Strongly Dipolar Bose-Einstein Condensate of Dysprosium

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 $1.5\times {10}^4$ ${}^{164}\mathrm{Dy}$ atoms form below $T=30\mathrm{nK}$. 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.

Figure 1

(a) The relevant ${}^{164}\mathrm{Dy}$-level scheme. The nuclear spin is $I=0$, and the total electronic angular momentum is $J=L+S=8$, with $L=6$ and $S=2$. (b) Experimental setup and (c) typical timing diagram. The trapezoid and diagonal line in the rf row represent the rf power ramp and the 0.7-MHz sweep about 5.65 MHz, respectively.

Figure 2

TOF profiles of the spin-purified Dy gas for three evaporation time constants, with $\tau =15\mathrm{s}$ in (e) and (f). (a),(c),(e) Data at centers are fit to a parabolic profile (upper curve), which underestimates the condensate fraction, whereas the distributions’ wings are fit to a Gaussian profile (lower curve). (b),(d),(f) Absorption images of the emerging BEC. (b) The transition temperature is 99(5) nK, with condensate fraction $2.0(4)\%$; (d) $44(2)\%$ condensate fraction at 56(3) nK; (f) a BEC of condensate fraction of $73(4)\%$ and $1.5(2)\times {10}^4$ atoms forms at 28(2) nK with density ${10}^{14}{\mathrm{cm}}^{-3}$.

Figure 3

Anisotropic expansion profile versus time after trap release. (a) $r_z$ and $r_{\rho }$ are the dimensions of the parabolic profile fit to the BEC for $\theta =0°$. Inset: Schematic of the oblate trap and magnetic-field orientation. (b) Images of the expanding condensate after trap release. The condensate rotates by $7(1)°$ [$9.4(6)°$] with respect to the $\theta =0°$ expansion orientation for $\theta =45°$ [$\theta =60°$]. No BEC forms for $\theta =90°$.