General quantum fidelity susceptibilities for the J1-J2 chain

We study slightly generalized quantum fidelity susceptibilities where the differential change in the fidelity is measured with respect to a different term than the one used for driving the system toward a quantum phase transition. As a model system we use the spin-1/2 J1-J2 antiferromagnetic Heisenberg chain. For this model, we study three fidelity susceptibilities, χρ, χD, and χAF, which are related to the spin stiffness, the dimer order, and antiferromagnetic order, respectively. All these ground-state fidelity susceptibilities are sensitive to the phase diagram of the J1-J2 model. We show that they all can accurately identify a quantum critical point in this model occurring at J2c∼0.241J1 between a gapless Heisenberg phase for J2J2c. This phase transition, in the Berezinskii-Kosterlitz-Thouless universality class, is controlled by a marginal operator and is therefore particularly difficult to observe.