Properly deal with measurements for lost qubits

Author: david-pl

src/bloqade/pyqrack/squin/qubit.py

@@ -37,9 +37,11 @@ def broadcast(
         qubits: ilist.IList[PyQrackQubit, Any] = frame.get(stmt.qubits)
         operator.broadcast_apply(qubits)
 
-    def _measure_qubit(self, qbit: PyQrackQubit):
+    def _measure_qubit(self, qbit: PyQrackQubit, interp: PyQrackInterpreter):
         if qbit.is_active():
             return bool(qbit.sim_reg.m(qbit.addr))
+        else:
+            return interp.loss_m_result
 
     @interp.impl(qubit.MeasureQubitList)
     def measure_qubit_list(
@@ -49,15 +51,15 @@ def measure_qubit_list(
         stmt: qubit.MeasureQubitList,
     ):
         qubits: ilist.IList[PyQrackQubit, Any] = frame.get(stmt.qubits)
-        result = ilist.IList([self._measure_qubit(qbit) for qbit in qubits])
+        result = ilist.IList([self._measure_qubit(qbit, interp) for qbit in qubits])
         return (result,)
 
     @interp.impl(qubit.MeasureQubit)
     def measure_qubit(
         self, interp: PyQrackInterpreter, frame: interp.Frame, stmt: qubit.MeasureQubit
     ):
         qbit: PyQrackQubit = frame.get(stmt.qubit)
-        result = self._measure_qubit(qbit)
+        result = self._measure_qubit(qbit, interp)
         return (result,)
 
     @interp.impl(qubit.MeasureAndReset)
@@ -70,10 +72,7 @@ def measure_and_reset(
         qubits: ilist.IList[PyQrackQubit, Any] = frame.get(stmt.qubits)
         result = []
         for qbit in qubits:
-            if qbit.is_active():
-                qbit_result = bool(qbit.sim_reg.m(qbit.addr))
-            else:
-                qbit_result = None
+            qbit_result = self._measure_qubit(qbit, interp)
 
             if qbit_result:
                 qbit.sim_reg.x(qbit.addr)

src/bloqade/pyqrack/squin/wire.py

@@ -43,6 +43,10 @@ def measure(
     ):
         w: PyQrackWire = frame.get(stmt.wire)
         qbit = w.qubit
+
+        if not qbit.is_active():
+            return (interp.loss_m_result,)
+
         res: bool = bool(qbit.sim_reg.m(qbit.addr))
         return (res,)
 
@@ -55,6 +59,10 @@ def measure_and_reset(
     ):
         w: PyQrackWire = frame.get(stmt.wire)
         qbit = w.qubit
+
+        if not qbit.is_active():
+            return (w, interp.loss_m_result)
+
         res: bool = bool(qbit.sim_reg.m(qbit.addr))
 
         if res:
@@ -69,6 +77,9 @@ def reset(self, interp: PyQrackInterpreter, frame: interp.Frame, stmt: wire.Rese
         w: PyQrackWire = frame.get(stmt.wire)
         qbit = w.qubit
 
+        if not qbit.is_active():
+            return (w,)
+
         if bool(qbit.sim_reg.m(qbit.addr)):
             qbit.sim_reg.x(qbit.addr)