Merge pull request tensorflow#484 from quantumlib/qsim-invert-masks

Support invert_mask in qsimcirq

Author: 95-martin-orion

qsimcirq/qsim_simulator.py

@@ -379,8 +379,9 @@ def _sample_measure_results(
             for i in range(repetitions):
                 for key, op in meas_ops.items():
                     meas_indices = [qubit_map[qubit] for qubit in op.qubits]
+                    invert_mask = op.gate.full_invert_mask()
                     for j, q in enumerate(meas_indices):
-                        results[key][i][j] = full_results[i][q]
+                        results[key][i][j] = full_results[i][q] ^ invert_mask[j]
         else:
             options["c"] = self._translate_circuit(
                 program,
@@ -391,8 +392,11 @@ def _sample_measure_results(
                 options["s"] = self.get_seed()
                 measurements = sampler_fn(options)
                 for key, bound in bounds.items():
+                    invert_mask = meas_ops[key].gate.full_invert_mask()
                     for j in range(bound[1] - bound[0]):
-                        results[key][i][j] = int(measurements[bound[0] + j])
+                        results[key][i][j] = int(
+                            measurements[bound[0] + j] ^ invert_mask[j]
+                        )
 
         return results
 

qsimcirq_tests/qsimcirq_test.py

@@ -361,6 +361,46 @@ def test_cirq_qsim_run(mode: str):
         assert value.shape == (5, 1)
 
 
+def test_qsim_invert_mask():
+    q0, q1 = cirq.LineQubit.range(2)
+    circuit = cirq.Circuit(
+        cirq.measure(q0, q1, key="d", invert_mask=[False, True]),
+    )
+    cirq_sample = cirq.Simulator().sample(circuit, repetitions=5)
+    qsim_sample = qsimcirq.QSimSimulator().sample(circuit, repetitions=5)
+    assert qsim_sample.equals(cirq_sample)
+
+
+def test_qsim_invert_mask_different_qubits():
+    q0, q1 = cirq.LineQubit.range(2)
+    circuit = cirq.Circuit(
+        cirq.measure(q1, key="a", invert_mask=[True]),
+        cirq.measure(q0, key="b", invert_mask=[True]),
+        cirq.measure(q0, q1, key="c", invert_mask=[False, True]),
+        cirq.measure(q1, q0, key="d", invert_mask=[False, True]),
+    )
+    cirq_sample = cirq.Simulator().sample(circuit, repetitions=5)
+    qsim_sample = qsimcirq.QSimSimulator().sample(circuit, repetitions=5)
+    assert qsim_sample.equals(cirq_sample)
+
+
+def test_qsim_invert_mask_intermediate_measure():
+    q0, q1 = cirq.LineQubit.range(2)
+    # The dataframe generated by this should be all zeroes.
+    circuit = cirq.Circuit(
+        cirq.measure(q0, q1, key="a", invert_mask=[False, False]),
+        cirq.X(q0),
+        cirq.measure(q0, q1, key="b", invert_mask=[True, False]),
+        cirq.X(q1),
+        cirq.measure(q0, q1, key="c", invert_mask=[True, True]),
+        cirq.X(q0),
+        cirq.measure(q0, q1, key="d", invert_mask=[False, True]),
+    )
+    cirq_sample = cirq.Simulator().sample(circuit, repetitions=5)
+    qsim_sample = qsimcirq.QSimSimulator().sample(circuit, repetitions=5)
+    assert qsim_sample.equals(cirq_sample)
+
+
 @pytest.mark.parametrize("mode", ["noiseless", "noisy"])
 def test_qsim_run_vs_cirq_run(mode: str):
     # Simple circuit, want to check mapping of qubit(s) to their measurements