The quantum bacterial foraging algorithm is a relatively new combinatorial algorithm which combines the quantum evolutionary algorithm and the bacterial foraging algorithm. Although the algorithm has made some significant progress in the convergence speed, the algorithm still has the problem of longer searching time. In view of this, a quantum bacterial foraging algorithm with a nonlinear adaptive rotation angle is proposed. The performance test of the benchmark function proves the correctness of the algorithm. The proposed algorithm is applied to tune the PID parameters of the fractional-order servo system. The results show that the proposed algorithm can effectively tune the parameters of the PID controller in the servo system.