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Outofequilibrium dynamics of the Kitaev model on the Bethe lattice via coupled Heisenberg equations
by Oleksandr Gamayun, Oleg Lychkovskiy
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Submission summary
Authors (as registered SciPost users):  Oleksandr Gamayun · Oleg Lychkovskiy 
Submission information  

Preprint Link:  https://arxiv.org/abs/2110.13123v2 (pdf) 
Date submitted:  20211027 10:37 
Submitted by:  Lychkovskiy, Oleg 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
The Kitaev model on the honeycomb lattice, while being integrable via the spinfermion mapping, has generally resisted an analytical treatment of the farfromequilibrium dynamics due to the extensive number of relevant configurations of conserved charges. Here we study a close proxy of this model, the isotropic Kitaev spin$1/2$ model on the Bethe lattice. Instead of relying on the spinfermion mapping, we take a straightforward approach of solving Heisenberg equations for a tailored subset of spin operators. The simplest operator in this subset corresponds to the energy contribution of a single bond direction. As an example, we calculate the timedependent expectation value of this observable for a factorized translationinvariant (or staggeredtranslationinvariant) initial state with arbitrary initial (staggered) polarization.
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Reports on this Submission
Anonymous Report 2 on 20211219 (Invited Report)
 Cite as: Anonymous, Report on arXiv:2110.13123v2, delivered 20211219, doi: 10.21468/SciPost.Report.4064
Strengths
 innovative idea to access time evolution of kitaev model and in general of a number of interesting manybody system
Weaknesses
 clarifications and some extra checks needed
Report
The idea of using Heisenberg time evolution in manybody systems is usually overlooked, and this paper is a great example of how instead it can be a very useful tool. I recommend publication provided the following points are carefully addressed:
 include a broader introduction of the model, write the Hamiltonian in Pauli matrices and clarify why the Bethe lattice is easier to access with this method compared to hexagonal and other lattices.
 compare the final result with exact results available for quenches with initial states where single fermionic sector can be used
 clarify the meaning of operator of eq 16 and write an explicit derivation of eq 1419, possible in appendices.
 the large time limit of eq 35 can be reduced to a single integral, reminding of diagonal ensemble. Is there a GGE associated to the large time value of correlator?
Requested changes
see report.
Report 1 by Benjamin Doyon on 20211217 (Invited Report)
 Cite as: Benjamin Doyon, Report on arXiv:2110.13123v2, delivered 20211217, doi: 10.21468/SciPost.Report.4062
Strengths
Clear and to the point
Interesting technical idea, showing that it works (proof of concept)
Potential for many new results of interest in quantum manybody
Weaknesses
very special model, still need to see how general the technique can be
Report
In this paper, the authors provide exact solutions to the Heisenberg equations for a particular subset of operators in the Kitaev model on the Bethe lattice. The purpose is to illustrate that it is possible to evaluate exactly time evolution of nontrivial and interesting operators from nontrivial states in spin models, without resorting to exact diagonalisation, and, for instance in the case of the Kitaev model, to mapping to free fermions. This is a short paper, to the point, presenting a clear calculation with explicit results. I find it very well written, and the idea is extremely interesting. The construction is quite stunning, and this, along with previous works by the authors, seems to open up many possibilities, going beyond the standard solution methods. The model here is relatively simple, and the lattice is a regular tree, which drastically simplifies the calculation. Nevertheless, I think the results, and especially the techniques introduces, are extremely interesting.
I do not have any specific comment for improvement, I believe this is publishable as is.