PhasePoly: An Optimization Framework forPhase Polynomials in Quantum Circuits

Abstract: Quantum computing has transformative computational power to make classically intractable computing feasible. As the algorithms that achieve practical quantum advantage are beyond manual tuning, quantum circuit optimization has become extremely important and integrated into today's quantum software stack. This paper focuses on a critical type of quantum circuit optimization -- phase-polynomial optimization. Phase polynomials represents a class of building-block circuits that appear frequently in quantum modular exponentials (the most time-consuming component in Shor's factoring algorithm), in quantum approximation optimization algorithms (QAOA), and in Hamiltonian simulations. Compared to prior work on phase polynomials, we focus more on the impact of phase polynomial synthesis in the context of whole-circuit optimization, from single-block phase polynomials to multiple block phase polynomials, from greedy equivalent sub-circuit replacement strategies to a systematic parity matrix optimization approach, and from hardware-oblivious logical circuit optimization to hardware-friendly logical circuit optimization. We also provide a utility of our phase polynomial optimization framework to generate hardware-friendly building blocks. Our experiments demonstrate improvements of up to 50%-with an average total gate reduction of 34.92%-and reductions in the CNOT gate count of up to 48.57%, averaging 28.53%, for logical circuits. Additionally, for physical circuits, we achieve up to 47.65% CNOT gate reduction with an average reduction of 25.47% across a representative set of important benchmarks.