Universal Wilson Loop Bound of Quantum Geometry

We define the absolute Wilson loop winding and prove that it bounds the (integrated) quantum metric from below. This Wilson loop lower bound naturally reproduces the known Chern and Euler bounds of the integrated quantum metric and provides an explicit lower bound of the integrated quantum metric due to the time-reversal protected Z_{2} index, answering a hitherto open question. In general, the Wilson loop lower bound can be applied to any other topological invariants characterized by Wilson loop winding, such as the particle-hole Z_{2} index. As physical consequences of the Z_{2} bound, we show that the time-reversal Z_{2} index bounds superfluid weight and optical conductivity from below and bounds the direct gap of a band insulator from above.