Quantum reduced fidelity and quantum phase crossover in a spin ladder system with four‐spin exchange

Abstract

The quantum phase crossover in a spin ladder model with fourspin exchange is investigated. Previous studies show that the crossover cannot be detected by the singularity or finite-size analysis of ground-state observables for finite ladders. In this work, we find that the first-excited-state fidelity shows a sudden drop exactly at the crossover point, regardless of the length of the ladder. It suggests that the excited-state fidelity for finite systems is very effective in detecting the crossover in infinite systems. The underlying mechanism is understood through the analysis of re-construction of the low-lying energy levels of the systems.

Odd-even effect of quantum discord in the spin-1/2 Heisenberg two-leg ladder with ring exchange

“…Recently the QPTs of the ladder have been studied through quantum information theory . The first‐order QPT points and are identified ambitiously by the sudden change of the entanglement concurrence ().…”

“…The critical point , which is a highly symmetric point of the system, is identified by the size‐independent extremal point of entanglement entropy (). In addition, recently we have found an effective way to identify the crossover point by analyzing the first‐excited state of the system (). Thus, in this paper, we will just pay our attention to the other two critical points and .…”

“…Recently the QPTs of the ladder have been studied through quantum information theory. [22,27,28] The firstorder QPT points θ 1 and θ 2 are identified ambitiously by the sudden change of the entanglement concurrence. [22] The critical point θ 4 , which is a highly symmetric point of the system, is identified by the size-independent extremal point of entanglement entropy.…”

“…[22] For the crossover point θ 6 , recently we have provided a very effective approach to identify its location by analyzing the first-excited state of the system. [28] Thus, in this paper, we will just pay our attention to the other two critical points θ 3 and θ 5 .…”