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Measurement-induced criticality in extended and long-range unitary circuits

by Shraddha Sharma, Xhek Turkeshi, Rosario Fazio, Marcello Dalmonte

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Submission summary

Authors (as registered SciPost users): Marcello Dalmonte · Shraddha Sharma · Xhek Turkeshi
Submission information
Preprint Link: https://arxiv.org/abs/2110.14403v4  (pdf)
Date submitted: 2022-01-19 16:34
Submitted by: Turkeshi, Xhek
Submitted to: SciPost Physics Core
Ontological classification
Academic field: Physics
Specialties:
  • Condensed Matter Physics - Theory
  • Quantum Physics
Approach: Theoretical

Abstract

We explore the dynamical phases of unitary Clifford circuits with variable-range interactions, coupled to a monitoring environment. We investigate two classes of models, distinguished by the action of the unitary gates, which either are organized in clusters of finite-range two-body gates, or are pair-wise interactions randomly distributed throughout the system with a power-law distribution. We find the range of the interactions plays a key role in characterizing both phases and their measurement-induced transitions. For the cluster unitary gates we find a transition between a phase with volume-law scaling of the entanglement entropy and a phase with area-law entanglement entropy. Our results indicate that the universality class of the phase transition is compatible to that of short range hybrid Clifford circuits. Oppositely, in the case of power-law distributed gates, we find the universality class of the phase transition changes continuously with the parameter controlling the range of interactions. In particular, for intermediate values of the control parameter, we find a non-conformal critical line which separates a phase with volume-law scaling of the entanglement entropy from one with sub-extensive scaling. Within this region, we find the entanglement entropy and the logarithmic negativity present a cross-over from a phase with algebraic growth of entanglement with system size, and an area-law phase.

Current status:
Has been resubmitted


Author comments upon resubmission

Dear Editor,

We thank the Referees for their careful reading of our manuscript and for their constructive comments and criticisms.
We have embodied these discussions in the new version of the manuscript, which we now hope is suitable for publication in Scipost Physics Core.

List of changes

In response of the Referee reports, we have implemented the following changes:
- Corrected typos;
- Added Ref [90] in bibliography;
- Changes in Sec. 2 clarifying the models and the difference with Hamiltonian setups;
- Updated caption of Fig 1;
- Replaced linear scale with logarithmic scale in the x-axis of Fig 8;
- Expanded discussion in Sec 5 .


Reports on this Submission

Anonymous Report 3 on 2022-3-15 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:2110.14403v4, delivered 2022-03-15, doi: 10.21468/SciPost.Report.4688

Report

The authors have included all the requested changes of the referees (especially report 4) and I stand by my previous recommendation that this paper is a worthy contribution to scipost physics core.
The paper provides thorough numerical study of long range Clifford dynamics under measurement. While I partly agree that a stronger statement could be made in conjunction with analytics, I also believe that this is a highly non-trivial endeavor and well beyond the scope and intention of this article.

  • validity: -
  • significance: -
  • originality: -
  • clarity: -
  • formatting: -
  • grammar: -

Anonymous Report 2 on 2022-2-6 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:2110.14403v4, delivered 2022-02-06, doi: 10.21468/SciPost.Report.4327

Strengths

same as in my previous report

Weaknesses

1 - The description of the CHRC model in Sec. 2.1 is still somewhat misleading

Report

The authors have done a good job addressing the referees' remarks from the first round. However, the formal description of the CHRC model in Sec. 2.1 remains a problem, despite the authors' efforts to improve it. Indeed, Eq. (3) appears to be a product of elementary two-body gates U_i,i+r,t. Here, t is the elementary time-step (the vertical size of the smallest rectangular element in the left panel of Fig. 1b). On the other hand, the first sentence of Sec. 2.1 says: "The unitary evolution is a sequence of M-body cluster unitary gates Ui,j,t, each of which is build stacking two body unitary gates". This implies that Ui,j,t is a composite (cluster) gate comprising three two-body elementary gates in Fig. 1b, so that time step t is the vertical size of such a cluster, which is 3 elementary layers in the figure. If I use this definition of the quantity Ui,j,t in Eq. (3), I would get a nonsensical result. Let us, therefore, assume that Ui,j,t is a two-body gate. Figure 1b suggests that, with this definition, at each time t there is only one two-body gate. On the contrary, Eq. (3) tells us that at each time t we should multiply many two-body gates. In particular, for L=6 (with periodic boundary conditions) and M=4, as in Fig. 1b, one gets the following product, if one literally follows the prescription of Eq. (3): U_1,2,t*U_1,3,t*U_1,4,t*U_2,3,t*U_2,4,t*U_2,5,t*... This is not what I see in Fig. 1b, where, for example, for the bottom layer (t=1) I see only U_1,2,1, while all other two-body gates in this product are clearly trivial, i.e., U=1. Note that in the product of two-body operators, as written in Eq. (3), again, the ordering of operators is not specified explicitly, in contrast to what is written in the footnote. In order to have a formal correspondence between Eq. (3) and Fig. 1b, the authors should (i) modify the first sentence of Sec. 2.1; (ii) write explicitly that, for a given value of t, only a single factor in the product in Eq. (3) is not equal to unity in the example of Fig. 1b (this would automatically resolve the problem of the operators' ordering); (iii) to give an explicit expression (perhaps, in terms of a Kronecker delta-symbol involving i, r, and t) specifying the indexes of the non-trivial two-body gate in the product (3) for the shoulder-like arrangement of Fig. 1b.

Requested changes

Improve the mathematical definition of the CHRC model

  • validity: high
  • significance: good
  • originality: high
  • clarity: good
  • formatting: excellent
  • grammar: excellent

Author:  Marcello Dalmonte  on 2022-03-19  [id 2304]

(in reply to Report 2 on 2022-02-06)
Category:
answer to question

We thank the Referee of their reading of our revised version. We have changed the text before and after Eq. 3, to accommodate extra explanations following the points in the report. We have also revised Fig. 1b caption accordingly."

Anonymous Report 1 on 2022-1-20 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:2110.14403v4, delivered 2022-01-20, doi: 10.21468/SciPost.Report.4207

Strengths

1- The topic is very relevant and the numerical investigation of the two-different long-range circuit models is comprehensive to a set of other recently appeared long-range models.
2- The paper is very accessible and provides a short and crisp summary of the obtained results. I find it particularly well written.
3- The summary of the entanglement-based observables and the numerical procedure are very precise and helpful.

Weaknesses

1- After the revision by the authors, the paper still has a strong focus on the numerical results and less on providing a physical picture of the underlying dynamics.

Report

The authors have considered the suggestions from my previous report and revised the manuscript accordingly. While I agree that an analytical understanding of the presented results is probably not straightforwardly obtained, I also think it is a chance missed by the authors to significantly improve their work and the impact it will have in the future.
However, there are plenty of new and interesting results on the topic of measurement-induced phase transitions presented in the manuscript. It is well written and very accessible and I believe it is a good paper that should be published in SciPost Physics Core.

  • validity: high
  • significance: good
  • originality: good
  • clarity: high
  • formatting: excellent
  • grammar: good

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