Ignore boxes when applying KAK decomposition to a circuit (#1740)

pytket/conanfile.py

@@ -38,7 +38,7 @@ def requirements(self):
         self.requires("pybind11_json/0.2.15")
         self.requires("symengine/0.13.0")
         self.requires("tkassert/0.3.4@tket/stable")
-        self.requires("tket/1.3.61@tket/stable")
+        self.requires("tket/1.3.62@tket/stable")
         self.requires("tklog/0.3.3@tket/stable")
         self.requires("tkrng/0.3.3@tket/stable")
         self.requires("tktokenswap/0.3.9@tket/stable")

pytket/docs/changelog.rst

@@ -11,6 +11,7 @@ Features:
 Fixes:
 
 * Fix issue with custom gates in qasm to circuit conversion.
+* Ignore boxes when applying `KAKDecomposition`.
 
 1.38.0 (January 2025)
 ---------------------

pytket/tests/transform_test.py

@@ -1237,6 +1237,13 @@ def test_KAK_with_ClassicalExpBox() -> None:
     assert not kak.apply(circ)
 
 
+def test_KAK_with_CircBox() -> None:
+    # https://github.com/CQCL/tket/issues/1553
+    cbox = CircBox(Circuit(2))
+    c = Circuit(2).add_circbox(cbox, [0, 1]).add_circbox(cbox, [0, 1])
+    assert not Transform.KAKDecomposition().apply(c)
+
+
 def test_round_angles() -> None:
     circ0 = Circuit(3).H(0).CRz(0.001, 0, 1).TK2(0.5, 0.499, 0.501, 1, 2)
     circ1 = Circuit(3).H(0).TK2(0.5, 0.5, 0.5, 1, 2)

tket/conanfile.py

@@ -23,7 +23,7 @@
 
 class TketConan(ConanFile):
     name = "tket"
-    version = "1.3.61"
+    version = "1.3.62"
     package_type = "library"
     license = "Apache 2"
     homepage = "https://github.com/CQCL/tket"

tket/src/Transformations/BasicOptimisation.cpp

@@ -267,7 +267,9 @@ Transform two_qubit_squash(
                   circ.get_next_edge(*v, current_edge_on_qb[q]);
             }
           }
-        } else if (circ.n_in_edges_of_type(*v, EdgeType::Quantum) == 2) {
+        } else if (
+            is_gate_type(type) &&
+            circ.n_in_edges_of_type(*v, EdgeType::Quantum) == 2) {
           // Check for 2qb gate
           Qubit q0 = v_to_qb.at({*v, 0});
           Qubit q1 = v_to_qb.at({*v, 1});