Fix conversion of controllled gates

docs/changelog.rst

@@ -5,6 +5,8 @@ Unreleased
 ----------
 
 * Fix conversion of qiskit `UnitaryGate` to and from pytket (up to 3 qubits).
+* Fix handling of qiskit controlled gates in the :py:meth:`qiskit_to_tk` converter.
+* Handle CCZ and CSX gates in circuit converters.
 
 0.40.0 (June 2023)
 ------------------

pytket/extensions/qiskit/qiskit_convert.py

@@ -124,6 +124,7 @@
     qiskit_gates.CU1Gate: OpType.CU1,
     qiskit_gates.CU3Gate: OpType.CU3,
     qiskit_gates.CXGate: OpType.CX,
+    qiskit_gates.CSXGate: OpType.CSX,
     qiskit_gates.CYGate: OpType.CY,
     qiskit_gates.CZGate: OpType.CZ,
     qiskit_gates.ECRGate: OpType.ECR,
@@ -139,6 +140,7 @@
     qiskit_gates.C3XGate: OpType.CnX,
     qiskit_gates.C4XGate: OpType.CnX,
     qiskit_gates.CCXGate: OpType.CCX,
+    qiskit_gates.CCZGate: OpType.CnZ,
     qiskit_gates.CSwapGate: OpType.CSWAP,
     # Multi-controlled gates (qiskit expects a list of controls followed by the target):
     qiskit_gates.MCXGate: OpType.CnX,
@@ -350,8 +352,12 @@ def add_qiskit_data(self, data: "QuantumCircuitData") -> None:
                 pass
             self.add_xs(num_ctrl_qubits, ctrl_state, qargs)
             optype = None
-            if type(instr) == ControlledGate:
-                if type(instr.base_gate) == qiskit_gates.RYGate:
+            if isinstance(instr, ControlledGate):
+                if type(instr) in _known_qiskit_gate:
+                    # First we check if the gate is in _known_qiskit_gate
+                    # this avoids CZ being converted to CnZ
+                    optype = _known_qiskit_gate[type(instr)]
+                elif type(instr.base_gate) == qiskit_gates.RYGate:
                     optype = OpType.CnRy
                 elif type(instr.base_gate) == qiskit_gates.YGate:
                     optype = OpType.CnY

tests/qiskit_convert_test.py

@@ -961,3 +961,46 @@ def test_unitary_gate() -> None:
     assert cmds[0].op.type == OpType.Unitary1qBox
     assert cmds[1].op.type == OpType.Unitary2qBox
     assert cmds[2].op.type == OpType.Unitary3qBox
+
+
+def test_ccz_conversion() -> None:
+    qc_ccz = QuantumCircuit(4)
+    qc_ccz.append(qiskit_gates.CCZGate(), [0, 1, 2])
+    qc_ccz.append(qiskit_gates.CCZGate(), [3, 1, 0])
+    tkc_ccz = qiskit_to_tk(qc_ccz)
+    assert tkc_ccz.n_gates_of_type(OpType.CnZ) == tkc_ccz.n_gates == 2
+    # bidirectional CnZ conversion already supported
+    qc_ccz2 = tk_to_qiskit(tkc_ccz)
+    assert qc_ccz2.count_ops()["ccz"] == 2
+    tkc_ccz2 = qiskit_to_tk(qc_ccz2)
+    assert compare_unitaries(tkc_ccz.get_unitary(), tkc_ccz2.get_unitary())
+
+
+def test_csx_conversion() -> None:
+    qc_csx = QuantumCircuit(2)
+    qc_csx.append(qiskit_gates.CSXGate(), [0, 1])
+    qc_csx.append(qiskit_gates.CSXGate(), [1, 0])
+    converted_tkc = qiskit_to_tk(qc_csx)
+    assert converted_tkc.n_gates == 2
+    assert converted_tkc.n_gates_of_type(OpType.CSX) == 2
+    u1 = converted_tkc.get_unitary()
+    new_tkc_csx = Circuit(2)
+    new_tkc_csx.add_gate(OpType.CSX, [0, 1]).add_gate(OpType.CSX, [1, 0])
+    u2 = new_tkc_csx.get_unitary()
+    assert compare_unitaries(u1, u2)
+    converted_qc = tk_to_qiskit(new_tkc_csx)
+    assert converted_qc.count_ops()["csx"] == 2
+    qc_c3sx = QuantumCircuit(4)
+    qc_c3sx.append(qiskit_gates.C3SXGate(), [0, 1, 2, 3])
+    tkc_c3sx = qiskit_to_tk(qc_c3sx)
+    assert tkc_c3sx.n_gates == tkc_c3sx.n_gates_of_type(OpType.QControlBox) == 1
+
+
+def test_CS_and_CSdg() -> None:
+    qiskit_qc = QuantumCircuit(2)
+    qiskit_qc.append(qiskit_gates.CSGate(), [0, 1])
+    qiskit_qc.append(qiskit_gates.CSdgGate(), [0, 1])
+    qiskit_qc.append(qiskit_gates.CSGate(), [1, 0])
+    qiskit_qc.append(qiskit_gates.CSdgGate(), [1, 0])
+    tkc = qiskit_to_tk(qiskit_qc)
+    assert tkc.n_gates_of_type(OpType.QControlBox) == 4