use fisher exact test

tests/devices/qubit/test_simulate.py

@@ -16,7 +16,7 @@
 import numpy as np
 import pytest
 from dummy_debugger import Debugger
-from scipy.stats import ttest_1samp
+from scipy.stats import ttest_1samp, fisher_exact
 
 import pennylane as qml
 from pennylane.devices.qubit import get_final_state, measure_final_state, simulate
@@ -1190,6 +1190,20 @@ def test_qinfo_tf(self):
 ]
 
 
+def verify_binary_sample(actual, expected, outcomes=(0, 1), threshold=0.1):
+ """Checks that a binary sample matches the expected distribution using the Fisher exact test."""
+
+ actual, expected = np.asarray(actual), np.asarray(expected)
+ contingency_table = np.array(
+ [
+ [np.sum(actual == outcomes[0]), np.sum(actual == outcomes[1])],
+ [np.sum(expected == outcomes[0]), np.sum(expected == outcomes[1])],
+ ]
+ )
+ _, p_value = fisher_exact(contingency_table)
+ assert p_value > threshold, "The sample does not match the expected distribution."
+
+
 # pylint:disable=too-few-public-methods
 @pytest.mark.unit
 class TestMidCircuitMeasurements:
@@ -1228,20 +1242,29 @@ def test_simulate_one_shot_native_mcm(self, ml_framework, postselect_mode):
 
  if postselect_mode == "fill-shots":
  assert all(ms == 0 for ms in mcm_results)
- ttest_result = ttest_1samp(terminal_results, np.cos(np.pi / 4))
- assert ttest_result.pvalue > 0.05
+ equivalent_tape = qml.tape.QuantumScript(
+ [qml.RX(np.pi / 4, wires=0)], [qml.expval(qml.Z(0))], shots=n_shots
+ )
+ expected_sample = simulate(equivalent_tape, rng=rng)
+ verify_binary_sample(terminal_results, expected_sample, outcomes=(-1, 1))
 
  else:
- expected_mcm_average = (1 - np.cos(np.pi / 4)) / 2
- ttest_result = ttest_1samp(mcm_results, expected_mcm_average)
- assert ttest_result.pvalue > 0.05
+ equivalent_tape = qml.tape.QuantumScript(
+ [qml.RX(np.pi / 4, wires=0)], [qml.sample(wires=0)], shots=n_shots
+ )
+ expected_result = simulate(equivalent_tape, rng=rng)
+ verify_binary_sample(mcm_results, expected_result)
 
  subset = [ts for ms, ts in zip(mcm_results, terminal_results) if ms == 0]
- expected_average = np.cos(np.pi / 4)
- ttest_result = ttest_1samp(subset, expected_average)
- assert ttest_result.pvalue > 0.05
+ equivalent_tape = qml.tape.QuantumScript(
+ [qml.RX(np.pi / 4, wires=0)], [qml.expval(qml.Z(0))], shots=n_shots
+ )
+ expected_sample = simulate(equivalent_tape, rng=rng)
+ verify_binary_sample(subset, expected_sample, outcomes=(-1, 1))
 
  subset = [ts for ms, ts in zip(mcm_results, terminal_results) if ms == 1]
- expected_average = -np.cos(np.pi / 4)
- ttest_result = ttest_1samp(subset, expected_average)
- assert ttest_result.pvalue > 0.05
+ equivalent_tape = qml.tape.QuantumScript(
+ [qml.X(0), qml.RX(np.pi / 4, wires=0)], [qml.expval(qml.Z(0))], shots=n_shots
+ )
+ expected_sample = simulate(equivalent_tape, rng=rng)
+ verify_binary_sample(subset, expected_sample, outcomes=(-1, 1))