Implementation of a many-qubit Grover search by cavity QED

We explore the possibility of an N-qubit (N > 3) Grover search in cavity QED,based on a fast operation of an N-qubit controlled phase-flip with atoms in resonance with the cavity mode.We demonstrate both analytically and numerically that our scheme can be achieved efficiently to find a marked state with high fidelity and high success probability.As an example,a ten-qubit Grover search is simulated specifically under the discussion of experimental feasibility and challenge.We argue that our scheme is applicable to the case involving an arbitrary number of qubits.As cavity decay is involved in our quantum trajectory treatment,we can analytically understand the implementation of a Grover search subject to dissipation,which will be very helpful for relevant experiments.     

Entanglement concentration with strong projective measurement in an optomechanical system

In this work, we study an entanglement concentration scheme in a 3-mode optomechanical system. The scheme is based on phonon counting measurements, which can be performed through photon counting of an auxiliary cavity connected to the mechanical resonator. The amount of entanglement between the two cavity output modes is found to increase logarithmically with the number of detected phonons(photons). Such an entanglement concentration scheme is deterministic since, independently of the number of detected phonons(photons), the measurement always leads to an increase in output entanglement. Besides numerical simulations,we provide analytical results and physical insight for the improved entanglement and the concentration efficiency.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source （LUCX） is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm·mrad to 3.66 πmm·mrad.     

Frequency stabilization of a single-frequency all-solid-state laser for Doppler wind lidar

The master laser of an injection-seeded laser for Doppler wind lidar is frequency stabilized to a Fabry- Perot(FP)cavity using Pound-Drever-Hall technique.The FP cavity is specially designed to gain high temperature stability with Zerodur cavity and spacer.A computer based controller is used to sample and process the error signal.After the master laser is locked,the relative frequency drift,is±25 kHz in 1s, and±55 kHz in 1h,which can satisfy the need of Doppler wind lidar.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough.A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform.In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance.With the uniform driving laser and the unbalanced RF gun,the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm.mrad to 3.66 πmm.mrad.     

Scheme for Generating Cluster States with Charge Qubits in a Cavity

Based on superconducting charge qubits （SCCQs） coupled to a single-mode microwave cavity, we propose a scheme for generating charge cluster states. For all SCCQs, the controlled gate voltages are all in their degeneracy points, the quantum information is encoded in two logic states of charge basis. The generation of the multi-qubit cluster state can be achieved step by step on a pair of nearest-neighbor qubits. Considering effective long-rang coupling, we provide an efficient way to one-step generating of a highly entangled cluster state, in which the qubit-qubit coupling is mediated by the cavity mode. Our quantum operations are insensitive to the initial state of the cavity mode by removing the influence of the cavity mode via the periodical evolution of the system. Thus, our operation may be against the decoherence from the cavity.     

Nonlocal Gate of a Quantum Network via Cavity Quantum Electrodynamics

We propose an experimentally feasible scheme to realize the nonlocal gate between two different nodes of a quantum network. With an entanglement-qubit acts as a quantum channel, our scheme is resist to actual environment noise and can get a high fidelity in current cavity quantum electrodynamics （C-QED） system.     

Nonreciprocal Phonon Laser in an Asymmetric Cavity with an Atomic Ensemble

Phonon lasers, as a novel kind of lasers for generating coherent sound oscillation, has attracted extensive attention. Here, we theoretically propose a nonreciprocal phonon laser in a hybrid optomechanical system, which is composed of an asymmetric Fabry–Pérot cavity, an ensemble of N identical two-level atoms, and a mechanical oscillator. The effective driving amplitude related to driving direction leads to an obvious difference in mechanical gain and threshold power, bringing about a nonrecipr...     

Efficient generation of two-dimensional cluster states in a cavity QED

We propose a scheme to achieve a kind of nontrivial multipartite pair-wise controlled phase operation in a cavity QED setup. The operation implemented is of geometrical nature and is not sensitive to the thermal state of the cavity. In particular, we have managed to avoid the conventional dispersive coupling so that high speed gate operation is achieved which is very important in view of decoherence. We show that this multipartite pair-wise controlled phase operation makes the generation of two-dimensional cluster states very efficient.     

Optomechanical force gradient sensing with levitated nanosphere pair

Guided by recent progress in ground state cooling and ultraweak force sensing in the optomechanical systems with optically levitated particles,we propose a novel quantum sensing protocol that can detect the gradient of a force field directly with extremely high sensitivity.The system consists of a pair of nanospheres levitated in the high vacuum environment with optical tweezers and an optical resonator.By positioning the two spheres suitably relative to the cavity,only the collective breathing mode of the sphere pair couples to the cavity field.This optomechanical coupling will transfer the information of force difference acting on the two sensors to cavity photons,which can then be detected directly at the output of the cavity.Given the optimal control of various technical noise sources,the sensitivity could reach 10^-15N m^-1/√HZ with a high spatial resolution of micron scale on a state-of-the-art experimental setup.The potential application of this protocol in searching for short range“new force”is analyzed.Compared with conventional searching protocols with a single levitated sphere,the method proposed here can increase the signal-to-noise ratio by more than one magnitude in a large searching parameter space.     

A simple method for automatic cavity alignment of a solid-state laser

Misalignment of a laser cavity would result in the displacement of beam location on the cavity mirrors. We present a simple method for automatic cavity alignment of a solid-state laser through detecting the location of the laser beam on the rear mirror, with which neither external alignment beams nor modifications to the cavity are required. The rear mirror of the laser cavity is replaced by a tip/tilt mirror to compensate for the misalignment. Experiments show that this method could effectively correct the misalignment of the laser cavity and restore the output power to almost the original value when the resonator is well aligned.     

多程放大腔镜准直研究

 针对高功率激光装置对多程放大器腔镜准直的要求,利用小孔的像传递和光路自动准直的原理,设计出一套创新的腔镜准直调整方法,并且在SG-Ⅲ原型装置4程放大模拟实验平台上进行了实验验证。实验结果表明：自动准直系统能够在15min之内顺利完成主放大级系统的光路调整,光束近场调整精度值小于近场光斑直径的0.5%,光束远场调整精度小于0.3"。     

Unstable resonator alignment based on the fringe analysis

The existing cavity mirrors alignment method aligns cavities according to the symmetry of the near-field interference fringes of the guided lights by the unstable resonator. Its precision is restricted due to the lack of objective criterion for the fringe symmetry. This article proposes a high-precision cavity mirrors alignment method using the grey projection of fringe patterns as a solution to the problem. First, vertical and horizontal grey projection on the concerned fringe patterns; then an evaluation function for the cavity mirrors alignment is established using the distances between peak/valley values of all the levels in the projection curve as variables; finally, the function value is employed to characterize the fringe symmetry and thus to provide an objective criterion for the alignment effect of the stable resonator cavity mirrors. Experiments show that the proposed method is able to give effective evaluation for the symmetry of the near-field interference fringes of the guided lights and improve the alignment precision greatly.     

基于图像边沿特征的强激光腔镜准直处理方法

 激光束光路自动准直系统用于高功率激光装置光束精密准直。基于某激光原型装置总体对腔镜准直调整流程，针对高功率激光系统腔镜准直过程光斑图像，仿真处理并定量分析了光斑边缘特征;结合腔镜准直监测单元光传输分析，使用激光光斑边缘不同部分曲率的相似性和光斑圆形度实现了对腔镜调节的量化评估。在腔镜准直结束时圆形度指标为12.222；边缘相似度达到99.62%。     

Alignment locking to suspended Fabry-Perot cavity

In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.     

国产首台交变相位聚焦漂移管加速器的冷测与试运行

质子直线注入器是质子治癌系统的重要组成部分。出于项目进度的考虑,上海先进质子治癌示范装置APTRON采用了进口自美国的直线注入器。为了加快质子治癌产业进程,掌握质子放疗关键技术,保证产业链安全可控,注入器团队研发了国产医用质子直线注入器。该直线注入器采用了电子回旋共振（ECR）离子源和四翼型射频四极加速器（RFQ）的技术方案,并在漂移管加速器（DTL）段创新性地采用了交变相位聚焦（APF）结构。在这个过程中,通过研究APF DTL的束流运动规律和设计思想,自主开发了APF DTL的底层物理设计软件,相继完成了物理设计、电磁设计、机械设计、加工建造、腔体冷测、高频老练和载束实验等多个阶段的工作,最终成功引出了7 MeV、7 mA的质子束流。经过束诊系统的测量分析,认定束流中心能量为6.975 MeV,动量分散在±0.35%以内的束流流强为6.07 mA。成为国产首台医用质子直线注入器和首个实现成功载束的APF加速腔。     

外腔式He-Ne激光器的调整方法

本文提出了一套外腔式He-Ne激光器的调整方法,研究了腔长变化对纵模的影响,进而发展出一种可以有效提高谱线单色性的技术.     

高斯光束与谐振腔基模模式光路谐振匹配的分析与校准

为了降低高斯光束与谐振腔耦合过程中失调量和失配量对基于无源谐振腔测量技术精度的影响, 采用高斯光束变换规律、模式耦合有关理论以及光束传播坐标变换等相关理论, 就失调量和失配量对基模耦合效率的影响分别进行分析和模拟, 并据此给出了一般情况下两个参考量同时存在时基模耦合效率的表达式. 分析表明: 失配量的存在主要影响激光器与谐振腔的耦合效率, 而对高阶模式的激发影响较小, 因此对谐振腔的衰减线型影响较小; 失调量的存在对谐振腔高阶模式的激发起主要作用, 给测量带来严重误差. 该结论为利用腔出射光信号来确定误调参量值的实验方案提供了依据. 因此, 在考虑光源光谱线宽的情况下, 就光源光谱线宽的特性提出两种装调校准方案: 基于法布里-珀罗干涉仪法和基于多维象限探测器探测谐振腔出射光的调节回路, 这将为分析基于无源谐振腔的相关技术测量误差来源以及实现测量系统的高精度装调提供理论指导.     

高功率高重频U型腔激光器的仿真与实验研究

 为了得到结构紧凑的高功率、高重复频率固体激光器,设计了“U”型光学谐振腔,并利用LAS-CAD软件分析了激光晶体的热效应和激光输出特性。根据仿真结果进行了具体实验,最终得到了腔长400 mm的紧凑型固体激光器。在重复频率为100 kHz,泵浦功率为60 W时,输出功率达到21.6 W,光-光转换效率为36%,斜率效率为39.9%。     

Positioning photonic crystal cavities to single InAs quantum dots

We have investigated the optical properties of planar photonic crystal cavities formed by removing a single hole from a two-dimensional square lattice of air holes etched through a thin GaAs slab. We have demonstrated cavity resonances with quality factors (Q’s) as high as 8500, using an internal light source provided by an ensemble of InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE). The high-Q modes are confined to a very small mode volume, V = 0.7(λ/n)³, making them attractive to study in the context of cavity quantum electrodynamics with single QDs, where a high is needed to observe the strong coupling between an electronic state of the dot and the optical cavity mode. To this end, we have developed an accurate and robust alignment technique that positions a photonic crystal cavity to a single QD with 25 nm resolution. We present the details of this new technology and demonstrate its effectiveness by strategically positioning a number of QDs within photonic crystal cavities at points where the electric field intensity is high.