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Phase diagram for strong-coupling Bose polarons
by Arthur Christianen, J. Ignacio Cirac, Richard Schmidt
Submission summary
| Authors (as registered SciPost users): | Arthur Christianen |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2306.09075v2 (pdf) |
| Date accepted: | Feb. 22, 2024 |
| Date submitted: | Jan. 17, 2024, 10:30 a.m. |
| Submitted by: | Arthur Christianen |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
Important properties of complex quantum many-body systems and their phase diagrams can often already be inferred from the impurity limit. The Bose polaron problem describing an impurity atom immersed in a Bose-Einstein condensate is a paradigmatic example. One of the most interesting features of this model is the competition between the emergent impurity-mediated attraction between the bosons and their intrinsic repulsion. The arising higher-order correlations make the physics rich and interesting, but also complex to describe theoretically. To tackle this challenge, we develop a quantum chemistry-inspired computational technique and compare two state-of-the-art variational methods that fully include both the boson-impurity and boson-boson interactions on a non-perturbative level. For a sweep of the boson-impurity interaction strength, we find two regimes of qualitatively different behaviour. If the impurity-mediated interactions overcome the repulsion between the bosons, the polaron becomes unstable due to the formation of large bound clusters. If instead the interboson interactions dominate, the impurity will experience a crossover from a polaron into a small molecule. We achieve a unified understanding incorporating both of these regimes and the transition between them. We show that both the instability and crossover regime can be studied in realistic cold-atom experiments. Moreover, we develop a simple analytical model that allows us to interpret these phenomena in the typical Landau framework of first-order phase transitions that turn second-order at a critical endpoint, revealing a deep connection of the Bose polaron model to both few- and many-body physics.
Author comments upon resubmission
Yours sincerely,
Arthur Christianen
List of changes
- We have added the references referee 2 suggested in our discussion of cooperative binding in the beginning of section 3,
- To better explain the connection between our work and our previous work, and the regime of validity of our previous work, we have thoroughly revised the section 3 “Current theoretical status”.
- In this section we have further changed the sentence where we refer to Ref. [68] to state more precisely what was done there, and we added Ref. [85].
- In this section we have explicitly explained now as well how the coherent-state approach compares to the Gross-Pitaevskii equation.
- We have added a comment to table 1 stating that the CS1 approach is equivalent to the GPE approach.
- At the end of section 4.2 we have nuanced our discussion of the Born approximation breaking down and the importance of quantum fluctuations, and we have added a footnote further elaborating on this point.
- In the beginning of the results section we have more clearly explained the limitations of our previous work in Refs. [70,71] and emphasized how our current work connects to this previous work. We have added a footnote explicitly stating that we recover the results from our previous work in the limit of small interboson repulsion.
- In section 5.2 we have rephrased the first sentence of the second paragraph, to reflect more clearly that we are talking about the weakly interacting regime.
- At the end of section 5.4 we have added a paragraph discussing how our results relate to Quantum Monte Carlo results in the literature
- In the beginning of section 5.6 we added a discussion of how inclusion of higher-order correlations would affect the onset of the polaronic instability.
- Later in section 5.6 we rewrote the paragraph discussing the description of the interboson interactions with the double-excitation approach, to more clearly reflect that the problems which arise from our implementation of the double-excitation approach do not appear in other situations.
- In section 6.1 we emphasize once more in the discussion of Eq. (23) that interboson interactions are not included at this point.
- In the conclusion we added a paragraph discussing how the spectral function of the polaron could be extracted from dynamical calculations, and how recombination would affect these results.
- We greatly expanded Appendix C with more explanations and with the newly added Fig. 13.
Published as SciPost Phys. 16, 067 (2024)