ABSTRACT
In recent years, ultracold lanthanide atoms, including dysprosium and erbium, have become a focal point in many-body physics [7]and quantum simulation [8]. Their large magnetic dipole-dipole interaction[9] and abundance of Feshbach resonances[10] have led to the exploration of exotic phenomena like quantum droplets[11], supersolids[12], and the extended Bose-Hubbard model[13]. Moreover, the unique atomic structure of lanthanide atoms is favorable to create systems featuring long-lived spin-orbit coupling fermions[14], synthetic gauge fields[15], and closely spaced bilayers[16]. However, despite these advancements,achieving quantum degeneracy of lanthanide atoms remains a formidable challenge due to factors such as the high operating temperature required for generating sufficient atomic flux in the oven, the narrow linewidth of optical cooling transitions, the stability of the magnetic field, and other related challenges.
The first section will introduce a newly developed apparatus designed for the production of Erbium (Er) Bose-Einstein Condensates (BEC)[17]. A detailed description of the key components of the apparatus will be provided. Additionally, it will cover various enhancements made to the apparatus, including the implementation of a two-stage slower [18]aimed at increasing the number of saturated atoms number and improving the loading speed of a narrow magneto-optical trap (MOT). Other improvements discussed will encompass the utilization of saturation fluorescence spectroscopy for narrow linewidth transitions, and the integration of a Radio Frequency system equipped with a designed impedance matching circuit for precise calibration of the magnetic field. Moreover, an increase in the number of BEC atoms will be achieved through an optimized experimental sequence.
The second section will present the study of Superradiant light scattering from a dipolar Bose-Einstein condensate. Dicke superradiance occurs when two or more emitters cooperatively interact via the electromagnetic field. This collective light scattering process has been extensively studied across various platforms, from atoms to quantum dots and organic molecules. Despite extensive research, the precise role of direct interactions between emitters in superradiance remains elusive, particularly in many-body systems where the complexity of interactions poses significant challenges. In this study, we investigate the effect of dipole-dipole interaction in dipolar Bose-Einstein condensates (BECs) on the superradiance process. In dipolar BECs, we simplify the complex effect of anisotropic magnetic dipole-dipole interaction with Bogoliubov transformation. We observe that anisotropic Bogoliubov excitation breaks the mirror symmetry in decay modes of superradiance.
The Third part will present the study of the BEC-Droplet phase crossover using Rayleigh superradiant scattering. We study the transition from BEC to the Macro-droplet regime using superradiant scattering, which is a sensitive probe for matter-wave coherence. The emergence and characteristics of superradiant scattering serves as a marker for the transition point. The efficiency of superradiant scattering shows the same non-monotonic behaviour as the expansion rate of the sample, suggesting it reflects the orignal quantum state of the sample. It is supported by theoretical calculations based on Gaussian variational ansatz. This new approach allows us not only to investigate the droplet-BEC transition at variable atom numbers (in a precise manner) but also to monitor the shift of phase transition points with different magnetic field direction. This research offers a comprehensive investigation of superradiance as a probe, shedding light on the BEC-droplet crossover and the underlying physics governing this transition.
