code: def plot_state_histogram(self, ax):
          
          title = "Estimated state"
          nqc = int(round(np.log2(self.rho_est.data.shape[0])))
          labels = ut.basis_labels(nqc)
          return ut.state_histogram(self.rho_est, ax, title)
docs: Visualize the complex matrix elements of the estimated state.
  
          :param matplotlib.Axes ax: A matplotlib Axes object to plot into.