content: import numpy as np
  import matplotlib.pyplot as plt
  import qutip
  
  times = np.linspace(0, 10.0, 200)
  a = qutip.destroy(10)
  x = a.dag() + a
  H = a.dag() * a
  alpha = 2.5
  rho0 = qutip.coherent_dm(10, alpha)
  corr = qutip.correlation_2op_2t(H, rho0, times, times, [np.sqrt(0.25) * a], x, x)
  
  plt.pcolor(np.real(corr))
  plt.xlabel(r'Time $t_2$')
  plt.ylabel(r'Time $t_1$')
  plt.title(r'Correlation $\left<x(t)x(0)\right>$')
  plt.show()
  