def _construct_qpe_evolution(self):
"""Implement the Quantum Phase Estimation algorithm"""
a = QuantumRegister(self._num_ancillae, name='a')
c = ClassicalRegister(self._num_ancillae, name='c')
q = QuantumRegister(self._operator.num_qubits, name='q')
qc = QuantumCircuit(a, q, c)
# initialize state_in
qc.data += self._state_in.construct_circuit('circuit', q).data
# Put all ancillae in uniform superposition
qc.u2(0, np.pi, a) if self._use_basis_gates else qc.h(a)
# phase kickbacks via dynamics
pauli_list = self._operator.reorder_paulis(
grouping=self._paulis_grouping)
if len(pauli_list) == 1:
slice_pauli_list = pauli_list
else:
if self._expansion_mode == 'trotter':
slice_pauli_list = pauli_list
elif self._expansion_mode == 'suzuki':
slice_pauli_list = Operator._suzuki_expansion_slice_pauli_list(
pauli_list, 1, self._expansion_order)
else:
raise ValueError('Unrecognized expansion mode {}.'.format(
self._expansion_mode))
for i in range(self._num_ancillae):
qc.data += self._operator.construct_evolution_circuit(
slice_pauli_list,
-2 * np.pi,
self._num_time_slices,
q,
a,
ctl_idx=i,
use_basis_gates=self._use_basis_gates).data
# global phase shift for the ancilla due to the identity pauli term
qc.u1(2 * np.pi * self._ancilla_phase_coef * (2**i), a[i])
# inverse qft on ancillae
self._iqft.construct_circuit('circuit', a, qc)
# measuring ancillae
qc.measure(a, c)
self._circuit = qc
def _estimate_phase_iteratively(self):
"""Iteratively construct the different order of controlled evolution circuit to carry out phase estimation"""
pauli_list = self._operator.reorder_paulis(
grouping=self._paulis_grouping)
if len(pauli_list) == 1:
slice_pauli_list = pauli_list
else:
if self._expansion_mode == 'trotter':
slice_pauli_list = pauli_list
else:
slice_pauli_list = Operator._suzuki_expansion_slice_pauli_list(
pauli_list, 1, self._expansion_order)
self._ret['top_measurement_label'] = ''
omega_coef = 0
# k runs from the number of iterations back to 1
for k in range(self._num_iterations, 0, -1):
omega_coef /= 2
qc = self._construct_kth_evolution(slice_pauli_list, k,
-2 * np.pi * omega_coef)
measurements = self.execute(qc).get_counts(qc)
if '0' not in measurements:
if '1' in measurements:
x = 1
else:
raise RuntimeError(
'Unexpected measurement {}.'.format(measurements))
else:
if '1' not in measurements:
x = 0
else:
x = 1 if measurements['1'] > measurements['0'] else 0
self._ret['top_measurement_label'] = '{}{}'.format(
x, self._ret['top_measurement_label'])
omega_coef = omega_coef + x / 2
logger.info(
'Reverse iteration {} of {} with measured bit {}'.format(
k, self._num_iterations, x))
return omega_coef
