All-optical realization of quantum degeneracy of Yb atoms

双电子原子（如镱和碱土原子）的bec具有极窄的互合跃迁（这是未来光学频率标准的理想选择）和对外部磁场不敏感（这是精密相干原子光学的重要特点）等明显的特点。在这里，我们报道了在一种新型的交叉远共振阱（FORT）中，用全光手段实现了Yb原子的BEC。蒸发冷却是通过在2秒内逐渐降低水平FORT光束功率，同时保持垂直FORT光束功率恒定来实现的。当最终陷阱深度为2.2，K时，从陷阱中释放后出现了各向异性膨胀。凝结物中的原子数通常是5×10^3。临界温度约为0.7 K，峰值原子密度为7×10^<14> cm^<-3>。凝析液的寿命约为500 ms，我们推断出三体损失系数的上限为4×10^<-30> cm^ 6s ^<-1>。根据凝聚体的行为，我们估计了^<174>Yb的散射长度。在10次TOF下，与水平扩展宽度拟合得到化学势0.55，K，得到散射长度为6 nm，不确定度为-5和+10 nm。将此结果与我们最近的光关联实验相结合，我们得出散射长度在1 ~ 3nm之间的结论。五种玻色子（^<168>Yb, ^<170>Yb, ^<172>Yb, ^<174 b> Yb和^<176>Yb）和两种费米子（^<171>Yb和^<173>Yb）的丰富稳定同位素的存在将使我们能够利用Yb原子研究各种有趣的量子简并气体。此外，本工作中Yb BEC的成功证明也为碱土原子BEC的形成提供了可能。

BECs of two-electron atoms such as ytterbium (Yb) and alkali-earth atoms have distinct features such as the extremely narrow intercombination transitions which are ideal for future optical frequency standard and the insensitivity to external magnetic field which is important for precision coherent atom optics. Here we report the achievement of BEC of Yb atoms by all-optical means in a novel crossed far-off resonant trap (FORT). The evaporative cooling is carried out by gradually decreasing the horizontal FORT beam power in 2 sec., while keeping the vertical FORT beam power constant. When the final trap depth is 2.2 ,, K, anisotropic expansion after release from the trap has appeared. The number of atoms in the condensate is typically 5×10^3. The critical temperature is about 0.7 ,, K and the peak atom density is 7×10^<14> cm^<-3>. The lifetime of the condensate is about 500 ms, and we infer an upper bound for the three-body loss coefficient of 4×10^<-30> cm^6 s^<-1>.From the behavior of the condensate, we have estimated the scattering length of ^<174>Yb. The chemical potential of 0.55, K is obtained from the fit with the horizontally expanded widths at ten TOF times, which gives the scattering length of 6 nm with the uncertainty of -5 and +10 nm. By combining this result with our recent photoassociation experiment, we conclude that the scattering length is between 1 to 3 nm.The existence of rich varieties of stable isotopes of five bosons (^<168>Yb, ^<170>Yb, ^<172>Yb, ^<174>Yb, and ^<176>Yb) and two fermions (^<171>Yb and ^<173>Yb) will allow us to study various interesting quantum degenerate gases using Yb atoms. In addition, the successful demonstration of Yb BEC in the present work would also promise the formation of BEC of alkali-earth atoms.