Remove correlated error nonce from stim IR (#560)

Author: rafaelha

src/bloqade/stim/dialects/noise/emit.py

@@ -93,7 +93,11 @@ def non_stim_corr_error(
         prob: tuple[str, ...] = frame.get_values(stmt.probs)
         prob_str: str = ", ".join(prob)
 
-        res = f"I_ERROR[{stmt.name}:{stmt.nonce}]({prob_str}) " + " ".join(targets)
+        res = (
+            f"I_ERROR[{stmt.name}:{emit.correlated_error_count}]({prob_str}) "
+            + " ".join(targets)
+        )
+        emit.correlated_error_count += 1
         emit.writeln(frame, res)
 
         return ()

src/bloqade/stim/dialects/noise/stmts.py

@@ -1,5 +1,3 @@
-import random
-
 from kirin import ir, types, lowering
 from kirin.decl import info, statement
 
@@ -91,8 +89,6 @@ class NonStimError(ir.Statement):
 class NonStimCorrelatedError(ir.Statement):
     name = "NonStimCorrelatedError"
     traits = frozenset({lowering.FromPythonCall()})
-    # nonce must be a unique value, otherwise stim might merge two correlated errors
-    nonce: int = info.attribute(default_factory=lambda: random.getrandbits(32))
     probs: tuple[ir.SSAValue, ...] = info.argument(types.Float)
     targets: tuple[ir.SSAValue, ...] = info.argument(types.Int)
 

src/bloqade/stim/emit/stim_str.py

@@ -20,11 +20,13 @@ class EmitStimMain(EmitStr):
     keys = ["emit.stim"]
     dialects: ir.DialectGroup = field(default_factory=_default_dialect_group)
     file: StringIO = field(default_factory=StringIO)
+    correlation_identifier_offset: int = 0
 
     def initialize(self):
         super().initialize()
         self.file.truncate(0)
         self.file.seek(0)
+        self.correlated_error_count = self.correlation_identifier_offset
         return self
 
     def eval_stmt_fallback(

src/bloqade/stim/parse/lowering.py

@@ -627,10 +627,13 @@ def visit_I_ERROR(
         # Parse tag
         tag_parts = node.tag.split(";", maxsplit=1)[0].split(":", maxsplit=1)
         nonstim_name = tag_parts[0]
-        nonce = 0
         if len(tag_parts) == 2:
+            # This should be a correlated error of the form, e.g.,
+            # I_ERROR[correlated_loss:<identifier>](0.01) 0 1 2
+            # The identifier is a unique number that prevents stim from merging
+            # correlated errors. We discard the identifier, but verify it is an integer.
             try:
-                nonce = int(tag_parts[1])
+                _ = int(tag_parts[1])
             except ValueError:
                 # String was not an integer
                 if self.error_unknown_nonstim:
@@ -643,22 +646,14 @@ def visit_I_ERROR(
                 f"Unknown non-stim statement name: {nonstim_name!r} ({node!r})"
             )
         statement_cls = self.nonstim_noise_ops.get(nonstim_name)
+        stmt = None
         if statement_cls is not None:
-            if issubclass(statement_cls, noise.NonStimCorrelatedError):
-                stmt = statement_cls(
-                    nonce=nonce,
-                    probs=self._get_float_args_ssa(state, node.gate_args_copy()),
-                    targets=self._get_multiple_qubit_or_rec_ssa(
-                        state, node, node.targets_copy()
-                    ),
-                )
-            else:
-                stmt = statement_cls(
-                    probs=self._get_float_args_ssa(state, node.gate_args_copy()),
-                    targets=self._get_multiple_qubit_or_rec_ssa(
-                        state, node, node.targets_copy()
-                    ),
-                )
+            stmt = statement_cls(
+                probs=self._get_float_args_ssa(state, node.gate_args_copy()),
+                targets=self._get_multiple_qubit_or_rec_ssa(
+                    state, node, node.targets_copy()
+                ),
+            )
         return stmt
 
     def visit_CircuitInstruction(

src/bloqade/stim/rewrite/squin_noise.py

@@ -15,7 +15,6 @@
 
 @dataclass
 class SquinNoiseToStim(RewriteRule):
-    _correlated_loss_counter: int = 0
 
     def rewrite_Statement(self, node: Statement) -> RewriteResult:
         match node:
@@ -135,9 +134,7 @@ def rewrite_CorrelatedQubitLoss(
         stim_stmt = stim_noise.CorrelatedQubitLoss(
             targets=qubit_idx_ssas,
             probs=(stmt.p,),
-            nonce=self._correlated_loss_counter,
         )
-        self._correlated_loss_counter += 1
 
         return stim_stmt
 

test/stim/dialects/stim/emit/test_stim_noise.py

@@ -1,6 +1,16 @@
 from bloqade import stim
+from bloqade.stim.emit import EmitStimMain
+from bloqade.stim.parse import loads
+from bloqade.stim.dialects import noise
 
-from .base import codegen
+emit = EmitStimMain()
+
+
+def codegen(mt):
+    # method should not have any arguments!
+    emit.initialize()
+    emit.run(mt=mt, args=())
+    return emit.get_output()
 
 
 def test_noise():
@@ -45,7 +55,43 @@ def test_qubit_loss():
 def test_correlated_qubit_loss():
     @stim.main
     def test_correlated_qubit_loss():
-        stim.correlated_qubit_loss(probs=(0.1,), targets=(0, 1, 2), nonce=3)
+        stim.correlated_qubit_loss(probs=(0.1,), targets=(0, 1, 2))
 
     out = codegen(test_correlated_qubit_loss)
-    assert out.strip() == "I_ERROR[correlated_loss:3](0.10000000) 0 1 2"
+    assert out.strip() == "I_ERROR[correlated_loss:0](0.10000000) 0 1 2"
+
+
+def test_correlated_qubit_loss_multiple():
+
+    @stim.main
+    def test_correlated_qubit_loss_multiple():
+        stim.correlated_qubit_loss(probs=(0.1,), targets=(0, 1))
+        stim.correlated_qubit_loss(probs=(0.1,), targets=(2, 3))
+
+    for i in range(2):  # repeat the test to ensure the identifier is reset each time
+        out = codegen(test_correlated_qubit_loss_multiple).strip()
+        print(out)
+        assert (
+            out.strip()
+            == "I_ERROR[correlated_loss:0](0.10000000) 0 1\n"
+            + "I_ERROR[correlated_loss:1](0.10000000) 2 3"
+        )
+
+
+def test_correlated_qubit_codegen_roundtrip():
+    @stim.main
+    def test():
+        stim.correlated_qubit_loss(probs=(0.1,), targets=(0, 1, 2))
+        stim.qubit_loss(probs=(0.2,), targets=(2,))
+        stim.correlated_qubit_loss(probs=(0.3,), targets=(3, 4))
+
+    stim_str = codegen(test)
+
+    mt = loads(
+        stim_str,
+        nonstim_noise_ops={
+            "loss": noise.QubitLoss,
+            "correlated_loss": noise.CorrelatedQubitLoss,
+        },
+    )
+    assert codegen(mt) == stim_str

test/stim/parse/test_parse_custom.py

@@ -27,7 +27,7 @@ def test_parse_trivial_correlated():
 
     # test roundtrip
     out = codegen(mt)
-    assert out.strip() == "I_ERROR[TRIV_CORR_ERROR:3](0.20000000, 0.30000000) 5 0 1 2"
+    assert out.strip() == "I_ERROR[TRIV_CORR_ERROR:0](0.20000000, 0.30000000) 5 0 1 2"
 
 
 def test_qubit_loss():

test/stim/passes/test_squin_noise_to_stim.py

@@ -242,6 +242,22 @@ def test():
     assert codegen(test) == expected
 
 
+def test_correlated_qubit_loss_codegen_with_offset():
+
+    @kernel
+    def test():
+        q = sq.qalloc(4)
+        sq.correlated_qubit_loss(0.1, qubits=q)
+
+    SquinToStimPass(test.dialects)(test)
+
+    emit = EmitStimMain(correlation_identifier_offset=10)
+    emit.initialize()
+    emit.run(mt=test, args=())
+    stim_str = emit.get_output().strip()
+    assert stim_str == "I_ERROR[correlated_loss:10](0.10000000) 0 1 2 3"
+
+
 def get_stmt_at_idx(method: ir.Method, idx: int) -> ir.Statement:
     return method.callable_region.blocks[0].stmts.at(idx)
 

test/stim/wrapper/test_wrapper.py

@@ -466,11 +466,11 @@ def main_ry_wrap():
 def test_wrap_correlated_qubit_loss():
     @stim.main
     def main_correlated_qubit_loss():
-        noise.CorrelatedQubitLoss(probs=(0.1,), targets=(0, 1, 2), nonce=3)
+        noise.CorrelatedQubitLoss(probs=(0.1,), targets=(0, 1, 2))
 
     @stim.main
     def main_correlated_qubit_loss_wrap():
-        stim.correlated_qubit_loss(probs=(0.1,), targets=(0, 1, 2), nonce=3)
+        stim.correlated_qubit_loss(probs=(0.1,), targets=(0, 1, 2))
 
     assert main_correlated_qubit_loss.callable_region.is_structurally_equal(
         main_correlated_qubit_loss_wrap.callable_region