Added z basis transformation to circuit_parser. (tensorflow#162)

Co-authored-by: Michael Broughton <[email protected]>
maneeshs · Mar 17, 2020 · 4fbd426 · 4fbd426
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diff --git a/tensorflow_quantum/core/src/circuit_parser.cc b/tensorflow_quantum/core/src/circuit_parser.cc
@@ -159,4 +159,45 @@ Status CircuitFromPauliTerm(const tfq::proto::PauliTerm& term,
   return CircuitFromProgram(measurement_program, num_qubits, circuit);
 }
 
+Status ZBasisCircuitFromPauliTerm(const tfq::proto::PauliTerm& term,
+                                  const int num_qubits, Circuit* circuit) {
+  Program measurement_program;
+  measurement_program.mutable_circuit()->set_scheduling_strategy(
+      cirq::google::api::v2::Circuit::MOMENT_BY_MOMENT);
+  Moment* term_moment = measurement_program.mutable_circuit()->add_moments();
+  float transform_exponent = 0.0;
+  std::string gate_type;
+  for (const tfq::proto::PauliQubitPair& pair : term.paulis()) {
+    if (pair.pauli_type() == "Z") {
+      // Z requires no transform.
+      continue;
+    }
+
+    // Assume it is X and the transform is Y^-0.5
+    transform_exponent = -0.5;
+    gate_type = "Y";
+    if (pair.pauli_type() == "Y") {
+      // Y regquires X**0.5 transform.
+      transform_exponent = 0.5;
+      gate_type = "X";
+    }
+
+    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(gate_type + "P");
+    (*new_op->mutable_args())["exponent"].mutable_arg_value()->set_float_value(
+        transform_exponent);
+    (*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 CircuitFromProgram(measurement_program, num_qubits, circuit);
+}
+
 }  // namespace tfq
diff --git a/tensorflow_quantum/core/src/circuit_parser.h b/tensorflow_quantum/core/src/circuit_parser.h
@@ -32,10 +32,15 @@ tensorflow::Status CircuitFromProgram(
     const cirq::google::api::v2::Program& program, const int num_qubits,
     Circuit* circuit);
 
-// build the circuit taking the computational basis to the measurement basis
+// build the circuit representing the pauli operations.
 tensorflow::Status CircuitFromPauliTerm(const tfq::proto::PauliTerm& term,
                                         const int num_qubits, Circuit* circuit);
 
+// build the circuit taking pauliterms to z basis.
+tensorflow::Status ZBasisCircuitFromPauliTerm(const tfq::proto::PauliTerm& term,
+                                              const int num_qubits,
+                                              Circuit* circuit);
+
 }  // namespace tfq
 
 #endif  // TFQ_CORE_SRC_CIRCUIT_PARSER_H_
diff --git a/tensorflow_quantum/core/src/circuit_parser_test.cc b/tensorflow_quantum/core/src/circuit_parser_test.cc
@@ -238,5 +238,154 @@ TEST(CircuitParserTest, CircuitFromPauliTermPauli) {
   ASSERT_EQ(test_circuit, real_circuit);
 }
 
+TEST(CircuitParserTest, ZBasisFromPauliTermX) {
+  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
+  Circuit real_circuit;
+  YPowGateBuilder builder;
+  Gate gate_y;
+  ::tensorflow::Status status;
+
+  real_circuit.num_qubits = 1;
+  absl::flat_hash_map<std::string, float> arg_map;
+  arg_map["global_shift"] = 0.0;
+  arg_map["exponent"] = -0.5;
+  arg_map["exponent_scalar"] = 1.0;
+  status = builder.Build(0, {0}, arg_map, &gate_y);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate_y);
+
+  // Check conversion
+  Circuit test_circuit;
+  status = ZBasisCircuitFromPauliTerm(pauli_proto, 1, &test_circuit);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  ASSERT_EQ(test_circuit, real_circuit);
+}
+
+TEST(CircuitParserTest, ZBasisFromPauliTermY) {
+  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("Y");
+
+  // Build the corresponding correct circuit
+  Circuit real_circuit;
+  XPowGateBuilder builder;
+  Gate gate_x;
+  ::tensorflow::Status status;
+
+  real_circuit.num_qubits = 1;
+  absl::flat_hash_map<std::string, float> arg_map;
+  arg_map["global_shift"] = 0.0;
+  arg_map["exponent"] = 0.5;
+  arg_map["exponent_scalar"] = 1.0;
+  status = builder.Build(0, {0}, arg_map, &gate_x);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate_x);
+
+  // Check conversion
+  Circuit test_circuit;
+  status = ZBasisCircuitFromPauliTerm(pauli_proto, 1, &test_circuit);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  ASSERT_EQ(test_circuit, real_circuit);
+}
+
+TEST(CircuitParserTest, ZBasisFromPauliTermZ) {
+  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("Z");
+
+  // Build the corresponding correct circuit
+  Circuit empty_circuit;
+  empty_circuit.num_qubits = 1;
+  ::tensorflow::Status status;
+
+  // Check conversion
+  Circuit test_circuit;
+  status = ZBasisCircuitFromPauliTerm(pauli_proto, 1, &test_circuit);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  ASSERT_EQ(test_circuit, empty_circuit);
+}
+
+TEST(CircuitParserTest, ZBasisFromPauliTermMulti) {
+  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");
+  pair_proto = pauli_proto.add_paulis();
+  pair_proto->set_qubit_id("1");
+  pair_proto->set_pauli_type("Z");
+  pair_proto = pauli_proto.add_paulis();
+  pair_proto->set_qubit_id("2");
+  pair_proto->set_pauli_type("X");
+  pair_proto = pauli_proto.add_paulis();
+  pair_proto->set_qubit_id("3");
+  pair_proto->set_pauli_type("Y");
+
+  // Build the corresponding correct circuit
+  Circuit real_circuit;
+  XPowGateBuilder x_builder;
+  YPowGateBuilder y_builder;
+  I2GateBuilder i_builder;
+  Gate gate;
+  ::tensorflow::Status status;
+
+  real_circuit.num_qubits = 4;
+
+  // X -> Y**-0.5
+  absl::flat_hash_map<std::string, float> arg_map;
+  arg_map["global_shift"] = 0.0;
+  arg_map["exponent"] = -0.5;
+  arg_map["exponent_scalar"] = 1.0;
+  status = y_builder.Build(0, {3}, arg_map, &gate);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate);
+
+  // Z -> nothing
+
+  // X -> Y**-0.5
+  arg_map["global_shift"] = 0.0;
+  arg_map["exponent"] = -0.5;
+  arg_map["exponent_scalar"] = 1.0;
+  status = y_builder.Build(0, {1}, arg_map, &gate);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate);
+
+  // Y -> X^0.5
+  arg_map["global_shift"] = 0.0;
+  arg_map["exponent"] = 0.5;
+  arg_map["exponent_scalar"] = 1.0;
+  status = x_builder.Build(0, {0}, arg_map, &gate);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate);
+
+  // Identity padding for orphan gates added here.
+  status = i_builder.Build(1, {0, 1}, {}, &gate);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate);
+  status = i_builder.Build(1, {2, 3}, {}, &gate);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  real_circuit.gates.push_back(gate);
+
+  // Check conversion
+  Circuit test_circuit;
+  status = ZBasisCircuitFromPauliTerm(pauli_proto, 4, &test_circuit);
+  ASSERT_EQ(status, tensorflow::Status::OK());
+  ASSERT_EQ(test_circuit, real_circuit);
+}
+
 }  // namespace
 }  // namespace tfq