Swift Quantum: Library and Application for Quantum Computing Research and Education

Abstract

Quantum computing promises computational advantages for problems ranging from number factorisation to optimisation. Since access to real quantum hardware remains scarce, state‑vector simulators on classical computers continue to play a critical role in algorithm development and education. However, most existing simulators are implemented in Python or C++ and expose APIs that are difficult to extend and not well aligned with modern native application development ecosystems. This paper presents Swift Quantum, an open-source modular quantum computing library written in Swift, and a companion application for end users. The library has been designed specifically for educational and/or research purposes, and supports the simulation of quantum circuits using sparse amplitude matrices. It provides a type‑safe API for constructing custom qubits, registers, gates, circuit compositions and sparse quantum state representations. Additionally, it provides JSON serialisation of circuits and automated validation through unit testing. Moreover, it uses idiomatic Swift abstractions that allow a better understanding of fundamental quantum computing abstractions from a software engineer's perspective. The companion application, available for free in Apple's App Store, offers a visual editor including the possibility of building custom gates and reusable circuits, and allows step-by-step simulations that can represent intermediate states on an interactive Bloch sphere. Finally, we analyze the design decisions behind Swift Quantum, compare it with state-of-the-art frameworks, and evaluate its correctness and performance characteristics. Current limitations and an outline of future research directions, including noise modeling, interoperability, and hardware acceleration, are also discussed.