The mechanism of producing energy-polarization entangled photon pairs in the cavity-quantum electrodynamics scheme

We investigate theoretically two photon entanglement processes in a photonic-crystal cavity embedding a quantum dot in tile strong-coupling regime. The model proposed by Johne et al. （Johne R, Gippius N A, Pavlovic G, Solnyshkov D D, Shelykh I A and Malpuech G 2008 Phys. Rev. Lett. 100 240404）, and by Robert et al. （Robert J, Gippius N A and Malpuech G 2009 Phys. Rev. B 79 155317） is modified by considering irreversible dissipation and incoherent continuous pumping for the quantum dot, which is necessary to connect the realistic experiment. The dynamics of tile system is analysed by employing the Born Markov master equation, through which the spectra for the system are computed as a fnnction of various parameters. By means of this analysis the photon-reabsorption process in the strong- coupling regime is first observed and analysed from the perspective of radiation spectrum and the optimal parameters for observing energy-entangled photon pairs are identified.

Entangled Photon Pairs and Young’s Experiment

Bohm’s variation of the Einstein-Podolsky-Rosen thought experiment may be used to reveal the path a photon travels in Young’s experiment without destroying the observed interference pattern. Photons emitted by a light-source with zero spin are incident on a screen with two narrow slits separated by a small distance, with antiparallel polarized photonic spin filters placed in front of both slits. It follows that the slit through which an incident photon passed to form an interference pattern can be determined by performing an intermediate delayed choice measurement. This experimental probe is ideal for penetrating the shroud of mystery surrounding the wave-particle duality exhibited by quantum phenomena.

Polarization-entangled photon pairs with factorable spectra engineered by using an uneven four-stage nonlinear interferometer

We report the generation of polarization-entangled photon pairs in the 1550 nm band by pumping an uneven nonlinear interferometer loop with two orthogonally polarized counterpropagating pump pulses.The uneven nonlinear interferometer,providing a more ideal interference pattern due to the elimination of secondary maxima,consists of four pieces of dispersion-shifted fibers sandwiched with three pieces of standard single-mode fibers,and the lengths of the nonlinear fibers follow the binomial distribution.The mode number of the photon pairs deduced from the measured joint spectrum is∼1.03.The collection efficiency of the photon pairs is found to be∼94%(after background noise correction).The directly measured visibility of two-photon interference of the polarization-entangled photon pairs is∼92%,while no interference is observed in the direct detection of either the signal or idler photons.

Generation of broadband polarization-orthogonal photon pairs via the dispersion-engineered thin-film lithium niobate waveguide

Broadband photon pairs are highly desirable for quantum metrology,quantum sensing,and quantum communication.Such sources are usually designed through type-0 phase-matching spontaneous parametric down-conversion(SPDC)that makes the photon pairs hard to separate in the frequency-degenerate case and thus limits their applications.In this paper,we design a broadband frequency-degenerate telecom-band photon pair source via the type-II SPDC in a dispersion-engineered thin-film lithium niobate waveguide,where the polarization modes of photon pairs are orthogonal and thus are easily separated deterministically.With a 5-mm-long waveguide,our design can achieve a bandwidth of 5.56 THz(44.8 nm),which is 8.6 times larger than that of the bulk lithium niobate,and the central wavelength can be flexibly adjusted.Our design is a promising approach towards high-quality integrated photon sources and may have wide applications in photonic quantum technologies.

Photon pair generation in lithium niobate waveguide periodically poled by femtosecond laser

Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency,benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches~8000 counts per second for average pump power of 3.2 m W[peak power is 2.9 k W).Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures,which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.

Bose-Einstein Condensation of Photons and Photon Pairs

We investigate the Bose-Einstein condensation of photons and photon pairs in a two-dimension optical microcavity. We find that in the paraxial approximation, the mixed gas of photons and photon pairs is formally equivalent to a two dimension system of massive bosons with non-vanishing chemical potential, which implies the existence of two possible condensate phase. We also discuss the quantum phase transition of the system and obtain the critical point analytically. Moreover, we find that the quantum phase transition of the system can be interpreted as second harmonic generation.

Narrowband photon pair generation and waveform reshaping

In this article, we review on narrowband photon pairs produced in nonlinear crystals, and especially in atomic ensembles. In atomic ensembles, ＂write-read＂ process in pulse mode and spontaneous four-wave mixing process （SFWM） in continuous mode are two popular photon pair generation schemes. We specifically discuss the experimental works with continuous SFWM scheme in cold atomic ensembles. Photon pairs produced in these systems are characteristic of controllable long coherence time, and therefore are accessible with direct temporal modulation. We elaborate on the recent techniques on modulation and waveform reshaping of narrow-band paired photons.

Phase Transition and Superfluid of Photons and Photon Pairs in a Two-Dimensional Optical Microcavity

We analyze the ground-state properties and the excitation spectrum of Bose-Einstein condensates of photons and PPs in a two-dimensional optical microcavity. First, using the variational method, we discuss the ground-state phase transition of the two-component system. We also investigate the energy gap between the ground state and the first excited state. Moreover, by investigating the excitation spectrum, we also illustrate how the superfluid behavior of photons and PPs can be associated with the phase transition of the system.

Efficient generation of non-classical photon pairs in a hot atomic ensemble

We demonstrate the generation of non-classical photon pairs in a warm S-Rb atomic vapor （＇ell with no buffer gas or polarization preserving coatings via spontaneous four-wave mixing. We obtain the photon pairs with a 1/e correlation time of 40 ns and the violation of Cauchy-Sehwartz inequality by a factor of 23 - 3. This provides a convenient and efficient method to generate photon pair sources based on an atomic ensemble.

Single Photon Scattering in a Pair of Waveguides Coupled by a Whispering-Gallery Resonator Interacting with a Semiconductor Quantum Dot

The single photon scattering properties in a pair of waveguides coupled by a whispering-gallery resonator in- teracting with a semiconductor quantum dot are investigated theoretically. The two waveguides support four possible ports for an incident single photon. The quantum dot is considered a V-type system. The incident direction-dependent single photon scattering properties are studied and equal-output probability from the four ports for a single photon incident is discussed. The influences of backscattering between the two modes of the whispering-gallery resonator for incident direction-dependent single photon scattering properties are also pre- sented.

An Electron Model Consistent with Electron-Positron Pair Production from High Energy Photons

This is a rotating charge loop model of an electron which explains the electron’s de Broglie base frequency to an accuracy of over 6 decimal places. The model also predicts the magnetic moment of the electron to over 6 decimal places and helps explain the transition from a purely electromagnetic photon to a fermion state of matter. The model also explains how charge and spin are conserved in the transition. Finally, this concept might be extended to explain the muon and tau higher energy states of the electron as well.

Numerical studies on pair production in ultra-intense laser interaction with a thin solid-foil

A theoretical and numerical model of photon and electron–positron pair production in strong-field quantum electrodynamics（QED） is described. Two processes are contained in our QED theoretical model, one is photon emission in the interaction of ultra-intense laser with relativistic electron（or positron）, and the other is pair production by a gamma-ray photon interacting with the laser field.This model has been included in a PIC/MCC simulation code named BUMBLEBEE 1 D, which is used to simulate the laser plasma interaction. Using this code, the evolutions of electron–positron pair and gamma-ray photon production in ultra-intense laser interaction with aluminum foil target are simulated and analyzed. The simulation results revealed that more positrons are moved in the opposite direction to the incident direction of the laser under the charge separation field.

量子纠缠光纤陀螺的态演变和偏振互易性分析

量子纠缠光纤陀螺仪利用非经典光量子态的光子纠缠特性,对载体角运动引起的Sagnac相移进行超高灵敏度测量。Fink团队在2019年最早报道了基于共线型正交偏振纠缠光子对的量子纠缠光纤陀螺仪,得到突破散粒噪声极限的实验测量结果,但并未给出光量子态经历光纤陀螺各环节的具体演变过程。因此,针对Fink的光路结构,首次对量子纠缠光纤陀螺仪中量子态及算符的动力学演变以及相位检测灵敏度进行了理论分析,证实该光路结构基本上可达到2002态量子纠缠光纤陀螺仪的海森堡极限,同时研究发现,Fink的光路结构由于感生双折射引起的相位误差寄生在Sagnac相移中,实际上是一种偏振非互易性光路结构,会严重削弱相位检测灵敏度。基于此,设计了一种具有偏振互易性的量子纠缠光纤陀螺仪光路结构,光子源为非共线型自发参量向下转换(SPDC)产生的正交偏振纠缠光子对,线圈中的光量子态为i(1_(CCM-H))1_(CW-H)1_(CW-V))/√2理论研究证明,该结构不存在任何偏振非互易性相位误差。

不同频率的组合振荡场下产生正负电子对

吸收组合低频外场提供的多个不同能量的光子发生跃迁可以在真空中激发正负电子对.本文探究了在组合振荡场作用下,不同的外场频率对正负电子对产生的影响,研究结果表明:与单个振荡场类似,当双振荡场的频率和约为2.3m_(e)c^(2)时,电子对产量达到极值.在双振荡场的频率和固定为2.3m_(e)c^(2)的情况下,对不同组合频率下正负电子对的产量以及能谱分布进行了研究,发现当两场频率差较小时,电子对产量随时间演化会出现显著的“拍”现象.还发现两个振荡场频率差越小,电子对的单能性越好;场频率差越大时,电子对的产量越高、能谱范围越宽.通过对跃迁概率分布图的比较和分析,发现主要原因是频率差较大时能够发生显著跃迁的多光子跃迁形式数量增加,从而促进正负电子对(尤其是高能端电子对)的产生.

从激光测距到量子纠缠光子对测距

激光测距通过测量激光往返目标的单光子飞行时间与时钟之差来计算目标的距离,针对该技术目前已经有比较成熟的研究成果,因而激光测距技术在地面、地卫、地月测距上均有应用。量子纠缠光子对测距通过对一个在卫星与目标之间往返的纠缠光子与另一个纠缠光子之间的符合计数,经过数据拟合获得往返目标的飞行时间差。由于纠缠光子对是同时产生,所获得的测距结果从原理上就比包括激光测距在内的所有测距方法要高。目前,针对量子纠缠光子对测距已进行了十几年的理论研究,但实际应用才刚刚开始。主要对激光测距与量子纠缠光子对测距的原理、系统结构、设备与装置及其关键技术进行综述,同时对激光雷达和量子雷达以及与测距相关的研究进行了综述,分析了它们各自的特点,对比了其中的相似之处与不同之处,为量子纠缠光子对测距及定位导航提供了理论依据,并在此基础上对未来量子测距及定位导航领域的发展进行了展望。

基于周期极化晶体MgO:PPLN的纠缠光子对制备过程的研究

基于二阶非线性效应的自发参量转换技术制备纠缠光子对过程中,以掺5 mol%MgO:PPLN周期极化晶体为研究对象,将光参量变换过程中的动量守恒和能量守恒条件与该晶体的色散方程,以及晶体极化周期随温度变化的热膨胀方程相联系,得到了355 nm、405 nm、532 nm、780 nm和1 064 nm这5个实验室常用波长点在制备纠缠光子对时的周期调谐特性和温度调谐特性。研究过程中发现,出现了晶体极化周期过小和产生两对纠缠光子对问题,总结并归纳了各波长点在一定极化周期和温度下与非线性晶体作用所产生的纠缠光波段范围。当选用其他非线性周期极化晶体进行实验时,改变QPM动量守恒条件中的极化周期项,同时根据具体使用的晶体改变色散方程。该研究方案可直接推广到使用不同非线性晶体产生通信光波段或红外光波段的纠缠光子对研究中,在制备量子光源等领域具有重要研究价值。

粒子物理中量子纠缠的历史起源

本文系统深入地梳理了粒子物理中量子纠缠的历史起源。1957年,玻姆和阿哈诺罗夫指出,1949年吴健雄和萨克诺夫的实验实现了爱因斯坦–波多尔斯基–罗森关联。事实上,这是历史上第一次在实验中明确实现空间分离的量子纠缠。惠勒最早建议这个实验,作为对量子电动力学的检验,但是计算有误,正确的理论计算来自沃德和普赖斯,以及斯奈德、帕斯特纳克和奥恩博斯特尔,也符合杨振宁1949年的选择定则。1964年贝尔不等式发表后,人们考虑,它是否可以通过吴–萨克诺夫实验检验。这推动了该领域的发展,吴健雄小组也做了新的实验。1957年,李政道、厄梅和杨振宁确立了K介子的量子力学形式,并发现中性K介子是一个双态系统。1958年,基于与杨振宁1949年选择定则类似的方法,戈德哈贝尔、李政道和杨振宁最早写下K介子对的纠缠态,其中单个K介子可以带电,也可以电中性。这首次给出光子以外的高能粒子的内部自由度纠缠。1960年,作为没有发表的工作,李政道和杨振宁又讨论了中性K介子对的纠缠态。本文也顺便介绍了几位物理学家,特别是沃德。

增加光子对和减少光子对相干态的统计性质

引入增加光子对相干态|ζ,q;m>_a=a^(+m)|ζ,q>和减少光子对相干态|ζ,q;+-m>_b=b^m|ζ,q>,研究了这些态所描写的光场的统计性质．结果显示当在对相干态的ａ模增加光子时，两模的平均光子数均增加，亚泊松分布性质增强；当在对相干态的ｂ模取走光子时，ｂ模的平均光子数减少，而ａ模的平均光子数却增加；ｂ模的亚泊松分布性质减弱，而ａ模的亚泊松分布性质却增强．我们还计算了场模间的相关度和场模的压缩．

基于N个有序纠缠光子对的量子机密共享方案

提出了一种基于N个有序纠缠光子对量子机密共享方案.用纠缠光子作为信息的载体,密钥管理者Alice将纠缠光子对分成两个序列,其中一个序列直接发送给合作者之一Bob,在确保第一个序列发送安全后,再对第二个序列进行编码,发送给另一个合作者Charlie.Bob和Charlie分别对他们所接收到的光子序列进行Bell基联合测量,从而得到Alice所发布的密钥,完整密钥的获得需要管理者和所有合作者共同实现.本方案采用两体纠缠态,相对三体纠缠态来说,在实验上更容易实现,仅需要线性光学元件和简单的纠缠源.

增加光子对和减少光子对相干态的等阶Y压缩效应

通过数值计算,研究了增加光子对相干态|,ξq;m〉A=a+m|,ξq〉和减少光子对相干态|,ξq;-m〉S=bm|,ξq〉的等阶Y压缩效应.结果表明:对于增加光子对相干态a+m|,ξq〉和减少光子对相干态bm|,ξq〉,光场都存在着等阶K(=2,3,4,5…)次方Y压缩效应,但是增加a模的光子或取走b模的光子,即随着场模上光子增加(减少)数m的增大,二者的等阶K次方Y压缩效应均减弱,且有相似的曲线变化规律.