def _max_weight_state(states: Iterable[value.ProductState]) \
-> Union[None, value.ProductState]:
"""Create a new state that is compatible with all input states
and has the maximum weight.
The returned TensorProductState is constructed by taking the
single-qubit state at each qubit position.
This function will return `None` if the input states are not compatible
For example, the max_weight_state of [+X(0), -Z(1)] is
"+X(0) * -Z(1)". Asking for the max weight state of something like
[+X(0), +Z(0)] will return None.
"""
qubit_state_map = dict() # type: Dict[ops.Qid, _NamedOneQubitState]
for state in states:
for qubit, named_state in state:
if qubit in qubit_state_map:
if qubit_state_map[qubit] != named_state:
return None
else:
qubit_state_map[qubit] = named_state
return value.ProductState(qubit_state_map)
def zeros_state(qubits: Iterable['cirq.Qid']):
"""Return the ProductState that is |00..00> on all qubits."""
return value.ProductState({q: value.KET_ZERO for q in qubits})