Quantum principal 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 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 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.