Consider adding StateVectorMixin to ProductState, _NamedOneQubitState

[balopat]

StateVectorMixin provides a couple of useful features on the state vector itself. ProductState and _NamedOneQubitState and its subclasses could benefit from it.

cc @mpharrigan wdyt?

[mpharrigan]

The mixin uses qubit_map which is designed for a vector (aka ndarray) based representation so you can map qubits to indices in a contiguous array. ProductState is like a dictionary (so this isn't applicable) and NamedOneQubitState only has one qubit (per its name (it's also named per its name)). The mixin also has qid_shape which similarly doesn't make as much sense for ProductState.

There's a couple of helpful methods, however, that only require the .state_vector() method to be implemented, which the classes do implement

Is StateVectorMixin used anywhere? Either "no" or my pycharm is broken :) my pycharm was/is broken

[vtomole]

According to @viathor , this points to a more general problem of Cirq not having a philosophy with which to make technical decisions when it come to state representation. He'll file an issue about this.

[viathor]

Filed #4582 for discussion. Keeping this issue open for now, but if we decide to consolidate our representations of quantum states then it will become moot and should be closed.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days

[github-actions]

Issue closed due to inactivity.