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Tachyonic and parametric instabilities in an extended bosonic Josephson junction
by Laura Batini, Sebastian Erne, Jörg Schmiedmayer, Jürgen Berges
Submission summary
| Authors (as registered SciPost users): | Laura Batini · Jörg Schmiedmayer |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202411_00054v2 (pdf) |
| Date submitted: | Sept. 30, 2025, 11:13 a.m. |
| Submitted by: | Laura Batini |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Computational |
Abstract
We study the decay of phase coherence in an extended bosonic Josephson junction realized via two tunnel-coupled Bose-Einstein condensates. Specifically, we focus on the π-trapped state of large population and phase imbalance, which, similar to the breakdown of macroscopic quantum self-trapping, becomes dynamically unstable due to the amplification of quantum fluctuations. We analytically identify early tachyonic and parametric instabilities connected to the excitation of atom pairs from the condensate to higher momentum modes along the extended direction. Furthermore, we perform Truncated Wigner numerical simulations to observe the build-up of non-linearities at later times and explore realistic experimental parameters.
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
List of changes
- Eq. (1) is now normal-ordered to remove the singular self-interaction term.
- We corrected the footnote with the correct figure reference (Fig. 3).
- We substantially revised the introduction with a clearer structure and expanded the comparison with previous theoretical and experimental work.
- We clarified the role of momentum-dependent instabilities vs. uniform modes and provided additional intuitive understanding of the instabilities.
- We revised the discussion of the primary instability mechanism, adding a new appendix introducing mode details on the tachyonic and parametric instabilities.
- We added the comparison between the $\pi$-state instability with the Kapitza pendulum.
- We extended and systematized the discussion of experimental feasibility (now Sec. 5). We added two new figures (Fig. 12 and Fig. 13) with preliminary experimental data (Sec. 5).
Current status:
Reports on this Submission
Report
To be honest, I am still not fully happy regarding the term "tachyonic instability"
but I understand that the authors use this term to distinguish that mechanism
from the parametric instability (which is clearly different).
However, this slight misgiving is not a reason to prevent publication.
Recommendation
Publish (easily meets expectations and criteria for this Journal; among top 50%)