基于微型光学偶极阱中单个铯原子俘获与操控的852 nm触发式单光子源∗

摘要

Single-atom-based single-photon source has several advantages, such as narrow bandwidth, wavelength matching with the absorption line of the same atomic ensemble, and insensitivity to the environment disturbing, and it is very important not only for basic researches in quantum optic field but also for applications in quantum information processing. In this paper, we report the generation of a 10-MHz-repetition-rate triggered single-photon source at 852 nm based on a trapped single cesium atom in a far-off-resonance microscopic optical dipole trap (FORT). To generate an optical dipole trap, a far-red-detuned 1064 nm laser beam is tightly focused by using a high numerical aperture lens, a typical trap depth is 2 mK and trap waist is 2.3 µm. To obtain a maximum probability of pulsed excitation, the frequency of the pulsed laser should be resonant with the atomic energy levels and the trapped single atom must be excited with aπ-pulse. However, the interaction between the FORT laser and the atoms causes AC Stark shifts of the atomic energy levels. Thus, in order to demonstrate the resonant pulsed excitation, it is important to calculate and measure the shift of 6S1/2 |Fg = 4, mF = +4⟩-6P3/2|F e = 5, mF = +5⟩ cyclical transition in the FORT. For a two-level system, the probability of pulsed excitation can be described by Rabi oscillations with a characteristic Rabi frequency Ω. With an optimized time sequence, we experimentally demonstrate the Rabi oscillation between the ground state and the excited state, and the peak power of π-pulse laser is about 1.25 mW. We also measure the temporal envelope of single photons after aπ-pulse excitation. A gated pulsed excitation and cooling technique are used to reduce the possibility that atoms are heated byπ-pulse laser. The typical trapping lifetime of single cesium atom is extended from∼108 µs to∼2536 ms. The corresponding number of excitations is improved from 108 to 360000. The second-order intensity correlations of the emitted single-photon are characterized by implementing Hanbury Brown-Twiss setup. The statistics shows a strong anti-bunching with a value of 0.09 for the second-order correlation at zero delay. In the future, we will perform a Hong-Ou-Mandel two-photon interference experiment to analyze the indistinguishability of the single photons. We will also trap single atoms in a magic-wavelength optical dipole trap where the ground and the excited states have the same shift.%基于单原子操控的单光子源具有窄带宽、可与同类原子吸收线匹配、基本不受外界环境因素的影响等特点,在量子光学基本问题研究及量子信息处理等方面具有重要价值.本文研究了强聚焦1064 nm基模高斯光束形成的光学偶极阱中铯原子6S1/2|Fg =4, mF =+4⟩-6P3/2|F e =5, mF =+5⟩循环跃迁的光频移,并在实验上进行了测量.基于共振脉冲光激发俘获在远失谐微型光学偶极阱中的单个铯原子,实验演示了10 MHz重复频率的触发式852 nm单光子源.采用基于单光子探测器的Hanbry Brown-Twiss实验系统,对单光子源的二阶相干度进行了测量,零延时处符合计数值为0.09,实验显示单光子源呈现显著的光子反群聚特性.