surfacecodeja

Surfacecodeja is an open‑source Java library designed for simulating and analyzing two‑dimensional surface codes, a class of topological quantum error‑correcting codes. The project was initiated in 2017 by a group of researchers at the Quantum Information Science Center of the University of Techland to provide a modular, easy‑to‑use framework for exploring surface‑code fault‑tolerance thresholds and error‑correction protocols. The library is released under the MIT License and is available on GitHub.

The core of surfacecodeja implements standard L×L surface‑code lattices where logical qubits are encoded by the parity of edges surrounding a plaquette. Users can define arbitrary error models, including depolarizing noise, measurement errors, and qubit loss, and run Monte‑Carlo simulations to estimate logical failure rates. The API supports both stabilizer measurement cycles and the application of recovery operations derived from minimum‑weight perfect matching algorithms. Performance is optimized by using photon‑level concurrency and low‑level bit‑vector arithmetic.

Key features include: a configurable noise model engine, an automated data‑collection framework for benchmarking, support for punctured lattices to model defective qubit arrays, and integration with the JUnit testing framework for regression tests. The project also offers a command‑line tool that accepts a JSON description of the code parameters and outputs histograms of error probabilities.

Since its release, surfacecodeja has been cited in several peer‑reviewed publications on quantum error correction in the early 2020s. The development community maintains a continuous integration pipeline that runs over 500 unit tests on each pull request. Contributions to the library are encouraged, and the developers maintain an issue tracker and a Discord channel for user support.