qubit_set() → FrozenSet[cirq.GridQubit]¶
Returns a set or frozenset of qubits on the device, if possible.
If the device has a finite set of qubits, then a set or frozen set of all qubits on the device is returned.
If the device has no well defined finite set of qubits (e.g. cirq.UnconstrainedDevice has this property), then None is returned.