Abstract
We investigated quantum critical behaviors in the nonequilibrium steady state of a XXZ spin chain with boundary Markovian noise using Fisher information. The latter represents the distance between two infinitesimally close states, and its superextensive size scaling witnesses a critical behavior due to a phase transition since all the interaction terms are extensive. Perturbatively, in the noise strength, we found superextensive Fisher information at anisotropy and irrational irrespective of the order of two noncommuting limits, i.e., the thermodynamic limit and the limit of sending to an irrational number via a sequence of rational approximants. From this result we argue the existence of a nonequilibrium quantum phase transition with a critical phase . From the nonsuperextensivity of the Fisher information of reduced states, we infer that this nonequilibrium quantum phase transition does not have local order parameters but has nonlocal ones, at least at . In the nonperturbative regime for the noise strength, we numerically computed the reduced Fisher information which lower bounds the full-state Fisher information and is superextensive only at . From the latter result, we derived local order parameters at in the nonperturbative case. The existence of critical behavior witnessed by the Fisher information in the phase is still an open problem. The Fisher information also represents the best sensitivity for any estimation of the control parameter, in our case the anisotropy , and its superextensivity implies enhanced estimation precision which is also highly robust in the presence of a critical phase.
- Received 23 February 2017
- Revised 26 June 2017
DOI:https://doi.org/10.1103/PhysRevB.96.104402
©2017 American Physical Society