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On-demand analog space-time in superconducting networks: grey holes, dynamical instability and exceptional points
by Mohammad Atif Javed, Daniel Kruti, Ahmed Kenawy, Tobias Herrig, Christina Koliofoti, Oleksiy Kashuba, Roman-Pascal Riwar
Submission summary
| Authors (as registered SciPost users): | Mohammad Atif Javed · Roman-Pascal Riwar |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2406.01261v5 (pdf) |
| Date submitted: | Dec. 19, 2025, 11:15 a.m. |
| Submitted by: | Mohammad Atif Javed |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Computational |
Abstract
There has been considerable effort to mimic analog black holes and wormholes in solid state systems. Lattice realizations in particular present specific challenges. One of those is that event horizons in general have both white and black hole (grey hole) character, a feature guaranteed by the Nielsen-Ninomiya theorem. We here explore and extend the capability of superconducting circuit hardware to implement on-demand spacetime geometries on lattices, combining nonreciprocity of gyrators with the nonlinearity of Josephson junctions. We demonstrate the possibility of the metric sharply changing within a single lattice point, thus entering a regime where the modulation of system parameters is "trans-Planckian", and the Hawking temperature ill-defined. Instead of regular Hawking radiation, we find an instability in the form of an exponential burst of charge and phase quantum fluctuations over short time scales - a robust signature even in the presence of an environment. Moreover, we present a loop-hole for the typical black/white hole ambiguity in lattice simulations: exceptional points in the dispersion relation allow for the creation of pure black (or white) hole horizons, at the expense of a radical change in the dynamics of the wormhole interior.
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 would like to thank you for the opportunity to revise our paper after the first round of review, we also thank the referees for their constructive comments on our work. We believe that our responses to their questions and the modifications made to the manuscript will be to their satisfaction.
The first referee had an overall positive assessment of our work and recommended it for publication. The referee had additional questions regarding some aspects of our work, such as the effect of breaking time reversal symmetry, quantization of gyrator conductance, and the effect of disorder. We have submitted our reply to the referee and modified our manuscript to include a discussion on these topics.
The second referee also has an overall positive assessment of our work, but suggested some revisions before recommending it for publication. The referee had questions regarding the novelty of using gyrators to induce a tilt in the dispersion relation, potential of using SQUIDs instead of Josephson junctions in the circuit, how our work provides a first step towards investigating the backaction of quantum fields on spacetime, the inclusion of higher order terms in the expansion of the cosine potential, the reason for using two-point correlation functions, and our choice of system parameters for the numerics. We have submitted our reply to the referee and modified our manuscript to include a discussion on these topics with additional figures and equations.
The complete list of changes made to the paper has also been submitted. We believe that the revised manuscript is now suitable for publication in SciPost Physics Core.
Sincerely,
The authors.
List of changes
List of major changes made to the manuscript:
1) Included additional text with citations in the second paragraph on Page 5 to support the claim that a variety of non-relativistic systems are described by Equation (1). The relevant text is “However, it is understood …… waves in Josephson junction arrays.”
2) Included a footnote on Page 5 (footnote 1) discussing the necessity of breaking time reversal symmetry (TRS) in order to simulate event horizons in condensed matter systems.
3) Added text in the first paragraph on Page 8 regarding the advantage of using gyrators, in circuit QED systems, to induce a tilt in the dispersion relation. The text is “This anisotropy in the group velocities ……. co-moving frame that moves with the sweeping electromagnetic field.”
4) Included a footnote on Page 13 (footnote 3) discussing the reason we can ignore the quantization of gyrator conductance (G) due to compactness of the phase variable in this work.
5) Added text in the last paragraph on Page 14 motivating the choice of system parameters to perform numerics in Section 5. The text is “Therefore, the central object …….. creating an overtilt. ”
6) Changed the color of the imaginary part of eigenvalues in Figure (4a) from yellow to green.
7) Added text in the third paragraph on Page (20), including Equation (25), discussing the potential of using a SQUID instead of a JJ to induce a phase shift of \Pi in order to achieve negative inductance for transient times. The text is “Alternatively ….. flux control hardware.”
8) Added text in the fourth paragraph on Page 21, motivating the use of two-point correlation functions to study analog event horizons. The text is “Additionally, ….. the Hawking temperature.”
9) Added text in the third paragraph on Page 22, motivating the use of Klich’s determinant formula instead of diagonalizing a possibly defective matrix. The text is “(non-diagonalizable) ……. a defective matrix.”
10) Added text in the third paragraph on Page 23 including Equation (29), explaining the presence of oscillatory behavior observed in Figure (7a) and providing the expression for the modulating frequency.
11) Added Figure (8) to support the text mentioned in the bullet point 10.
12) Added discussion at the end of Section 5 (beginning on Page 24 “Lastly, we also …….”) regarding the effect of disorder in gyrators and inductors on the time evolution of the two-point correlation functions after the quench.
13) Added a new appendix (Appendix F) with detailed numerics to investigate the effect of disorder, as mentioned in bullet point 12, along with new figures (Figures 12, 13, 14 and 15).
14) Added text in Section 7 on Page 28 as an outlook, discussing the possible effect of using higher order terms in the expansion of the cosine potential, and the possibility of studying the backaction of quantum fields on spacetime geometry in circuit QED. The text is “This work also …….. suitable for follow-up research.”
15) Removed the Figure (9) (in the old manuscript) in Appendix E, and replaced it with two new ones Figures (10) and (11).