Merge pull request tensorflow#278 from tensorflow/pauli_parse

Add pauli parsing for new qsim.

tensorflow_quantum/core/src/BUILD

@@ -45,6 +45,7 @@ cc_library(
     srcs = ["circuit_parser_qsim.cc"],
     hdrs = ["circuit_parser_qsim.h"],
     deps = [
+        "//tensorflow_quantum/core/proto:pauli_sum_cc_proto",
         "//tensorflow_quantum/core/proto:program_cc_proto",
         "@com_google_absl//absl/container:flat_hash_map",
         "@local_config_tf//:libtensorflow_framework",
@@ -63,6 +64,7 @@ cc_test(
     linkstatic = 0,
     deps = [
         ":circuit_parser_qsim",
+        "//tensorflow_quantum/core/proto:pauli_sum_cc_proto",
         "//tensorflow_quantum/core/proto:program_cc_proto",
         "@com_google_absl//absl/container:flat_hash_map",
         "@com_google_absl//absl/strings",

tensorflow_quantum/core/src/circuit_parser_qsim.cc

@@ -26,13 +26,15 @@ limitations under the License.
 #include "absl/strings/numbers.h"
 #include "cirq/google/api/v2/program.pb.h"
 #include "tensorflow/core/lib/core/status.h"
+#include "tensorflow_quantum/core/proto/pauli_sum.pb.h"
 
 namespace tfq {
 
 using ::cirq::google::api::v2::Moment;
 using ::cirq::google::api::v2::Operation;
 using ::cirq::google::api::v2::Program;
 using ::tensorflow::Status;
+using ::tfq::proto::PauliTerm;
 
 namespace {
 
@@ -374,4 +376,32 @@ tensorflow::Status QsimCircuitFromProgram(
   return Status::OK();
 }
 
+Status QsimCircuitFromPauliTerm(
+    const PauliTerm& term, const int num_qubits, QsimCircuit* circuit,
+    std::vector<qsim::GateFused<QsimGate>>* fused_circuit) {
+  Program measurement_program;
+  SymbolMap empty_map;
+  measurement_program.mutable_circuit()->set_scheduling_strategy(
+      cirq::google::api::v2::Circuit::MOMENT_BY_MOMENT);
+  Moment* term_moment = measurement_program.mutable_circuit()->add_moments();
+  for (const tfq::proto::PauliQubitPair& pair : term.paulis()) {
+    Operation* new_op = term_moment->add_operations();
+
+    // create corresponding eigen gate op.
+    new_op->add_qubits()->set_id(pair.qubit_id());
+    new_op->mutable_gate()->set_id(pair.pauli_type() + "P");
+    (*new_op->mutable_args())["exponent"].mutable_arg_value()->set_float_value(
+        1.0);
+    (*new_op->mutable_args())["global_shift"]
+        .mutable_arg_value()
+        ->set_float_value(0.0);
+    (*new_op->mutable_args())["exponent_scalar"]
+        .mutable_arg_value()
+        ->set_float_value(1.0);
+  }
+
+  return QsimCircuitFromProgram(measurement_program, empty_map, num_qubits,
+                                circuit, fused_circuit);
+}
+
 }  // namespace tfq

tensorflow_quantum/core/src/circuit_parser_qsim.h

@@ -25,6 +25,7 @@ limitations under the License.
 #include "absl/container/flat_hash_map.h"
 #include "cirq/google/api/v2/program.pb.h"
 #include "tensorflow/core/lib/core/status.h"
+#include "tensorflow_quantum/core/proto/pauli_sum.pb.h"
 
 namespace tfq {
 
@@ -37,6 +38,13 @@ tensorflow::Status QsimCircuitFromProgram(
     const int num_qubits, qsim::Circuit<qsim::Cirq::GateCirq<float>>* circuit,
     std::vector<qsim::GateFused<qsim::Cirq::GateCirq<float>>>* fused_circuit);
 
+// parse a serialized pauliTerm from a larger cirq.Paulisum proto
+// into a qsim Circuit and fused circuit.
+tensorflow::Status QsimCircuitFromPauliTerm(
+    const tfq::proto::PauliTerm& term, const int num_qubits,
+    qsim::Circuit<qsim::Cirq::GateCirq<float>>* circuit,
+    std::vector<qsim::GateFused<qsim::Cirq::GateCirq<float>>>* fused_circuit);
+
 }  // namespace tfq
 
 #endif  // TFQ_CORE_SRC_CIRCUIT_PARSER_QSIM_H_

tensorflow_quantum/core/src/circuit_parser_qsim_test.cc

@@ -555,5 +555,40 @@ TEST(QsimCircuitParserTest, EmptyTest) {
   ASSERT_EQ(fused_circuit.size(), 0);
 }
 
+TEST(QsimCircuitParserTest, CircuitFromPauliTermPauli) {
+  tfq::proto::PauliTerm pauli_proto;
+  // The created circuit should not depend on the coefficient
+  pauli_proto.set_coefficient_real(3.14);
+  tfq::proto::PauliQubitPair* pair_proto = pauli_proto.add_paulis();
+  pair_proto->set_qubit_id("0");
+  pair_proto->set_pauli_type("X");
+
+  // Build the corresponding correct circuit
+  auto reference = qsim::Cirq::XPowGate<float>::Create(0, 0, 1.0, 0.0);
+  QsimCircuit test_circuit;
+  std::vector<qsim::GateFused<QsimGate>> fused_circuit;
+  tensorflow::Status status;
+
+  // Check conversion
+  status =
+      QsimCircuitFromPauliTerm(pauli_proto, 1, &test_circuit, &fused_circuit);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  ASSERT_EQ(test_circuit.num_qubits, 1);
+  ASSERT_EQ(test_circuit.gates.size(), 1);
+  AssertOneQubitEqual(test_circuit.gates[0], reference);
+}
+
+TEST(QsimCircuitParserTest, CircuitFromPauliTermEmpty) {
+  tfq::proto::PauliTerm pauli_proto;
+  tensorflow::Status status;
+  QsimCircuit test_circuit;
+  std::vector<qsim::GateFused<QsimGate>> fused_circuit;
+  status =
+      QsimCircuitFromPauliTerm(pauli_proto, 0, &test_circuit, &fused_circuit);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  ASSERT_EQ(test_circuit.num_qubits, 0);
+  ASSERT_EQ(test_circuit.gates.size(), 0);
+}
+
 }  // namespace
 }  // namespace tfq