code: def evolve(self, rho: Density) -> Density:
          
          qubits = rho.qubits
          results = [op.evolve(rho) for op in self.operators]
          tensors = [rho.tensor * w for rho, w in zip(results, self.weights)]
          tensor = reduce(add, tensors)
          return Density(tensor, qubits)
docs: Apply the action of this Kraus quantum operation upon a density