对Λ型三能级原子电磁感应透明(EIT)过程中辐射场的二阶相干度进行了研究。理论分析表明,在电磁感应透明系统中,由于原子的相干效应导致其上能级共振荧光场的二阶相干度将呈现单光子场的量子统计特性。并对其随耦合场强度和探测光失谐的变化进行了详细的分析和讨论,结果发现:在Ω>(Γ2+Γ3)/2情况下,采用较弱的耦合光功率(由拉比频率Ω表征)及较大的探测光失谐,在较长时间延迟范围内,二阶相干度保持小于1,更利于实现非经典场的量子统计行为;相反,在Ω≤(Γ2+Γ3)/2情况下,探测光的失谐量越小,越利于获得二阶相干度小于1的量子统计光场。由此可见选取合适的参量可优化电磁感应透明过程中单光子场的量子统计特性。

The second-order coherence of radiation field in Λ-type three-energy level electromagnetically induced transparency (EIT) system is investigated theoretically. The result of calculation indicates that the coherence effect of atom in EIT system induces the second-order coherence of the resonance fluorescence field of upper level to present the quantum statistical property of single photon. And the second-order coherence of the radiation field dependence of intensity of coupling light and detuning of probe light is considered. Under the condition of Ω>(Γ2+Γ3)/2, if the weaker power of coupling light or far-off-resonance of probe light is applied, second-order coherence can retain smaller than 1 in longer time delay, which can make for realizing the quantum statistical action of nonclassical field; contrarily, under the condition of Ω≤(Γ2+Γ3)/2, the smaller off-resonance of probe light is applied, the better the quantum statistical nonclassical field realizes that second-order coherence can retain smaller than 1 in longer time delay. So the quantum statistical property of single-photon field in EIT can be optimized in different conditions when appropriate parameters are chosen.