Strategic Duality in Quantum Games

This paper studies a two-firm entry game in which quantum interference endogenously reshapes strategic interaction. In contrast to classical models, where fixed primitives determine whether firms are strategic complements or substitutes, quantum strategies permit multiple equilibria with opposing cross-partials. I characterize the inflection point at which interference offsets classical competition and derive a closed-form contour mapping between entry costs and rivalry intensity. As interference strengthens, both the range and dispersion of equilibrium behaviors expand, yielding robust strategic duality—that is, the coexistence of cooperative and competitive regimes under common fundamentals. To empirically validate the model, I conduct a structural estimation exercise using retail entry data from the home improvement sector. The estimated primitives reveal that quantum interference generates substantial equilibrium dispersion, confirming that strategic duality manifests empirically even in observationally similar markets.