Excitation of a Bose-Einstein condensate: A Pedagogical Experiment on quantum states change

In this work, we have used a 87Rb Bose-Einstein condensate to study the effects of electrical noise, embedded into the magnetic trap field, on the atomic population distribution spread over different quantum states of the confining potential. The noisy external field comes from unwanted fluctuations taking place in the electronic stabilization control circuit for the electric current flowing through the magnetic trap coils, which operate at frequencies close to that of the trapping potential. We will show that these small electric fluctuations are able to couple adjacent vibrational levels of the potential resulting in the population spread, which was initially pure, over a manifold of nearby states. This reduces the lifetime of the trapped condensate and also increase the average temperature of the system, as the population diffuses towards the upper energy levels. The results were modeled via ladder transitions, and directly compared to the experimental results, and were found to be in good agreement. We believe that this theoretical-experimental study is didactic, as it allows for the freshmen students to observe macroscopic quantum effects taking place on experimental physical systems.

本研究采用87Rb玻色-爱因斯坦凝聚体（Bose-Einstein condensate），探究嵌入磁阱（magnetic trap）场中的电噪声对约束势不同量子态上原子布居分布的影响。该带噪声外场源于磁阱线圈供电电流的电子稳定控制电路中产生的非期望波动，其工作频率与约束势的特征频率相近。本研究将证明，这些微弱的电波动可耦合势场的相邻振动能级，使初始布居纯净的原子扩散至邻近的多个量子态中。随着原子布居向高能级扩散，这会缩短被捕获凝聚体的寿命，并提升系统的平均温度。研究结果通过梯级跃迁（ladder transitions）模型进行模拟，并与实验结果直接比对，二者吻合度良好。我们认为该项理论-实验结合研究具有教学示范意义，可帮助低年级本科生在实验物理系统中观测宏观量子效应。