Fast simulation of quantum algorithms using circuit optimization

Classical simulators play a major role in the development and benchmark of quantum algorithms, and are an important component of most software frameworks for quantum computation. However, the development of simulators was substantially separated from the rest of the software frameworks which focus on usability and compilation. Here, we demonstrate the advantage of co-developing and integrating simulators and compilers by proposing a specialized compiler pass to reduce the simulation time for arbitrary circuits. While the concept is broadly applicable, we present a concrete implementation based on the Intel Quantum Simulator, a high-performance distributed simulator. First, we extend its implementation with additional functionalities related to the representation of quantum states. The communication overhead is reduced by changing the order in which state amplitudes are stored in the distributed memory. Then, we implement a compiler pass to exploit the novel functionalities by introducing special instructions governing data movement as part of the quantum circuit. Those instructions target unique capabilities of simulators. To quantify the advantage, we compare the time required to simulate random circuits with and without our optimization. The simulation time is typically halved.