QIn: Enabling Formal Methods to Deal with Quantum Circuits

Quantum computers open up new fields of application for hard-to-compute problems due to potential super-polynomial speedup. The design of quantum algorithms is complex and thus error-prone, which makes them a prime target for formal methods. We present our tool QIn to translate quantum circuits into a classical host language (Java). As a result, we can use any tool developed for the host language – and thereby leverage the full power of available formal methods for that language to reason about quantum circuits and create a verification/validation toolchain. Furthermore, QIn enables us to reason about hybrid programs, consisting of classical code and quantum circuits. This is crucial as, for the time being, only single subroutines of a program will be implemented on quantum computers. To show the possibilities of our approach, we present an example of a toolchain based on QIn. This toolchain relies on a software bounded-model checker and can prove the correctness of hybrid programs combining the host language Java with quantum circuits. We use the Java Modeling Language (JML) as the specification language and show the feasibility of our approach on several examples including a bounded version of Shor’s algorithm.