arXiv subjects

Leandra Vranješ Markić

Publications and source records attributed to Leandra Vranješ Markić.

7 recordsLinked to original sources

arXiv2026

Ultradilute quasi-two-dimensional Bose-Bose liquid mixtures

We study ultradilute $^{39}$K Bose-Bose bulk mixtures and droplets in an external harmonic potential that confines them in one spatial direction towards the two-dimensional (2D) limit. Equations of state for several confinements are obtained with quantum Monte Carlo (QMC) at $T=0$, using interaction potentials that include information on the $s$-wave scattering length $a$ and the effective range $r_{\rm eff}$. Performing the calculations using two different interaction potential models we have determined the range of confinements for which equations of state are universal in terms of $a$ and $r_{\rm eff}$. Based on the QMC equation of state, we develop a 2D QMC density functional for each confinement strength and use it together with the local density approximation to determine properties of the self-bound drops. For moderate squeezing, energies and droplet profiles obtained using the 2D QMC functional agree well with those obtained using 3D functionals, while offering a substantial reduction in computational cost, and a consistent approach in crossover to 2D. Noticeably, our results approach 2D mean-field (MF) + Lee-Huang-Yang (LHY) predictions only for the most strongly confined systems for which universality in terms of $a$ and $r_{\rm eff}$ is observed. This implies a very narrow range of confinements for which 2D LHY functionals are applicable, which has important consequences for the study of vortices.

cond-mat.quant-gas↗

arXiv2025

Empty and filled vortices in squeezed 39K Bose-Bose liquid drops

Using density functional theory, we have theoretically studied the formation and the stability of vortices in quantum liquid droplets composed of a mixture of hyperfine states of potassium. Following the experimental setup that produced quantum droplets for the first time, we work with squeezed drops that are compressed in one direction. By squeezing the drops even more, towards a quasi-two dimensional geometry, we study the minimum atom number able to show a stable vortex and obtain that this number is significantly smaller than previous predictions for spherical droplets. The reduction of the critical atom number for forming a stable vortex could make their experimental observation in these droplets, which is still lacking, more feasible. Contrary to results obtained in heteronuclear mixtures, where the energetically preferred vortices are partially filled with the species not participating in the rotation, our results show a relevant stability island of fully empty vortices. Increasing the number of particles in the drop and the speed of rotation, we estimate the transition line between empty and filled vortices.

cond-mat.quant-gas↗

arXiv2022

Van der Waals five-body size-energy universality

A universal relationship between scaled size and scaled energy is explored in five-body self-bound quantum systems. The ground-state binding energy and structure properties are obtained by means of the diffusion Monte Carlo method. We use pure estimators to eliminate any residual bias in the estimation of the cluster size. Strengthening the inter-particle interaction, we extend the exploration from the halo region to classical systems. Universal scaled size-scaled energy line, which does not depend on the short-range potential details and binding strength, is found for homogeneous pentamers with interaction potentials decaying at long range predominantly as $r^{-6}$. For mixed pentamers, we discuss under which conditions the universal line can approximately describe the size-energy ratio. Our data is compatible with generalized Tjon lines, which assume a linear dependence between the binding energy of the pentamers and the one of tetramers, when both are divided by the trimer energies.

cond-mat.quant-gas↗

arXiv2021

Dilute quantum liquid in a K-Rb Bose mixture

A quantum liquid in a heterogeneous mixture of $^{41}$K and $^{87}$Rb atoms is studied using the diffusion Monte Carlo method and Density Functional Theory. The perturbative Lee-Huang-Yang term for a heterogeneous mixture is verified and it is proved to be valid only near the gas-liquid transition. Based on the equations of state of the bulk mixture, calculated with diffusion Monte Carlo, extensions to Lee-Huang-Yang corrected mean-field energy functionals (MF+LHY) are presented. Using Density Functional Theory, a systematic comparison between different functionals is performed, focusing on the critical atom number, surface tension, surface width, Tolman length, and compressibility. These results are given as a function of the inter-species interaction strength, within the stability domain of the liquid mixture.

cond-mat.quant-gas↗

arXiv2021

Dynamics of equilibration and collisions in ultradilute quantum droplets

Employing time-dependent density-functional theory, we have studied dynamical equilibration and binary head-on collisions of quantum droplets made of a $^{39}$K-$^{39}$K Bose mixture. The phase space of collision outcomes is extensively explored by performing fully three-dimensional calculations with effective single-component QMC based and two-components LHY-corrected mean-field functionals. We exhaustively explored the important effect -- not considered in previous studies -- of the initial population ratio deviating from the optimal mean-field value $N_2/N_1 = \sqrt{a_{11} / a_{22}}$. Both stationary and dynamical calculations with an initial non-optimal concentration ratio display good agreement with experiments. Calculations including three-body losses acting only on the $\left|F, m_{F}\right\rangle=|1,0\rangle$ state show dramatic differences with those obtained with the three-body term acting on the total density.

cond-mat.quant-gas↗

arXiv2020

Finite-range effects in ultradilute quantum drops

In the first experimental realization of dilute Bose-Bose liquid drops using two hyperfine states of $^{39}$K some discrepancies between theory and experiment were observed. The standard analysis of the data using the Lee-Huang-Yang beyond mean-field theory predicted critical numbers which were significantly off the experimental measurements. Also, the radial size of the drops in the experiment proved to be larger than expected from this theory. Using a new functional, which is based on quantum Monte Carlo results of the bulk phase incorporating finite-range effects, we can explain the origin of the discrepancies in the critical number. This result proves the necessity of including finite-range corrections to deal with the observed properties in this setup. The controversy on the radial size is reasoned in terms of the departure from the optimal concentration ratio between the two species of the mixture.

cond-mat.quant-gas↗

arXiv2016

Elusive structure of helium trimers

Over the years many He-He interaction potentials have been developed, some very sophisticated, including various corrections beyond Born-Oppenheimer approximation. Most of them were used to predict properties of helium dimers and trimers, examples of exotic quantum states, whose experimental study proved to be very challenging. Recently, detailed structural properties of helium trimers were measured for the first time, allowing a comparison with theoretical predictions and possibly enabling the evaluation of different interaction potentials. The comparisons already made included adjusting the maxima of both theoretical and experimental correlation functions to one, so the overall agreement between theory and experiment appeared satisfactory. However, no attempt was made to evaluate the quality of the interaction potentials used in the calculations. In this work, we calculate the experimentally measured correlation functions using both new and old potentials, compare them with experimental data and rank the potentials. We use diffusion Monte Carlo simulations at $T=0\ \mathrm{K}$, which give within statistical noise exact results of the ground state properties. All models predict both trimers $^4\mathrm{He}_{3}$ and $^4\mathrm{He}_2{}^3\mathrm{He}$ to be in a quantum halo state.

physics.atm-clus↗