Cannot serialize identity gate on Quantum Engine

[viathor]

Description of the issue

Cannot serialize identity gate when using SQRT_ISWAP_GATESET.

How to reproduce the issue

sampler = engine.get_sampler(processor_id='...', gate_set=cg.SQRT_ISWAP_GATESET)
q = cirq.GridQubit(7, 4)
c = cirq.Circuit(cirq.I(q))
r = sampler.run(c, repetitions=1)
...
ValueError: Cannot serialize op cirq.I(cirq.GridQubit(7, 4)) of type <class 'cirq.ops.identity.IdentityGate'>

Cirq version

0.14.0.dev20211210220312

[tanujkhattar]

If we decide to add serialization for Identity, it should also be added to the new CircuitSerializer.

Cirq/cirq-google/cirq_google/serialization/circuit_serializer.py

Line 120 in 89f88b0

def _serialize_gate_op(

[tonybruguier]

I might be interested, but I can certainly yield on this one.

[dstrain115]

I don't think this gate should be serialized, as it has no effect by design in the hardware (and this serialization is only for Google hardware).

I would support cirq.I gates being stripped by default from serialization.

[dstrain115]

Confirmed with @viathor that we should just strip these gates out when serializing. Let's do this in CircuitSerializer too. @verult