Add only_reduce parameter to GreedyPauliSimp

pytket/binders/passes.cpp

@@ -961,11 +961,13 @@ PYBIND11_MODULE(passes, m) {
       "implement 2-qubit rotations using ZZPhase gates when deemed "
       "optimal. Defaults to False."
       "\n:param timeout: Sets maximum out of time spent finding solution."
+      "\n:param only_reduce: Only returns modified circuit if it has "
+      "fewer two-qubit gates."
       "\n:return: a pass to perform the simplification",
       py::arg("discount_rate") = 0.7, py::arg("depth_weight") = 0.3,
       py::arg("max_lookahead") = 500, py::arg("max_tqe_candidates") = 500,
       py::arg("seed") = 0, py::arg("allow_zzphase") = false,
-      py::arg("timeout") = 100);
+      py::arg("timeout") = 100, py::arg("only_reduce") = false);
   m.def(
       "PauliSquash", &PauliSquash,
       "Applies :py:meth:`PauliSimp` followed by "
@@ -1038,7 +1040,7 @@ PYBIND11_MODULE(passes, m) {
 
   m.def(
       "CnXPairwiseDecomposition", &CnXPairwiseDecomposition,
-      "Decompose CnX gates to 2-qubit gates and single qubit gates. "
+      "Decompose CnX gates to 2-qubit gates `fand single qubit gates. "
       "For every two CnX gates, reorder their control qubits to improve "
       "the chance of gate cancellation");
 

pytket/conanfile.py

@@ -38,7 +38,7 @@ def requirements(self):
         self.requires("pybind11_json/0.2.14")
         self.requires("symengine/0.12.0")
         self.requires("tkassert/0.3.4@tket/stable")
-        self.requires("tket/1.3.42@tket/stable")
+        self.requires("tket/1.3.43@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

@@ -13,6 +13,7 @@ Features:
 * Add `custom_deserialisation` argument to `BasePass` and `SequencePass` 
   `from_dict` method to support construction of `CustomPass` from json.
 * Add `timeout` argument to `GreedyPauliSimp`.
+* Add `only_reduce` argument to `GreedyPauliSimp`.
 * Add option to not relabel `ClassicalExpBox` when calling `rename_units`
   and `flatten_registers`
 

pytket/pytket/_tket/passes.pyi

@@ -290,7 +290,7 @@ def CliffordSimp(allow_swaps: bool = True) -> BasePass:
     """
 def CnXPairwiseDecomposition() -> BasePass:
     """
-    Decompose CnX gates to 2-qubit gates and single qubit gates. For every two CnX gates, reorder their control qubits to improve the chance of gate cancellation
+    Decompose CnX gates to 2-qubit gates `fand single qubit gates. For every two CnX gates, reorder their control qubits to improve the chance of gate cancellation
     """
 def CommuteThroughMultis() -> BasePass:
     """
@@ -445,7 +445,7 @@ def GlobalisePhasedX(squash: bool = True) -> BasePass:
 
     It is not recommended to use this pass with symbolic expressions, as in certain cases a blow-up in symbolic expression sizes may occur.
     """
-def GreedyPauliSimp(discount_rate: float = 0.7, depth_weight: float = 0.3, max_lookahead: int = 500, max_tqe_candidates: int = 500, seed: int = 0, allow_zzphase: bool = False, timeout: int = 100) -> BasePass:
+def GreedyPauliSimp(discount_rate: float = 0.7, depth_weight: float = 0.3, max_lookahead: int = 500, max_tqe_candidates: int = 500, seed: int = 0, allow_zzphase: bool = False, timeout: int = 100, only_reduce: bool = False) -> BasePass:
     """
     Construct a pass that converts a circuit into a graph of Pauli gadgets to account for commutation and phase folding, and resynthesises them using a greedy algorithm adapted from arxiv.org/abs/2103.08602. The method for synthesising the final Clifford operator is adapted from arxiv.org/abs/2305.10966.
 
@@ -456,6 +456,7 @@ def GreedyPauliSimp(discount_rate: float = 0.7, depth_weight: float = 0.3, max_l
     :param seed:  Unsigned integer seed used for sampling candidates and tie breaking. Default to 0.
     :param allow_zzphase: If set to True, allows the algorithm to implement 2-qubit rotations using ZZPhase gates when deemed optimal. Defaults to False.
     :param timeout: Sets maximum out of time spent finding solution.
+    :param only_reduce: Only returns modified circuit if it has fewer two-qubit gates.
     :return: a pass to perform the simplification
     """
 def GuidedPauliSimp(strat: pytket._tket.transform.PauliSynthStrat = pytket._tket.transform.PauliSynthStrat.Sets, cx_config: pytket._tket.circuit.CXConfigType = pytket._tket.circuit.CXConfigType.Snake) -> BasePass:

pytket/tests/passes_serialisation_test.py

@@ -297,6 +297,7 @@ def nonparam_predicate_dict(name: str) -> Dict[str, Any]:
             "seed": 2,
             "allow_zzphase": True,
             "timeout": 5000,
+            "only_reduce": False,
         }
     ),
     # lists must be sorted by OpType value

pytket/tests/predicates_test.py

@@ -1036,7 +1036,7 @@ def test_greedy_pauli_synth() -> None:
     ).SWAP(regb[1], rega[0])
     d = circ.copy()
     pss = GreedyPauliSimp(0.5, 0.5)
-    assert not GreedyPauliSimp(0.5, 0.5, timeout=0).apply(d)
+    assert not GreedyPauliSimp(0.5, 0.5, timeout=0, only_reduce=False).apply(d)
     assert pss.apply(d)
     assert np.allclose(circ.get_unitary(), d.get_unitary())
     assert d.name == "test"

schemas/compiler_pass_v1.json

@@ -377,6 +377,10 @@
         "timeout": {
           "type": "number",
           "definition": "parameter controlling the maximum runtime of \"GreedyPauliSimp\""
+        },
+        "only_reduce": {
+          "type": "boolean",
+          "definition": "parameter controlling whether \"GreedyPauliSimp\" can return circuits with more two qubit gates"
         }
       },
       "required": [
@@ -909,9 +913,10 @@
               "max_tqe_candidates",
               "seed",
               "allow_zzphase",
-              "timeout"
+              "timeout",
+              "only_reduce"
             ],
-            "maxProperties": 8
+            "maxProperties": 9
           }
         },
         {

tket/conanfile.py

@@ -23,7 +23,7 @@
 
 class TketConan(ConanFile):
     name = "tket"
-    version = "1.3.42"
+    version = "1.3.43"
     package_type = "library"
     license = "Apache 2"
     homepage = "https://github.com/CQCL/tket"

tket/include/tket/Predicates/PassGenerators.hpp

@@ -356,12 +356,14 @@ PassPtr gen_special_UCC_synthesis(
  * @param seed
  * @param allow_zzphase
  * @param timeout
+ * @param only_reduce
  * @return PassPtr
  */
 PassPtr gen_greedy_pauli_simp(
     double discount_rate = 0.7, double depth_weight = 0.3,
     unsigned max_lookahead = 500, unsigned max_tqe_candidates = 500,
-    unsigned seed = 0, bool allow_zzphase = false, unsigned timeout = 100);
+    unsigned seed = 0, bool allow_zzphase = false, unsigned timeout = 100,
+    bool only_reduce = false);
 
 /**
  * Generate a pass to simplify the circuit where it acts on known basis states.

tket/src/Predicates/CompilerPass.cpp

@@ -523,9 +523,10 @@ PassPtr deserialise(
       unsigned seed = content.at("seed").get<unsigned>();
       bool allow_zzphase = content.at("allow_zzphase").get<bool>();
       unsigned timeout = content.at("timeout").get<unsigned>();
+      bool only_reduce = content.at("only_reduce").get<bool>();
       pp = gen_greedy_pauli_simp(
           discount_rate, depth_weight, max_lookahead, max_tqe_candidates, seed,
-          allow_zzphase, timeout);
+          allow_zzphase, timeout, only_reduce);
 
     } else if (passname == "PauliSimp") {
       // SEQUENCE PASS - DESERIALIZABLE ONLY

tket/src/Predicates/PassGenerators.cpp

@@ -1018,10 +1018,24 @@ PassPtr gen_synthesise_pauli_graph(
 PassPtr gen_greedy_pauli_simp(
     double discount_rate, double depth_weight, unsigned max_lookahead,
     unsigned max_tqe_candidates, unsigned seed, bool allow_zzphase,
-    unsigned timeout) {
-  Transform t = Transforms::greedy_pauli_optimisation(
-      discount_rate, depth_weight, max_lookahead, max_tqe_candidates, seed,
-      allow_zzphase, timeout);
+    unsigned timeout, bool only_reduce) {
+  Transform t =
+      Transform([discount_rate, depth_weight, max_lookahead, max_tqe_candidates,
+                 seed, allow_zzphase, timeout, only_reduce](Circuit& circ) {
+        Transform gpo = Transforms::greedy_pauli_optimisation(
+            discount_rate, depth_weight, max_lookahead, max_tqe_candidates,
+            seed, allow_zzphase, timeout);
+        if (only_reduce) {
+          Circuit gpo_circ = circ;
+          if (gpo.apply(gpo_circ) &&
+              gpo_circ.count_n_qubit_gates(2) < circ.count_n_qubit_gates(2)) {
+            circ = gpo_circ;
+            return true;
+          }
+          return false;
+        }
+        return gpo.apply(circ);
+      });
   OpTypeSet ins = {
       OpType::Z,
       OpType::X,
@@ -1071,6 +1085,7 @@ PassPtr gen_greedy_pauli_simp(
   j["seed"] = seed;
   j["allow_zzphase"] = allow_zzphase;
   j["timeout"] = timeout;
+  j["only_reduce"] = only_reduce;
 
   return std::make_shared<StandardPass>(precons, t, postcon, j);
 }

tket/test/src/test_GreedyPauli.cpp

@@ -22,6 +22,7 @@
 #include "tket/Gate/SymTable.hpp"
 #include "tket/Ops/ClassicalOps.hpp"
 #include "tket/Predicates/PassGenerators.hpp"
+#include "tket/Predicates/PassLibrary.hpp"
 #include "tket/Transformations/GreedyPauliOptimisation.hpp"
 #include "tket/Utils/Expression.hpp"
 
@@ -749,6 +750,15 @@ SCENARIO("Test GreedyPauliSimp pass construction") {
     CHECK(gen_greedy_pauli_simp(0.3, 0.5)->apply(cu));
     REQUIRE(test_unitary_comparison(c, cu.get_circ_ref(), true));
   }
+  GIVEN("Preserving a circuit with only_reduce set to true.") {
+    Circuit c(4);
+    c.add_op<unsigned>(OpType::CX, {0, 1});
+    c.add_op<unsigned>(OpType::CX, {1, 2});
+    c.add_op<unsigned>(OpType::CX, {2, 3});
+    CompilationUnit cu(c);
+    REQUIRE(!gen_greedy_pauli_simp(0.3, 0.5, 500, 500, 0, false, 100, true)
+                 ->apply(cu));
+  }
 }
 }  // namespace test_GreedyPauliSimp
 }  // namespace tket