Cavity cooling of a microlever

The prospect of realizing entangled quantum states between macroscopic objects and photons has recently stimulated interest in new laser-cooling schemes. For example, laser-cooling of the vibrational modes of a mirror can be achieved by subjecting it to a radiation or photothermal pressure, actively controlled through a servo loop adjusted to oppose its brownian thermal motion within a preset frequency window. In contrast, atoms can be laser-cooled passively without such active feedback, because their random motion is intrinsically damped through their interaction with radiation. Here we report direct experimental evidence for passive (or intrinsic) optical cooling of a micromechanical resonator. We exploit cavity-induced photothermal pressure to quench the brownian vibrational fluctuations of a gold-coated silicon microlever from room temperature down to an effective temperature of 18 K. Extending this method to optical-cavity-induced radiation pressure might enable the quantum limit to be attained, opening the way for experimental investigations of macroscopic quantum superposition states involving numbers of atoms of the order of 10(14).     

双色激光场对运动原子的激光冷却

研究了双色激光场对运动三能级原子的激光冷却,通过数值计算,分别得到了在不同光强、不同频率、不同传播方向条件下,原子在双色场中冷却的最终温度与双光子失谐的关系.结果表明,当双色激光场的传播方向相同时,冷却原子可以得到更低的温度;当双光子跃迁过程加强时,原子可以实现较单光子过程更低的温度.     

Observation of entanglement between a single trapped atom and a single photon

An outstanding goal in quantum information science is the faithful mapping of quantum information between a stable quantum memory and a reliable quantum communication channel. This would allow, for example, quantum communication over remote distances, quantum teleportation of matter and distributed quantum computing over a 'quantum internet'. Because quantum states cannot in general be copied, quantum information can only be distributed in these and other applications by entangling the quantum memory with the communication channel. Here we report quantum entanglement between an ideal quantum memory--represented by a single trapped 111Cd+ ion--and an ideal quantum communication channel, provided by a single photon that is emitted spontaneously from the ion. Appropriate coincidence measurements between the quantum states of the photon polarization and the trapped ion memory are used to verify their entanglement directly. Our direct observation of entanglement between stationary and 'flying' qubits is accomplished without using cavity quantum electrodynamic techniques or prepared non-classical light sources. We envision that this source of entanglement may be used for a variety of quantum communication protocols and for seeding large-scale entangled states of trapped ion qubits for scalable quantum computing.     

Trapping an atom with single photons

The creation of a photon-atom bound state was first envisaged for the case of an atom in a long-lived excited state inside a high-quality microwave cavity. In practice, however, light forces in the microwave domain are insufficient to support an atom against gravity. Although optical photons can provide forces of the required magnitude, atomic decay rates and cavity losses are larger too, and so the atom-cavity system must be continually excited by an external laser. Such an approach also permits continuous observation of the atom's position, by monitoring the light transmitted through the cavity. The dual role of photons in this system distinguishes it from other single-atom experiments such as those using magneto-optical traps, ion traps or a far-off-resonance optical trap. Here we report high-finesse optical cavity experiments in which the change in transmission induced by a single slow atom approaching the cavity triggers an external feedback switch which traps the atom in a light field containing about one photon on average. The oscillatory motion of the trapped atom induces oscillations in the transmitted light intensity; we attribute periodic structure in intensity-correlation-function data to 'long-distance' flights of the atom between different anti-nodes of the standing-wave in the cavity. The system should facilitate investigations of the dynamics of single quantum objects and may find future applications in quantum information processing.     

Measurement of the internal state of a single atom without energy exchange

A measurement necessarily changes the quantum state being measured, a phenomenon known as back-action. Real measurements, however, almost always cause a much stronger back-action than is required by the laws of quantum mechanics. Quantum non-demolition measurements have been devised that keep the additional back-action entirely within observables other than the one being measured. However, this back-action on other observables often imposes its own constraints. In particular, free-space optical detection methods for single atoms and ions (such as the shelving technique, a sensitive and well-developed method) inevitably require spontaneous scattering, even in the dispersive regime. This causes irreversible energy exchange (heating), which is a limitation in atom-based quantum information processing, where it obviates straightforward reuse of the qubit. No such energy exchange is required by quantum mechanics. Here we experimentally demonstrate optical detection of an atomic qubit with significantly less than one spontaneous scattering event. We measure the transmission and reflection of an optical cavity containing the atom. In addition to the qubit detection itself, we quantitatively measure how much spontaneous scattering has occurred. This allows us to relate the information gained to the amount of spontaneous emission, and we obtain a detection error below 10 per cent while scattering less than 0.2 photons on average. Furthermore, we perform a quantum Zeno-type experiment to quantify the measurement back-action, and find that every incident photon leads to an almost complete state collapse. Together, these results constitute a full experimental characterization of a quantum measurement in the 'energy exchange-free' regime below a single spontaneous emission event. Besides its fundamental interest, this approach could significantly simplify proposed neutral-atom quantum computation schemes, and may enable sensitive detection of molecules and atoms lacking closed transitions.     

二能级原子与单模光场相互作用系统的量子场熵演化特性

利用全量子理论,研究了二能级原子与单模相干态光场相互作用系统的量子场熵演化特性;通过数值计算,讨论了光场的平均光子数、光场-原子之间的耦合系数g对量子场熵演化特性的影响.结果表明:量子场熵随时间的演化呈现出周期或非周期性的振荡、崩塌与回复等现象,说明、g对量子场熵演化特性的影响具有非线性的特征.     

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.     

Amplitude spectroscopy of a solid-state artificial atom

The energy-level structure of a quantum system, which has a fundamental role in its behaviour, can be observed as discrete lines and features in absorption and emission spectra. Conventionally, spectra are measured using frequency spectroscopy, whereby the frequency of a harmonic electromagnetic driving field is tuned into resonance with a particular separation between energy levels. Although this technique has been successfully employed in a variety of physical systems, including natural and artificial atoms and molecules, its application is not universally straightforward and becomes extremely challenging for frequencies in the range of tens to hundreds of gigahertz. Here we introduce a complementary approach, amplitude spectroscopy, whereby a harmonic driving field sweeps an artificial atom through the avoided crossings between energy levels at a fixed frequency. Spectroscopic information is obtained from the amplitude dependence of the system's response, thereby overcoming many of the limitations of a broadband-frequency-based approach. The resulting 'spectroscopy diamonds', the regions in parameter space where transitions between specific pairs of levels can occur, exhibit interference patterns and population inversion that serve to distinguish the atom's spectrum. Amplitude spectroscopy provides a means of manipulating and characterizing systems over an extremely broad bandwidth, using only a single driving frequency that may be orders of magnitude smaller than the energy scales being probed.     

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。     

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。     

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。     

Coupling effects of Zn single atom and high curvature supports for improved performance of CO2 reduction

Single-atom catalysts(SACs)have emerged as one of the most competitive catalysts toward a variety of important electrochemical reactions,thanks to their maximum...     

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。     

元素的Z^＊/r对元素的原子、离子及单质性质的影响

系统探讨了元素的Z^＊/r对元素的原子性质、离子性质、单质性质的广泛影响。     

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.