Fix RuntimeError when converting qiskit instructions. (#203)

* Don't use CustomGateDef in qiskit_to_tk

* add test for RealAmplitudes handling

* remove lines for debugging

* remove a single line

* fix assert for circuit naming

* remove some unused imports

* Add test of unitary equivalence

* add ipynb to .gitignore

* add isinstance check to keep mypy happy

* add a check for equivalence with the qiskit operator

* add comment with issue link

* remove spaces

.gitignore

@@ -12,3 +12,4 @@ obj
 docs/extensions
 .ipynb_checkpoints
 pytket/extensions/qiskit/_metadata.py
+*.ipynb

pytket/extensions/qiskit/qiskit_convert.py

@@ -154,7 +154,7 @@
     # Special types:
     Barrier: OpType.Barrier,
     Instruction: OpType.CircBox,
-    Gate: OpType.CustomGate,
+    Gate: OpType.CircBox,
     Measure: OpType.Measure,
     Reset: OpType.Reset,
     Initialize: OpType.StatePreparationBox,
@@ -476,7 +476,7 @@ def add_qiskit_data(self, data: "QuantumCircuitData") -> None:
 
             elif optype == OpType.Barrier:
                 self.tkc.add_barrier(qubits)
-            elif optype in (OpType.CircBox, OpType.CustomGate):
+            elif optype == OpType.CircBox:
                 qregs = (
                     [QuantumRegister(instr.num_qubits, "q")]
                     if instr.num_qubits > 0
@@ -490,17 +490,9 @@ def add_qiskit_data(self, data: "QuantumCircuitData") -> None:
                 builder = CircuitBuilder(qregs, cregs)
                 builder.add_qiskit_data(instr.definition)
                 subc = builder.circuit()
-                if optype == OpType.CircBox:
-                    cbox = CircBox(subc)
-                    self.tkc.add_circbox(cbox, qubits + bits, **condition_kwargs)  # type: ignore
-                else:
-                    # warning, this will catch all `Gate` instances
-                    # that were not picked up as a subclass in _known_qiskit_gate
-                    params = [param_to_tk(p) for p in instr.params]
-                    gate_def = CustomGateDef.define(
-                        instr.name, subc, list(subc.free_symbols())
-                    )
-                    self.tkc.add_custom_gate(gate_def, params, qubits + bits)  # type: ignore
+                subc.name = instr.name
+                self.tkc.add_circbox(CircBox(subc), qubits + bits, **condition_kwargs)  # type: ignore
+
             elif optype == OpType.CU3 and type(instr) == qiskit_gates.CUGate:
                 if instr.params[-1] == 0:
                     self.tkc.add_gate(
@@ -744,6 +736,7 @@ def append_tk_command_to_qiskit(
     _supported_tket_gates
     | _additional_multi_controlled_gates
     | {OpType.Unitary1qBox, OpType.Unitary2qBox, OpType.Unitary3qBox}
+    | {OpType.CustomGate}
 )
 
 

tests/qiskit_convert_test.py

@@ -24,14 +24,14 @@
     ClassicalRegister,
     execute,
 )
-from qiskit.quantum_info import Pauli, SparsePauliOp  # type: ignore
+from qiskit.quantum_info import SparsePauliOp  # type: ignore
 from qiskit.transpiler import PassManager  # type: ignore
-from qiskit.circuit.library import RYGate, MCMT, XXPlusYYGate, PauliEvolutionGate, UnitaryGate  # type: ignore
+from qiskit.circuit.library import RYGate, MCMT, XXPlusYYGate, PauliEvolutionGate, UnitaryGate, RealAmplitudes  # type: ignore
 import qiskit.circuit.library.standard_gates as qiskit_gates  # type: ignore
 from qiskit.circuit import Parameter
 from qiskit.synthesis import SuzukiTrotter  # type: ignore
 from qiskit_aer import Aer  # type: ignore
-from qiskit.quantum_info import Statevector
+from qiskit.quantum_info import Statevector, Operator
 
 from pytket.circuit import (
     Circuit,
@@ -1013,3 +1013,30 @@ def test_failed_conversion_error() -> None:
         NotImplementedError, match=r"Conversion of qiskit's xx_plus_yy instruction"
     ):
         qiskit_to_tk(qc)
+
+
+# https://github.com/CQCL/pytket-qiskit/issues/200
+def test_RealAmplitudes_numeric_params() -> None:
+    qc = QuantumCircuit(3)
+    params = [np.pi / 2] * 9
+    real_amps1 = RealAmplitudes(3, reps=2)
+    real_amps2 = real_amps1.assign_parameters(params)
+    qc.compose(real_amps2, qubits=[0, 1, 2], inplace=True)
+    # Unitary operator of the qiskit circuit. Order reversed from little -> big endian.
+    # The reversal means we can check it for equivalence with a tket unitary
+    qiskit_unitary = Operator(qc.reverse_bits()).data
+    converted_tkc = qiskit_to_tk(qc)
+    assert converted_tkc.n_gates == 1
+    assert converted_tkc.n_gates_of_type(OpType.CircBox) == 1
+    circbox_op = converted_tkc.get_commands()[0].op
+    assert isinstance(circbox_op, CircBox)
+    assert circbox_op.get_circuit().name == "RealAmplitudes"
+    DecomposeBoxes().apply(converted_tkc)
+    assert converted_tkc.n_gates_of_type(OpType.CX) == 4
+    assert converted_tkc.n_gates_of_type(OpType.Ry) == 9
+    unitary1 = converted_tkc.get_unitary()
+    qc2 = tk_to_qiskit(converted_tkc)
+    tkc2 = qiskit_to_tk(qc2)
+    unitary2 = tkc2.get_unitary()
+    assert compare_unitaries(qiskit_unitary, unitary1)
+    assert compare_unitaries(unitary1, unitary2)