Extending Modern C++ for Heterogeneous Quantum-Classical Computing

Software frameworks for quantum computing have progressed significantly over the past few years. Most approaches have put forward vendor-specific frameworks leveraging high-level languages like Python. As quantum hardware improves, we expect that these high-level approaches will detract from overall performance gains garnered from quantum computation. Tighter integration models will require low-level, system software and compilers extending commonly-used languages. We present QCOR, a C++ language extension specification with an associated compiler that enables the programming of quantum expressions alongside standard C++ in a single-source context. Our specification puts forward abstractions and concepts that are common to typical quantum-classical algorithmic workflows. We implement this language extension via light-weight extensions to Clang and build off the system-level, quantum-classical XACC framework. Our approach represents the state-of-the-art with regards to enabling quantum programming alongside standard languages leveraged in existing high-performance domain scientific computing.