Photon bunching and anti-bunching with two dipole-coupled atoms in an optical cavity

We investigate the effect of the dipole–dipole interaction(DDI) on the photon statistics with two atoms trapped in an optical cavity driven by a laser field and subjected to cooperative emission. By means of the quantum trajectory analysis and the second-order correlation functions, we show that the photon statistics of the cavity transmission can be flexibly modulated by the DDI while the incoming coherent laser selectively excites the atom–cavity system's nonlinear Jaynes–Cummings ladder of excited states. Finally, we find that the effect of the cooperatively atomic emission can also be revealed by the numerical simulations and can be explained with a simplified picture. The DDI induced nonlinearity gives rise to highly nonclassical photon emission from the cavity that is significant for quantum information processing and quantum communication.     

基于两原子同时和腔场共振作用制备两原子纠缠态的腔QED方案(英文)

我们提出了一个将两个远离的原子制备成纠缠态的腔QED方案,该方案基于两个原子同时和一个腔场发生共振作用.在这个方案里,我们利用一个事先制备好的纠缠态将另外两个分离的原子制备成纠缠态.该方案仅包含两个原子和腔场的共振相互作用,不需要用腔场存储量子信息,并且原子和腔场作用时间极短.因此,我们的方案基于目前的腔QED技术是可以实现的.     

两二能级原子在共同环境下的量子关联动力学

通过精确求解带有偶极-偶极相互作用的两个二能级原子与一个共同热库相互作用模型, 得到了两原子间量子纠缠和量子失谐(quantum discord)的解析表达式. 综合考虑了环境的非马尔可夫效应、原子间的偶极-偶极相互作用以及原子的本征频率同腔模中心频率之间的失谐量对两原子间量子纠缠和quantum discord的影响. 研究显示: 在非马尔可夫机制下, 且原子的本征频率与腔模中心频率是共振时, 当两原子初态处于纠缠态时, 原子间偶极-偶极相互作用可以显著抑制包括量子纠缠和quantum discord等量子关联的衰减, 更特别的是, 如果原子的本征频率同腔模中心频率有一定的失谐时, 利用原子间偶极-偶极相互作用可大大地延长两原子退纠缠的时间; 当两原子初态处于可分离态时, 从短时间来看, 原子间偶极-偶极相互作用可以提高量子纠缠和quantum discord振荡的振幅,而在长时间极限下, 原子间偶极-偶极相互作用不会改变量子纠缠和quantum discord达到的稳定值. 最后, 讨论了原子间偶极-偶极相互作用对量子纠缠和quantum discord动力学不同的影响. 关键词： 量子纠缠 量子失谐 共同环境 偶极-偶极相互作用     

Kerr介质中压缩真空场与耦合双原子依赖强度耦合系统的光子统计性质

研究了存在Kerr介质时依赖强度耦合单模压缩真空场与耦合双原子非共振相互作用系统中光子的统计性质,运用数值方法讨论了系统参数对光子统计性质的影响.结果表明:Kerr介质、失谐量、原子间相互作用、光场初始压缩因子和原子的初始状态对光子的统计性质有较大的影响.     

稀薄里德伯原子气体中的两体纠缠

量子纠缠是量子信息处理和量子计算中不可或缺的物理资源,制备稳定可操控的量子纠缠是研究的热点之一.里德伯原子具有不同于普通中性原子的特点,长寿命和原子之间强烈的偶极相互作用,使得它成为量子信息处理和量子计算的最优候选者.本文在稀薄里德伯原子气体中,构建了空间四面体排布的里德伯原子模型(空间等距的四个原子模型),通过数值求解主方程来研究两体纠缠和里德伯激发的稳态和瞬态动力学性质,发现偶极阻塞机制下的量子纠缠最大,其他满足反偶极阻塞条件的高阶激发引起的纠缠较小,进而从理论上分析了这两种机制下量子纠缠的物理实质.     

Measurement-induced disturbance between two atoms in Tavis-Cummings model with dipole dipole interaction

Quantum correlation, measured by measurement-induced disturbance （MID）, between two two-level atoms is investi- gated in detail in Tavis-Cummings model with dipole--dipole interaction （DDI）. We find that MID can be determined only by the dipole-dipole interaction between the two atoms when the cavity and atoms are at resonance. Moreover, DDI will have different effects on MID for two different kinds of initial states.     

Sum and two—atom dipole squeezing in a system of a two—mode vacuum field interacting with two coupled atoms

We discuss the effects of the initial atomic coherent factors (including the phase and the distribution parameter) and the dipole-dipole interaction on the sum and two-atom dipole squeezing in the system.The results show that the maximum squeezing in both cases is determined by the phase and the distribution parameter,and the duration of squeezing becomes longer by strengthening the dipole-dipole interaction.In addition,the comparison of the two types of squeezing shows that one type of squeezing is obtained at the expense of increased fluctuations in the other squeezing function.     

内禀退相干下Tavis-Cummings模型中原子的纠缠演化与贝尔不等式破坏

通过求解系统的Milburn方程，研究了两个二能级原子和单模场相互作用系统中原子间纠缠和贝尔不等式破坏随时间的演化特性，讨论了偶极相互作用、场与原子的失谐量对纠缠度以及贝尔不等式破坏的影响.结果表明：原子间偶极-偶极相互作用对纠缠度和贝尔不等式破坏有显著影响，失谐量增大会使两原子的纠缠度和贝尔不等式破坏变大，并且两原子所能达到稳定的纠缠受偶极相互作用系数与失谐量两者之差的影响.同时还发现两原子的纠缠与贝尔不等式破坏并不是单调的函数关系，很小的纠缠也可以产生贝尔不等式破坏. 关键词： Milburn理论 偶极-偶极相互作用 失谐量 贝尔不等式破坏     

Quantum nondemolition measurement of photon—number distribution for a weak cavity field with resonant atoms

We propose a quantum nondemolition measurement of the photon-number distribution for a weak cavity field with no more than two photons. The scheme is based on the resonant interaction of atoms with the cavity field, and thus the required interaction time is much shorter than that using dispersive interaction. This is important in view of decoherence. Our scheme can also be used to generate even and odd coherent states for a weak cavity field with resonant atoms.     

二项式光场和负二项式光场与耦合双原子依赖强度耦合系统原子反转的时间演化

研究了二项式光场和负二项式光场与耦合双原子依赖强度耦合相互作用系统原子布居反转的时间演化规律,讨论了原子间相互作用和光场初态对原子反转的时间演化的影响.     

A system with two photon states and two polarization-entangled photon modes as configuration of minimal coupling to a classical pump field

The configuration of minimum interaction energy between two polarization-entangled photon modes and a classical pump field is determined by treating the corresponding interaction Hamiltonian operator. In fact, the above configuration is found to be of two photon states.     

耦合双原子与压缩真空场Raman相互作用系统的量子纠缠

利用全量子理论,研究了耦合双原子与单模压缩真空场Raman相互作用系统的量子纠缠特性,运用数值方法讨论了系统耦合常数和初始状态对纠缠特性的影响.     

Entanglement in a system of two two-level atoms interacting with a single-mode field

We investigate the entanglement in a system of two coupling atoms interacting with a single-mode field by means of quantum information entropy theory. The quantum entanglement between the two atoms and the coherent field is discussed by using the quantum reduced entropy, and the entanglement between the two coupling atoms is also investigated by using the quantum relative entropy. In addition, the influences of the atomic dipole--dipole interaction intensity and the average photon number of the coherent field on the degree of the entanglement is examined. The results show that the evolution of the degree of entanglement between the two atoms and the field is just opposite to that of the degree of entanglement between the two atoms. And the properties of the quantum entanglement in the system rely on the atomic dipole--dipole interaction and the average photon number of the coherent field.     

Kerr介质中耦合双原子与双模压缩真空场相互作用系统的光子统计性质

研究了存在Kerr介质时，双模压缩真空场与耦合二能级原子相互作用系统中光子的统计性质，讨论了Kerr介质与光场的耦合强度、光场的初始压缩因子和原子的初态对光子统计性质的影响.数值计算结果表明，光子周期性地交替呈现聚束和反聚束效应，光场两模之间总是呈现正相关，并且这种相关为非经典相关；Kerr介质的影响使光场的二阶相干度演化曲线呈现周期性的崩塌-回复现象，随着Kerr效应的加强，崩塌-回复周期变短，以至消失. 关键词： Kerr介质 耦合双原子 双模压缩真空场 光子统计性质     

脉冲激发三能级体系半导体量子点的单光子发射效率

研究了脉冲激发下单个半导体量子点中单光子发射的统计特性.在旋转波近似条件下，由系统粒子数演化主方程并结合量子回归理论推导了二阶相关函数的运动方程，利用此方程讨论了二阶相关函数随输入脉冲面积的关系.在窄脉冲宽度的脉冲激发下，单光子的发射概率p和效率η都随着强度的增强而产生振荡.研究表明，采用窄脉冲宽度，当输入脉冲面积在π附近时可以得到较高的单光子发射效率. 关键词： 半导体量子点 单光子发射 三能级系统     

原子在弱相干场光纤耦合腔系统中的纠缠特性

研究由两个相同的二能级原子分别处于用单模光纤耦合的两弱相干光场系统的共生纠缠特性, 通过数值计算研究了光纤模-腔模与原子-腔模的耦合强度比、弱相干光场的强度和两光场相对相位差等因素对系统纠缠演化的影响. 结果表明: 两腔中的两原子之间、两光场之间和每个腔中的原子与光场之间的纠缠随时间呈现周期或准周期性演化, 两腔场之间的纠缠与腔中的两原子的纠缠可以相互转换, 与两原子之间和两光场之间的纠缠相比, 每个腔中光场与原子之间的纠缠随时间变化的周期缩短. 光纤模-腔模与原子-腔模的耦合强度比与两腔中光场相位差对系统纠缠的影响很大, 较小的光纤模-腔模与原子-腔模的耦合强度之比可以获得较大的系统纠缠度. 关键词： 弱相干场 光纤耦合腔 耦合强度 量子纠缠     

纠缠态原子与压缩真空场Raman 相互作用的量子信息保真度

利用全量子理论和数值计算方法研究了两个全同的纠缠二能级原子与压缩真空场Raman相互作用的量子信息保真度.结果表明,系统、原子和场的保真度随初始光场的压缩参数的增加而急剧减小,且与两原子体系的纠缠度和原子间偶极-偶极相互作用强度相关联.     

外场驱动对双原子Tavis-Cummings模型中原子和腔场性质的影响

研究受外部经典场驱动的双原子Tavis-Cummings模型中原子和腔场的特性. 分析了腔场初态为相干态的情况,求出外场驱动下原子系统粒子布居差、光场的平均光子数和Mandel Q参数，并进行了数值分析. 特别讨论了外部驱动场对此模型中原子和腔场性质的影响.     

非等同两个原子与双模腔场相互作用模型中双原子偶极振幅平方压缩

本文研究了具有不同耦合系数的两个二能级原子与双模腔场相互作用系统中原子偶极振幅平方压缩随时间的演化规律.并讨论了两个原子与双模腔场的相对耦合常数(R=g1/g2)和腔场的初态对原子偶极振幅平方压缩的影响.     

Conservation issue of pairwise quantum discord and entanglement of two coupled qubits in a two-mode vacuum cavity

The conservation issues of pairwise quantum discord and entanglement of two qubits coupled to a two-mode vacuum cavity are investigated by considering the dipole-dipole interaction between two qubits.It is found that the sum of the square of the pairwise quantum discords and the sum of the square of the pairwise concurrences are both conserved in the strong dipole-dipole interaction limit.However,in the middle dipole-dipole and weak dipole-dipole interaction limits,the sum of the square of the pairwise concurrences is still conserved while the sum of the square of the pairwise discords is not.The crucial reason for this is that the quantum discords are not equivalent if the measurements are performed on different subsystems in a general situation.So it is very important for quantum computation depending on the quantum discord to select the target performed by the measurements.