code: def prepare_w4():
      
      circ = qf.Circuit()
      circ += qf.X(1)
  
      circ += qf.ISWAP(1, 2) ** 0.5
      circ += qf.S(2)
      circ += qf.Z(2)
  
      circ += qf.ISWAP(2, 3) ** 0.5
      circ += qf.S(3)
      circ += qf.Z(3)
  
      circ += qf.ISWAP(0, 1) ** 0.5
      circ += qf.S(0)
      circ += qf.Z(0)
  
      ket = circ.run()
  
      return ket
docs: Prepare a 4-qubit W state using sqrt(iswaps) and local gates