We show that a quantum Szilard engine containing many bosons with attractive interactions enhances the conversion between information and work. Using an ab initio approach to the full quantum-mechanical many-body problem, we find that the average work output increases significantly for a larger number of bosons. The highest overshoot occurs at a finite temperature, demonstrating how thermal and quantum effects conspire to enhance the conversion between information and work. The predicted effects occur over a broad range of interaction strengths and temperatures.

Quantum droplets may form out of a gaseous Bose-Einstein condensate, stabilized by quantum fluctuations beyond mean field. We show that multiple singly-quantized vortices may form in these droplets at moderate angular momenta in two dimensions. Droplets carrying these precursors of an Abrikosov lattice remain selfbound for certain timescales after switching off an initial harmonic confinement. Furthermore, we examine how these vortex-carrying droplets can be formed in a more pertubation-resistant setting, by starting from a rotating binary Bose-Einstein condensate and inducing a metastable persistent current via a non-monotonic trapping potential.The formation of self-bound droplets is a well-known macroscopic phenomenon. For an exemplary droplet of water, stability and shape rely on the balance of effective forces between its constituent particles -attractive ones that keep it together, and repulsive ones that prevent it from collapse. Their interplay defines the droplets' surface tension, stabilizing the system in a metastable state. Such droplets do not only occur at a macroscopic level, but are ubiquitous also in the quantum realm, where nuclei [1] and superfluid helium droplets [2][3][4] are prominent examples. While these are rather dense and strongly interacting many-body systems, recent experiments with ultra-cold quantum gases of bosonic atoms uncovered a novel type of quantum liquid: Self-bound droplets may form out of a gaseous Bose-Einstein condensate (BEC) of dysprosium [5][6][7][8][9] or erbium [10], atomic species that are known for their strong dipolar interactions [11][12][13]. Similar droplet states have more recently also been realized with binary Bose gases of potassium in different hyperfine states [14,15], where the inter-and intracomponent interactions are short-ranged. These quantum droplets can be large, containing thousands of atoms. Importantly, they are very dilute -by more than eight orders of magnitude when compared with liquid helium [14]. While the discovery with dysprosium [5-7] at first came as a surprise, the binary self-bound droplet states were theoretically predicted a year before [16] for a scenario similar to the experiments with potassium, and also in lower dimensions [17]. That higher-order corrections beyond mean field may lead to self-bound states was discussed earlier in a different setting in Refs. [18,19]. For the dipolar or binary self-bound bosonic systems of 14,15] the physical mechanism of droplet formation is based on tuning the interactions in gas such that only a weak effective attraction remains. While in pure mean field this would lead to a collapse of the system, weak first-order corrections to the mean field energy, often referred to as the Lee-Huang-Yang (LHY)correction [20], can become comparable in size and may thus stabilize the system.

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Supersolidity-a coexistence of superfluidity and crystalline or amorphous density variations-has been vividly debated ever since its conjecture. While the initial focus was on helium-4, recent experiments uncovered supersolidity in ultracold dipolar quantum gases. Here we propose a self-bound supersolid phase in a binary mixture of Bose gases with short-range interactions, making use of the nontrivial properties of spin-orbit coupling. We find that a first-order phase transition from a self-bound supersolid stripe phase to a zero-minimum droplet state of the Bose gas occurs as a function of the Rabi coupling strength. These phases are characterized using the momentum distribution, the transverse spin polarization, and the superfluid fraction. The critical point of the transition is estimated in an analytical framework. The predicted density-modulated supersolid stripe and zero-minimum droplet phase should be experimentally observable in a binary mixture of 39 K with spin-orbit coupling.

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