Update demo file

Author: ElePT

test_midcircuit.py

@@ -0,0 +1,121 @@
+import io
+
+from qiskit import QuantumCircuit
+from qiskit.circuit import Instruction, Measure
+from qiskit.circuit.singleton import SingletonInstruction, stdlib_singleton_key
+from qiskit.circuit.exceptions import CircuitError
+from qiskit._accelerate.circuit import StandardInstructionType
+from qiskit.qpy import dump, load
+from qiskit.transpiler.passes import ResetAfterMeasureSimplification
+
+
+# IDEA 1: Subclass Measure
+# Pitfall: can't change name
+class MidCircuitMeasureSubclass(Measure):
+    pass
+
+# IDEA 1.2: Subclass Measure
+class CustomMeasurement(Measure):
+    """A custom specialized measurement."""
+
+    def __init__(self, label=None):
+        super().__init__(label=label)
+        if label:
+            self.name= label
+        else:
+            self.name="measure_2"
+
+
+# IDEA 2: Just build an instruction
+# Pitfall: the transpiler doesn't detect it as a measurement
+class MidCircuitMeasureInstruction(Instruction):
+    def __init__(self, label=None):
+        super().__init__("mid_circuit_measure", 1, 1, [], label=label)
+
+
+# IDEA 3: copy Measure() definition. Works!
+# Pitfall:
+# - setting the standard instruction type like this looks a bit sketchy
+# - if we do this from outside qiskit (qiskit-ibm-runtime), we'd have to import 
+#    StandardInstructionType from qiskit._accelerate.circuit
+class NamedMeasure(SingletonInstruction):
+    """Quantum measurement in the computational basis."""
+
+    # Just force the standard instruction type?
+    _standard_instruction_type = StandardInstructionType.Measure
+
+    def __init__(self, name="measure_2", label=None):
+        """
+        Args:
+            label: optional string label for this instruction.
+        """
+        super().__init__(name, 1, 1, [], label=label)
+
+    def __init_subclass__(cls, **kwargs):
+        super().__init_subclass__(**kwargs)
+        # Subclasses of Measure are not "standard", so we set this to None to
+        # prevent the Rust code from treating them as such.
+        cls._standard_instruction_type = None
+
+    _singleton_lookup_key = stdlib_singleton_key()
+
+    def broadcast_arguments(self, qargs, cargs):
+        qarg = qargs[0]
+        carg = cargs[0]
+
+        if len(carg) == len(qarg):
+            for qarg, carg in zip(qarg, carg):
+                yield [qarg], [carg]
+        elif len(qarg) == 1 and carg:
+            for each_carg in carg:
+                yield qarg, [each_carg]
+        else:
+            raise CircuitError("register size error")
+
+loaded = {}
+for cls in [CustomMeasurement]:
+    circ = QuantumCircuit(2, 2)
+    circ.append(cls(), [0], [0])
+    circ.append(cls("measure_3"), [0], [1])
+    circ.measure_all()
+    print(circ.draw())
+
+    with io.BytesIO() as f:
+        dump(circ, f)
+        f.seek(0)
+        loaded[str(cls)] = load(f)
+
+
+for cls, loaded_circ in loaded.items():
+    print(cls)
+    print(list(loaded_circ[0].data))
+
+def test_bv_circuit():
+    """Test Bernstein Vazirani circuit with midcircuit measurement."""
+    bitstring = "11111"
+    qc = QuantumCircuit(2, len(bitstring))
+    qc.x(1)
+    qc.h(1)
+    for idx, bit in enumerate(bitstring[::-1]):
+        qc.h(0)
+        if int(bit):
+            qc.cx(0, 1)
+        qc.h(0)
+        qc.append(CustomMeasurement(label="measure_3"), [0], [idx])
+        # qc.measure(0, idx)
+        if idx != len(bitstring) - 1:
+            qc.reset(0)
+            # reset control
+            qc.reset(1)
+            qc.x(1)
+            qc.h(1)
+    print(qc.draw())
+    new_qc = ResetAfterMeasureSimplification()(qc)
+    print(new_qc.draw())
+
+    for op in new_qc.data:
+        if op.operation.name == "reset":
+            print(op.qubits[0] == new_qc.qubits[1])
+            # self.assertEqual(op.qubits[0], new_qc.qubits[1])
+
+# test_bv_circuit()