Simulating Quantum Software with Density Matrices: Reading Feynman on Fast-Forward

Richard P. Feynman’s 1982 paper “Simulating Physics with Computers” is often recognized as a pioneer of quantum computing. However, careful reading between the lines finds further meaningful content. This work reinterprets the pioneering paper, as a precursor of Quantum Software. Feynman’s proposal to represent the simulated system by a Density Matrix opens the way toward a mathematical Quantum Software systems theory. Density Matrix modularization leads to software modules as high-level abstractions unifying conceptual software units and matrix basis kets, stimulating new software-related questions and novel quantum solutions. Software modules are building blocks for any imaginable Quantum Software computations in practice, such as software system evolution, measurement, compositionality, and future potential applications.