Commit 6fed858d authored by Nguyen, Thien Minh's avatar Nguyen, Thien Minh
Browse files

Debug IQPE implementation 



- Add a global phase rotation for the identity term.

- Updated the example for testing.

Needs to figure out converting the observable to the canonical weighted pauli form.

Signed-off-by: default avatarThien Nguyen <nguyentm@ornl.gov>
parent 74030040

lib/qsim/impls/qsim_impl.cpp

+19 −7
Original line number Diff line number Diff line
@@ -13,7 +13,6 @@ Ansatz TrotterEvolution::create_ansatz(Observable *obs, 
  if (params.keyExists<double>("dt")) {

    dt = params.get<double>("dt");

  }



  // Just use exp_i_theta for now

  // TODO: formalize a standard library kernel for this.

  auto expCirc = std::dynamic_pointer_cast<xacc::quantum::Circuit>(
@@ -130,7 +129,6 @@ bool IterativeQpeWorkflow::initialize(const HeterogeneousMap &params) { 
  if (params.keyExists<int>("iterations")) {

    num_iters = params.get<int>("iterations");

  }



  return (num_steps >= 1) && (num_iters >= 1);

}
@@ -164,14 +162,27 @@ IterativeQpeWorkflow::constructQpeCircuit(const QuantumSimulationModel &model, 


  // Apply C-U^n

  int power = 1 << (k - 1);

  // std::cout << "Power = " << power << "\n"; 

  for (int i = 0; i < power; ++i) {

    for (int j = 0; j < num_steps; ++j) {

      for (int instId = 0; instId < ctrlKernel->nInstructions(); ++instId) {

        // We need to clone the instruction since it'll be repeated.

        kernel->addInstruction(ctrlKernel->getInstruction(instId)->clone());

      }

    }

  }



  // Rz on ancilla qubit

  // Global phase due to identity pauli

  if (model.observable->getIdentitySubTerm()) {

    const double idCoeff =

        model.observable->getIdentitySubTerm()->coefficient().real();

    const double globalPhase = 2 * M_PI * idCoeff * power;

    // std::cout << "Global phase = " << globalPhase << "\n";

    kernel->addInstruction(

        provider->createInstruction("Rz", {ancBit}, {globalPhase}));

  }



  kernel->addInstruction(provider->createInstruction("Rz", {ancBit}, {omega}));



  // Hadamard on ancilla qubit
@@ -232,12 +243,13 @@ IterativeQpeWorkflow::execute(const QuantumSimulationModel &model) { 
      }

    }();

    

    std::cout << "Iter " << iterIdx << ": Result = " << bitResult << "\n";

    if (bitResult) {

      omega_coef = omega_coef + 0.5;

    }

    // std::cout << "Iter " << iterIdx << ": Result = " << bitResult << "; omega_coef = " << omega_coef << "\n";



  }

  std::cout << "Final phase = " << omega_coef << "\n";

  // std::cout << "Final phase = " << omega_coef << "\n";

  return { {"phase", omega_coef}};

}

lib/qsim/impls/tests/IterativeQpeWorkflow.cpp

+12 −11
Original line number Diff line number Diff line
@@ -6,25 +6,26 @@ 
// Compile and run with:

/// $ qcor -qpu qpp IterativeQpeWorkflow.cpp

/// $ ./a.out



// Ansatz to bring the state into an eigenvector state of the Hamiltonian.

__qpu__ void eigen_state_prep(qreg q) {

  auto theta = 0.297113;

  X(q[0]);

  auto exponent_op = X(0) * Y(1) - Y(0) * X(1);

  exp_i_theta(q, theta, exponent_op);

  using qcor::openqasm;

  u3(pi / 4, 0, 0) q[0];

}



int main(int argc, char **argv) {

  // Create Hamiltonian

  auto H = 5.907 - 2.1433 * X(0) * X(1) - 2.143 * Y(0) * Y(1) + 0.21829 * Z(0) -

           6.125 * Z(1);

  // Create Hamiltonian:

  // Important: this must be a weighted pauli operator list.

  // TODO: add function to convert arbitrary Hamiltonian to the weighted form.

  auto H = 0.5 + 0.25 * X(0) + 0.25 * Z(0);

  auto problemModel =

      qsim::ModelBuilder::createModel(eigen_state_prep, H, 2, 0);

      qsim::ModelBuilder::createModel(eigen_state_prep, H, 1, 0);



  // Instantiate an IQPE workflow.

  auto workflow = qsim::getWorkflow("iqpe", {{"iterations", 8}});

  auto workflow =

      qsim::getWorkflow("iqpe", {{"time-steps", 4}, {"iterations", 4}});



  // Result should contain the observable expectation value along Trotter steps.

  auto result = workflow->execute(problemModel);

  const double phaseValue = result.get<double>("phase");

  std::cout << "Final phase = " << phaseValue << "\n";

  return 0;

}
 
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