This transformer is useful when using a density matrix simulator, when
wishing to calculate the final density matrix of a circuit and not simulate
the measurements themselves.
Args
circuit
The circuit to transform. It will not be modified.
A copy of the circuit, with dephase operations in place of all
measurements.
Raises
ValueError
If the circuit contains classical controls. In this case,
it is required to change these to quantum controls via
cirq.defer_measurements first. Since deferral adds ancilla qubits
to the circuit, this is not done automatically, to prevent
surprises.