Scientists have developed a method to certify fidelity susceptibility, a crucial quantity for studying quantum phase transitions and quantum metrology. Direct evaluation of this property on quantum devices is challenging, which has limited its application. This new approach allows for a more efficient and reliable determination, opening new avenues for the characterization of complex quantum systems.

The method integrates Krylov-subspace techniques with a resolvent-based reformulation. It relies on randomized single-copy measurements, performed after repeated ground-state preparations of the system. The approximations obtained in this way not only form monotonic lower bounds to the exact fidelity susceptibility but also converge geometrically towards its true value, ensuring the precision and efficiency of the process.

This advance has significant implications for quantum metrology, where fidelity susceptibility is a key indicator of a quantum sensor's sensitivity to external perturbations. Furthermore, the method is applicable to the study of linear static susceptibilities, extending its utility in the characterization of materials and quantum phenomena. The ability to certify this quantity more easily could accelerate the development of quantum technologies and the understanding of their fundamental principles.