Open quantum system control based on reinforcement learning

The fast preparation of a quantum state with high fidelity is a key problem for a quantum system. We propose two modified algorithms based on the cutting-edge reinforcement learning methods for the flip from an initial state to a target one in a quantum spin system. The balance between exploration and exploitation and the size of a state space are key factors for reinforcement learning methods. In the first algorithm, we propose a modified $\epsilon$-greedy strategy instead of the ϵ-greedy strategy to balance exploration and exploitation. Furthermore, we use the fidelity of the final state as the reward and leverage piecewise-constant driving protocols in every duration. The results show that the rate of correction of this algorithm is greater than that of Q-learning with ϵ-greedy strategy. However, it will still cost much time resource if the rotation angle from a state to the next state is too small. Thus, we initialize the state-action value table to reduce the state space in the second modified Q-learning algorithm (MQL), which can be found that the efficiency of learning is greatly improved.