def sample(self, variables, samples, *args, **kwargs) -> numpy.array:
# todo: generalize in baseclass. Do Hamiltonian mapping on initialization
self.update_variables(variables)
result = []
for H in self._abstract_hamiltonians:
E = 0.0
for ps in H.paulistrings:
# change basis, measurement is destructive so copy the state
# to avoid recomputation
bc = QCircuit()
zero_string = False
for idx, p in ps.items():
if idx not in self.U.qubit_map:
# circuit does not act on the qubit
# case1: paulimatrix is 'Z' -> unit factor: ignore that part
# case2: zero factor -> continue with next ps
if p.upper() != "Z":
zero_string = True
else:
bc += change_basis(target=idx, axis=p)
if zero_string:
continue
qbc = self.U.create_circuit(abstract_circuit=bc,
variables=None)
Esamples = []
for sample in range(samples):
state_tmp = qulacs.QuantumState(self.U.n_qubits)
self.U.circuit.update_quantum_state(state_tmp)
if len(
bc.gates
) > 0: # otherwise there is no basis change (empty qulacs circuit does not work out)
qbc.update_quantum_state(state_tmp)
ps_measure = 1.0
for idx in ps.keys():
if idx not in self.U.qubit_map:
continue # means its 1 or Z and <0|Z|0> = 1 anyway
else:
M = qulacs.gate.Measurement(
self.U.qubit_map[idx], self.U.qubit_map[idx])
M.update_quantum_state(state_tmp)
measured = state_tmp.get_classical_value(
self.U.qubit_map[idx])
ps_measure *= (-2.0 * measured + 1.0
) # 0 becomes 1 and 1 becomes -1
Esamples.append(ps_measure)
E += ps.coeff * sum(Esamples) / len(Esamples)
result.append(E)
return numpy.asarray(result)
def sample(self, variables, samples, *args, **kwargs) -> numpy.array:
"""
Sample this Expectation Value.
Parameters
----------
variables:
variables, to supply to the underlying circuit.
samples: int:
the number of samples to take.
args
kwargs
Returns
-------
numpy.ndarray:
the result of sampling as a number.
"""
self.update_variables(variables)
state = self.U.initialize_state(self.n_qubits)
self.U.circuit.update_quantum_state(state)
result = []
for H in self._reduced_hamiltonians: # those are the hamiltonians which where non-used qubits are already traced out
E = 0.0
if H.is_all_z() and not self.U.has_noise:
E = super().sample(samples=samples,
variables=variables,
*args,
**kwargs)
else:
for ps in H.paulistrings:
# change basis, measurement is destructive so the state will be copied
# to avoid recomputation (except when noise was required)
bc = QCircuit()
for idx, p in ps.items():
bc += change_basis(target=idx, axis=p)
qbc = self.U.create_circuit(abstract_circuit=bc,
variables=None)
Esamples = []
for sample in range(samples):
if self.U.has_noise and sample > 0:
state = self.U.initialize_state(self.n_qubits)
self.U.circuit.update_quantum_state(state)
state_tmp = state
else:
state_tmp = state.copy()
if len(
bc.gates
) > 0: # otherwise there is no basis change (empty qulacs circuit does not work out)
qbc.update_quantum_state(state_tmp)
ps_measure = 1.0
for idx in ps.keys():
assert idx in self.U.abstract_qubits # assert that the hamiltonian was really reduced
M = qulacs.gate.Measurement(
self.U.qubit(idx), self.U.qubit(idx))
M.update_quantum_state(state_tmp)
measured = state_tmp.get_classical_value(
self.U.qubit(idx))
ps_measure *= (-2.0 * measured + 1.0
) # 0 becomes 1 and 1 becomes -1
Esamples.append(ps_measure)
E += ps.coeff * sum(Esamples) / len(Esamples)
result.append(E)
return numpy.asarray(result)