Controlled expansion of shell-shaped Bose–Einstein condensates

Motivated by the recent experimental realization of ultracold quantum gases in shell topology, we propose a straightforward implementation of matter-wave lensing techniques for shell-shaped Bose–Einstein condensates. This approach allows to significantly extend the free evolution time of the condensate shell after release from the trap and enables the study of novel quantum many-body effects on curved geometries. With both analytical and numerical methods we derive optimal parameters for realistic schemes to conserve the shell shape of the condensate for times up to hundreds of milliseconds

Shell-shaped Bose-Einstein condensates realized with dual-species mixtures

Confining Bose-Einstein condensates (BECs) in shell-shaped trapping potentials enables the generation of hollow quasi-2D topologies with superfluid properties. Motivated by recent microgravity experiments, these shell-shaped BECs are nowadays actively studied both theoretically and experimentally, with radio-frequency (rf) dressing being the main trapping mechanism under study. Here we present an alternative approach that utilizes the repulsive interaction in a dual-species mixture to achieve shell-shaped BECs, which could be realized in the future BECCAL mission. In contrast to the rf case, which relies on a dynamical transition from a filled to a hollow condensate, the mixture approach is based on realizing the shell structure as the ground state of the system, where one species is located at the center of the trap surrounded by the other and kept in place by the repulsive inter-species interaction. We compare both approaches by analyzing the initial states, the free expansion dynamics, and the collective excitation spectrum with analytical and numerical methods. In all three categories the mixture performs similar to the rf approach. Moreover, the interaction-driven expansion of the mixture allows to increase the size of the shell during time-of-flight without distorting its shape and therefore magnifying the dynamics within the shell; a mechanism not realizable in the rf case. We conclude by performing a feasibility analysis for both approaches that takes residual gravitational effects and possible trap asymmetries into account, which currently are the main obstacles to experimentally realize shell-shaped BECs

Asymmetric Tunneling of Bose-Einstein Condensates

In his celebrated textbook, \textit{Quantum Mechanics: Nonrelativistic Theory}, Landau argued that, for single particle systems in 1D, tunneling probability remains the same for a particle incident from the left or the right of a barrier. This left-right symmetry of tunneling probability holds regardless of the shape of the potential barrier. However, there are a variety of known cases that break this symmetry, e.g. when observing composite particles. We computationally (and analytically, in the simplest case) show this breaking of the left-right tunneling symmetry for Bose-Einstein condensates (BEC) in 1D, modelled by the Gross-Pitaevskii equation (GPE). By varying $g$, the parameter of inter-particle interaction in the BEC, we demonstrate that the transition from symmetric ($g=0$) to asymmetric tunneling is a threshold phenomenon. Our computations employ experimentally feasible parameters such that these results may be experimentally demonstrated in the near future. We conclude by suggesting applications of the phenomena to design atomtronic diodes, synthetic gauge fields, Maxwell's demons, and black-hole analogues.Comment: 15 pages, 16 figure

Perspective on Quantum Bubbles in Microgravity

Progress in understanding quantum systems has been driven by the exploration of the geometry, topology, and dimensionality of ultracold atomic systems. The NASA Cold Atom Laboratory (CAL) aboard the International Space Station has enabled the study of ultracold atomic bubbles, a terrestrially-inaccessible topology. Proof-of-principle bubble experiments have been performed on CAL with an rf-dressing technique; an alternate technique (dual-species interaction-driven bubbles) has also been proposed. Both techniques can drive discovery in the next decade of fundamental physics research in microgravity.Comment: 17 pages, 2 figure

Quantum Gas Mixtures and Dual-Species Atom Interferometry in Space

The capability to reach ultracold atomic temperatures in compact instruments has recently been extended into space. Ultracold temperatures amplify quantum effects, while free-fall allows further cooling and longer interactions time with gravity - the final force without a quantum description. On Earth, these devices have produced macroscopic quantum phenomena such as Bose-Einstein condensation (BECs), superfluidity, and strongly interacting quantum gases. Quantum sensors interfering the superposition of two ultracold atomic isotopes have tested the Universality of Free Fall (UFF), a core tenet of Einstein's classical gravitational theory, at the $10^{-12}$ level. In space, cooling the elements needed to explore the rich physics of strong interactions and preparing the multiple species required for quantum tests of the UFF has remained elusive. Here, utilizing upgraded capabilities of the multi-user Cold Atom Lab (CAL) instrument within the International Space Station (ISS), we report the first simultaneous production of a dual species Bose-Einstein condensate in space (formed from $^{87}$Rb and $^{41}$K), observation of interspecies interactions, as well as the production of $^{39}$K ultracold gases. We have further achieved the first space-borne demonstration of simultaneous atom interferometry with two atomic species ($^{87}$Rb and $^{41}$K). These results are an important step towards quantum tests of UFF in space, and will allow scientists to investigate aspects of few-body physics, quantum chemistry, and fundamental physics in novel regimes without the perturbing asymmetry of gravity

Terrestrial Very-Long-Baseline Atom Interferometry:Workshop Summary

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more km-scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions

Terrestrial very-long-baseline atom interferometry: Workshop summary

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more kilometer--scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions

Interacting matter waves quantum gases in box and shell geometries

Bose-Einstein condensates are interacting quantum gases, that are used for a variety of applications ranging from basic scientific research to precision measurement devices. All this is possible due to the precise controllability of atom-atom interactions, via Feshbach resonances, as well as the interaction of atoms with optical and magnetic potentials. These achievements paved the way for the articles [1–3] presented in this thesis. Due to good control of the scattering length via Feshbach resonances, we are able to analyze the effect of diffractive focusing for interacting systems. Strong interaction allows us to create the required box-shaped ground state, whereas small interaction is crucial to investigate the influence of interaction on diffractive focusing. Moreover, by trapping two interacting Bose gases in an optical harmonic trap and tuning the inter-species interaction, we explore an alternative approach to create shell-shaped BECs. This scheme is shown to be more robust compared to the conventional method of rf-dressing. By compensating the gravitational sag and tuning the trap frequencies to the right value, this scheme has been successfully realized in experiments on Earth [4]. A shell without any external potential expands inwards and outwards, giving rise to fast destruction of the shell form of the BEC. To avoid this issue, we present schemes based on well-established methods, namely the delta kick and in-trap collimation, for extension of the free expansion times to several 100 ms. Additionally, we introduce and develop the one-dimensional analytical approach to describe the dynamics of a shell with a large radius and to predict the experimental outcomes