Generation of Competitive and Coexisting Two Pairs of Biphotons in Single Hot Atomic Vapor Cell

The non-classical states of light serve as a potential candidate for emerging quantum information process. A processing trend to enhance its scalability is to integrate multiple nonlinear processes with the dressed-state picture into a single device, and therefore, are useful for quantum computations. Here, a novel method is proposed to experimentally achieve the generation of coexisting two pairs of narrow-band biphotons by two four-wave mixing processes in a single hot rubidium vapor cell. Based on the photon-atom nonlinear interfaces, the generated biphotons exhibits genuine entanglement in time–energy. Meanwhile, the nonlinear susceptibility with the dressed-state picture decides the temporal correlation of the biphotons wave packet as a damped periodic Rabi oscillation, suggesting the property of the high-dimensional time–energy entangled state. Such a high-dimensional entangled state also is an efficient way to enhance information carrying capacity. By alternating two nonlinear susceptibilities in a single device, respectively, there exists a competition of the generation rate between such two pairs of biphotons. Moreover, both generated two pairs of biphotons that violate the Cauchy–Schwarz inequality and show their non-classical behavior.     

The influence of the icosahedral percolation transition in supercooled liquid iron on the diffusion mobility of atoms

An experiment on preparation of entangled photon pairs (biphotons) in an arbitrary polarization state is described. The biphotons are qutrits (three-state quantum systems). They can be used in ternary quantum cryptography protocols. A theoretically derived orthogonality criterion for the prepared biphotons is validated experimentally. The criterion can be used to identify orthogonal biphoton states.     

脉冲光场作用下啁啾双光子量子特性研究

基于量子理论和非线性光学,研究了脉冲光场作用啁啾准相位匹配非线性晶体的第Ⅱ类自发参变下转换过程中,脉冲宽度和啁啾系数对产生的纠缠双光子特性及Hong-Ou-Mandel(HOM)量子干涉结果的影响。结果表明,啁啾系数一定时,随着脉冲宽度的增加,双光子谱的不可区分性降低,HOM量子干涉可见度下降。当脉冲宽度一定时,随着啁啾系数的增加使双光子谱带宽增加,HOM量子干涉陷落变窄,双光子谱的不可区分性增强,从而提高了相干精度和干涉可见度。理论上得到了超宽带的双光子谱和对应超窄的HOM量子干涉图。     

Ultrabroadband biphotons generated via chirped quasi-phase-matched optical parametric down-conversion

We generate ultrabroadband biphotons via the process of spontaneous parametric down-conversion (SPDC) in quasi-phase-matched nonlinear gratings that have a linearly chirped wave vector. By using these ultrabroadband biphotons (300-nm bandwidth), we measure the narrowest Hong-Ou-Mandel dip to date, having a full width at half maximum of 7.1 fs. This enables the generation of a high flux of nonoverlapping biphotons with ultrabroad bandwidth, thereby promoting the use of SPDC light in many nonclassical applications.     

Low-pump sum frequency generation of frequency-stabilized 453 nm blue laser for photonic quantum interface

Generation of a cavity-enhanced nondegenerate narrow-band photon pair source is a potential way to realize a perfect photonic quantum interface for a hybrid quantum network. However, to ensure the high quality of the photon source, the pump laser for the narrow-band photon source should be generated in a special way. Here, we experimentally generate the blue 453 nm laser with a sum frequency generation process in a periodically poled lithium niobate waveguide. A 13 mW laser at 453 nm can be achieved with a low-power 880 nm laser and 935 nm laser input, and the internal conversion efficiency is 21.6% after calculation. The frequency of a 453 nm laser is stabilized by locking two pump lasers on one ultrastable optical cavity. The single pass process without employing cavity enhancement can ensure a good robustness of the whole system.     

High-power single-mode emission from a broad-area semiconductor laser with a pseudoexternal cavity and a Fabry Perot etalon

A simple pseudoexternal cavity with a commerically available broad-area laser diode, standard optics, and a thin FabryPerot etalon provides single-mode emission with 1-W optical power and a tuning range of ~0.5nm . The linewidth is estimated at 200MHz. Such high-power semiconductor laser systems are promising light sources for atomic physics, in which narrow-band high-power light is necessary, for example, for optical pumping of alkali metal vapor. Methods for expanding the tuning range and achieving higher narrow-band optical power are discussed.     

Interferometric optical path measurement of a glass wedge with single photons and biphotons

We have measured the phase structure of a glass wedge with single photons and biphotons in a Mach-Zehnder interferometer using parametric downconverted light from a Hong-Ou-Mandel particle interferometer as the source. By scanning the wedge through the focus of a microscope objective we find a doubling of the period of the interference pattern in the coincidence counts for biphotons compared to the single-photon experiment. We compare our measurement setup with classical ones and discuss some of the problems of superresolution in quantum lithography.     

Generation of arbitrary frequency-entangled states of two-photon light

We consider a new method for the generation of polarization-frequency entangled states of photon pairs. We use a frequency-nondegenerate regime of spontaneous parametric down conversion where the photon pairs (biphotons) are produced with identical polarizations, propagate mostly in the same direction, but differ in frequency. Entanglement is achieved by a coherent superposition of pairs emitted from two nonlinear crystals, with the polarization of the biphotons from the first crystal being changed by a transformer placed between the two crystals. We show that this scheme allows the degree of entanglement to be controlled by the choice of biphoton frequencies.     

Transverse compression of two-photon wave packets

A method for generating two-photon wave packets (biphotons) with a small width of the spatial intensity correlation function (correlation radius) has been considered. We propose to prepare a two-photon wave packet inhomogeneously broadened in the angle by means of spontaneous parametric down-conversion in an inhomogeneous crystal. Such biphotons are not diffraction limited; i.e., their correlation radius is much larger than the inverse width of the spatial spectrum. However, the correlation radius of such a biphoton decreases as the biphoton propagates in free space, and transverse compression occurs at a certain distance from the crystal; i.e., the biphoton becomes diffraction limited.     

阵列信号源中的窄带噪声实时生成与时延控制技术研究

针对鱼雷声自导测试信号源中的目标辐射信号模拟问题,集中探讨窄带噪声的生成及其通道间时延控制算法。首先研究窄带噪声实时生成算法,基于线性同余法生成均匀噪声,以其作为查询噪声池的地址,产生宽带噪声,并通过带通滤波得到窄带噪声。为保证模拟目标的方位角精度,精确控制各个通道的时延量,提出适用于宽带信号的延时滤波算法,基于多采样率信号处理技术,通过对噪声信号进行插值、延迟、选抽、滤波等操作,提高时延控制精度。结合算法原理分析,得到延时滤波的简化算法。数字仿真表明,提出算法适用于窄带信号实时生成,时延控制精度高。     

一种基于矩形腔的MIM波导滤波器的滤波特性研究（英文）

理论提出并研究了一种基于矩形腔的窄带金属-介质-金属波导滤波器.建立滤波器内电场的传递矩阵模型,研究了矩形微腔与直通波导间耦合特性对器件滤波特性的影响.同时,研究了耦合长度、矩形微腔腔长、传输损耗等因素对滤波带宽的影响.研究结果表明,对于不同的矩形微腔腔长,存在一个可使器件滤波带宽达到最窄的耦合系数.此外,当微腔腔长越长且传输损耗越小时,滤波带宽也将越窄.该研究为表面等离子体波导的研究与设计提供了一定的参考.     

Observation of time correlation function of multimode two-photon pairs on a rubidium D2 line

We report on the generation of a type-I multimode two-photon state on a rubidium D(2) line (780 nm) using periodically poled KTiOPO(4) crystals. With a degenerate optical parametric oscillator far below threshold, we observe an oscillatory correlation function; the cross correlation between two photons shows a cavity bandwidth of about 7.8 MHz. We also use a Fabry-Perot etalon to filter its most longitudinal modes and observe its time correlation function. The experimental data are well fitted to theoretical curves. This system could be utilized for demonstrating storage and retrieval of narrow-band photons in Rb atomic ensembles, which is important for long-distance quantum communication.     

A 657-nm narrow bandwidth interference filter-stabilized diode laser

We present a 657-nm external cavity diode laser (ECDL) system,where the output frequency is stabilized by a narrow-band high transmission interference filter.This novel diode laser system emits laser with an instantaneous linewidth of 7 kHz and a broadened linewidth of 432 kHz.     

High-resolution spectroscopy at steady-state lasing with multiphoton backscattering

A steady-state self-consistent lasing regime in a laser cavity is investigated with allowance for the back action of the output radiation at four-wave low-frequency scattering in the external sample. The scattering is by the photoelastic potential in the field of the additional opposing laser. General expressions for steady-state amplitudes of field oscillation in the cavity are obtained and employed for investigation of lasing features. Experiments were carried out with narrow-band (line width 1 MHz) continuously tunable diode lasers. The four-wave scattering occurred in solid and liquid dielectrics. It is shown that the fourwave scattering of the pumping laser radiation into the cavity of the signal laser substantially changes its lasing spectrum and can be used to measure dispersion of acousto-optic parameters.     

Experimental demonstration of a simple method to engineer a single qutrit state with biphotons

A simple method to engineer qutrit state with biphotons is realized. The method is based on Hong–Ou–Mandel interferometer and it is insensitive to disturbance comparing to Mach–Zehnder interferometer in principle. Moreover, a tomography procedure is employed to reconstruct the output states.     

The spectral narrowing of a high-power flashlamp-pumped dye laser by injection of external narrow-band radiation

A method of increasing the injection-locking efficiency by external narrow-band radiation relying on a space-frequency separation in a nonlinear absorber (spectral contraster) placed into the high-power dye-laser cavity is proposed. It is shown that this method permits an increase of the energy conversion efficiency into a narrow-band line ( 10^–3 nm) up to 90% with a laser output energy of about 1 J and a pulse duration of more than 1 µs.     

Biphoton light generation in polarization-frequency bell states

Four polarization-frequency Bell states are obtained experimentally for photon pairs (biphotons) emitted during spontaneous parametric scattering from continuous pumping in the collinear frequency-nondegenerate regime. The polarization properties of such states are investigated. It is shown that biphoton light in the singlet Bell state is not polarized in the second or fourth order in the field.     

The logical gates from biphotons

A set of deterministic gates based on the quantum measurement is considered. These gates exploit bipartite entanglement, allow performing any operations on the given qubit states and can be implemented from biphotons. The text was submitted by the authors in English.     

Narrow-band spectral features of structured silver surface with rectangular resonant cavities

This paper is aimed to investigate spectral properties of structured silver surface with periodic rectangular hollow cavities. Numerical computation is conducted to obtain spectral distribution of surface absorptance with different structural parameters using the finite-difference time-domain (FDTD) method. By means of numerical examples, the effects of structural parameters, incident angle and azimuthal angle on the spectral features of the structured surface are discussed. It is found that the structured surface shows the characteristics of the peak absorption in the vicinity of resonant wavelength of rectangular cavity. For some special structure parameters, the peak absorptance of the incident plane wave can reach as high as above 80% due to the excitation of microcavity effect. The optimal narrow-band absorption can be achieved by the rational design of the structural parameters of rectangular cavity. The directional dependence of spectral absorptance is also analyzed and the results reveal that the absorption peak positions are incident-angle-independent. The results show that the microscaled rectangular cavities fabricated on the low-emissivity silver surface are very efficient for selective improvement of the radiative features, which provides guidance for the design of narrow-band infrared thermal emitters.     

Quantum interference and diffraction of parametric down-converted biphotons

We present two-photon diffraction and interference experiments utilizing parametric down-converted photon pairs (biphotons) and a transmission grating. The biphoton exhibits a diffraction-interference pattern equivalent to an effective single particle with half wavelength of the constituent photons.