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arXiv:1204.1725 · Physical Review Letters

Bose-Einstein Condensation of Erbium

K. Aikawa, Albert Frisch, Manfred J. Mark, Simon Baier, Alexander Rietzler, Rudolf Grimm, Francesca Ferlaino

Published May 21, 2012• 832 citations
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Abstract

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.

DOI
10.1103/physrevlett.108.210401

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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.
We report on the realization of Bose-Einstein condensation (BEC) of 168Er atoms in a crossed optical dipole trap. A magneto-optical trap is realized with just one laser driving the narrow-line transition which increases the phase space density and facilitates the evaporative cooling. A pure BEC with 3 × 104 atoms is achieved by forced evaporative cooling. The complex Feshbach resonance and anisotropic expansion of 168Er are investigated by the loss spectroscopy and controlling the rotating dipoles.
The achievement of a Bose-Einstein condensate of cesium in the lowest internal state (F=3, m/sub F/=3) by evaporative cooling in an optical trap is reported. The corresponding scattering length shows a strong dependence on magnetic field, varying from large negative to large positive values in a conveniently accessible magnetic field range due to a unusual combination of broad and narrow Feshbach resonances. The inelastic processes resulting from this complex scattering behavior in thermal ensembles is studied. These measurements have been of crucial importance for identifying a suitable path in phase space towards condensation. In first experiments, the strong dependence of the condensate mean-field energy on the magnetic field is demonstrated. By briefly switching to different scattering lengths just before releasing the sample from the trap, imploding, exploding, and non-interacting 'frozen' condensates are produced. We will employ the tunable interaction in further experiments by looking at molecule formation on Feshbach resonances and exploring condensate dynamics at extreme values of the scattering length.
We report the realization of a Bose-Einstein condensate of europium atoms, which is a strongly dipolar species with unique properties, a highly symmetric [Xe]4f^{7}6s^{2} ^{8}S_{7/2} electronic ground state and a hyperfine structure. By means of evaporative cooling in a crossed optical dipole trap, we produce a condensate of ^{151}Eu containing up to 5×10^{4} atoms. We estimate the scattering length of ^{151}Eu to be a_{s}=110(4) a_{B} after comparing the velocities of expansion of condensates to different orientations of the atomic magnetic moments, where a_{B} is the Bohr radius. We observe deformation of the condensate in the vicinity of the Feshbach resonance at 1.32 G with a width of 10 mG.
We report on experiments with ultracold chromium atoms. Preparing a cloud of 52Cr atoms in a crossed optical dipole trap (CODT) and applying magnetic fields between 4 and 600 G, we observe 14 Feshbach resonances by the occurrence of increased atom loss at distinct magnetic field values. A comparison with theory taking only dipole–dipole coupling into account shows very good agreement between experimental and theoretical resonance positions and allows us to extract the s-wave scattering lengths a 6=112(14) a 0, a 4= 58(6) a 0, a 2=−7(20) a 0 of the involved molecular potentials as well as the dispersion coefficients C 6= 733(70) au and au. The strongest resonance at 589 G has a calculated width of 1.7 G and reveals a three-body loss coefficient below L 3, max∼3×10−36 m6 s−1. Further evaporative cooling within the CODT leads to the formation of a Bose–Einstein condensate (BEC) with up to 100 000 condensed atoms. The magnetic dipole–dipole interaction between the Cr atoms is so strong that, as a first mechanical manifestation of dipole–dipole interaction, we observe a modification of the condensate expansion which depends on the alignment of the atomic magnetic dipoles with respect to the axis of the CODT. This magnetostrictive effect is in very good agreement with the theory of dipolar quantum gases and shows that a Cr-BEC is an excellent model system to study dipole–dipole interactions in degenerate quantum gases.
We report the Bose-Einstein condensation (BEC) of the most magnetic element, dysprosium. The Dy BEC is the first for an open f-shell lanthanide (rare-earth) element and is produced via forced evaporation in a crossed optical dipole trap loaded by an unusual, blue-detuned and spin-polarized narrowline magneto-optical trap. Nearly pure condensates of 1.5 × 10(4) (164)Dy atoms form below T = 30 nK. We observe that stable BEC formation depends on the relative angle of a small polarizing magnetic field to the axis of the oblate trap, a property of trapped condensates only expected in the strongly dipolar regime. This regime was heretofore only attainable in Cr BECs via a Feshbach resonance accessed at a high-magnetic field.
The Bose-Einstein condensation (BEC) of 133Cs atoms offers an appealing platform for studying the many-body physics of interacting Bose quantum gases, owing to the rich Feshbach resonances that can be readily achieved in the low magnetic field region. However, it is notoriously difficult to cool 133Cs atoms to their quantum degeneracy. Here we report a hybrid evaporative cooling of 133Cs atoms to BEC. Our approach relies on a combination of the magnetically tunable evaporation with the optical evaporation of atoms in a magnetically levitated optical dipole trap overlapping with a dimple trap. The magnetic field gradient is reduced for the magnetically tunable evaporation. The subsequent optical evaporation is performed by lowering the depth of the dimple trap. We study the dependence of the peak phase space density (PSD) and temperature on the number of atoms during the evaporation process, as well as how the PSD and atom number vary with the trap depth. The results are in excellent agreement with the equation model for evaporative cooling.