Remove redundant name check when adding QuantumCircuit registers.

create-registers.py

@@ -0,0 +1,33 @@
+import time
+
+from qiskit.circuit import ClassicalRegister, QuantumCircuit
+
+start = time.time()
+size = 10
+qc = QuantumCircuit(*(ClassicalRegister(5, f"cr_{i:05}") for i in range(size)))
+end = time.time()
+elapsed = (end - start) * 1000
+print("n=10: ", elapsed)
+
+start = time.time()
+size = 100
+qc = QuantumCircuit(*(ClassicalRegister(5, f"cr_{i:05}") for i in range(size)))
+end = time.time()
+elapsed = (end - start) * 100
+print("n=100: ", elapsed)
+
+start = time.time()
+size = 1000
+qc = QuantumCircuit(*(ClassicalRegister(5, f"cr_{i:05}") for i in range(size)))
+end = time.time()
+elapsed = (end - start) * 1000
+print("n=1000: ", elapsed)
+
+start = time.time()
+size = 10_000
+qc = QuantumCircuit(*(ClassicalRegister(5, f"cr_{i:05}") for i in range(size)))
+end = time.time()
+elapsed = (end - start) * 1000
+print("n=10000: ", elapsed)
+
+qc = QuantumCircuit(ClassicalRegister(5, "a"), ClassicalRegister(5, "b"))

qiskit/circuit/quantumcircuit.py

@@ -3636,11 +3636,6 @@ def add_register(self, *regs: Register | int | Sequence[Bit]) -> None:
                 )
 
         for register in regs:
-            if isinstance(register, Register) and any(
-                register.name == reg.name for reg in self.qregs + self.cregs
-            ):
-                raise CircuitError(f'register name "{register.name}" already exists')
-
             if isinstance(register, AncillaRegister):
                 for bit in register:
                     if bit not in self._qubit_indices:

releasenotes/notes/create-register-performance-fe392209793d151f.yaml

@@ -0,0 +1,7 @@
+performance:
+  - |
+    Improves runtime performance when creating `QuantumCircuit` with many
+    registers. See PR `#16678 <https://github.com/Qiskit/qiskit/pull/16678>`
+    for performance details.
+
+