Classical control (#4631)

Sits on top of #4627

Creates `ConditionalOperation` class and executes operations conditionally upon the classical bits. Most of this is done in commit 06883d5.

Reimplements quantum teleportation example based off this class.

Parts 8, 9, 10 of https://tinyurl.com/cirq-feedforward.

cirq-core/cirq/__init__.py

@@ -190,6 +190,7 @@
     CCZPowGate,
     CCNOT,
     CCNotPowGate,
+    ClassicallyControlledOperation,
     CNOT,
     CNotPowGate,
     ControlledGate,
@@ -538,6 +539,7 @@
     measurement_key_obj,
     measurement_key_names,
     measurement_key_objs,
+    measurement_keys_touched,
     mixture,
     mul,
     num_qubits,

cirq-core/cirq/circuits/circuit.py

@@ -2422,9 +2422,7 @@ def _draw_moment_in_diagram(
     max_x = x0
     for op in non_global_ops:
         qubits = tuple(op.qubits)
-        cbits = tuple(
-            (protocols.measurement_key_objs(op) | protocols.control_keys(op)) & label_map.keys()
-        )
+        cbits = tuple(protocols.measurement_keys_touched(op) & label_map.keys())
         labels = qubits + cbits
         indices = [label_map[label] for label in labels]
         y1 = min(indices)

cirq-core/cirq/circuits/circuit_test.py

@@ -86,28 +86,6 @@ def validate_moment(self, moment):
 moment_and_op_type_validating_device = _MomentAndOpTypeValidatingDeviceType()
 
 
-class ControlOp(cirq.Operation):
-    def __init__(self, keys, qubits=None):
-        self._keys = [cirq.MeasurementKey(k) if isinstance(k, str) else k for k in keys]
-        self._qubits = qubits or []
-
-    def with_qubits(self, *new_qids):
-        pass  # coverage: ignore
-
-    @property
-    def qubits(self):
-        return self._qubits
-
-    def _control_keys_(self):
-        return self._keys
-
-    def _circuit_diagram_info_(
-        self, args: 'cirq.CircuitDiagramInfoArgs'
-    ) -> 'cirq.CircuitDiagramInfo':
-        symbols = ['X'] * len(self._qubits) + ['^'] * len(self._keys)
-        return cirq.CircuitDiagramInfo(symbols)
-
-
 def test_alignment():
     assert repr(cirq.Alignment.LEFT) == 'cirq.Alignment.LEFT'
     assert repr(cirq.Alignment.RIGHT) == 'cirq.Alignment.RIGHT'
@@ -250,190 +228,19 @@ def test_append_single():
 
 
 def test_append_control_key():
-    q = cirq.LineQubit(0)
+    q0, q1, q2 = cirq.LineQubit.range(3)
     c = cirq.Circuit()
-    c.append(cirq.measure(q, key='a'))
-    c.append(ControlOp(['a']))
+    c.append(cirq.measure(q0, key='a'))
+    c.append(cirq.X(q1).with_classical_controls('a'))
     assert len(c) == 2
 
     c = cirq.Circuit()
-    c.append(cirq.measure(q, key='a'))
-    c.append(ControlOp(['b']))
-    c.append(ControlOp(['b']))
+    c.append(cirq.measure(q0, key='a'))
+    c.append(cirq.X(q1).with_classical_controls('b'))
+    c.append(cirq.X(q2).with_classical_controls('b'))
     assert len(c) == 1
 
 
-def test_control_key_diagram():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(cirq.measure(q0, key='a'), ControlOp(qubits=[q1], keys=['a']))
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-0: ───M───────
-      ║
-1: ───╫───X───
-      ║   ║
-a: ═══@═══^═══
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_pauli():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(
-        cirq.measure_single_paulistring(cirq.X(q0), key='a'), ControlOp(qubits=[q1], keys=['a'])
-    )
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-0: ───M(X)───────
-      ║
-1: ───╫──────X───
-      ║      ║
-a: ═══@══════^═══
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_extra_measurements():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(
-        cirq.measure(q0, key='a'), cirq.measure(q0, key='b'), ControlOp(qubits=[q1], keys=['a'])
-    )
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-0: ───M───M('b')───
-      ║
-1: ───╫───X────────
-      ║   ║
-a: ═══@═══^════════
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_extra_controlled_bits():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(cirq.measure(q0, key='a'), ControlOp(qubits=[q0, q1], keys=['a']))
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-0: ───M───X───
-      ║   ║
-1: ───╫───X───
-      ║   ║
-a: ═══@═══^═══
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_extra_control_bits():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(
-        cirq.measure(q0, key='a'),
-        cirq.measure(q0, key='b'),
-        ControlOp(qubits=[q1], keys=['a', 'b']),
-    )
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-0: ───M───M───────
-      ║   ║
-1: ───╫───╫───X───
-      ║   ║   ║
-a: ═══@═══╬═══^═══
-          ║   ║
-b: ═══════@═══^═══
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_multiple_ops_single_moment():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(
-        cirq.measure(q0, key='a'),
-        cirq.measure(q1, key='b'),
-        ControlOp(qubits=[q0], keys=['a']),
-        ControlOp(qubits=[q1], keys=['b']),
-    )
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-      ┌──┐   ┌──┐
-0: ────M──────X─────
-       ║      ║
-1: ────╫M─────╫X────
-       ║║     ║║
-a: ════@╬═════^╬════
-        ║      ║
-b: ═════@══════^════
-      └──┘   └──┘
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_subcircuit():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(
-        cirq.CircuitOperation(
-            cirq.FrozenCircuit(cirq.measure(q0, key='a'), ControlOp(qubits=[q1], keys=['a']))
-        )
-    )
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-      [ 0: ───M─────── ]
-      [       ║        ]
-0: ───[ 1: ───╫───X─── ]───
-      [       ║   ║    ]
-      [ a: ═══@═══^═══ ]
-      │
-1: ───#2───────────────────
-""",
-        use_unicode_characters=True,
-    )
-
-
-def test_control_key_diagram_subcircuit_layered():
-    q0, q1 = cirq.LineQubit.range(2)
-    c = cirq.Circuit(
-        cirq.measure(q0, key='a'),
-        cirq.CircuitOperation(
-            cirq.FrozenCircuit(cirq.measure(q0, key='a'), ControlOp(qubits=[q1], keys=['a'])),
-        ),
-        ControlOp(qubits=[q1], keys=['a']),
-    )
-
-    cirq.testing.assert_has_diagram(
-        c,
-        """
-          [ 0: ───M─────── ]
-          [       ║        ]
-0: ───M───[ 1: ───╫───X─── ]───────
-      ║   [       ║   ║    ]
-      ║   [ a: ═══@═══^═══ ]
-      ║   ║
-1: ───╫───#2───────────────────X───
-      ║   ║                    ║
-a: ═══@═══╩════════════════════^═══
-""",
-        use_unicode_characters=True,
-    )
-
-
 def test_append_multiple():
     a = cirq.NamedQubit('a')
     b = cirq.NamedQubit('b')

cirq-core/cirq/json_resolver_cache.py

@@ -63,6 +63,7 @@ def _parallel_gate_op(gate, qubits):
         'CCXPowGate': cirq.CCXPowGate,
         'CCZPowGate': cirq.CCZPowGate,
         'CNotPowGate': cirq.CNotPowGate,
+        'ClassicallyControlledOperation': cirq.ClassicallyControlledOperation,
         'ControlledGate': cirq.ControlledGate,
         'ControlledOperation': cirq.ControlledOperation,
         'CSwapGate': cirq.CSwapGate,

cirq-core/cirq/ops/__init__.py

@@ -82,6 +82,10 @@
     ParallelGateFamily,
 )
 
+from cirq.ops.classically_controlled_operation import (
+    ClassicallyControlledOperation,
+)
+
 from cirq.ops.controlled_gate import (
     ControlledGate,
 )