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small fixes to allow initial density matrix for faster noisy sampling with cirq #84

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Nov 5, 2021
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small fixes to allow initial density matrix for faster noisy sampling with cirq #84

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7 changes: 4 additions & 3 deletions qsdk/backendbuddy/simulator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -108,8 +108,9 @@ def simulate(self, source_circuit, return_statevector=False, initial_statevector
if source_circuit.width == 0:
raise ValueError("Cannot simulate an empty circuit (e.g identity unitary) with unknown number of qubits.")

# If the unitary is the identity (no gates), no need for simulation: return all-zero state
if source_circuit.size == 0:
# If the unitary is the identity (no gates) and no noise model, no need for simulation:
# return all-zero state or sample from statevector
if source_circuit.size == 0 and not self._noise_model:
if initial_statevector is not None:
statevector = initial_statevector
frequencies = self._statevector_to_frequencies(initial_statevector)
Expand Down Expand Up @@ -392,7 +393,7 @@ def _get_expectation_value_from_frequencies(self, qubit_operator, state_prep_cir
n_qubits = state_prep_circuit.width
if not self.statevector_available or state_prep_circuit.is_mixed_state or self._noise_model:
initial_circuit = state_prep_circuit
if initial_statevector is not None:
if initial_statevector is not None and not self.statevector_available:
raise ValueError(f'Backend {self._target} does not support statevectors')
else:
updated_statevector = initial_statevector
Expand Down