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Fail loudly on unknown gate types in with_noise and Stim export; add RXYXY2Q #809

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83 changes: 83 additions & 0 deletions crates/pecos-qec/src/fault_tolerance/propagator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -152,6 +152,52 @@ pub fn is_supported_noop_or_metadata_gate(gate_type: GateType) -> bool {
)
}

/// Gate classification for compiling gate-triggered quantum noise.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum GateNoiseKind {
/// Preparation or allocation receiving preparation noise.
Prep,
/// Single-qubit operation receiving single-qubit noise.
Single,
/// Two-qubit operation receiving one noise channel per pair.
Two,
/// Measurement receiving no post-gate quantum noise.
Measurement,
/// Operation left unchanged by the noise callback.
Transparent,
/// Unsupported operation that must be rejected when noise is active.
Error,
}

/// Classify a gate for preparation, single-qubit, or two-qubit quantum noise.
///
/// Identity and idle gates retain single-qubit noise even though they are
/// transparent to Pauli propagation. Custom gates have no known arity.
#[inline]
#[must_use]
pub fn gate_noise_kind(gate_type: GateType) -> GateNoiseKind {
match gate_type {
// Custom has placeholder arity 1, not a known single-qubit operation.
GateType::Custom => GateNoiseKind::Error,
gate if is_supported_prep_gate(gate) => GateNoiseKind::Prep,
// consumes_measurement_record excludes MeasureLeaked, which still collapses
// the qubit. A complete measurement predicate belongs in pecos_core::GateType,
// alongside consumes_measurement_record (see also Gate::validate).
gate if gate.consumes_measurement_record() || gate == GateType::MeasureLeaked => {
GateNoiseKind::Measurement
}
// Identity and idle operations retain their physical single-qubit noise.
GateType::I | GateType::Idle => GateNoiseKind::Single,
// The core rejects Channel upstream of the noise callback.
gate if is_supported_noop_or_metadata_gate(gate) || gate == GateType::Channel => {
GateNoiseKind::Transparent
}
gate if gate.is_single_qubit() => GateNoiseKind::Single,
gate if gate.is_two_qubit() => GateNoiseKind::Two,
_ => GateNoiseKind::Error,
}
}

/// Circuit position of a gate that cannot be faithfully Pauli-propagated.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum UnsupportedGateLocation {
Expand Down Expand Up @@ -759,6 +805,43 @@ mod tests {
use super::*;
use pecos_quantum::TickCircuit;

#[test]
fn every_gate_has_an_explicit_noise_classification() {
for value in u8::MIN..=u8::MAX {
let Ok(gate) = GateType::try_from(value) else {
continue;
};
let prep = is_supported_prep_gate(gate);
let measurement = gate.consumes_measurement_record() || gate == GateType::MeasureLeaked;
let transparent = (is_supported_noop_or_metadata_gate(gate)
&& !matches!(gate, GateType::I | GateType::Idle))
|| gate == GateType::Channel;
let single = gate.is_single_qubit()
&& gate != GateType::Custom
&& !prep
&& !measurement
&& !transparent;
let two = gate.is_two_qubit();
// Intentionally enumerate errors: a future unclassified variant must fail.
let error = matches!(gate, GateType::CCX | GateType::Custom);
let buckets = [
(prep, GateNoiseKind::Prep),
(single, GateNoiseKind::Single),
(two, GateNoiseKind::Two),
(measurement, GateNoiseKind::Measurement),
(transparent, GateNoiseKind::Transparent),
(error, GateNoiseKind::Error),
];
assert_eq!(
buckets.iter().filter(|(member, _)| *member).count(),
1,
"{gate:?}"
);
let expected = buckets.iter().find(|(member, _)| *member).unwrap().1;
assert_eq!(gate_noise_kind(gate), expected, "{gate:?}");
}
}

fn simple_syndrome_circuit() -> TickCircuit {
// Simple Z-stabilizer measurement: Z0 Z1
// Ancilla qubit 2 measures the parity
Expand Down
4 changes: 4 additions & 0 deletions python/pecos-rslib/pecos_rslib.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -1741,6 +1741,10 @@ class llvm:

PHYSICAL_DURATION_META_KEY: str

def is_supported_noop_or_metadata_gate(gate_type: GateType) -> bool:
"""Return whether the gate is transparent to Pauli propagation."""
...

class GateType:
"""Gate type marker."""

Expand Down
114 changes: 47 additions & 67 deletions python/pecos-rslib/src/dag_circuit_bindings.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,9 @@
use crate::dtypes::AngleParam;
use crate::gate_registry_bindings::PyGateRegistry;
use pecos_core::{Angle64, ChannelExpr, GateQubits, GateSignature, Pauli, TimeUnits};
use pecos_qec::fault_tolerance::propagator::{
GateNoiseKind, gate_noise_kind, is_supported_noop_or_metadata_gate,
};
use pecos_quantum::{
Attribute, DagCircuit, Gate, GateType, PHYSICAL_DURATION_META_KEY, QubitId, Tick, TickCircuit,
TickGateError,
Expand Down Expand Up @@ -88,25 +91,6 @@ fn validate_probability(name: &str, p: f64) -> PyResult<()> {
}
}

fn receives_two_qubit_noise(gate_type: GateType) -> bool {
matches!(
gate_type,
GateType::CX
| GateType::CY
| GateType::CZ
| GateType::SZZ
| GateType::SZZdg
| GateType::SXX
| GateType::SXXdg
| GateType::SYY
| GateType::SYYdg
| GateType::SWAP
| GateType::RXX
| GateType::RYY
| GateType::RZZ
)
}

/// Convert a Rust Attribute to a Python object.
fn attribute_to_py(py: Python<'_>, attr: &Attribute) -> Py<PyAny> {
match attr {
Expand Down Expand Up @@ -647,6 +631,12 @@ impl PyGateType {
}
}

/// Whether a gate is transparent to Pauli propagation.
#[pyfunction(name = "is_supported_noop_or_metadata_gate")]
fn py_is_supported_noop_or_metadata_gate(gate_type: PyGateType) -> bool {
is_supported_noop_or_metadata_gate(gate_type.inner)
}

impl From<GateType> for PyGateType {
fn from(inner: GateType) -> Self {
Self { inner }
Expand Down Expand Up @@ -2895,9 +2885,22 @@ impl PyTickCircuit {
));
}

if p2 > 0.0 {
if p1 > 0.0 || p2 > 0.0 || p_prep > 0.0 {
for (tick_idx, gate) in self.inner.iter_gate_batches_with_tick() {
if receives_two_qubit_noise(gate.gate_type) && !gate.qubits.len().is_multiple_of(2)
match gate_noise_kind(gate.gate_type) {
GateNoiseKind::Prep
| GateNoiseKind::Single
| GateNoiseKind::Two
| GateNoiseKind::Measurement
| GateNoiseKind::Transparent => {}
GateNoiseKind::Error => {
return Err(pyo3::exceptions::PyValueError::new_err(format!(
"Unsupported gate type {:?} at tick {tick_idx} for with_noise",
gate.gate_type
)));
}
}
if p2 > 0.0 && gate.gate_type.is_two_qubit() && !gate.qubits.len().is_multiple_of(2)
{
return Err(pyo3::exceptions::PyValueError::new_err(format!(
"{:?} at tick {tick_idx} has {} qubits; expected pairs",
Expand All @@ -2912,63 +2915,36 @@ impl PyTickCircuit {
.inner
.try_with_noise(&|gate: &Gate| -> Vec<ChannelExpr> {
let mut channels = Vec::new();
match gate.gate_type {
GateType::PZ | GateType::QAlloc if p_prep > 0.0 => {
channels.extend(
gate.qubits
.iter()
.map(|q| pecos_core::channel::BitFlip(p_prep, q.index())),
);
match gate_noise_kind(gate.gate_type) {
GateNoiseKind::Prep if p_prep > 0.0 => {
// Match pecos-qec's dem_builder/mem_builder.rs: PX errors are Z flips.
channels.extend(gate.qubits.iter().map(|q| {
if gate.gate_type == GateType::PX {
pecos_core::channel::Dephasing(p_prep, q.index())
} else {
pecos_core::channel::BitFlip(p_prep, q.index())
}
}));
}
GateType::I
| GateType::X
| GateType::Y
| GateType::Z
| GateType::H
| GateType::F
| GateType::Fdg
| GateType::SX
| GateType::SXdg
| GateType::SY
| GateType::SYdg
| GateType::SZ
| GateType::SZdg
| GateType::T
| GateType::Tdg
| GateType::RX
| GateType::RY
| GateType::RZ
| GateType::U
| GateType::RXY1Q
| GateType::Idle
if p1 > 0.0 =>
{
GateNoiseKind::Single if p1 > 0.0 => {
channels.extend(
gate.qubits
.iter()
.map(|q| pecos_core::channel::Depolarizing(p1, q.index())),
);
}
GateType::CX
| GateType::CY
| GateType::CZ
| GateType::SZZ
| GateType::SZZdg
| GateType::SXX
| GateType::SXXdg
| GateType::SYY
| GateType::SYYdg
| GateType::SWAP
| GateType::RXX
| GateType::RYY
| GateType::RZZ
if p2 > 0.0 =>
{
GateNoiseKind::Two if p2 > 0.0 => {
channels.extend(gate.qubits.as_chunks::<2>().0.iter().map(|pair| {
pecos_core::channel::Depolarizing2(p2, pair[0].index(), pair[1].index())
}));
}
_ => {}
// Unsupported gates were rejected above whenever noise is active.
GateNoiseKind::Prep
| GateNoiseKind::Single
| GateNoiseKind::Two
| GateNoiseKind::Measurement
| GateNoiseKind::Transparent
| GateNoiseKind::Error => {}
}
channels
})
Expand Down Expand Up @@ -4128,6 +4104,10 @@ pub fn register_quantum_circuit_types(parent_module: &Bound<'_, PyModule>) -> Py
// Add classes to parent module
parent_module.add_class::<PyQubitId>()?;
parent_module.add_class::<PyGateType>()?;
parent_module.add_function(wrap_pyfunction!(
py_is_supported_noop_or_metadata_gate,
parent_module
)?)?;
parent_module.add_class::<PyGate>()?;
parent_module.add_class::<PyDagCircuit>()?;
parent_module.add_class::<PyTick>()?;
Expand Down
29 changes: 28 additions & 1 deletion python/quantum-pecos/src/pecos/qec/surface/circuit_builder.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3191,6 +3191,8 @@ def tick_circuit_to_stim(
import json
import math

from pecos_rslib import is_supported_noop_or_metadata_gate

lines = []

simple_gate_map = {
Expand Down Expand Up @@ -3302,7 +3304,32 @@ def _gate_to_stim(
msg = f"Unsupported traced Clifford RXY1Q angles: theta={theta!r}, phi={phi!r}"
raise ValueError(msg)

return [], None
if gate_name == "RXYXY2Q":
if len(gate.angles) < 2:
return [], None
theta = float(gate.angles[0])
phi = float(gate.angles[1])
if _is_close_turn(theta, 0.0):
return [], None
axis = None
if _is_close_turn(phi, 0.0) or _is_close_turn(phi, math.pi):
axis = "X"
elif _is_close_turn(phi, math.pi / 2) or _is_close_turn(phi, 3 * math.pi / 2):
axis = "Y"
if axis is not None:
if _is_close_turn(theta, math.pi / 2):
return [(f"SQRT_{axis}{axis}", qubits)], "two"
if _is_close_turn(theta, 3 * math.pi / 2):
return [(f"SQRT_{axis}{axis}_DAG", qubits)], "two"
if _is_close_turn(theta, math.pi):
return [(axis, qubits)], "two"
msg = f"Unsupported traced Clifford RXYXY2Q angles: theta={theta!r}, phi={phi!r}"
raise ValueError(msg)

if is_supported_noop_or_metadata_gate(gate.gate_type):
return [], None
msg = f"Unsupported gate for Stim export: {gate_name}"
raise ValueError(msg)

for tick_idx in range(tc.num_ticks()):
tick = tc.get_tick(tick_idx)
Expand Down
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