SciPost Submission Page

On computing non-equilibrium dynamics following a quench

by Neil J. Robinson, Albertus J. J. M. de Klerk, Jean-Sébastien Caux

Submission summary

As Contributors: Neil Robinson · Albertus de Klerk
Arxiv Link: (pdf)
Date submitted: 2021-02-16 14:05
Submitted by: de Klerk, Albertus
Submitted to: SciPost Physics
Academic field: Physics
  • Atomic, Molecular and Optical Physics - Theory
  • Condensed Matter Physics - Theory
  • Condensed Matter Physics - Computational
Approaches: Theoretical, Computational


Computing the non-equilibrium dynamics that follows a quantum quench is difficult, even in exactly solvable models. Results are often predicated on the ability to compute overlaps between the initial state and eigenstates of the Hamiltonian that governs time evolution. Except for a handful of known cases, it is generically not possible to find these overlaps analytically. Here we develop a numerical approach to preferentially generate the states with high overlaps for a quantum quench starting from the ground state or an excited state of an initial Hamiltonian. We use these preferentially generated states, in combination with a "high overlap states truncation scheme" and a modification of the numerical renormalization group, to compute non-equilibrium dynamics following a quench in the Lieb-Liniger model. The method is non-perturbative, works for reasonable numbers of particles, and applies to both continuum and lattice systems. It can also be easily extended to more complicated scenarios, including those with integrability breaking.

Current status:
Editor-in-charge assigned

Author comments upon resubmission

With the resubmission we have addressed the comments raised by the referees. We did not include the computation of the entanglement entropy because of the computational difficulty, as detailed in the reponse to referee 1.

List of changes

To address the report of referee 1 we have included the following comment in the conclusions section of the paper.

"Finally, we would like to point out that the method developed in this paper provides, in principle, all the ingredients necessary to compute for example the time evolution of the entanglement entropy. However, the computation of this quantity still represents a significant computational challenge, which we leave for future work. "

Reports on this Submission

Anonymous Report 2 on 2021-2-27 Invited Report


I maintain my previous recommendation, which was for the paper to be accepted for publication in Scipost Physics. In addition, I thank the authors for the clarifying remark regarding the applicability of the approach.

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Anonymous Report 1 on 2021-2-24 Invited Report


I am really surprised by the authors reply that clearly did not read properly my report. I am still very much in favour of publication in SciPost physics, but what the authors wrote in their reply and added to the paper is a complete misunderstanding of my comment.

Calculating ab-initio the entanglement entropy, as the authors write, is so obviously a hopeless task that nobody will dare to do or to mention. I just wrote to use the knowledge of the root density and to plug in the quasiparticles picture formula, to be clear Eq. (4) of the paper (as one of the many places where this formula can be found). This not only is doable, but it is basically already done in the manuscript.

Requested changes

The authors should remove the comment about the ab-initio evaluation of the entanglement entropy and possibly add one about its quasiparticle determination.

  • validity: top
  • significance: top
  • originality: top
  • clarity: top
  • formatting: perfect
  • grammar: perfect

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