Add Quantum Engine support for cirq.CZPowGate (#6562)

* Add Quantum Engine support for cirq.CZPowGate

* build protos

* update test

* update test

* add _CZ_POWER_GATE_FAMILY and keep _CZ_GATE_FAMILY

* small revert to original

* black

* update test

* update test

* update test

* add _CZ_POWER_TARGET_GATES

* update target gateset

* update test

* update gatesets

* update gatesets

* update gatesets

* update test

* update test

* update test

* POW instead of POWER

* POW instead of POWER

Author: eliottrosenberg

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

@@ -57,6 +57,7 @@ message GateSpecification {
     Measurement meas = 10;
     Wait wait = 11;
     FSimViaModel fsim_via_model = 12;
+    CZPowGate cz_pow_gate = 13;
   }
 
   // Gate types available to Google devices.
@@ -74,6 +75,7 @@ message GateSpecification {
   message Measurement {}
   message Wait {}
   message FSimViaModel {}
+  message CZPowGate {}
 }
 
 message GateSet {

cirq-google/cirq_google/api/v2/device_pb2.py

@@ -53,6 +53,7 @@
 _SQRT_ISWAP_GATE_FAMILY = cirq.GateFamily(cirq.SQRT_ISWAP)
 _SQRT_ISWAP_INV_GATE_FAMILY = cirq.GateFamily(cirq.SQRT_ISWAP_INV)
 _CZ_GATE_FAMILY = cirq.GateFamily(cirq.CZ)
+_CZ_POW_GATE_FAMILY = cirq.GateFamily(cirq.CZPowGate)
 
 
 # TODO(#5050) Add GlobalPhaseGate
@@ -63,6 +64,8 @@
     _PHASED_XZ_GATE_FAMILY,
     _MEASUREMENT_GATE_FAMILY,
 ]
+# Target gates of cirq.CZTargetGateset with allow_partial_czs=True.
+_CZ_POW_TARGET_GATES = [_CZ_POW_GATE_FAMILY, _PHASED_XZ_GATE_FAMILY, _MEASUREMENT_GATE_FAMILY]
 # Target gates of `cirq_google.SycamoreTargetGateset`.
 _SYC_TARGET_GATES = [
     _SYC_FSIM_GATE_FAMILY,
@@ -127,6 +130,7 @@ class _GateRepresentations:
     _GateRepresentations(
         gate_spec_name='cz', supported_gates=[_CZ_FSIM_GATE_FAMILY, _CZ_GATE_FAMILY]
     ),
+    _GateRepresentations(gate_spec_name='cz_pow_gate', supported_gates=[_CZ_POW_GATE_FAMILY]),
     _GateRepresentations(
         gate_spec_name='phased_xz',
         supported_gates=[
@@ -306,6 +310,13 @@ def _build_compilation_target_gatesets(
                 additional_gates=list(gateset.gates - set(_SQRT_ISWAP_TARGET_GATES))
             )
         )
+    if all(gate_family in gateset.gates for gate_family in _CZ_POW_TARGET_GATES):
+        target_gatesets.append(
+            cirq.CZTargetGateset(
+                allow_partial_czs=True,
+                additional_gates=list(gateset.gates - set(_CZ_POW_TARGET_GATES)),
+            )
+        )
 
     return tuple(target_gatesets)