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Escaping fronts in local quenches of a confining spin chain

by A. Krasznai, G. Takács

Submission summary

Authors (as registered SciPost users): Gabor Takacs
Submission information
Preprint Link:  (pdf)
Date accepted: 2024-05-13
Date submitted: 2024-04-17 18:58
Submitted by: Takacs, Gabor
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • Condensed Matter Physics - Theory
  • Quantum Physics
  • Statistical and Soft Matter Physics
Approaches: Theoretical, Computational


We consider local quenches from initial states generated by a single spin-flip in either the true or the false vacuum state of the confining quantum Ising spin chain in the ferromagnetic regime. Contrary to global quenches, where the light-cone behaviour is strongly suppressed, we find a significant light-cone signal propagating with a nonzero velocity besides the expected localised oscillating component. Combining an analytic representation of the initial state with a numerical description of the relevant excitations using the two-fermion approximation, we can construct the spectrum of post-quench excitations and their overlaps with the initial state, identifying the underlying mechanism. For confining quenches built upon the true vacuum, the propagating signal consists of superpositions of left and right-moving mesons escaping confinement. In contrast, for anti-confining quenches built upon the false vacuum it is composed of superpositions of left and right-moving bubbles which escape Wannier-Stark localisation.

Author indications on fulfilling journal expectations

  • Provide a novel and synergetic link between different research areas.
  • Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
  • Detail a groundbreaking theoretical/experimental/computational discovery
  • Present a breakthrough on a previously-identified and long-standing research stumbling block

Author comments upon resubmission

We thank both Referees for their careful reading and valuable comments on the submitted manuscript. We give our replies together with the implied changes below.

Report 1:

1&2: We followed the Referee’s recommendation and reformulated the interpretation. For this, we changed the title, abstract, conclusions, and discussions at the end of Sections 4.3 and 5.

The main modification is that now we write superpositions instead of the expression ’Schrödinger cat’. We now only refer to the superpositions of the right and left-moving mesons as ’Schrödinger kitten’ states in the discussion at the end of Section 4.3 to abbreviate the text. We do not find it misleading as the reformulated interpretation itself does not build upon this notion.

In the conclusions, we added a sentence explaining that the reason we found this aspect interesting is that contrary to classical intuition and also the quasi-particle picture of global quench time evolution, for the local quenches, we get a two-pronged light cone from single-particle states, which are superpositions of left and right moving one-particle states with equal weight.

To emphasize the main difference between the local and global quenches regarding the translational in- variance, as pointed out by the Referee, we included a short explanation at the end of Section 2.1 and in the discussion part at the end of Section 4.3.

3: We agree and therefore grouped the figures (now Figs. 2.1 and 2.2) as the referee suggested.

4: We have done the requested redefinition of the eigenvector.

5: We agree and change the notation accordingly everywhere in the main text.

6: We considered several possible explanations for the eventual phases, but we could not find any fully satisfactory explanation, so we prefer to leave this as an observed fact for now.

Report 2:

The questions raised by the Referee are answered by the changes listed above under item 1&2 of our response to report 1.

List of changes

See resubmission letter.

Current status:
Accepted in target Journal

Editorial decision: For Journal SciPost Physics: Publish
(status: Editorial decision fixed and (if required) accepted by authors)

Reports on this Submission

Anonymous Report 1 on 2024-5-2 (Invited Report)


The authors have followed the recommendation and removed the misleading interpretation in terms of Schrödinger cat states. The manuscript contains very nice results and can now be accepted in its present form.


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