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.     

Transition from antibunching to bunching in cavity QED

The photon statistics of the light emitted from an atomic ensemble into a single field mode of an optical cavity is investigated as a function of the number of atoms. The light is produced in a Raman transition driven by a pump laser and the cavity vacuum, and a recycling laser is employed to repeat this process continuously. For weak driving, a smooth transition from antibunching to bunching is found for about one intracavity atom. Remarkably, the bunching peak develops within the antibunching dip. The observed behavior is well explained by a model describing an ensemble of independent emitters.     

Theory of an entanglement laser

We consider the creation of polarization entangled light from parametric down-conversion driven by an intense pulsed pump field inside a cavity. The multiphoton states produced are close approximations to singlet states of two very large spins. A criterion is derived to quantify the entanglement of such states. We study the dynamics of the system in the presence of losses and other imperfections, concluding that the creation of strongly entangled states with photon numbers up to a million seems achievable.     

Effects of magnetic field on photon-induced quantum transport in a single dot-cavity system

In this study,we show how a static magnetic field can control photon-induced electron transport through a quantum dot system coupled to a photon cavity.The quantum dot system is connected to two electron reservoirs and exposed to an external perpendicular static magnetic field.The propagation of electrons through the system is thus influenced by the static magnetic and the dynamic photon fields.It is observed that the photon cavity forms photon replica states controlling electron transport in the system.If the photon field has more energy than the cyclotron energy,then the photon field is dominant in the electron transport.Consequently,the electron transport is enhanced due to activation of photon replica states.By contrast,the electron transport is suppressed in the system when the photon energy is smaller than the cyclotron energy.     

Freezing coherent field growth in a cavity by the quantum zeno effect

We have frozen the coherent evolution of a field in a cavity by repeated measurements of its photon number. We use circular Rydberg atoms dispersively coupled to the cavity mode for an absorption-free photon counting. These measurements inhibit the growth of a field injected in the cavity by a classical source. This manifestation of the quantum Zeno effect illustrates the backaction of the photon number determination onto the field phase. The residual growth of the field can be seen as a random walk of its amplitude in the two-dimensional phase space. This experiment sheds light onto the measurement process and opens perspectives for active quantum feedback.     

Squeezing up to fourth-order in the pump mode of eight-wave mixing process

Squeezing of the electromagnetic field is investigated in the pump mode during an eight-wave mixing process under short time approximation on the basis of quantum mechanical approach. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operator are established. Occurrence of squeezing in the first, second, third and fourth-order field amplitude in the pump mode has been investigated. It depends upon the coupling constant ‘g’ and the phase values of the field amplitude. The process involves absorption of three pump photons of the same frequency, one pump photon of a different frequency and emission of four probe photons of the same frequency. The dependence of squeezing on photon number is established with investigations into the degree of squeezing in the first and higher order. The photon statistics of the pump mode in the process has also been investigated and found to be sub-Poissonian in nature.     

Achieving Strong Magnon Blockade through Magnon Squeezing in a Cavity Magnetomechanical System

A scheme that harnesses magnon squeezing under weak pump driving within a cavity magnomechanical system to achieve a robust magnon (photon) blockade is proposed. Through meticulous analytical calculations of optimal parametric gain and detuning values, the objective is to enhance the second-order correlation function. The findings demonstrate a substantial magnon blockade effect under ideal conditions, accompanied by a simultaneous photon blockade effect. Impressively, both numerical and analytical results are found to be in complete accord, providing robust validation for the consistency of the findings. It is anticipated that the proposed scheme will serve as a pioneering approach toward the practical realization of magnon (photon) blockade in experimental cavity magnomechanical systems.     

脉冲抽运光啁啾对全光纤量子关联光子对纯度的影响

信号与闲置光子波长均为1550 nm 通信波段的全光纤关联光子对源, 具有低成本以及可与现有光纤网络低损耗连接的特点. 进一步优化其纯度, 将有助于提高这种量子光源的实用化程度.当抽运脉冲光在光纤中传输时, 由于色散和Kerr非线性效应的影响, 会不可避免地引入啁啾. 本文利用脉冲激光抽运零色散位移光纤, 研究了抽运光啁啾对关联光子对纯度的影响. 结果表明, 通信波段小失谐关联光子对的纯度随啁啾的增大而下降. 若采用变换极限的锁模激光为抽运源, 将有助于抑制Raman散射对自发四波混频的影响, 提高光子对的纯度. 关键词： 关联光子对 光纤 自发四波混频 啁啾     

Optomechanical Entanglement Between an Ion and an Optical Cavity Field

I study an optomechanical system in which the mechanical motion of a single trapped ion is coupled to a cavity field for the realization of a strongly quantum correlated two-mode system. I show that for large pump intensities the steady state photon number exhibits bistable behaviour. I further analyze the occurrence of normal mode splitting (NMS) due to mixing of the fluctuations of the cavity field and the fluctuations of the ion motion which indicates a coherent energy exchange. I also find that in the parameter regime where NMS exists, the steady state of the system shows continuous variable entanglement. Such a two-mode optomechanical system can be used for the realization of continuous variable quantum information interfaces and networks.     

Temporal dynamics of high repetition rate pulsed single longitudinal mode dye laser

Theoretical and experimental studies of temporal dynamics of grazing incidence grating (GIG) cavity, single-mode dye laser pumped by high repetition rate copper vapour laser (CVL) are presented. Spectral chirp of the dye laser as they evolve in the cavity due to transient phase dynamics of the amplifier gain medium is studied. Effect of grating efficiency, focal spot size, pump power and other cavity parameters on the temporal behaviour of narrow band dye laser such as build-up time, pulse shape and pulse width is studied using the four level dye laser rate equation and photon evolution equation. These results are compared with experimental observations of GIG single-mode dye laser cavity. The effect of pulse stretching of CVL pump pulse on the temporal dynamics of the dye laser is studied.     

Λ型原子与单模光场的非共振作用制备四光子相干态

根据简并Λ型三能级原子与单模光场的改进型有效哈密顿量 ,通过矩阵形式法推导出原子光场系统的波函数 ,提出利用简并Λ型三能级原子与单模光场的远离共振相互作用制备四光子相干态的有效方案。并且证明按照同样的方法不能制备出四成分以上的相干叠加态 ,即当在腔中注入的第三个原子的速度与第二个原子的速度相等时 ,腔场将保持这种四光子相干叠加态不变     

非简并双光子Jaynes-Cummings模型腔场谱中的量子干涉

研究了两模二项式光场与二能级原子在高Q腔中发生双光子相互作用过程的腔场谱,给出了弱初始场条件下腔场谱的数值计算结果,讨论了两模腔场谱间的量子干涉.结果表明:两模腔场谱间的量子干涉随着频差的增大而呈现出周期性的衰减振荡,其振荡周期约为0·16g(g为原子与光场的相互作用强度系数),频差大于1·6g时干涉效应已经很弱.量子干涉还与初始场强度有关,随着初始场最大光子数的增加,量子干涉效应逐渐增强,但当光子数大于4时,干涉效应迅速减弱,当最大光子数大于6时,量子干涉现象几乎消失.     

对双模反关联光场非经典特性的远程控制

考虑初始处于纠缠态的两个V型三能级原子之一注入腔场中,并且与初始处于SU(2)相干态的双模场发生共振相互作用的情况。采用数值计算方法研究了双模关联场的非经典特性。讨论了对腔外原子选择性测量、双模总光子数和配分参量对双模关联场的差压缩、柯西-施瓦茨(Cauchy-Schwarz)不等式、模间相干性以及光子亚泊松(sub-Poisson)分布的影响。研究结果表明:对腔外原子的选择性测量或增加两模的总光子数,a模的差压缩和光子sub-Poisson分布都明显地增强,但两模之间的反相关明显地减弱。     

Evolution of Atomic Entanglement for Different Cavity-Field Statistics in Single-Mode Two-Photon Process

We study the evolution of entanglement for a pair of two-level Rydberg atoms passing one after another into an ideal cavity filled with a single mode radiation field. The atoms interact with the cavity field via two-photon transitions. The initial joint state of two atoms that enter the cavity one after the other is unentangled. Interactions intervened by the single mode cavity photon field brings out the final two-atom mixed entangled type state. We use the well known measure appropriate for the mixed states, i.e. the entanglement of formation to quantify the entanglement. We calculate the entanglement of formation of the joint two-atom state as a function of the Rabi angle, for the Fock state field, coherent field and thermal field respectively inside the cavity. The change in the magnitude of atomic entanglement with cavity photon number has been discussed.     

双模腔场与一个V型三能级原子共振相互作用的量子统计性质

采用全量子理论和数值计算方法,研究了初始处于相干态的双模腔场与一个V型三能级原子共振相互作用的量子统计性质,讨论了在没有对原子进行态选择性测量、直接对原子进行态选择性测量和应用经典微波场并对原子进行态选择性测量的三种情况下,腔模平均光子数、耦合系数及相互作用时间对亚泊松统计、模间相干性、光子聚束反聚束效应和违背Cauchy-Schwarz不等式的影响。结果表明:对原子进行态选择性测量后,亚泊松统计特性明显地增强、模间反相关性明显地减弱、Cauchy-Schwarz不等式总是被违背;两个腔模平均光子数差比较大时,对原子进行态选择性测量后,a模腔场总是呈现反聚束效应。     

Optical control of spin-dependent thermal transport in a quantum ring

We report on calculation of spin-dependent thermal transport through a quantum ring with the Rashba spin-orbit interaction. The quantum ring is connected to two electron reservoirs with different temperatures. Tuning the Rashba coupling constant, degenerate energy states are formed leading to a suppression of the heat and thermoelectric currents. In addition, the quantum ring is coupled to a photon cavity with a single photon mode and linearly polarized photon field. In a resonance regime, when the photon energy is approximately equal to the energy spacing between two lowest degenerate states of the ring, the polarized photon field can significantly control the heat and thermoelectric currents in the system. The roles of the number of photon initially in the cavity, and electron–photon coupling strength on spin-dependent heat and thermoelectric currents are presented.     

Quantum frequency up-conversion with a cavity

The quantum state transfer from subharmonic frequency to harmonic frequency based on asymmetrically pumped second harmonic generation in a cavity is investigated theoretically.The performance of noise-free frequency up-conversion is evaluated by the signal transfer coefficient and the conversion efficiency,in which both the quadrature fluctuation and the average photon number are taken into consideration.It is shown that the quantum property can be preserved during frequency up-conversion via operating the cavity far below the threshold.The dependences of the transfer coefficient and the conversion efficiency on pump parameter,analysing frequency,and cavity extra loss are also discussed.     

原子—场耦合系统中非局域性和纯度

本文讨论了光场初态和热库对原子——场耦合系统中量子非局域性和线性熵的影响。我们发现如果腔场无损耗且处于真空库，原子——场态会周期性的展现量子非局域性，原子和场的线性熵也会周期性地振荡，其周期和量子非局域性变化的周期相同。如果腔场损耗很弱而且热库的平均光子数很小，量子非局域性会消失，原子和场振荡的振幅逐渐减小。量子非局域性消失的速度取决于初始压缩相干态的幅度、腔的衰减系数和热库的平均光子数N。场越强、平均光子数和衰减系数越大，非局域性减弱的越快。     

An ultra-bright two-photon source with a type-I bulk periodically poled potassium titanyl phosphate

We experimentally demonstrate an ultra-bright two-photon source with a type-I bulk periodically poled potassium titanyl phosphate. With the 390 nm cw laser from our home-made frequency doubler in a ring cavity as the pump, we detect about 340 k/s coincidence counts with a pump power of 0.11 mW in a Hanbury–Brown–Twiss-type experiment, which corresponds to the production rate of 94 MHz/mW with 40 nm bandwidth. With a 3 nm interference filter, we detect about 11.5 k/s coincidence counts with the same pump power, corresponding to the production rate of 4.3 MHz/mW/nm. This is very promising for many applications in quantum information field, such as transferring the information between a photon and an atomic system and so on.     

压缩现象与光子统计分布

本文研究压缩现象与光子统计分布之间的关系。通过逐次注入处于激发态的原子,无损光学腔内的光子数概率分布会有有趣的变化,腔场有可能取得较深的压缩。 关键词：