Multicritical quantum sensors driven by symmetry-breaking

Abstract: Quantum criticality has been demonstrated as a useful quantum resource for parameter estimation. This includes second-order, topological and localization transitions. In all these works reported so far, gap-to-gapless transition at criticality has been identified as the ultimate resource for achieving the quantum enhanced sensing, although there are several important concepts associated with criticality, such as long-range correlation, symmetry breaking. In this work, we analytically demonstrate that symmetry-breaking can drive a quantum enhanced sensing in single- or multiparameter estimation. We show this in the well-known Kitaev model, a lattice version of the 1D p-wave superconductor, which consists of a pairing term and an onsite potential term. The model is characterized by two critical lines and a multi-critical point at the intersection of these two lines. We show that Heisenberg scaling can be obtained in precision measurement of the superconducting coupling by preparing the system at or near the multicritical point despite the fact that parameter variation follows the critical lines, i.e., without an explicit requirement of gap-to-gapless transition. Quantum enhancement in such situations solely occurs due to a global U(1) symmetry-breaking by the pairing term. Extending our analysis in the realm of multiparameter estimation we show that it is possible to obtain super-Heisenberg scaling by combining the effects of symmetry-breaking and gapless-to-gapped transition.