Collisions of Self-Bound Quantum Droplets

Abstract

We report on the study of binary collisions between quantum droplets formed by an attractive mixture of ultracold atoms. We distinguish two main outcomes of the collision, i.e. merging and separation, depending on the velocity of the colliding pair. The critical velocity vc that discriminates between the two cases displays a different dependence on the atom number N for small and large droplets. By comparing our experimental results with numerical simulations, we show that the non-monotonic behavior of vc(N ) is due to the crossover from a compressible to an incompressible regime, where the collisional dynamics is governed by different energy scales, i.e. the droplet binding energy and the surface tension. These results also provide the first evidence of the liquid-like nature of quantum droplets in the large N limit, where their behavior closely resembles that of classical liquid droplets.

Immiscible and miscible states in binary condensates in the ring geometry

“…In this figure, the demixed single-peak mode terminates at g 0.845 cr = , only the uniformly mixed state existing at g>g cr . This numerically identified critical value exactly coincides with the analytical prediction given by equation (18). Further, the existence area for demixed single-peak and mixed modes is presented in figure 2 (b).…”

“…Superfluid mixtures are currently routinely probed in experiments with ultracold atomic gases. In addition to Bose-Bose mixtures of different isotopes and atomic species [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], experimentalists have in the past few years created condensates with a spin degree of freedom [19], also implementing spin-orbit coupling which gives rise to exciting new states [20][21][22][23][24]; moreover, recent achievements have led to the generation of doubly-superfluid Bose-Fermi mixtures [25], in which both components are condensed, a state so far inaccessible in other settings (such as superfluid helium). Although the stability and phase diagrams of such systems have been extensively studied in the course of more than 20 years , even simple hetero-species binary mixtures still reveal unexpected features, such as the role of the trap sag, atom number and kinetic energy contribution to the extent of miscibility in trapped configurations [42,50,52], and nontrivial effects of the expansion on the mixtures' dynamics [51,53].…”

Modulational Instability, Inter-Component Asymmetry, and Formation of Quantum Droplets in One-Dimensional Binary Bose Gases

“…These options suggest a possibility to check the stability of the solutions of the symmetric system, reduced to the singlecomponent form, against symmetry-breaking perturbations. That objective is relevant because, in the real experiment, scattering lengths of the self-interaction in the two components are never exactly equal [21]- [24]. We address, first, an asymmetric single-droplet solution, and, subsequently, MI of the PW states in the two-component system.…”

“…Collective modes of QDs are a subject of special interest, as they reveal internal dynamics of the droplets [20,24,32,37,38]. In particular, the stable existence of the QDs is secured if the particle-emission threshold lies below all excitation modes, hence a perturbation in the form of such modes will not cause decay of the droplet.…”

Effective expression of the Lee-Huang-Yang energy functional for heteronuclear mixtures

“…stable states self-bound by interatomic attractive interactions. Such states resemble a liquid even if their density is several orders of magnitude lower than in ordinary liquids [14][15][16][17][18][19][20]. Similarly, LHY corrections also stabilize droplets with attractive dipolar forces [21,22].…”