We report on the achievement of Bose-Einstein condensation of erbium atoms and on the observation of magnetic Feshbach resonances at low magnetic fields. By means of evaporative cooling in an optical dipole trap, we produce pure condensates of 168Er, containing up to 7×10(4) atoms. Feshbach spectroscopy reveals an extraordinary rich loss spectrum with six loss resonances already in a narrow magnetic-field range up to 3 G. Finally, we demonstrate the application of a low-field Feshbach resonance to produce a tunable dipolar Bose-Einstein condensate and we observe its characteristic d-wave collapse.

Citation for published item:kekoshiD etsu nd eihs¤ ollnerD vuks nd hindewolfD endres nd rutsonD teremy wF nd ve ueurD gF uth nd hulieuD ylivier nd perlinoD prnes nd qrimmD udolf nd x¤ gerlD rnnsEghristoph @PHIRA 9ltrold dense smples of dipolr gs moleules in the rovirtionl nd hyper(ne ground stteF9D hysil review lettersFD IIQ F pF PHSQHIF Further information on publisher's website: eprinted with permission from the emerin hysil oietyX etsu kekoshiD vuks eihs¤ ollnerD endres hindewolfD teremy wF rutsonD gF uth ve ueurD ylivier hulieuD prnes perlinoD udolf qrimmD nd rnnsEghristoph x¤ gerl @PHIRA 9ltrold dense smples of dipolr gs moleules in the rovirtionl nd hyper(ne ground stteF9D hysil review lettersFD IIQ F pF PHSQHIF PHIR y the emerin hysil oietyF eders my viewD rowseD ndGor downlod mteril for temporry opying purposes onlyD provided these uses re for nonommeril personl purposesF ixept s provided y lwD this mteril my not e further reproduedD distriutedD trnsmittedD modi(edD dptedD performedD displyedD pulishedD or sold in whole or prtD without prior written permission from the emerin hysil oietyF Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

In a joint experimental and theoretical effort, we report on the formation of a macro-droplet state in an ultracold bosonic gas of erbium atoms with strong dipolar interactions. By precise tuning of the s-wave scattering length below the so-called dipolar length, we observe a smooth crossover of the ground state from a dilute Bose-Einstein condensate (BEC) to a dense macro-droplet state of more than 10 4 atoms. Based on the study of collective excitations and loss features, we quantitative prove that quantum fluctuations stabilize the ultracold gas far beyond the instability threshold imposed by mean-field interactions. Finally, we perform expansion measurements, showing the evolution of the normal BEC towards a three-dimensional self-bound state and show that the interplay between quantum stabilization and three-body losses gives rise to a minimal expansion velocity at a finite scattering length.