Quantum Droplets

Topic Information

Dear Colleagues,

One of the major advances in the field of ultracold atoms is the recent prediction and observation of ultradilute quantum liquids. In normal liquids, the distance between atoms is of the order of the van der Waals radius, set by the competition between the short-range repulsion and long-range attraction. Instead, ultradilute quantum liquids are formed due to a near cancellation of mean-field and beyond mean-field energy terms, which is possible due to different scaling of those terms with the density. This balance has made it possible to experimentally realize liquids at densities which are eight orders of magnitude more dilute compared to that of usual liquids, such as helium, which is a paradigmatic quantum liquid. Another important feature of the novel class of liquids is that they are almost fully coherent, while the condensate fraction in a liquid helium is smaller than ten percent. Ultradilute quantum liquids have already been created in two types of settings: (i) dipolar atoms with tunable short-range interactions and (ii) two-component mixtures with short-range interactions between atoms. Ultracold atoms offer an exquisite degree of controllability of the interactions (Feshbach resonances, confinement-induced resonances, etc.), a variety of external fields (traps, optical lattices, etc.) and various geometries (three-, two- and one-dimensional), resulting in the rapid expansion of the field. There is great interest in understanding and quantifying the properties of already available ultradilute liquids, as well as the prediction for novel species. A significant number of proposals have been elaborated for this type of quantum matter for different geometries, statistics (Bose, Fermi and mixtures) and nonlinearities, including the settings with the spin-orbit and Rabi couplings, multi-component compositions, etc. The aim of this Topic is to collect important contributions in the field of ultradilute quantum liquids, including theoretical and experimental works.

Prof. Dr. Boris Malomed
Dr. Chiara D’Errico
Prof. Dr. Enguo Chen
Dr. Grigori E. Astrakharchik
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Condensed Matter condensedmatter	1.9	2.9	2016	21 Days	CHF 1600
Liquids liquids	-	-	2021	27.7 Days	CHF 1000
Nanomaterials nanomaterials	4.4	8.5	2010	13.8 Days	CHF 2900
Particles particles	1.7	3.2	2018	27.4 Days	CHF 1600
Photonics photonics	2.1	2.6	2014	14.8 Days	CHF 2400
Quantum Reports quantumrep	-	3.3	2019	18.1 Days	CHF 1400

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Published Papers (4 papers)

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All Condensed Matter Liquids Nanomaterials Particles Photonics Quantum Reports

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17 pages, 2549 KiB  

Open AccessFeature PaperArticle

Interactions and Dynamics of One-Dimensional Droplets, Bubbles and Kinks

by Garyfallia C. Katsimiga, Simeon I. Mistakidis, Boris A. Malomed, Dimitris J. Frantzeskakis, Ricardo Carretero-Gonzalez and Panayotis G. Kevrekidis

Condens. Matter 2023, 8(3), 67; https://doi.org/10.3390/condmat8030067 - 4 Aug 2023

Cited by 12 | Viewed by 1766

Abstract

We explore the dynamics and interactions of multiple bright droplets and bubbles, as well as the interactions of kinks with droplets and with antikinks, in the extended one-dimensional Gross–Pitaevskii model including the Lee–Huang–Yang correction. Existence regions are identified for the one-dimensional droplets and [...] Read more.

We explore the dynamics and interactions of multiple bright droplets and bubbles, as well as the interactions of kinks with droplets and with antikinks, in the extended one-dimensional Gross–Pitaevskii model including the Lee–Huang–Yang correction. Existence regions are identified for the one-dimensional droplets and bubbles in terms of their chemical potential, verifying the stability of the droplets and exposing the instability of the bubbles. The limiting case of the droplet family is a stable kink. The interactions between droplets demonstrate in-phase (out-of-phase) attraction (repulsion), with the so-called Manton’s method explicating the observed dynamical response, and mixed behavior for intermediate values of the phase shift. Droplets bearing different chemical potentials experience mass-exchange phenomena. Individual bubbles exhibit core expansion and mutual attraction prior to their destabilization. Droplets interacting with kinks are absorbed by them, a process accompanied by the emission of dispersive shock waves and gray solitons. Kink–antikink interactions are repulsive, generating counter-propagating shock waves. Our findings reveal dynamical features of droplets and kinks that can be detected in current experiments. Full article

(This article belongs to the Topic Quantum Droplets)

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12 pages, 2914 KiB  

Open AccessCommunication

Rotational Dynamics Induced by Low-Energy Binary Collisions of Quantum Droplets

by J. E. Alba-Arroyo, S. F. Caballero-Benitez and R. Jáuregui

Photonics 2023, 10(7), 823; https://doi.org/10.3390/photonics10070823 - 14 Jul 2023

Viewed by 1110

Abstract

A theoretical analysis of the rotational dynamics induced by off-axis binary collisions of quantum droplets constituted by ultracold atoms is reported. We focus on quantum droplets formed by degenerate dilute Bose gases made from binary mixtures of alkaline atoms under feasible experimental conditions. [...] Read more.

A theoretical analysis of the rotational dynamics induced by off-axis binary collisions of quantum droplets constituted by ultracold atoms is reported. We focus on quantum droplets formed by degenerate dilute Bose gases made from binary mixtures of alkaline atoms under feasible experimental conditions. The stability of the ground state is known to be longer for the chosen heteronuclear gases than for the homonuclear ones. In both cases, we find that the dynamics seem to privilege high similarity of the density of each atomic species. However, the evolution of the phase of the corresponding order parameter differs significantly for heteronuclear admixtures. We evaluate the fidelity as a figure of merit for the overlap between the order parameters of each atomic species. Dynamical evidence of the differences between the phases of the order parameters is predicted to manifest in their corresponding linear and angular momenta. We numerically verify that the total angular and linear momenta are both conserved during the collision. Some direct correlations between the Weber number and the impact parameter with the distribution of the dynamical variables are established. Full article

(This article belongs to the Topic Quantum Droplets)
(This article belongs to the Section Quantum Photonics and Technologies)

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10 pages, 1029 KiB  

Open AccessCommunication

Two-Dimensional Quantum Droplets in Binary Dipolar Bose-Bose Mixture

by Aowei Yang, Guilong Li, Xunda Jiang, Zhiwei Fan, Zhaopin Chen, Bin Liu and Yongyao Li

Photonics 2023, 10(4), 405; https://doi.org/10.3390/photonics10040405 - 4 Apr 2023

Cited by 3 | Viewed by 1518

Abstract

We study two-dimensional (2D) isotropic quantum droplets (QDs) in dipolar binary Bose–Einstein condensates (BECs). The QDs are supported by the competition between the 2D form of the Lee-Huang-Yang (LHY) term and the isotropic dipole-dipole interactions (DDIs). Moreover, the DDIs in the 2D plane [...] Read more.

We study two-dimensional (2D) isotropic quantum droplets (QDs) in dipolar binary Bose–Einstein condensates (BECs). The QDs are supported by the competition between the 2D form of the Lee-Huang-Yang (LHY) term and the isotropic dipole-dipole interactions (DDIs). Moreover, the DDIs in the 2D plane can be tuned to be either repulsive or attractive. Before that, QDs in dipolar BECs were often explored in three-dimensional (3D) systems, with competition between the attractive DDIs and the repulsive LHY term. Unlike the 3D system, the LHY term of the 2D binary system behaves in a logarithmic form, which can feature both attraction and repulsion. In this case, the QDs can be produced regardless of the interactions (attraction, repulsion, or zero) that the mean-field effect represents. In this paper, we model the aforementioned QDs via the 2D binary dipolar BECs with the competition between isotropic DDIs and the logarithmic LHY term. Their characteristic parameters (the peak density, $I_{\mathrm{P}}$, chemical potential, $\mu$, and effective area, $A_{\mathrm{eff}}$) using both numerical and theoretical methods are discussed. The centripetal collision and oblique collision between moving QDs are also studied. Full article

(This article belongs to the Topic Quantum Droplets)
(This article belongs to the Section Quantum Photonics and Technologies)

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9 pages, 2619 KiB  

Open AccessCommunication

Axial Collective Mode of a Dipolar Quantum Droplet

by Peter Blair Blakie

Photonics 2023, 10(4), 393; https://doi.org/10.3390/photonics10040393 - 1 Apr 2023

Cited by 2 | Viewed by 1811

Abstract

In this work, we investigate the ground state properties and collective excitations of a dipolar Bose–Einstein condensate that self-binds into a quantum droplet, stabilized by quantum fluctuations. We demonstrate that a sum rule approach can accurately determine the frequency of the low energy [...] Read more.

In this work, we investigate the ground state properties and collective excitations of a dipolar Bose–Einstein condensate that self-binds into a quantum droplet, stabilized by quantum fluctuations. We demonstrate that a sum rule approach can accurately determine the frequency of the low energy axial excitation, using properties of the droplet obtained from the ground state solutions. This excitation corresponds to an oscillation in the length of the filament-shaped droplet. Additionally, we evaluate the static polarizabilities, which quantify change in the droplet dimensions in response to a change in harmonic confinement. Full article

(This article belongs to the Topic Quantum Droplets)
(This article belongs to the Section Quantum Photonics and Technologies)

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