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Fix explain_detector_error_model_errors mixing up Y/Z of PAULI_CHANNEL_2 #1006

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Merged
Strilanc merged 1 commit into from
Oct 28, 2025
Merged

Fix explain_detector_error_model_errors mixing up Y/Z of PAULI_CHANNEL_2 #1006

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2 changes: 2 additions & 0 deletions src/stim/simulators/error_matcher.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -222,8 +222,10 @@ void ErrorMatcher::err_pauli_channel_2(const CircuitInstruction &op) {
}
bool x0 = p0 & 1;
bool z0 = p0 & 2;
x0 ^= z0;
bool x1 = p1 & 1;
bool z1 = p1 & 2;
x1 ^= z1;
uint32_t m0 = x0 * TARGET_PAULI_X_BIT + z0 * TARGET_PAULI_Z_BIT;
uint32_t m1 = x1 * TARGET_PAULI_X_BIT + z1 * TARGET_PAULI_Z_BIT;
pair[0].data = t[k].data | m0;
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307 changes: 307 additions & 0 deletions src/stim/simulators/error_matcher.test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -609,3 +609,310 @@ ExplainedError {
}
)RESULT");
}

TEST(ErrorMatcher, PAULI_CHANNEL_2) {
std::vector<ExplainedError> actual;

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0.1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{GateTargetWithCoords{GateTarget::x(1)}}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0.1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{GateTargetWithCoords{GateTarget::y(1)}}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0.1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{GateTargetWithCoords{GateTarget::z(1)}}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0.1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::x(0)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0.1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::x(0)},
GateTargetWithCoords{GateTarget::x(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0.1, 0, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::x(0)},
GateTargetWithCoords{GateTarget::y(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0.1, 0, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::x(0)},
GateTargetWithCoords{GateTarget::z(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0.1, 0, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::y(0)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::y(0)},
GateTargetWithCoords{GateTarget::x(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::y(0)},
GateTargetWithCoords{GateTarget::y(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::y(0)},
GateTargetWithCoords{GateTarget::z(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::z(0)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::z(0)},
GateTargetWithCoords{GateTarget::x(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::z(0)},
GateTargetWithCoords{GateTarget::y(1)},
}));

actual = ErrorMatcher::explain_errors_from_circuit(
Circuit(R"CIRCUIT(
MXX 0 2 1 3
MZZ 0 2 1 3
PAULI_CHANNEL_2(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1) 0 1
MXX 0 2 1 3
MZZ 0 2 1 3
DETECTOR rec[-1] rec[-5]
DETECTOR rec[-2] rec[-6]
DETECTOR rec[-3] rec[-7]
DETECTOR rec[-4] rec[-8]
)CIRCUIT"),
nullptr,
false);
ASSERT_EQ(actual.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations.size(), 1);
ASSERT_EQ(actual[0].circuit_error_locations[0].flipped_pauli_product, (std::vector<GateTargetWithCoords>{
GateTargetWithCoords{GateTarget::z(0)},
GateTargetWithCoords{GateTarget::z(1)},
}));
}
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