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Full Counting Statistics in the Transverse Field Ising Chain
by Stefan Groha, Fabian H. L. Essler, Pasquale Calabrese
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Submission summary
Authors (as registered SciPost users):  Pasquale Calabrese · Fabian Essler · Stefan Groha 
Submission information  

Preprint Link:  https://arxiv.org/abs/1803.09755v3 (pdf) 
Date accepted:  20180617 
Date submitted:  20180613 02:00 
Submitted by:  Groha, Stefan 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
We consider the full probability distribution for the transverse magnetization of a finite subsystem in the transverse field Ising chain. We derive a determinant representation of the corresponding characteristic function for general Gaussian states. We consider applications to the full counting statistics in the ground state, finite temperature equilibrium states, nonequilibrium steady states and time evolution after global quantum quenches. We derive an analytical expression for the time and subsystem size dependence of the characteristic function at sufficiently late times after a quantum quench. This expression features an interesting multiple lightcone structure.
Author comments upon resubmission
Referee 1:
We thank the referee for their careful reading of our manuscript and for the constructive comments. In the following we reply to the questions s/he raised.
 "The definitions of some relevant object are scattered in different parts of the paper, which makes the reading a bit uneasy. In particular, the notion of symbol for Toeplitz matrices and the associated winding number is used in eq. (47), but defined only in Appendix A, which is refered to afterwards. I would suggest to define those in a clearer fashion, and for generic Toeplitz matrices, in the bulk of the paper."
We thank the referee for pointing out the missing definition of the symbol of Toepliz matrices. We added this definition as Eq. (47).
 "In section III, the authors introduce a representation of the lattice spin operators in terms of a set of Majorana fermions. It would be useful to have the relation between those and the JordanWigner fermions of section II.A clarified."
We thank the referee for pointing out the missing definition of the relation between the complex fermions and Majorana fermions. We added it in the text after Eq. (18).
 "The multiple lightcone structure exhibited in section VI deserves to be commented further. Is there an interpretation of the associated velocities in terms of quasiparticles, for instance ?"
We agree with the referee that a comment on the lightcone structure in the discussion of the result is in place and have added a paragraph at the end of chapter VI.B. We agree that finding a quasiparticle interpretation would be interesting, but as this does not seem a trivial task we leave it for future work.
 "Some minor typos and comments :
 section III, after eq. (16): double occurrence of "the" in the sentence "Hence they are univocally determined by the the correlation matrices...."
 section V.B : "We now turn to the time evolution of P_w^(u)(m,t): P_w^(s)(m,t) should be mentioned as well, since it is studied in this section conclusion : missing word in the sentence "A more straightforward but interesting extension would be to certain observables...." "
We thank the referee for pointing out the typos and further comments. We have incorporated the changes in the current version.
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Referee 2:
The referee requested the following changes:
(1) "Address the work on FCS of charge transport. It would be nice if the authors could compare the finite time corrections in the IRLM with the findings in the current manuscript."
While we share the referee's opinion that the FCS of charge transport in quantum impurity problems is very interesting, we fail to see its relevance to the problem considered in our work. We determine the FCS of the transverse magnetization in a large, finite subsystem after a global quantum quench in a homogeneous system, which in our understanding is an altogether different problem. We therefore see no reason to either discuss the IRLM or attempt to provide a list of references for the analysis of FCS in such kinds of problems.
(2) "Possibly providing an independent numerical check."
We are extremely puzzled by this comment. As stated in the paper we have conducted extensive numerical tests of the analytic results, and some representative comparisons are in fact shown in the manuscript. For example Fig. 22 shows a comparison between the analytic calculation, which is based on an asymptotic expansion, to numerically exact results (no approximations) in the thermodynamic limit (L=\infty).
(3) "Correcting the typos."
We are grateful to the referee for pointing out these typos, which we have corrected.
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Referee 3:
We thank the referee for his/her helpful comments.
 "Optional change: Given the length of the manuscript, a short summary of the main results might be helpful for some readers (although this is a matter of taste)."
We have extended the summary of the paper along the lines suggested by the referee.
List of changes
 Added definition of symbol of Toeplitz matrices (Eq. 47)
 Added relation between complex fermions and Majoranas
 Added paragraph with comment on multiple lightcone structure at end of chapter VI.B
 Extended summary
 Fixed typos
Published as SciPost Phys. 4, 043 (2018)