SPICE Workshop on Quantum materials and quantum information science May 19th - 21st, 2026
Su-Yang Xu
Coherent quantum control is usually associated with isolated few-level systems, while transport in solids is often described by incoherent or perturbative carrier dynamics. Here we show that quantum geometry near critical point can promote Bloch electrons into macroscopic, phase-coherent, nonlinear response, resembling quantum-optics but for Bloch electrons in momentum space. In a dual-gated MnBi2Te4, we achieve a topological critical point where quantum geometry is enhanced. At the critical point, we observe higher harmonic Hall (HHH) effects up to the 41st order, all becoming linear in current above a small threshold. Away from the critical point, the HHH develops nonmonotonic I-V relationship, showing coherent oscillations with respect to inverse current, 1/I, whose systematic density or displacement field evolution shows a fan pattern, resembling the Landau fans but with current replacing magnetic field. These observations uncover a momentum-space Mach–Zehnder interferometer: quantum metric serves as coherent beamsplitter between bands, band dispersion sets the accumulated phase, and Berry curvature provides the HHH readout. We demonstrate a topological scaling law for the harmonic onset current, revealing the trend of diverging quantum metric near the singularity, analogous to universal scaling near a Landau critical point.