Invalid param type <class 'numpy.ndarray'> for gate unitary*1

[jiannanWang]

Environment

• Qiskit version: 1.0.2
• Python version: 3.11.8
• Operating system: Ubuntu 22.04.3 LTS

What is happening?

Running the below code triggered a qiskit.circuit.exceptions.CircuitError: "Invalid param type <class 'numpy.ndarray'> for gate unitary*1." I found this bug happens for some other Gates as well. Below is a minimal reproduction example using CUGate.

How can we reproduce the issue?

from qiskit import QuantumCircuit, ClassicalRegister, QuantumRegister
from qiskit.circuit.library.standard_gates import CUGate

qr = QuantumRegister(2, name='qr')
cr = ClassicalRegister(2, name='cr')
qc = QuantumCircuit(qr, cr, name='qc')

qc.append(CUGate(0, 0, 0, 0).power(1).repeat(1), qargs=qr)

What should happen?

Traceback (most recent call last):
  File "/mnt/tests/reproduction/reproduce_invalid_param_type.py", line 8, in <module>
    qc.append(CUGate(0, 0, 0, 0).power(1).repeat(1), qargs=qr)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/anaconda3/envs/qiskit1.0.2/lib/python3.11/site-packages/qiskit/circuit/instruction.py", line 591, in repeat
    instruction = self._return_repeat(n)
                  ^^^^^^^^^^^^^^^^^^^^^^
  File "/root/anaconda3/envs/qiskit1.0.2/lib/python3.11/site-packages/qiskit/circuit/gate.py", line 87, in _return_repeat
    return Gate(name=f"{self.name}*{exponent}", num_qubits=self.num_qubits, params=self.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/anaconda3/envs/qiskit1.0.2/lib/python3.11/site-packages/qiskit/circuit/gate.py", line 46, in __init__
    super().__init__(name, num_qubits, 0, params, label=label, duration=duration, unit=unit)
  File "/root/anaconda3/envs/qiskit1.0.2/lib/python3.11/site-packages/qiskit/circuit/instruction.py", line 108, in __init__
    self.params = params  # must be at last (other properties may be required for validation)
    ^^^^^^^^^^^
  File "/root/anaconda3/envs/qiskit1.0.2/lib/python3.11/site-packages/qiskit/circuit/instruction.py", line 287, in params
    self._params.append(self.validate_parameter(single_param))
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/anaconda3/envs/qiskit1.0.2/lib/python3.11/site-packages/qiskit/circuit/gate.py", line 242, in validate_parameter
    raise CircuitError(f"Invalid param type {type(parameter)} for gate {self.name}.")
qiskit.circuit.exceptions.CircuitError: "Invalid param type <class 'numpy.ndarray'> for gate unitary*1."

Any suggestions?

No response

[shailesh]

@jiannanWang To work around maybe you can manually create a composite gate by repeating the gate's unitary matrix

[Randl]

I think the fix should be to replace

qiskit/qiskit/circuit/gate.py

Line 100 in 9d03b4b

return Gate(name=f"{self.name}*{exponent}", num_qubits=self.num_qubits, params=self.params)

with

return self.__init__(name=f"{self.name}*{exponent}", num_qubits=self.num_qubits, params=self.params)

However, even though the UnitaryGate inherits from Gate, it doesn't include parameter name; so this fix should also involve unification of all Gate subclasses by parameters.

[Randl]

cc @mtreinish @chriseclectic @jakelishman