Optical Feshbach Resonances in a Bose-Einstein Condensate
Optical Feshbach Resonances in a Bose-Einstein Condensate
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发表时间：
2005
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通讯作者：
M. Theis
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作者：
M. Theis
本论文首次观测到超冷原子气体中相互作用的光学调谐。为了控制弹性相互作用，我们使用了光致散射共振。它们是通过在激光的帮助下将原子对耦合到束缚分子态来实现的。与众所周知的磁性Feshbach共振相比，这些光学Feshbach共振允许以空间分辨的方式非常快速地切换相互作用。这是因为激光的开启和关闭速度比磁场快得多，而且光强度可以在空间上形成结构。我们的实验是用我们在新的玻色-爱因斯坦凝聚装置中产生的Rb原子的玻色-爱因斯坦凝聚体(BEC)进行的。该装置是在本论文的框架内建造的，为超冷原子云提供了极好的光学访问途径。为了研究原子与单频激光相互作用的可调性，我们将自由原子对光学耦合到电子激发的分子态。耦合是通过调谐到各自的自由束缚光缔合跃迁附近的激光器来实现的。通过改变激光失谐，我们能够将原子散射长度调整到10a0到190a0之间的任何值，其中a0表示玻尔半径。原子散射长度是一个完全描述超冷弹性相互作用的单量。由于激光诱导的原子损失限制了实验的持续时间，布拉格光谱被用作测量散射长度的一种快速方法。我们还证明了利用双色拉曼耦合方案可以实现光学Feshbach共振。为了实现这一方案，添加了第二个激光器，它将激发的分子态耦合到基态势中的弱束缚分子能级。调谐第二个激光会导致原子散射长度的修正，类似于用单一激光观察到的结果。此外，该方案还允许通过第一个激光器的失谐来控制谐振的宽度。对于单色和双色耦合方案，我们研究了弹性散射特性如何依赖于不同的可用参数，即激光失谐量和强度。我们的实验结果可以成功地用一个可用的理论模型来描述，该模型处理在激光存在下的超冷碰撞。光学费什巴赫共振有可能成为快速切换相互作用的宝贵工具。这在中性原子的量子计算方案中特别令人感兴趣，其中需要控制不同原子量子比特之间的相互作用。
This thesis reports on the first observation of optical tuning of interactions in an ultracold atomic gas. To control the elastic interactions, we use optically induced scattering resonances. They are realized by coupling pairs of atoms to a bound molecular state with the help of laser light. In comparison to the well-known magnetic Feshbach resonances, these optical Feshbach resonances allow a very fast switching of interactions in a spatially resolved way. This is because laser light can be switched on and off much faster than magnetic fields and because the light intensity can be spatially structured. Our experiments are performed with a Bose-Einstein condensate (BEC) of Rb atoms, which we produce in our new BEC setup. This apparatus has been constructed in the framework of this thesis and offers excellent optical access to the ultracold atom cloud. To investigate the tunability of atomic interactions with single-frequency laser light, we optically couple pairs of free atoms to an electronically excited molecular state. The coupling is achieved with a laser that is tuned close to the respective free-bound photoassociation transition. By changing the laser detuning we are able to adjust the atomic scattering length to any value between 10 a0 and 190 a0, where a0 denotes the Bohr radius. The atomic scattering length is a single quantity that fully describes ultracold elastic interactions. Since laser induced atom losses restrict the duration of our experiments, Bragg spectroscopy is employed as a fast method to measure the scattering length. We also demonstrate that optical Feshbach resonances can be realized with a two-color Raman coupling scheme. To implement this scheme, a second laser is added that couples the excited molecular state to a weakly bound molecular level in a ground state potential. Tuning the second laser results in a modification of the atomic scattering length similar to the one observed with a single laser. In addition, this scheme allows to control the width of the resonance via the detuning of the first laser. For the one-color and two-color coupling schemes, we investigate how the elastic scattering properties depend on the different available parameters, i.e. the laser detunings and intensities. Our experimental findings can successfully be described with an available theoretical model, which treats ultracold collisions in the presence of laser light. Optical Feshbach resonances have the possibility of becoming a valuable tool for fast switching of interactions. This is of special interest in quantum computation schemes with neutral atoms, where interactions between different atomic qubits need to be controlled.