Cleaning up U3 in the unitary extension (#10597)

* Clean up to use U vs U3

Removing U3 from unitary and moving it to the U gate

* fixing test

* Create unitary-u-not-u3-0a32c2d968f7890e.yaml

qiskit/extensions/unitary.py

@@ -21,15 +21,15 @@
 from qiskit.circuit import QuantumRegister, Qubit
 from qiskit.circuit.exceptions import CircuitError
 from qiskit.circuit._utils import _compute_control_matrix
-from qiskit.circuit.library.standard_gates import U3Gate
+from qiskit.circuit.library.standard_gates import UGate
 from qiskit.extensions.quantum_initializer import isometry
 from qiskit.quantum_info.operators.predicates import matrix_equal
 from qiskit.quantum_info.operators.predicates import is_unitary_matrix
 from qiskit.quantum_info.synthesis.one_qubit_decompose import OneQubitEulerDecomposer
 from qiskit.quantum_info.synthesis.two_qubit_decompose import two_qubit_cnot_decompose
 from qiskit.extensions.exceptions import ExtensionError
 
-_DECOMPOSER1Q = OneQubitEulerDecomposer("U3")
+_DECOMPOSER1Q = OneQubitEulerDecomposer("U")
 
 
 class UnitaryGate(Gate):
@@ -125,7 +125,7 @@ def _define(self):
             q = QuantumRegister(1, "q")
             qc = QuantumCircuit(q, name=self.name)
             theta, phi, lam, global_phase = _DECOMPOSER1Q.angles_and_phase(self.to_matrix())
-            qc._append(U3Gate(theta, phi, lam), [q[0]], [])
+            qc._append(UGate(theta, phi, lam), [q[0]], [])
             qc.global_phase = global_phase
             self.definition = qc
         elif self.num_qubits == 2:

releasenotes/notes/unitary-u-not-u3-0a32c2d968f7890e.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    the definition of UnitaryGate for single qubit unitaries is now in terms of UGate instead of the legacy U3Gate class

test/python/circuit/test_circuit_qasm.py

@@ -348,7 +348,7 @@ def test_unitary_qasm(self):
         qasm = qc.qasm()
         expected = """OPENQASM 2.0;
 include "qelib1.inc";
-gate unitary q0 { u3(0,0,0) q0; }
+gate unitary q0 { u(0,0,0) q0; }
 qreg q[1];
 unitary q[0];
 """
@@ -367,9 +367,9 @@ def test_multiple_unitary_qasm(self):
         expected = re.compile(
             r"""OPENQASM 2.0;
 include "qelib1.inc";
-gate unitary q0 { u3\(0,0,0\) q0; }
-gate (?P<u1>unitary_[0-9]*) q0 { u3\(pi,-pi/2,pi/2\) q0; }
-gate (?P<u2>unitary_[0-9]*) q0 { u3\(0,pi/2,pi/2\) q0; }
+gate unitary q0 { u\(0,0,0\) q0; }
+gate (?P<u1>unitary_[0-9]*) q0 { u\(pi,-pi/2,pi/2\) q0; }
+gate (?P<u2>unitary_[0-9]*) q0 { u\(0,pi/2,pi/2\) q0; }
 gate custom q0 { (?P=u2) q0; }
 qreg q\[2\];
 unitary q\[0\];

test/python/circuit/test_unitary.py

@@ -217,7 +217,7 @@ def test_qasm_unitary_only_one_def(self):
         expected_qasm = (
             "OPENQASM 2.0;\n"
             'include "qelib1.inc";\n'
-            "gate unitary q0 { u3(0,0,0) q0; }\n"
+            "gate unitary q0 { u(0,0,0) q0; }\n"
             "qreg q0[2];\ncreg c0[1];\n"
             "x q0[0];\n"
             "unitary q0[0];\n"
@@ -241,7 +241,7 @@ def test_qasm_unitary_twice(self):
         expected_qasm = (
             "OPENQASM 2.0;\n"
             'include "qelib1.inc";\n'
-            "gate unitary q0 { u3(0,0,0) q0; }\n"
+            "gate unitary q0 { u(0,0,0) q0; }\n"
             "qreg q0[2];\ncreg c0[1];\n"
             "x q0[0];\n"
             "unitary q0[0];\n"