fix(squin): implement IsOne measurement predicate (#254)

Implement `IsOne` in the Squin simulator, with integration coverage for
zero, one, loss, and conditional correction.

Author: Krastanov

ppvm-python/src/ppvm/squin_interpreter/qubit.py

@@ -51,6 +51,16 @@ def measure(
         results_converted = ilist.IList(list(map(_measurement_result_conversion, results)))
         return (results_converted,)
 
+    @interp.impl(qubit.stmts.IsOne)
+    def is_one(
+        self,
+        interp_: GeneralizedTableauInterpreter,
+        frame: interp.Frame,
+        stmt: qubit.stmts.IsOne,
+    ):
+        measurements = frame.get(stmt.measurements)
+        return (ilist.IList([result == MeasurementResultValue.One for result in measurements]),)
+
     @interp.impl(qubit.stmts.Reset)
     def reset(
         self,

ppvm-python/test/generalized_tableau/test_simulator_device.py

@@ -71,6 +71,17 @@ def main():
     assert _run_kernel(main, 6) == [ZERO, ONE, ONE, ONE, ONE, ONE]
 
 
+def test_is_one_distinguishes_zero_one_and_loss():
+    @squin.kernel
+    def main():
+        q = squin.qalloc(3)
+        squin.x(q[1])
+        squin.qubit_loss(1.0, q[2])
+        return squin.broadcast.is_one(squin.broadcast.measure(q))
+
+    assert _run_kernel(main, 3) == [False, True, False]
+
+
 def test_bell_pair_measurements_are_correlated_after_collapse():
     @squin.kernel
     def main():
@@ -82,10 +93,10 @@ def main():
         first = squin.measure(q[0])
         second = squin.measure(q[1])
 
-        if first == MeasurementResultValue.One:
+        if squin.is_one(first):
             squin.x(q[2])
 
-        if second == MeasurementResultValue.One:
+        if squin.is_one(second):
             squin.x(q[3])
 
         return squin.broadcast.measure(q)