QTensor: Fast QAOA Quantum Simulator

We present a quantum circuit simulator* designed to execute large QAOA quantum circuits. The simulator is based on the tensor network representation of quantum circuits. To achieve this goal, we developed and implemented a number of techniques: lightcone optimization, custom gates to reduce tensor network complexity, and reduction of tensor dimensions through the utilization of diagonal structure of gates. As a result, we were able to execute large QAOA circuits to solve MaxCut. Using QTensor, we simulated quantum circuits with hundreds of qubits and large depths (p ≥ 7) within seconds and performed an extensive analysis of large QAOA circuits. We found that simulation complexity is non-monotonic with respect to the graph size due to the statistical properties of subgraphs of random-regular graphs.

*QTensor code is publicity available at https://github.com/danlkv/QTensor