]] for tup in qregs]
 
         if (instr.name == 'x' or gate.name == 'x'):
             if len(new_qubits) != 1:

qiskit/ignis/verification/randomized_benchmarking/rb_utils.py

@@ -144,10 +144,13 @@ def gates_per_clifford(
         else:
             for transpiled_circuit in transpiled_circuits:
                 if isinstance(transpiled_circuit, QuantumCircuit):
+                    bit_indices = {bit: index
+                                   for index, bit in enumerate(transpiled_circuit.qubits)}
+
                     for instr, qregs, _ in transpiled_circuit.data:
                         for qreg in qregs:
                             try:
-                                ngates[qreg.index][instr.name] += 1
+                                ngates[bit_indices[qreg]][instr.name] += 1
                             except KeyError:
                                 pass
                 else:

qiskit/ignis/verification/tomography/basis/circuits.py

@@ -388,22 +388,22 @@ def _tomography_circuits(
         raise QiskitError(
             "prepared_qubits and measured_qubits are different length.")
     num_qubits = len(meas_qubits)
-    meas_qubit_registers = set(q.register for q in meas_qubits)
     # Check qubits being measured are defined in circuit
-    for reg in meas_qubit_registers:
-        if reg not in circuit.qregs:
+    for meas_qubit in meas_qubits:
+        if meas_qubit not in circuit.qubits:
             logger.warning('WARNING: circuit does not contain '
-                           'measured QuantumRegister: %s', reg.name)
+                           'measured qubit: %s', meas_qubit)
 
-    prep_qubit_registers = set(q.register for q in prep_qubits)
     # Check qubits being measured are defined in circuit
-    for reg in prep_qubit_registers:
-        if reg not in circuit.qregs:
+    for prep_qubit in prep_qubits:
+        if prep_qubit not in circuit.qubits:
             logger.warning('WARNING: circuit does not contain '
-                           'prepared QuantumRegister: %s', reg.name)
+                           'prepared qubit: %s', prep_qubit)
 
     # Get combined registers
-    qubit_registers = prep_qubit_registers.union(meas_qubit_registers)
+    qubit_registers = {reg for reg in circuit.qregs
+                       if any(qubit in reg
+                              for qubit in prep_qubits + meas_qubits)}
 
     # Check if there are already measurements in the circuit
     for op in circuit:

qiskit/ignis/verification/tomography/basis/gatesetbasis.py

@@ -160,7 +160,7 @@ def measurement_circuit(self,
         Returns:
             The measurement circuit
         """
-        circ = QuantumCircuit(qubit.register, clbit.register)
+        circ = QuantumCircuit([qubit, clbit])
         self.add_spam_to_circuit(circ, qubit, op)
         circ.measure(qubit, clbit)
         return circ
@@ -191,7 +191,7 @@ def preparation_circuit(self,
         Returns:
             The preperation circuit
         """
-        circ = QuantumCircuit(qubit.register)
+        circ = QuantumCircuit([qubit])
         self.add_spam_to_circuit(circ, qubit, op)
         return circ
 

qiskit/ignis/verification/tomography/basis/paulibasis.py

@@ -43,7 +43,7 @@ def pauli_measurement_circuit(
         The measurement circuit for the given Pauli.
     """
 
-    circ = QuantumCircuit(qubit.register, clbit.register)
+    circ = QuantumCircuit([qubit, clbit])
     if op == 'X':
         circ.h(qubit)
         circ.measure(qubit, clbit)
@@ -73,7 +73,7 @@ def pauli_preparation_circuit(
         The preparation circuit for the given Pauli eigenstate.
     """
 
-    circ = QuantumCircuit(qubit.register)
+    circ = QuantumCircuit([qubit])
     if op == 'Xp':
         circ.h(qubit)
     if op == 'Xm':

qiskit/ignis/verification/tomography/basis/sicbasis.py

@@ -43,7 +43,7 @@ def sicpovm_preparation_circuit(op: str, qubit: QuantumRegister
     Returns:
         The preparation circuit
     """
-    circ = QuantumCircuit(qubit.register)
+    circ = QuantumCircuit([qubit])
     theta = -2 * np.arctan(np.sqrt(2))
     if op == 'S1':
         circ.append(U3Gate(theta, np.pi, 0.0), [qubit])