Add serialization support to more gates (#6479)

This PR adds serializatoin support to
- IdentityGate => fixes #4833
- HPowGate => allows sending circuits with cirq.H to backend
- changes the handling of SingleQubitCliffordGate from automatic conversion to PhasedXZGate to have its own proto (originally proposed in #6418)

cirq-core/cirq/testing/__init__.py

@@ -69,7 +69,12 @@
 
 from cirq.testing.equivalent_repr_eval import assert_equivalent_repr
 
-from cirq.testing.gate_features import SingleQubitGate, TwoQubitGate, ThreeQubitGate
+from cirq.testing.gate_features import (
+    SingleQubitGate,
+    TwoQubitGate,
+    ThreeQubitGate,
+    DoesNotSupportSerializationGate,
+)
 
 from cirq.testing.json import assert_json_roundtrip_works
 

cirq-core/cirq/testing/gate_features.py

@@ -36,3 +36,13 @@ class ThreeQubitGate(raw_types.Gate):
 
     def _num_qubits_(self) -> int:
         return 3
+
+
+class DoesNotSupportSerializationGate(raw_types.Gate):
+    """A gate that can't be serialized."""
+
+    def __init__(self, n_qubits: int = 1):
+        self.n_qubits = n_qubits
+
+    def _num_qubits_(self) -> int:
+        return self.n_qubits

cirq-google/cirq_google/api/v2/program.proto

@@ -209,6 +209,9 @@ message Operation {
     WaitGate waitgate = 16;
     InternalGate internalgate = 17;
     CouplerPulseGate couplerpulsegate = 18;
+    IdentityGate identitygate = 19;
+    HPowGate hpowgate = 20;
+    SingleQubitCliffordGate singlequbitcliffordgate = 21;
   }
 
   // Map from the argument name to the Argument needed to fully specify
@@ -434,4 +437,24 @@ message CouplerPulseGate{
   optional FloatArg coupling_mhz = 4;
   optional FloatArg q0_detune_mhz = 5;
   optional FloatArg q1_detune_mhz = 6;
+}
+
+message CliffordTableau {
+  optional int32 num_qubits = 1;  // Number of qubits the CliffordTableau acts on.
+  optional int32 initial_state = 2;  // The initial state.
+  repeated bool rs = 3;  // A flattened version of the `rs` array.
+  repeated bool xs = 4;  // A flattened version of the `xs` array.
+  repeated bool zs = 5;  // A flattened version of the `zs` array.
+}
+
+message SingleQubitCliffordGate {
+  CliffordTableau tableau = 1;
+}
+
+message IdentityGate {
+  repeated uint32 qid_shape = 1;
+}
+
+message HPowGate {
+  FloatArg exponent = 1;
 }

cirq-google/cirq_google/devices/grid_device_test.py

@@ -387,7 +387,9 @@ def test_grid_device_validate_operations_negative():
         device.validate_operation(cirq.CZ(q00, q10))
 
     with pytest.raises(ValueError, match='gate which is not supported'):
-        device.validate_operation(cirq.H(device_info.grid_qubits[0]))
+        device.validate_operation(
+            cirq.testing.DoesNotSupportSerializationGate()(device_info.grid_qubits[0])
+        )
 
 
 @pytest.mark.parametrize(

cirq-google/cirq_google/engine/engine_processor_test.py

@@ -288,7 +288,9 @@ def test_get_device():
     with pytest.raises(ValueError):
         device.validate_operation(cirq.X(cirq.GridQubit(1, 2)))
     with pytest.raises(ValueError):
-        device.validate_operation(cirq.H(cirq.GridQubit(0, 0)))
+        device.validate_operation(
+            cirq.testing.DoesNotSupportSerializationGate()(cirq.GridQubit(0, 0))
+        )
     with pytest.raises(ValueError):
         device.validate_operation(cirq.CZ(cirq.GridQubit(1, 1), cirq.GridQubit(2, 2)))
 

cirq-google/cirq_google/engine/engine_test.py

@@ -824,6 +824,8 @@ def test_get_engine_device(get_processor):
     with pytest.raises(ValueError):
         device.validate_operation(cirq.X(cirq.GridQubit(1, 2)))
     with pytest.raises(ValueError):
-        device.validate_operation(cirq.H(cirq.GridQubit(0, 0)))
+        device.validate_operation(
+            cirq.testing.DoesNotSupportSerializationGate()(cirq.GridQubit(0, 0))
+        )
     with pytest.raises(ValueError):
         device.validate_operation(cirq.CZ(cirq.GridQubit(1, 1), cirq.GridQubit(2, 2)))

cirq-google/cirq_google/engine/virtual_engine_factory_test.py

@@ -35,7 +35,9 @@ def _test_processor(processor: cg.engine.abstract_processor.AbstractProcessor):
     circuit = cirq.Circuit(cirq.X(bad_qubit), cirq.measure(bad_qubit))
     with pytest.raises(ValueError, match='Qubit not on device'):
         _ = processor.run(circuit, repetitions=100)
-    circuit = cirq.Circuit(cirq.H(good_qubit), cirq.measure(good_qubit))
+    circuit = cirq.Circuit(
+        cirq.testing.DoesNotSupportSerializationGate()(good_qubit), cirq.measure(good_qubit)
+    )
     with pytest.raises(ValueError, match='Cannot serialize op'):
         _ = processor.run(circuit, repetitions=100)
 
@@ -195,7 +197,9 @@ def test_create_default_noisy_quantum_virtual_machine():
         with pytest.raises(ValueError, match='Qubit not on device'):
             _ = processor.run(circuit, repetitions=100)
         good_qubit = cirq.GridQubit(5, 4)
-        circuit = cirq.Circuit(cirq.H(good_qubit), cirq.measure(good_qubit))
+        circuit = cirq.Circuit(
+            cirq.testing.DoesNotSupportSerializationGate()(good_qubit), cirq.measure(good_qubit)
+        )
         with pytest.raises(ValueError, match='.* contains a gate which is not supported.'):
             _ = processor.run(circuit, repetitions=100)
         device_specification = processor.get_device_specification()

cirq-google/cirq_google/serialization/arg_func_langs.py

@@ -19,6 +19,7 @@
 import sympy
 from cirq_google.api import v2
 from cirq_google.ops import InternalGate
+from cirq.qis import CliffordTableau
 
 SUPPORTED_FUNCTIONS_FOR_LANGUAGE: Dict[Optional[str], FrozenSet[str]] = {
     '': frozenset(),
@@ -455,3 +456,45 @@ def internal_gate_from_proto(
         num_qubits=int(msg.num_qubits),
         **gate_args,
     )
+
+
+def clifford_tableau_arg_to_proto(
+    value: CliffordTableau, *, out: Optional[v2.program_pb2.CliffordTableau] = None
+):
+    """Writes an CliffordTableau object into an CliffordTableau proto.
+    Args:
+        value: The gate to encode.
+        arg_function_language: The language to use when encoding functions. If
+            this is set to None, it will be set to the minimal language
+            necessary to support the features that were actually used.
+        out: The proto to write the result into. Defaults to a new instance.
+    Returns:
+        The proto that was written into.
+    """
+    msg = v2.program_pb2.CliffordTableau() if out is None else out
+    msg.num_qubits = value.n
+    msg.initial_state = value.initial_state
+    msg.xs.extend(value.xs.flatten())
+    msg.rs.extend(value.rs.flatten())
+    msg.zs.extend(value.zs.flatten())
+    return msg
+
+
+def clifford_tableau_from_proto(
+    msg: v2.program_pb2.CliffordTableau, arg_function_language: str
+) -> CliffordTableau:
+    """Extracts a CliffordTableau object from a CliffordTableau proto.
+    Args:
+        msg: The proto containing a serialized value.
+        arg_function_language: The `arg_function_language` field from
+            `Program.Language`.
+    Returns:
+        The deserialized InternalGate object.
+    """
+    return CliffordTableau(
+        num_qubits=msg.num_qubits,
+        initial_state=msg.initial_state,
+        rs=np.array(msg.rs, dtype=bool) if msg.rs else None,
+        xs=np.array(msg.xs, dtype=bool).reshape((2 * msg.num_qubits, -1)) if msg.xs else None,
+        zs=np.array(msg.zs, dtype=bool).reshape((2 * msg.num_qubits, -1)) if msg.zs else None,
+    )

cirq-google/cirq_google/serialization/arg_func_langs_test.py

@@ -28,8 +28,11 @@
     internal_gate_from_proto,
     ARG_LIKE,
     LANGUAGE_ORDER,
+    clifford_tableau_arg_to_proto,
+    clifford_tableau_from_proto,
 )
 from cirq_google.api import v2
+from cirq.qis import CliffordTableau
 
 
 @pytest.mark.parametrize(
@@ -249,3 +252,27 @@ def test_invalid_list():
 
     with pytest.raises(ValueError):
         _ = arg_to_proto([1.0, ''])
+
+
+@pytest.mark.parametrize('lang', LANGUAGE_ORDER)
+def test_clifford_tableau(lang):
+    tests = [
+        CliffordTableau(
+            1,
+            0,
+            rs=np.array([True, False], dtype=bool),
+            xs=np.array([[True], [False]], dtype=bool),
+            zs=np.array([[True], [False]], dtype=bool),
+        ),
+        CliffordTableau(
+            1,
+            1,
+            rs=np.array([True, True], dtype=bool),
+            xs=np.array([[True], [False]], dtype=bool),
+            zs=np.array([[False], [False]], dtype=bool),
+        ),
+    ]
+    for ct in tests:
+        proto = clifford_tableau_arg_to_proto(ct)
+        tableau = clifford_tableau_from_proto(proto, lang)
+        assert tableau == ct