Bugfix/incorrect serialisation for list of pairs (#1099)

* Add failling test

* Fix PauliExpPairBox serialisation issue

* Update changelog

* bump tket version

pytket/conanfile.py

@@ -32,7 +32,7 @@ def package(self):
         cmake.install()
 
     def requirements(self):
-        self.requires("tket/1.2.61@tket/stable")
+        self.requires("tket/1.2.62@tket/stable")
         self.requires("tklog/0.3.3@tket/stable")
         self.requires("tkrng/0.3.3@tket/stable")
         self.requires("tkassert/0.3.3@tket/stable")

pytket/docs/changelog.rst

@@ -14,6 +14,8 @@ Fixes:
 
 * When converting QASM expressions to ``ClassicalExpBox``, preserve the ordering
   of the bits in the expression in the resulting ``cmd.args``
+* Fix incorrect serialisation of ``PauliExpPairBox`` when the Pauli strings are of
+  length 2.
 
 1.21.0 (October 2023)
 ---------------------

pytket/tests/circuit_test.py

@@ -48,6 +48,7 @@
     Bit,
     BitRegister,
     QubitRegister,
+    CXConfigType,
 )
 from pytket.circuit.display import get_circuit_renderer, render_circuit_as_html
 from pytket.circuit.named_types import (
@@ -674,6 +675,15 @@ def test_boxes() -> None:
             command.op.get_unitary()
 
 
+def test_pauliexp_pair_box_serialisation() -> None:
+    # https://github.com/CQCL/tket/issues/1084
+    p = PauliExpPairBox(
+        [Pauli.Z, Pauli.X], 0.5, [Pauli.X, Pauli.Z], 0.2, CXConfigType.MultiQGate
+    )
+    c = Circuit(2).add_pauliexppairbox(p, [0, 1])
+    assert json_validate(c)
+
+
 def test_tofollibox_strats() -> None:
     permutation = [
         ([_0, _0, _0, _0], [_1, _1, _1, _1]),
@@ -1261,3 +1271,4 @@ def test_phase_order() -> None:
     test_measuring_registers()
     test_multi_controlled_gates()
     test_counting_n_qubit_gates()
+    test_pauliexp_pair_box_serialisation()

tket/conanfile.py

@@ -23,7 +23,7 @@
 
 class TketConan(ConanFile):
     name = "tket"
-    version = "1.2.61"
+    version = "1.2.62"
     package_type = "library"
     license = "Apache 2"
     homepage = "https://github.com/CQCL/tket"

tket/src/Circuit/PauliExpBoxes.cpp

@@ -190,7 +190,12 @@ bool PauliExpPairBox::is_equal(const Op &op_other) const {
 nlohmann::json PauliExpPairBox::to_json(const Op_ptr &op) {
   const auto &box = static_cast<const PauliExpPairBox &>(*op);
   nlohmann::json j = core_box_json(box);
-  j["paulis_pair"] = box.get_paulis_pair();
+  auto paulis_pair = box.get_paulis_pair();
+  // use vector to avoid serialising into a dictionary if the Pauli strings are
+  // of length 2
+  std::vector<std::vector<Pauli>> paulis_vec{
+      paulis_pair.first, paulis_pair.second};
+  j["paulis_pair"] = paulis_vec;
   j["phase_pair"] = box.get_phase_pair();
   j["cx_config"] = box.get_cx_config();
   return j;