Fidelity of the Kitaev honeycomb model under a quench

Abstract

Motivated by rapid developments in the field of quantum computing and the increasingly diverse nature of qubits, we theoretically study the influence that quenched outside disturbances have in an intermediately long time limit. We consider localized imperfections, uniform fields, noise, and couplings to an environment which we study in a unified framework using a prototypical but idealized interacting quantum device - the Kitaev honeycomb model. Our study focuses on the quantum state robustness in response to an outside magnetic field, a magnetic bath, magnetic noise, magnetic impurities, and a noisy impurity. As indicators for quantum robustness, we use the Uhlmann fidelty of the ground state and excited spinon states after a quench. We find that the time dependence of the fidelity often depends crucially on whether the system is gapped. We find that in the gapped case the fidelity decays to a constant value under noiseless quenches, while in a gapless system it exhibits algebraic decay. In all other situations studied, such as coupling to a bath and noisy quenches, both gapped and gapless systems exhibit a universal form for the long-time fidelity, $Ce^{-\alpha t}t^{-\beta}$, where the values of $C$, $\alpha$, and $\beta$ depend on physical parameters such as system size, disturbance strength, etc. Therefore, our work provides estimates for the intermediate-long time stability of a quantum device and it suggests under what conditions there appear the hallmarks of an orthogonality catastrophe in the time-dependence of the fidelity. Our work provides engineering guidelines for quantum devices in quench design and system size.