Cavity cooling of a single atom

All conventional methods to laser-cool atoms rely on repeated cycles of optical pumping and spontaneous emission of a photon by the atom. Spontaneous emission in a random direction provides the dissipative mechanism required to remove entropy from the atom. However, alternative cooling methods have been proposed for a single atom strongly coupled to a high-finesse cavity; the role of spontaneous emission is replaced by the escape of a photon from the cavity. Application of such cooling schemes would improve the performance of atom-cavity systems for quantum information processing. Furthermore, as cavity cooling does not rely on spontaneous emission, it can be applied to systems that cannot be laser-cooled by conventional methods; these include molecules (which do not have a closed transition) and collective excitations of Bose condensates, which are destroyed by randomly directed recoil kicks. Here we demonstrate cavity cooling of single rubidium atoms stored in an intracavity dipole trap. The cooling mechanism results in extended storage times and improved localization of atoms. We estimate that the observed cooling rate is at least five times larger than that produced by free-space cooling methods, for comparable excitation of the atom.     

Cavity QED with a Bose-Einstein condensate

Cavity quantum electrodynamics (cavity QED) describes the coherent interaction between matter and an electromagnetic field confined within a resonator structure, and is providing a useful platform for developing concepts in quantum information processing. By using high-quality resonators, a strong coupling regime can be reached experimentally in which atoms coherently exchange a photon with a single light-field mode many times before dissipation sets in. This has led to fundamental studies with both microwave and optical resonators. To meet the challenges posed by quantum state engineering and quantum information processing, recent experiments have focused on laser cooling and trapping of atoms inside an optical cavity. However, the tremendous degree of control over atomic gases achieved with Bose-Einstein condensation has so far not been used for cavity QED. Here we achieve the strong coupling of a Bose-Einstein condensate to the quantized field of an ultrahigh-finesse optical cavity and present a measurement of its eigenenergy spectrum. This is a conceptually new regime of cavity QED, in which all atoms occupy a single mode of a matter-wave field and couple identically to the light field, sharing a single excitation. This opens possibilities ranging from quantum communication to a wealth of new phenomena that can be expected in the many-body physics of quantum gases with cavity-mediated interactions.     

区域供冷系统逐时冷负荷的分析及数值预测

为了正确选择区域供冷系统设计负荷并优化其主机运行策略,对某区域供冷系统的逐时实际冷负荷变化规律及数值预测进行研究。通过对该区域供冷系统冷冻水供回水温度及流量进行实测,得到并分析实际逐时冷负荷;通过增加输入层数据,建立改进人工神经网络负荷预测模型并对预测值及其误差进行分析。研究结果表明:区域供冷系统在各负荷区间运行时间分布较均匀;在实测期间,系统在高负荷区间的运行时间所占比例为17.5%,最低负荷区间的运行时间所占比例为13.5%,其他负荷区间运行时间比例为15%～20%,这与单区域供冷系统负荷越大则运行时间越短的特点完全不同;并且区域供冷系统连续24h工作,实测日最小运行负荷仅为当日最大实际负荷的11.8%,逐时负荷变化范围大,这说明区域供冷系统更应注意机组容量选型和运行策略优化;由经改进人工神经网络算法得出的负荷预测值与实际值较吻合,其相对误差受用冷区域功能与特点的影响。     

带背腔平面天线的研究

带背腔平面天线的分析目前尚无人涉及，本文用谱域法结合本征函数技术为其建立了一个合适的理论模型。在傅里变换域导出了切向场分量和面电流密度分量之间的基本关系式之后，充分利用本征函数的正交特征，选择了合适的基函数和权函数，极大地简化了求解过程，成倍地缩短了计算时间，本文最后给出了天线方向图的计算结果和实验结果以资验证。     

光腔中两原子的布居数反转

研究在强相干场驱动条件下,置于光腔中的两个二能级原子在裸态表象中的布居数,发现在坏腔条件下,可以通过调节光腔与相干场的频率差到总的拉比频率值附近时实现布居数反转。     

空洞探测

本文讨论了空洞探测问题：针对确定误差限问题,提出了若干定义,同时阐述了一个判定空洞存在性的定理,根据这个定理,提出了对空洞位置判定的方法,并结合具体实例予以说明。     

Sub-kelvin optical cooling of a micromechanical resonator

Micromechanical resonators, when cooled down to near their ground state, can be used to explore quantum effects such as superposition and entanglement at a macroscopic scale. Previously, it has been proposed to use electronic feedback to cool a high frequency (10 MHz) resonator to near its ground state. In other work, a low frequency resonator was cooled from room temperature to 18 K by passive optical feedback. Additionally, active optical feedback of atomic force microscope cantilevers has been used to modify their response characteristics, and cooling to approximately 2 K has been measured. Here we demonstrate active optical feedback cooling to 135 +/- 15 mK of a micromechanical resonator integrated with a high-quality optical resonator. Additionally, we show that the scheme should be applicable at cryogenic base temperatures, allowing cooling to near the ground state that is required for quantum experiments--near 100 nK for a kHz oscillator.     

双板驱动矩形空腔STOKES流动的数值模拟

用边界元方法对A =1.5 ,s为任意值时的双板驱动矩形空腔Stokes流动进行数值模拟 .研究了矩形空腔内涡旋生成和发展的规律 .数值计算结果表明 :在s的绝对值不太大的范围内 ,伴随s的增加 ,矩形空腔内涡旋的生成、发展过程可由s的 5个临界点分成 6个阶段 .第一个临界点 ,s =- 8.5 5 ,1个涡旋变成 2个涡旋 .第二个临界点 ,s =- 0 .118,2个涡旋变成 1个涡旋 .第三个临界点 ,s =- 0 .0 0 0 1,1个涡旋变成 3个涡旋 .第四个临界点 ,s =0 .0 5 ,3个涡旋变成 2个涡旋 .第五个临界点 ,s=15 5 ,2个涡旋变成 3个涡旋 .s =- 1时的数值计算结果与理论分析结果以及实验结果比较完全一致 ,令人非常满意 .特别是 ,本文方法适用于不同高宽比和任意速率比的矩形空腔驱动流动问题 ,因此不但具有方法上的理论意义 ,而且数值计算结果还具有工程应用上的实际意义 .     

微球喇曼激光器的性能研究

由光学球微腔与光纤耦而构成的喇曼激光器大大降低了阈值泵浦功率,明显提高了总体效率.本文对微球喇曼激光器的性能进行了详细的理论模拟研究,从泵浦信号和喇曼信号的速率方程出发,推导出微球喇曼激光器的阈值公式,讨论和分析了微球喇曼激光器的球微腔与熔锥光纤的耦合特性及耦合对激光器阈值的影响,并提出了提高该激光器耦合效率的有效方案.     

Jaynes－Cummings模型微腔原子的非绝热跃迁

应用高阶量子绝热近似方法分析了非绝热效应对微腔中原子动力学演化的影响，研究了腔中原子非绝热跃迁几率．     

江淮中型卡车冷却系统的设计

文章介绍了江淮中卡冷却系统的开发、设计与计算,重点对冷却系统影响较大的因素如风扇、水泵、散热器,以及对整车散热量影响较大的因素如发动机、中冷器、冷凝器进行了详细的匹配计算,目的是使整个热循环系统能满足在恶劣情况下的使用要求。     

可穿透腔体外有裂缝的正散射问题

研究了时间调和的点源入射平面波通过腔体和裂缝的正散射问题,认为散射体是由一个可穿透腔体和一个外部不可穿透的裂缝构成,该问题归结为对具有一定边界条件的Helmholtz方程的求解.通过边界积分方程的方法,利用位势理论和Fredholm定理,证明了该问题解的存在唯一性.     

Radiation-pressure cooling and optomechanical instability of a micromirror

Recent table-top optical interferometry experiments and advances in gravitational-wave detectors have demonstrated the capability of optical interferometry to detect displacements with high sensitivity. Operation at higher powers will be crucial for further sensitivity enhancement, but dynamical effects caused by radiation pressure on the interferometer mirrors must be taken into account, and the appearance of optomechanical instabilities may jeopardize the stable operation of the next generation of interferometers. These instabilities are the result of a nonlinear coupling between the motion of the mirrors and the optical field, which modifies the effective dynamics of the mirror. Such 'optical spring' effects have already been demonstrated for the mechanical damping of an electromagnetic waveguide with a moving wall, the resonance frequency of a specially designed flexure oscillator, and the optomechanical instability of a silica microtoroidal resonator. Here we present an experiment where a micromechanical resonator is used as a mirror in a very high-finesse optical cavity, and its displacements are monitored with unprecedented sensitivity. By detuning the laser frequency with respect to the cavity resonance, we have observed a drastic cooling of the microresonator by intracavity radiation pressure, down to an effective temperature of 10 kelvin. For opposite detuning, efficient heating is observed, as well as a radiation-pressure-induced instability of the resonator. Further experimental progress and cryogenic operation may lead to the experimental observation of the quantum ground state of a micromechanical resonator, either by passive or active cooling techniques.     

腔中利用人工原子实现多量子比特相位门

在量子信息研究中,多量子比特相位门具有非常重要的意义。本文介绍了实现多量子比特相位门的两种模型,提出了一个利用腔中四能级超导人工原子实现多量子比特相位门的方案。该方案采用一个量子场和两个经典场控制各能级之间的跃迁,提高了多量子比特系统抵抗退相干的能力。     

Film cooling with using the decomposition of an NH3 cooling stream as a chemical heat sink

The inlet temperatures of gas turbines are generally increasing over time,so conventional cooling methods are likely to approach their useful limits.It is therefore essential to investigate novel cooling methods.Based on the theory of heat transfer enhancement,a novel film cooling method for gas turbine blades using a chemical heat sink is proposed.In this method,the endothermic reaction of an NH 3 cooling stream heated by the main gas stream takes place,reducing the convective heat transfer between the mainstream and the blades.Therefore,film cooling effectiveness is improved.To test the feasibility of the proposed method,numerical simulations were conducted,using the classical flat plate with a 30 degree angled cylindrical hole(diameter,D).Film cooling effectiveness at different blowing ratios(M = 0.5,1.0,and 1.5) were computed and compared with the results of conventional cooling methods.The simulation results show that the proposed method can enhance film cooling effectiveness not only in the stream-wise direction,but also in the span-wise direction.The span-averaged film effectiveness is improved in the presence of a chemical heat sink,with the value of X/D(the ratio of downstream distance from the center of the film hole to the diameter of the film hole) increasing downstream of the film hole.The novel film cooling approach showed the best performance at M = 0.5.     

高速航行体通气空泡形态

采用数值模拟方法,对高速航行体垂直发射上升过程重力场中的通气空泡流进行了研究.基于Mixture多相流模型和耦合自然空化模型,建立气、汽、液多相空泡流数学模型,求解整个流场域内的Reynolds平均Navier-Stokes方程.使用动网格技术(Dynamic Mesh Method)结合用户自定义函数(UDF)的程序,数值模拟了重力影响下高速航行体垂直发射水下运动过程,揭示了通气空泡的演化规律及流动载荷变化特征.     

关于谐振腔品质因数的数值计算

本文讨论如何采用数值方法计算谐振腔的有载品质因数。讨论了谐振腔损耗电阻对输入阻抗谐振曲线的影响。利用所得结果 ,在采用数值方法计算谐振腔的有载品质因数的时候 ,可以用腔体的介质损耗代替导体表面损耗计算谐振腔的有载品质因数     

牛顿冷却定律的冷却规律研究

对牛顿冷却定律的内容及适用范围进行了介绍,详细探讨了牛顿冷却定律在热学实验中散热修正方面的应用,同时提出了一种利用牛顿冷却定律求得物质比热的方法．