Hybrid Quantum Applications Need Two Orchestrations in Superposition: A Software Architecture Perspective

Quantum applications are most often hybrid, i.e., they are not only made of implementations of pure quantum algorithms but also of classical programs as well as workflows and topologies as key artifacts, and data they process. Since workflows and topologies are referred to as “orchestrations” in modern terminology (but with very different meanings), two orchestrations that go hand-in-hand are required to realize quantum applications. We motivate this by means of a nontrivial example, sketch these orchestration technologies, and reveal the overall structure of non-trivial quantum applications. Furthermore, we discuss the implied architecture of a runtime environment for such quantum applications. To validate the introduced architecture, we present a prototypical implementation based on the Camunda workflow engine, its associated modeling tool, as well as the OpenTOSCA ecosystem.