Rydberg原子nS1/2→(n+1)S1/2双光子激发EIT-AT光谱

主要研究了热原子蒸气池中铯Rydberg原子nS_1/2→(n+1)S_1/2微波耦合的双光子光谱.铯原子基态(6S_1/2)、第一激发态(6P_3/2)、Rydberg态(69S_1/2)形成阶梯型三能级系统,弱探测光作用于基态到激发态6S_1/2→6P_3/2的跃迁,强耦合光则作用于6P_3/2→69S_1/2的Rydberg跃迁形成电磁感应透明(EIT)效应,实现对Rydberg原子的光学探测.频率fMW=11.735 GHz的微波场耦合69S_1/2→70S_1/2的Rydberg跃迁,形成微波双光子光谱.利用EIT-AT分裂光谱研究微波电场强度对双光子光谱的影响.研究表明:在强微波场作用时,EIT-AT分裂与微波场功率成正比,而弱微波场时的EIT-AT分裂与微波场功率成非线性依赖关系,理论计算与实验测量结果相一致.本文的研究对微波电场的精密测量具有一定的指导意义.     

Rydberg原子nS1/2→(n+1)S1/2双光子激发EIT-AT光谱

主要研究了热原子蒸气池中铯Rydberg原子nS_1/2→(n+1)S_1/2微波耦合的双光子光谱.铯原子基态(6S_1/2)、第一激发态(6P_3/2)、Rydberg态(69S_1/2)形成阶梯型三能级系统,弱探测光作用于基态到激发态6S_1/2→6P_3/2的跃迁,强耦合光则作用于6P_3/2→69S_1/2的Rydberg跃迁形成电磁感应透明(EIT)效应,实现对Rydberg原子的光学探测.频率fMW=11.735 GHz的微波场耦合69S_1/2→70S_1/2的Rydberg跃迁,形成微波双光子光谱.利用EIT-AT分裂光谱研究微波电场强度对双光子光谱的影响.研究表明:在强微波场作用时,EIT-AT分裂与微波场功率成正比,而弱微波场时的EIT-AT分裂与微波场功率成非线性依赖关系,理论计算与实验测量结果相一致.本文的研究对微波电场的精密测量具有一定的指导意义.     

Enhancement of Rydberg atom interactions using ac Stark shifts

The ac Stark effect was used to induce resonant energy transfer between translationally cold 85Rb Rydberg atoms. When a 28.5 GHz dressing field was set at specific field strengths, the two-atom dipole-dipole process 43d5/2+43d5/2-->45p3/2+41f was dramatically enhanced, due to induced degeneracy of the initial and final states. This method for enhancing interactions is complementary to dc electric-field-induced resonant energy transfer, but has more flexibility due to the possibility of varying the applied frequency.     

Cooperative atom-light interaction in a blockaded Rydberg ensemble

By coupling a probe transition to a Rydberg state using electromagnetically induced transparency (EIT) we map the strong dipole-dipole interactions onto an optical field. We characterize the resulting cooperative optical nonlinearity as a function of probe strength and density. We demonstrate good quantitative agreement between the experiment and an N-atom cooperative model for N=3 atoms per blockade sphere and the n=60 Rydberg state. The measured linewidth of the EIT resonance places an upper limit on the dephasing rate of the blockade spheres of <110 kHz.     

铯原子里德伯态精细结构测量

里德伯态光谱是测量里德伯态能级结构和中性原子间相互作用的常用技术手段,特别是高精度的里德伯光谱,可以测量室温原子气室中由偶极相互作用等导致的原子能级频移.在实验中利用反向的852 nm激光和509 nm激光实现了室温原子气室中铯原子6S_(1/2)—6P_(3/2)—57S(D)跃迁的级联双光子激发,实现了里德伯态原子的制备.基于阶梯型电磁诱导透明获得了铯原子里德伯态的高分辨光谱.实验中,基于速度选择的射频边带调制技术,对光谱信号进行了频率标定,测量了铯原子里德伯态57D_(3/2)和57D_(5/2)的精细分裂,分裂间隔为(354.7±2.5)MHz,与理论计算结果基本一致.速度选择的射频调制光谱可以实现里德伯态原子的能级分裂测量,其测量精度对于单光子跃迁的绝对激光频率不敏感;实验中影响57D_(3/2)和57D_(5/2)精细分裂间隔测量精度的主要因素是功率加宽导致的电磁感应透明信号的展宽和509 nm激光频率扫描的非线性.     

弱射频场中Rydberg原子的电磁感应透明

在铯原子室温蒸气池中研究了弱射频场中Rydberg原子阶梯型三能级系统的电磁感应透明(EIT)效应.铯原子基态6S_(1/2)、第一激发态6P_(3/2)和Rydberg 48D_(5/2)态形成阶梯型三能级系统,探测光共振作用于6S_(1/2)(F=4)→6P_(3/2)(F′=5)的跃迁,耦合光在Rydberg跃迁线6P_(3/2)(F′=5)→48D_(5/2)附近扫描,形成Rydberg原子EIT.当对铯原子施加一个80 MHz的弱射频电场时,48D_(5/2)Rydberg原子的EIT光谱发生Stark频移和分裂,同时产生由射频场调制Rydberg能级的偶数级边带,测量结果与Floquet理论模拟的结果相符合.同时,改变弱射频电场的频率研究了铯Rydberg能级的自电离效应对Rydberg原子Stark谱的影响,据此,我们提出将电极板置于铯原子蒸气池内的方案以减少自电离效应的影响.在弱射频Stark谱中,mj=5/2的Stark谱与mj=1/2,3/2的二级边带形成多个能级交叉,这些能级交叉点提供了一种基于原子的精确校准射频电场的新方法.     

Investigation of cold rubidium Rydberg atoms in a magneto-optical trap

This paper reports on the results of experiments with cold rubidium Rydberg atoms in a magneto-optical trap. The specific feature of the experiments is the excitation of Rydberg atoms in a small volume within a cloud of cold atoms and the sorting of measured signals and spectra according to the number of detected Rydberg atoms. The effective lifetime of the 37P Rydberg state and its polarizability in a weak electric field are measured. The results obtained are in good agreement with theoretical calculations. It is demonstrated that the localization of the excitation volume in the vicinity of the zero-magnetic-field point makes it possible to improve the spectral resolution and to obtain narrow microwave resonances in Rydberg atoms without switching off the quadrupole magnetic field of the trap. The dependence of the amplitude of dipole-dipole interaction resonances in Rydberg atoms on the number of atoms is measured. This dependence exhibits a linear behavior and agrees with the theory for a weak dipole-dipole interaction.     

Spatially resolved observation of dipole-dipole interaction between Rydberg atoms

We have observed resonant energy transfer between cold Rydberg atoms in spatially separated cylinders. Resonant dipole-dipole coupling excites the 49s atoms in one cylinder to the 49p state while the 41d atoms in the second cylinder are transferred down to the 42p state. We have measured the production of the 49p state as a function of separation of the cylinders (0-80 microm) and the interaction time (0-25 micros). In addition, we measured the width of the electric field resonances. A full many-body quantum calculation reproduces the main features of the experiments.     

Electric field controlled, pulsed autoionization in two electron wave packets

In this paper, control of the evolution of a two electron wave packet through the application of a static electric field is demonstrated. Specifically, application of a small electric field is used to produce pulsed autoionization events, the timing of which can be controlled on a picosecond time scale. The technique is demonstrated by exciting calcium atoms using a short-pulsed laser to the 4p(3/2)19d doubly excited state, which is energy degenerate with the 4p(1/2)nk stark states. Evolution of the resultant wave packet is monitored through the application of a second short laser pulse, which stimulates the atoms to emit a photon producing singly excited Rydberg states which are detected using field ionization.     

Precise measurement of a weak radio frequency electric field using a resonant atomic probe

We present a precise measurement of a weak radio frequency electric field with a frequency of ■3 GHz employing a resonant atomic probe that is constituted with a Rydberg cascade three-level atom, including a cesium ground state |6S(1/2)〉,an excited state |6P(3/2)〉, and Rydberg state |nD(5/2)〉. Two radio frequency(RF) electric fields, noted as local and signal fields, couple the nearby Rydberg transition. The two-photon resonant Rydberg electromagnetically induced transparency(Rydberg-EIT) is employed to directly read out the weak signal field having hundreds of k Hz difference between the local and signal fields that is encoded in the resonant microwave-dressed Rydberg atoms. The minimum detectable signal fields of ESmin= 1.36 ± 0.04 mV/m for 2.18 GHz coupling |68D(5/2)〉→ |69P(3/2)〉 transition and 1.33 ± 0.02 mV/m for 1.32 GHz coupling |80D(5/2)〉→ |81P(3/2)〉 transition are obtained, respectively. The bandwidth dependence is also investigated by varying the signal field frequency and corresponding -3 dB bandwidth of 3 MHz is attained. This method can be employed to perform a rapid and precise measurement of the weak electric field, which is important for the atom-based microwave metrology.     

一价镧离子高n里德伯态

基于五步激光共振激发,经由中间态(Xe) 5d6d~3F_2的一价镧离子光谱,分析了该实验谱,确定了一价镧离子一强一弱两个自电离里德伯系列.同时利用多通道量子亏损理论(MQDT)框架下的相对论多通道理论(RMCT)计算,标识了这两个自电离里德伯系列,强的自电离里德伯系列标识为5dnp(5/2,1/2)_3和/或5dnp(5/2,1/2)_2,弱系列标识为为5dnf(5/2,5/2)_3和/或5dnf(5/2,5/2)_2.根据实验谱峰数据,发现有效量子数很高时,里德伯和自电离里德伯能级量子数亏损随激发能量不平滑变化,并分析了可能的原因.     

铯原子nP_(3/2)(n=70—94)里德伯态的紫外单光子激发及量子亏损测量

基于成熟的光纤激光器、光纤放大器及高效激光频率转换技术,我们在实验中研制了一套瓦级输出的窄线宽连续波单频可调谐318.6 nm紫外激光系统,并在室温铯原子气室中实现了6S_(1/2)—nP_(3/2)(n=70—94)单光子跃迁里德伯激发.借助由铯原子6S_(1/2)(F=4)基态、6P_(3/2)(F′=5)激发态和nP_(3/2)(n=70—94)里德伯态构成的V型三能级系统,通过频率锁定于铯原子6S_(1/2)(F=4)—6P_(3/2)(F′=5)超精细跃迁的852.3 nm探测光束的吸收减弱信号获得了里德伯态的信息,并利用高精度波长计测量了铯原子nP_(3/2)(n=70—94)里德伯态的量子亏损值.经过与理论计算值的变化趋势进行对比,我们认为由于原子气室的里德伯屏蔽效应并不能完全屏蔽外部直流电场,铯原子气室内存在残余的直流电场,影响了对里德伯态的量子亏损值的实验测量.利用残余直流电场的Stark效应理论模型及其与有效主量子数n*的依赖关系,对铯原子里德伯态的量子亏损实验测量值进行了修正.修正后的铯原子nP_(3/2)(n=70—94)态量子亏损测量值为3.5591±0.0007,与理论计算值相吻合.     

Rydberg原子的微波电磁感应透明-Autler-Townes光谱

主要研究了室温下微波场缀饰的铯Rydberg原子的电磁感应透明-Autler-Townes(EIT-AT)光谱.首先,以铯原子6S_(1/2)→6P_(3/2)→50S_(1/2)形成阶梯型三能级系统,利用强耦合光作用于6P_(3/2)→50S_(1/2)的Rydberg跃迁,弱探测光耦合基态跃迁6S_(1/2)→6P_(3/2)并探测由耦合光形成的电磁感应透明(EIT)效应.然后,以频率为30.582 GHz的微波电场耦合相邻的Rydberg能级50S_(1/2)→50P_(1/2)产生微波AT分裂.利用Rydberg EIT探测微波耦合相邻Rydberg能级产生的AT分裂,形成EIT-AT光谱,进而实现微波电场的测量.当微波场的强度增加到一定值时,EIT-AT光谱表现为多峰光谱结构.分析EIT-AT多峰光谱的成因,发现这主要是由场的不均匀性导致的,一定的EIT-AT光谱特征对应于特定的非均匀场分布.研究表明,利用Rydberg EIT-AT光谱可以实现微波电场的测量,利用其光谱特征可实现微波场的实时监测,进而提出了一种提高微波场空间分辨率的测量方法.     

基于Rydberg原子的高灵敏微波探测与通信

利用Rydberg原子作为微波传感器实现了微弱场的测量与通信.在铯原子蒸气池中,相向传输的探测光(852 nm)和耦合光(510 nm)与铯原子相互作用形成阶梯型三能级电磁感应透明光谱,用于实现Rydberg原子的光学探测.频率约为2.19 GHz的强微波场作为本地场(E_L),共振耦合相邻的两个Rydberg能级|68D_5/2>和|69P_3/2>,与具有一定失谐δf的待测微弱信号场(E_s)同时作用于Rydberg原子.Rydberg原子作为微波混频器可直接读出两束微波的差频信号,实现待测信号场的高灵敏探测,对应的最小测量值为E₀=1.7μV/cm,频率分辨率小于1 Hz.在此基础上,对微弱信号场进行编码,实验上很好地还原了加载到微波弱场上的基带信号,测量的传输带宽达200 MHz,实现了微弱场条件下的通信.     

调制激光场中Rydberg原子的电磁感应透明

本文主要研究了调制探测激光场中铯Rydberg 原子阶梯型三能级系统的电磁感应透明(EIT) 效应. 铯原子基态6S_1/2, 第一激发态6P_3/2 和Rydberg 态形成阶梯型三能级系统, 探测光作用于6S_1/2 (F = 4)→6P_3/2(F' = 5) 的跃迁, 耦合光在Rydberg 跃迁线6P_3/2→49S_1/2 附近扫描, 形成Rydberg 原子EIT. 当对探测光频率施加一个几kHz 的调制时, 调制解调后的EIT 信号分裂为两个峰, 双峰间距与调制频率无关,而与调制幅度导致的失谐量大小(频率调制幅度) 成正比, 双峰间隔的一半等于探测光频率调制幅度的λ_p/λ_c = 1.67 倍. 实验结果与理论计算相一致. 本文的研究结果可应用于激光线型和频率抖动的实时监测.     

超冷铯Rydberg原子的Autler-Townes分裂

主要研究超冷铯Rydberg原子阶梯型三能级系统的Autler-Townes(A-T)分裂.铯原子基态6S_(1/2)、第一激发态6P_(3/2)和Rydberg态形成阶梯型三能级系统,强耦合光共振作用于6P_(3/2)(F′=5)→34D_(5/2)的跃迁,探测光由偏振光谱锁定在6S_(1/2)(F=4)→6P_(3/2)(F′=5)的跃迁,并由双通的声光调制器在其共振跃迁附近扫描,形成的Rydberg原子A-T分裂谱由单光子计数器探测.A-T光谱的双峰间距与耦合光的拉比频率成正比,实验结果与理论计算在耦合光拉比频率Ω_c2π×9 MHz时符合得很好,在拉比频率Ω_c2π×9 MHz时,测量的A-T分裂比理论计算值小13%.产生偏差的主要原因是由于较大的耦合光拉比频率Ω_c增加了激发的Rydberg原子数,Rydberg原子间的相互作用产生了较大的退相干率所致.     

Double-resonance spectroscopy of interacting Rydberg-atom systems

The energy level spectrum of a many-body system containing two shared, collective Rydberg excitations is measured using cold atoms in an optical dipole trap. Two pairs of independently tunable laser pulses are employed to spectroscopically probe the spectrum in a double-resonance excitation scheme. Depending on the magnitude of an applied electric field, the Rydberg-atom interactions can vary from resonant dipole-dipole to attractive or repulsive van der Waals, leading to characteristic signatures in the measured spectra. Our results agree with theoretical estimates of the magnitude and sign of the interactions.     

基于里德堡原子的电场测量

里德堡原子具有大的极化率、低的场电离阈值和大的电偶极矩,对外部电磁场十分敏感,可以用来测量电场强度特别是微波电场的强度. 利用里德堡原子的量子干涉效应(电磁诱导透明和Autler-Townes效应)测量微波电场强度的灵敏度远高于传统采用偶极天线测量微波电场的灵敏度. 此外,里德堡原子电场计 可以溯源到标准物理量,不需要额外校准; 采用玻璃探头,对待测电场干扰少; 灵敏度也不依赖于探头的物理尺寸. 同时,该电场计还可以实现对微波电场的偏振方向的测量, 实现亚波长和近场区域电场成像与测量. 通过选择不同的里德堡能级,可以实现1-500 GHz超宽频段范围内微波电场强度的测量. 主要综述基于里德堡原子的电场精密测量研究, 详细介绍了里德堡原子电场计的原理与实验进展, 并简单讨论了其发展方向.     

49S里德堡态的射频双光子光谱

在室温铯原子蒸气池中, 由铯原子基态、激发态和里德堡态构建了阶梯型三能级系统, 研究了里德堡原子阶梯型三能级系统的电磁感应透明(EIT). 在实现电磁感应透明的基础上, 利用16.9 GHz的射频电场耦合相邻的原子里德堡态, 实现49S_1/2→47D_3/2的双光子跃迁, 测量了里德堡原子的射频双光子光谱, 观察到了电磁感应透明光谱的分裂, 进一步研究了电场强度对射频双光子光谱的影响. 利用里德堡原子的EIT效应可实现对射频电场幅值和极化的精密测量, 具有潜在的应用前景.     

Probing electronic coherence in a gas of dipole-dipole coupled Rydberg atoms

We demonstrate a novel time-domain method to probe electronic coherence in ensembles of cold Rydberg atoms coupled via nearly resonant dipole-dipole interactions. Short laser pulses create coherent superpositions of few-electron eigenstates which evolve under the influence of pulsed electric fields. The pulses steer the dynamics, enhancing the probability for finding atoms in np, rather than initially excited ns states. The enhancement reflects the underlying electronic coherence which persists for >10 μs, 2?orders of magnitude longer than previously measured dephasing times in the same system. Simulations suggest that atom motion is responsible for the eventual decoherence.