超短脉冲抽运下频率一致纠缠光源量子特性实验研究

利用自发参量下转换过程产生的频率纠缠光源在量子信息处理及相关领域中 具有十分重要的应用. 本文利用中心波长为792 nm, 脉冲宽度小于20 fs的脉冲激光源抽运满足II类准相位 匹配条件的周期极化磷酸氧钛钾晶体, 实验产生了偏振相互正交的频率一致纠缠光子对. 基于Hong-Ou-Mandel干涉仪的二阶量子符合干涉装置, 测量到该纠缠双光子对的干涉可见度约为42%, 表明其频率不可分特性较理想频率一致纠缠光源大大降低. 通过理论分析给出, 由于超短脉冲光源对应的宽频谱带宽影响, 相位匹配函数中的高阶色散项不再忽略, 从而导致纠缠光子对的频率不可分性减弱. 进一步利用实验参数给出的数值模拟结果与实验结果符合, 证实了脉冲抽运源带宽对频率一致纠缠光源的量子不可分特性的影响. 关键词： 频率一致纠缠 Hong-Ou-Mandel干涉测量 符合计数

Frequency indistinguishibility investigation of generated coincident-frequency entanglement via ultra-fast pulsed sources

The frequency entangled biphoton source generated via spontaneous parametric down-conversion process (SPDC) has found numerous applications in quantum information processing and relevant fields. We report on an experimental generation of coincident-frequency entanglement from periodically poled potassium titanyl phosphate, pumped by an ultra-short pulsed optical source with duration less than 20 fs. Based on the Hong-Ou-Mandel interferometric coincidence measurement setup, a visibility of about 42% is demonstrated, which indicates degraded frequency indistinguishibility of the down-converted biphotons. Through theoretical investigation, such a degradation can be perfectly explained by the nonnegligible second-order dispersion terms in the Taylor-expanded phase mismatching function for the case of ultra-broadband spectrum of the pulsed pump. The fitting to the experimental results is further used and perfect agreement is achieved. The results imply that the spectral bandwidth of the pump can affect the generated coincident-frequency entanglement.
Keywords： coincident-frequency entanglement Hong-Ou-Mandel interferometric measurement coincidence counts