Automated Discovery of Gadgets in Quantum Circuits for Efficient Reinforcement Learning

Abstract: Reinforcement learning (RL) has proven itself as a powerful tool for the discovery of quantum circuits and quantum protocols. We have recently shown that including composite quantum gates -- referred to as ``gadgets'' -- in the action space of RL agents substantially enhances the RL performance in the context of quantum error correction. However, up to now the gadgets themselves had to be constructed manually. In this paper, we suggest an algorithm for the automated discovery of new gadgets and families of related gadgets. The algorithm is based on the representation of quantum circuits as directed graphs and an automated search for repeated subgraphs. The latter are identified as gadgets. We demonstrate the efficiency of the algorithm, which allows us to find two new gadget families suitable for RL. We compare the performance of 4-qubit gadgets taken from a previously known and a newly discovered family and discuss their advantages and disadvantages.