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

我们研究了a型三能级原子系统中的电磁诱导透明（EIT）、相干居群俘获（CPT）和光信息存储等量子干涉效应。特别是激光冷却的Na原子和Na原子蒸汽已经得到了广泛的研究。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，在暗态中没有观察到共振荧光，这种现象称为CPT。利用这一效应，我们研究了钠基态的超精细塞曼光谱。观测到的光谱与理论预测和双光子共振的反射特性吻合得很好。荧光猝灭也可用于空间非均匀磁场的映射。利用CCD相机对荧光分布进行成像，成功地实现了反亥姆霍兹线圈磁场的二维成像。这种方法可以提供高分辨率、实时的成像……更多的磁场分布。EIT线宽可以变得非常窄，比气体介质的多普勒线宽或自然线宽窄得多。通过精心布置实验装置和利用外差探测技术，我们在Na原子中实现了亚千赫兹（440赫兹）线宽的观测。同时得到的色散或折射率光谱也显示出这种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。光信息以亚级相干存储，稍后通过将该亚级相干转换为光相干来检索。该思想的原理验证实验已经成功地进行了验证。通过改变数据读取时间的延迟时间，我们可以得到亚能级相干的弛豫时间，测量结果为72 μs。这个常数的评估是非常重要的，因为这个量决定了未来的“量子存储器”设备的数据存储时间，该设备应作为量子计算机系统中的寄存器存储器。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