Quantum fluctuations of a single trapped atom: transient Rabioscillations and magnetic bistability

Isolation of a single atomic particle and monitoring its resonance fluorescence is a powerful tool for studies of quantum effects in radiation-matter interactions. We present observations of quantum dynamics of an isolated neutral atom stored in a magneto-optical trap. By means of photon correlations in the atom's resonance fluorescence we demonstrate the well-known phenomenon of photon antibunching which corresponds to transient Rabi oscillations in the atom. Through polarization-sensitive photon correlations, we show a novel example of resolved quantum fluctuations: spontaneous magnetic orientation of an atom. These effects can only be observed with a single atom     

A proposed study of photon statistics in fluorescence through high resolution measurements of the transverse deflection of an atomic beam

Information about the photon statistics in fluorescence can be obtained from the study of the variance in the angular deflection of a beam of atoms interacting with a transverse laser beam. The quantity of interest, is a measure of the departure of the photon statistics from a Poisson distribution, where is the mean and is the variance of the number of photons emitted by a “two-level” atom. We demonstrate in this paper that our existing apparatus has sufficient resolution to make a statistically significant measurement of Q.     

劣腔内压缩真空光场驱动的二能级原子的荧光光谱

本文计算了劣腔内－受压缩真空光场驱动的二能级原子的荧光光谱及其二阶关联函数。     

一种新型有机染料HEASPS的激光上转换和光限幅性能

报道了一种新型上转换染料———反式 4 [4’ (N 羟乙基 N 乙基胺基 )苯乙烯基 ] N 甲基吡啶 对甲苯磺酸盐(trans 4 [4’ (N hydroxyethyl N ethylamino)styryl] N methylpyridiniump toluenesulfonate ,简称HEASPS)DMF溶液的激光上转换性质和光限幅性质。用Z 扫描技术测得其双光子吸收截面为σ2 =4.7× 10 -4 8cm4 ·s/photon ,研究了它在DMF溶剂中的线性吸收、单光子荧光、双光子荧光和双光子激射特性 ,用再吸收效应解释了双光子荧光峰相对单光子荧光峰的红移现象 ,该染料的激射和再吸收现象相互竞争导致了双光子激射峰相对于双光子荧光峰的蓝移现象。在 10 6 4nm皮秒脉冲激光的激发下 ,可得强烈的 6 2 6nm上转换激射光 ,上转换效率最高为 15 .5 % ,从抽运光到激射光的净转换效率为 2 6 %。该染料的DMF溶液表现出明显的光限幅特性     

Single-atom cavity-enhanced absorption. I. Photon statistics in thebad-cavity limit

The photon statistics of the transmitted light from a driven cavity containing a single resonant two-level atom are studied in the bad-cavity limit. For weak driving fields, the second-order intensity correlation function shows novel nonclassical behavior due to the interference of the driving field and forward reradiation from the atom. This behavior is related to squeezing in the cavity transmission. A physical interpretation is given in terms of the reduced quantum state of the coupled atom-field system following photodetection     

Schmidt modes and entanglement in continuous-variable quantum systems

The extraction of Schmidt modes for continuous-variable systems is considered. An algorithm based on the singular-value decomposition of a matrix is proposed. It is applied to the entanglement in (i) an atom—photon system with spontaneous emission and (ii) a system of biphotons with spontaneous parametric downconversion (SPDC) of type II. For the atom—photon system, the evolution of entangled states is found to be governed by a parameter approximately equal to the fine-structure constant times the atom-to-electron mass ratio. An analysis is made of the dynamics of atom—photon entanglement on the assumption that the system’s evolution is determined by the superposition of an initial and a final state. It is shown that in the course of emission the entanglement entropy first rises on a timescale of order the excited-state lifetime and then falls, approaching asymptotically a residual level due to the initial energy spread of the atomic packet (momentum spread squared). SPDC of type II is analyzed by means of the polarization density matrix and a newly introduced coherence parameter for two spatially separated modes. The loss of intermodal coherence is addressed that results from the difference in behavior between ordinary-and extraordinary-ray photons in a nonlinear crystal. The degree of intermodal coherence is investigated as a function of the product of crystal length and pump bandwidth.     

级联三能级运动原子与单模场相互作用系统中光子的反聚束效应

研究了一个型三能级运动原子与单模场相互作用系统中光子的反聚束效应，着重讨论了不同初始态下，原子运动速度和模场结构与强度对光子反聚束效应的影响．     

Laser experiments with single atoms as a test of basic physics

Two experiments with single atoms are reviewed. In the first experiment, the interaction of a single Rydberg atom with a single mode of an electromagnetic field was investigated. The quantum collapse and revivals of the atomic inversion predicted by the Jaynes-Cummings model were demonstrated for the first time. In the second experiment, a single atomic ion stored in a radio-frequency trap was probed by resonance fluorescence. In the fluorescent light, antibunching and sub-Poissonian photon statistics were detected. Furthermore, `crystallization' and `evaporation' of few ions in a trap were observed as the stored ions were cooled by the laser light and heated by the radio-frequency field of the trap     

多光子J-C模型的研究

本文推广二能级原子J-C模型到多光子过程。求得在存在偏调情况下,单模相干场对二能级原子激发时的光子数几率分布函数,由此研究了原子受激辐射性质。     

激光场噪声对原子共振荧光压缩性质的影响

研究了由相干场和随机场驱动的二能级原子荧光场的压缩谱.在强场驱动和大失谐条件下,荧光场正规噪音谱的in-phase振幅出现双模压缩,并且通过调节原子的拉比频率可以来控制压缩频率,同时压缩还随着随机强度的增大而减小,压缩谱还与相干场和随机场之间的相对相位有关.     

非相干变频转换实现室温下红外单光子源

纳米金刚石中的NV-center(Nitrogen-Vacancy center)是目前室温下具有高发射率和稳定性的可见光波段单光子源,而如何实现及优化红外单光子源则是未来实现量子信息和量子通信应用的一大挑战.介绍了一种近期提出的实现红外单光子源的新型机制.该方法以金刚石中的NV-center作为可见光波段的单光子源,利用非相干变频转换实现室温下近红外波段稳定、无闪烁的单光子源.具体的实施方案为在中空芯光子晶体光纤中选择性地填充含有量子点的溶液,以可见光波段的单光子源作为激励源,选择合适的量子点即可得到红外波段的单光子源.中空芯光子晶体光纤保证了较高的单光子吸收效率以及荧光收集效率.该方案的实施在理论上可以达到26%的转换效率,而初步的实验得到了0.1%的转换效率.进一步分析了一些影响转换效率的因素,并提出了一些解决方案.     

附加克尔介质依赖强度耦合J-C模型中原子的量子特性

研究了附加克尔介质依赖强度耦合Jaynes-Cummings模型中原子反转特性，并采用密度算符间的距离研究了该模型中原子量子态的演化规律。详细地讨论了克尔非线性作用的强弱以及初始相干光场的强弱对原子反和原子量子态的演化的影响。结果表明：克尔效应的增强使得原子反转演化的周期减小（gtR≈π/√x^2/g^2 1）；在初始相干光场较弱时（－↑n＝10），克尔介质的非线性相互作用破坏了原子态演化的周期性，但在初始相干光场较强时（－↑n＝50），克尔效应使原子态的演化仍近似具有周期性，且与原子反转演化的周期相同（gtR≈π/√x^2/g^2 1）。无论初始相干光场强弱如何，随着克尔效应的增强，原子回到初态的布居几率增大，当x/g=5时，原子几乎持续地处于初始的激发态。     

强场与级联三能级原子相互作用中的光子聚束与反聚束效应

本文采用数值计算方法研究了强相干初态光场与级联型三能级原子相互作用中的光子聚束与反聚束效应.结果表明:辐射光子主要表现为反聚束性质,且随着n值的不断增大,场与原子的非线性耦合越来越强,重复地出现复苏收缩现象。     

多光子反J-C模型下纠缠相干光场量子特性研究

利用多光子反Jaynes-Cummings(J-C)模型,研究了双模纠缠相干光场中一束光与受强经典场驱动的二能级原子相互作用时光场的量子特性,讨论了跃迁光子数、时间、光场初态等参量对未参加相互作用光场的反聚束效应和压缩效应的影响.结果表明:改变跃迁光子数、时间及选取参加相互作用光场的初态等参量,能使未参加相互作用的光场...     

Custom crystals control photons

To build future optical information superhighways, "photonic engineering" should be a common practice just like today's electrical engineering. As Purcell proposed in 1946, the radiation rate of photons from an excited atom can be controlled by modifying the space that surrounds the atom. Should this photon tailoring be positively adapted, dramatic improvement of photonic devices can be expected. For example, zero-threshold lasers, high-efficiency light-emitting diodes, and tight-bending waveguides for optical integrated circuits could be realized in the not-too-distant future. This article discuses the photonic crystal, which is expected to lead us through this new and expanding world of nanophotonics     

在双模相干光场作用下三能级原子的偶极压缩效应

本文研究了一“V”型三能级原于在双模相干光场作用下总偶极算符的演化规律。结果表明,在这种情况下存在偶极压缩效应,它明显受失调量、平均光子数的影响,其偶极演化规律比二能级情况复杂．     

多光子过程中单模热辐射场与原子相互作用的场熵特性

本文研究了处于热平衡状态的理想腔内与原子多光子相互作用的单模热辐射场的熵特性，讨论了平均光子数和跃迁光子数对场熵演化的影响。     

量子微腔双模驻波场中三能级原子的俘获

分析了量子微腔中双模驻波场与三能级原子的相互作用。讨论了三能级原子被真空双模腔场俘获的条件和大光子数条件下能级的重叠及其对原子俘获的影响。     

幅度损耗腔中V型原子与光场拉曼相互作用系统中的熵特性

推导了幅度损耗腔中Ⅴ型三能级原子与光场拉曼相互作用系统的密度算符，并由此研究了系统线性熵、光场线性熵和原子线性熵的特性．结果表明：损耗腔中系统和原子除初始时刻呈现纯态外，其它任何时刻均处于混合态，其混合程度经一段时间后保持不变，混合程度的高低与光场平均光子数有关且随其增加而升高，在td时刻，原子与光场完全退耦合，光场退回到初始纯态，但原子仍呈现混合态，当损耗系数增大时。原子和系统的线性熵趋于同一稳定值的速度加快，光场的平均光子数增大后，损耗系数对线性熵影响更为明显。     

A New Series of Quadrupolar Type Two‐Photon Absorption Chromophores Bearing 11, 12‐Dibutoxydibenzo[a,c]‐phenazine Bridged Amines; Their Applications in Two‐Photon Fluorescence Imaging and Two‐Photon Photodynamic Therapy

A new series of quadrupolar type two‐photon absorption (2PA) chromophores 3 – 9 bearing a core arylamine‐[a,c]phenazine‐arylamine motif are synthesized in high yields. Palladium‐catalyzed Stille coupling and C? N coupling reactions are utilized to prepare target chromophores. Detailed characterization and systematic studies of these molecules, including absorption and fluorescence emission, are conducted. These compounds are found to exhibit very large 2PA cross section values, for example, ～7000 GM at 800 nm for 8 in toluene. Two‐photon‐induced fluorescence imaging is successfully demonstrated in vitro using compound‐ 8 ‐encapsulated silica nanoparticles with excellent bio‐compatibility. In combination with the capability of both one‐ and two‐photon singlet‐oxygen sensitizations, this nanocomposite demonstrates its promising potential in dual functionality toward two‐photon fluorescence imaging and two‐photon photodynamic therapy.