Quantum principal $\mathrm{U}(1)$-bundles: differential, Riemannian, and metric geometry
In the commutative case, a Hermitian line bundle with unitary connection corresponds to an essentially unique principal $\mathrm{U}(1)$-bundle with principal connection over the same base, which then admits a canonical lift of any given Riemannian metric on the base. Recent advances in noncommutative Riemannian geometry permit a precise and cohesive generalization of this framework to the noncommutative setting through geometric analogues of Pimsner’s construction. In this talk, I shall illustrate this generalization with the case study of the quantum Hopf fibration: I shall sketch how the quantum Hopf line bundle with its Chern connection yields canonical lifts of differential, Riemannian, and metric geometry from the standard Podleś sphere to quantum $\mathrm{SU}(2)$. This provides a unified conceptual framework for disparate constructions of Woronowicz, Zampini, and Kaad–Kyed while delineating a hard boundary of the (twisted) spectral triple formalism.