多缀饰四波混频Autler-Townes分裂的相干控制 下载: 1042次
1 引言
相干激光场诱导的电磁诱导透明(EIT)是光与物质相互作用时表现出来的非线性量子相干效应,这种现象已经引起了许多学者的关注[1-2],因为此时弱信号场几乎可以无吸收地通过共振介质。而且EIT现象的研究也极大地推动无反转激光[3]、光速减慢[4]、光控制和信息存储[5-6]、量子通信[7]、非线性光学[8]和四波混频(FWM)[9-10]等物理现象的研究。欧特莱-汤斯(Autler-Townes,AT)分裂,也称作AC Stark效应,是指强激光场共振作用于原子或分子跃迁时产生的谱线分裂的现象,其物理实质是强控制场诱导的分离缀饰态出现的结果。当前,AT 分裂已经在原子分子系统[11-12]、量子点[13]、超导量子电路[14]中得到了广泛的研究,其研究成果被用于超导量子比特[11,15]、电偶极矩的测量[16-17]、空间成像测量[18]等方面。
本文通过改变缀饰场的数量实现了FWM信号从单缀饰向双缀饰的转变,同时扫描探测场失谐观察到了一级和二级AT分裂。计算结果表明,改变缀饰场参量可以实现对两级AT分裂的灵活控制。
2 基本理论
能级系统及空间配置如
图 1. 能级系统及空间配置。(a)级联三级系统能级图;(b)相位配置
Fig. 1. Related energy-level system and geometric configuration. (a) Energy-level of cascade three-level system; (b) phase-matching configuration
对DFWM 信号场
式中:
其中:
当缀饰场
式中:
当
式中:
3 数值分析与讨论
3.1 简并四波混频
在建立了上述理论模型后,研究了不同缀饰作用的DFWM信号。首先研究无缀饰作用的DFWM信号。此时,信号强度由(2)式给出。计算使用的参数为
图 2. DFWM信号的模拟结果。(a) Δ1与DFWM信号强度的关系曲线;(b) DFWM信号系统能级图
Fig. 2. Simulation results of DFWM signal. (a) Δ1versus DFWM signal intensity; (b) energy-level diagram of DFWM signal system
3.2 单缀饰四波混频
研究不同缀饰场失谐
图 3. 单缀饰DFWM信号的模拟结果。(a) Δ1、Δ2 与DFWM信号强度的关系曲线;(b)不同的Δ2处,Δ1与DFWM信号强度的关系曲线;(c) DFWM信号系统能级图,(c1) Δ2=-150 MHz;(c2) Δ2=0 MHz;(c3) Δ2=150 MHz
Fig. 3. Simulation results of singly-dressed DFWM signal. (a) Δ1, Δ2 versus DFWM signal intensity; (b) Δ1 versus DFWM signal intensity at different Δ2; (c) energy-level diagrams of DFWM signal system for (c1) Δ2=-150 MHz, (c2) Δ2=0 MHz and (c3) Δ2=150 MHz
上述的扫描结果也可以通过缀饰态模型得到解释。如
式中:sin
图 4. 双缀饰DFWM信号的模拟结果。(a)固定Δ2=0 MHz,改变的Δ3,Δ1与FWM信号强度关系曲线;(b) FWM信号系统能级图,Δ2=0 MHz;(b1) Δ3=-100 MHz;(b2) Δ3=0 MHz;(b3) Δ3=100 MHz
Fig. 4. Simulation results of doubly-dressed DFWM signal. (a) Δ1versus FWM signal intensity under different Δ3 at Δ2=0 MHz; (b) energy-level diagrams of FWM signal system at Δ2=0 MHz for (b1) Δ3=-100 MHz, (b2) Δ3=0 MHz and (b3) Δ3=100 MHz
3.3 双缀饰简并四波混频
接着研究不同缀饰场失谐
同样,上述的扫描结果也可以通过缀饰态模型得到解释。如
4 结论
通过改变外加缀饰场的数量使得FWM信号由无缀饰FWM信号、单缀饰FWM信号向级联双缀饰FWM信号转变。单缀饰FWM信号和双缀饰FWM信号在扫描探测场失谐可以观察到AT分裂现象,并且在双缀饰FWM信号中观察到了二级AT分裂现象。通过计算,发现AT分裂的位置和宽度取决于缀饰场Rabi频率和失谐。另外,理论计算使用的参数是铷85原子的真实参数,可以预见所有研究结论都可以在实验中观测到。这种对FWM信号进行灵活控制的方法,可以构成全光开关的与门和或门,用于制作光通信及光计算的单元器件。
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Article Outline
桑苏玲. 多缀饰四波混频Autler-Townes分裂的相干控制[J]. 激光与光电子学进展, 2019, 56(8): 081901. Suling Sang. Coherent Control of Multi-Dressed Four-Wave Mixing Autler-Townes Splitting[J]. Laser & Optoelectronics Progress, 2019, 56(8): 081901.