Study on quantum interference effects in cold atoms and Bose-Einstein condensates

研究了A型三能级原子系统中的电磁诱导透明(EIT)、相干布居俘获(CPT)和光信息存储等量子干涉效应。特别是对激光冷却的钠原子和钠原子蒸气进行了广泛的研究。在满足双光子共振条件的双色辐射下，原子被带入所谓的暗态，在这种状态下没有观察到共振荧光，这种现象被称为CPT。利用这一效应，我们研究了钠基态的超精细塞曼光谱。观察到的光谱与理论预测和双光子共振的反映性质符合得很好。荧光猝灭也可用于空间不均匀磁场的绘制。通过对荧光分布的成像，我们成功地对反亥姆霍兹线圈产生的磁场进行了二维测绘。这种方法提供了高分辨率、实时成像的…更多的是磁场分布。EIT的线宽可以变得非常窄，比气体介质的多普勒或自然线宽窄得多。通过精心安排实验装置和采用外差探测技术，我们实现了对钠原子亚千赫(440赫兹)线宽的观测。同时获得的色散或折射率谱也表明该介质的群速度非常慢。最后，我们对利用量子干涉效应进行光信息存储的可能性提出了挑战。光学信息被存储为子级相干，并且在稍后时间通过将该子级相干转换为光学相干来检索它。并成功地进行了原则性验证实验。通过改变数据读取时间的延迟时间，我们得到了次能级相干的驰豫时间，测得S的次能级相干性为72μ。这个常数的估计是非常重要的，因为这个量决定了未来的“量子存储器”器件的数据存储时间，它应该作为量子计算机系统中的寄存器存储器。较少

We have investigated quantum interference effects such as electromagnetically induced transparency (EIT), coherent population trapping (CPT), and optical information storage in A-type three level atomic systems. In particular, laser-cooled Na atoms and Na atomic vapor have been studied extensively. Under bichromatic radiation that satisfy two-photon resonance condition, the atoms are brought into so-called dark states in which no resonance fluorescence is observed, the phenomenon called CPT. Using this effect, we have studied hyperfine-Zeeman spectra of the Na ground state. The observed spectra agree well with theoretical predictions and reflected properties of two-photon resonance. Quenching of fluorescence can also be useful for mapping of spatially inhomogeneous magnetic field. By imaging the fluorescence distribution by a CCD camera, we have succeeded in two-dimensional mapping of magnetic field produced by anti-Helmholtz coils. This method gives high-resolution, real-time imaging … More of the magnetic field distribution. The EIT linewidth can become extremely narrow, much narrower than Doppler or natural linewidth of the gaseous medium. By careful arrangement of experimental setup and using heterodyne detection technique, we have achieved the observation of subkilohertz (440 Hz) linewidth in Na atoms. Simultaneously obtained dispersion, or refractive index, spectra also showed very slow group velocity of this medium. Finally, we have challenged the possibility of optical information storage by using quantum interference effect. The optical information is stored as sublevel coherence and at later time it is retrieved by converting this sublevel coherence into optical coherence. Proof-of-principle experiment of such idea has been successfully demonstrated. By varying the delay time of the data reading time, we were able to obtain the relaxation time of the sublevel coherence, which was measured to be 72 μs. The evaluation of this constant is quite important since this quantity determines the data-storage time of the futuristic "quantum memory" device that should be applied as a register memory in a quantum computer system. Less