Adding Confusion Matrix check for QSim. If a confusion matrix is spe…

…cified in a cirquit and Qsim is the target simulator a ValueError Exception will be thrown until confusion maps for Measurement Gates is supported in QSim.

qsimcirq/qsim_circuit.py

@@ -343,7 +343,6 @@ def __init__(
         cirq_circuit: cirq.Circuit,
         allow_decomposition: bool = False,
     ):
-
         if allow_decomposition:
             super().__init__()
             for moment in cirq_circuit:
@@ -352,6 +351,7 @@ def __init__(
                     self.append(op)
         else:
             super().__init__(cirq_circuit)
+        self._check_for_confusion_matrix()
 
     def __eq__(self, other):
         if not isinstance(other, QSimCircuit):
@@ -364,6 +364,24 @@ def _resolve_parameters_(
     ):
         return QSimCircuit(cirq.resolve_parameters(super(), param_resolver, recursive))
 
+    def _check_for_confusion_matrix(self):
+        """Checks cirq Circuit for Measurement Gates with confusion matrices.
+        Returns:
+            Throws a runtime exception if a MeasurementGate with a confusion matrix is included in the circuit
+        """
+        confusion_maps_on_measurement_gates = [
+            op.gate.confusion_map
+            for _, op, _ in self.findall_operations_with_gate_type(cirq.MeasurementGate)
+            if op.gate.confusion_map
+        ]
+        for confusion_map in confusion_maps_on_measurement_gates:
+            for map_values in confusion_map.values():
+                if map_values:
+                    raise ValueError(
+                        "Confusion Matrices are not currently supported in Qsim. "
+                        "See https://github.com/quantumlib/Cirq/issues/6305 for latest status"
+                    )
+
     def translate_cirq_to_qsim(
         self, qubit_order: cirq.QubitOrderOrList = cirq.QubitOrder.DEFAULT
     ) -> qsim.Circuit:

qsimcirq/qsim_simulator.py

@@ -213,7 +213,7 @@ def _run(
         """Run a simulation, mimicking quantum hardware.
 
         Args:
-            program: The circuit to simulate.
+            circuit: The circuit to simulate.
             param_resolver: Parameters to run with the program.
             repetitions: Number of times to repeat the run.
 

qsimcirq_tests/qsimcirq_test.py

@@ -336,6 +336,19 @@ def test_numpy_params():
     qsim_result = qsim_simulator.simulate_sweep(circuit, params=prs)
 
 
+def test_confusion_matrix_exception():
+    qubit = cirq.LineQubit(0)
+    cmap = {(0,): np.array([[0.8, 0.2], [0.2, 0.8]])}
+    circuit = cirq.Circuit()
+    circuit += cirq.X(qubit)
+    circuit += cirq.MeasurementGate(1, confusion_map=cmap)(qubit)
+    x, y = sympy.Symbol("x"), sympy.Symbol("y")
+    prs = [{x: np.int64(0), y: np.int64(1)}]
+    qsim_simulator = qsimcirq.QSimSimulator()
+    with pytest.raises(ValueError):
+        _ = qsim_simulator.simulate_sweep(circuit, params=prs)
+
+
 def test_invalid_params():
     # Parameters must have numeric values.
     q0 = cirq.LineQubit(0)
@@ -1219,7 +1232,6 @@ def test_multi_qubit_fusion():
 
 @pytest.mark.parametrize("mode", ["noiseless", "noisy"])
 def test_cirq_qsim_simulate_random_unitary(mode: str):
-
     q0, q1 = cirq.LineQubit.range(2)
     options = qsimcirq.QSimOptions(cpu_threads=16, verbosity=0)
     qsimSim = qsimcirq.QSimSimulator(qsim_options=options)