def do_sample(self,
samples,
circuit,
noise_model=None,
initial_state=0,
*args,
**kwargs) -> QubitWaveFunction:
assert (noise_model is None)
state = qulacs.QuantumState(self.n_qubits)
lsb = BitStringLSB.from_int(initial_state, nbits=self.n_qubits)
state.set_computational_basis(
BitString.from_binary(lsb.binary).integer)
self.circuit.update_quantum_state(state)
if hasattr(self, "measurements"):
result = {}
for sample in range(samples):
sample_result = {}
for t, m in self.measurements.items():
m.update_quantum_state(state)
sample_result[t] = state.get_classical_value(t)
sample_result = dict(
sorted(sample_result.items(), key=lambda x: x[0]))
binary = BitString.from_array(sample_result.values())
if binary in result:
result[binary] += 1
else:
result[binary] = 1
return QubitWaveFunction(state=result)
else:
# sample from the whole wavefunction (all-Z measurement)
result = state.sampling(samples)
return self.convert_measurements(backend_result=result)
def apply_paulistring(self, paulistring: 'PauliString'):
"""
Inefficient function which computes action of a single paulistring
:param paulistring: PauliString
:return: Expectation Value
"""
result = QubitWaveFunction()
for k, v in self.items():
arr = k.array
c = v
for idx, p in paulistring.items():
if p.lower() == "x":
arr[idx] = (arr[idx] + 1) % 2
elif p.lower() == "y":
c *= 1.0j * (-1) ** (arr[idx])
arr[idx] = (arr[idx] + 1) % 2
elif p.lower() == "z":
c *= (-1) ** (arr[idx])
else:
raise TequilaException("unknown pauli: " + str(p))
result[BitString.from_array(array=arr)] = c
return paulistring.coeff * result
