The positronium atom as a benchmark for Rydberg excitation experiments in atomic physics

Positronium is a hydrogen-like pure leptonic atom that has gained great attention in basic physics for its role in antimatter studies, in quantum electrodynamics tests and in material science. Positronium spectroscopy is also an interesting research field, especially in the again unexplored region of Rydberg states, where motional effects turns out of overwhelming importance in determining the level structure, at variance with the usual Rydberg atomic spectroscopy. In this paper we present a simple theory of optical excitation of positronium high-n levels in strong magnetic fields, and determine the conditions for obtaining saturation of the transitions. It is shown that positronium atom can be an atomic physics benchmark for laser excitation experiments on Rydberg states in magnetic environments.     

Observation of a resonant four-body interaction in cold cesium Rydberg atoms

Cold Rydberg atoms subject to long-range dipole-dipole interactions represent a particularly interesting system for exploring few-body interactions and probing the transition from 2-body physics to the many-body regime. In this work we report the direct observation of a resonant 4-body Rydberg interaction. We exploit the occurrence of an accidental quasicoincidence of a 2-body and a 4-body resonant Stark-tuned F?rster process in cesium to observe a resonant energy transfer requiring the simultaneous interaction of at least four neighboring atoms. These results are relevant for the implementation of quantum gates with Rydberg atoms and for further studies of many-body physics.     

A multi-band atomic candle with microwave-dressed Rydberg atoms

Stabilizing important physical quantities to atom-based standards lies at the heart of modern atomic, molecular and optical physics, and is widely applied to the field of precision metrology. Of particular importance is the atom-based microwave field amplitude stabilizer, the so-called atomic candle. Previous atomic candles are realized with atoms in their ground state, and hence suffer from the lack of frequency band tunability and small stabilization bandwidth, severely limiting their development and potential applications. To tackle these limitations, we employ microwave-dressed Rydberg atoms to realize a novel atomic candle that features multi-band frequency tunability and large stabilization bandwidth. We demonstrate amplitude stabilization of microwave field from C-band to Ka-band, which could be extended to quasi-DC and terahertz fields by exploring abundant Rydberg levels. Our atomic candle achieves stabilization bandwidth of 100 Hz, outperforming previous ones by more than two orders of magnitude. Our simulation indicates the stabilization bandwidth can be further increased up to 100 kHz. Our work paves a route to develop novel electric field control and applications with a noise-resilient, miniaturized, sensitive and broadband atomic candle.     

A concise review of Rydberg atom based quantum computation and quantum simulation

Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago.Recent experimental and theoretical progresses have shined exciting light on this avenue.In this concise review,we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation.We shall also include related discussions on quantum optics with Rydberg atomic ensembles,which are increasingly used to explore quantum computation and quantum simulation with photons.     

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.     

铯原子nP_(3/2)(n=70—94)里德伯态的紫外单光子激发及量子亏损测量

基于成熟的光纤激光器、光纤放大器及高效激光频率转换技术,我们在实验中研制了一套瓦级输出的窄线宽连续波单频可调谐318.6 nm紫外激光系统,并在室温铯原子气室中实现了6S_(1/2)—nP_(3/2)(n=70—94)单光子跃迁里德伯激发.借助由铯原子6S_(1/2)(F=4)基态、6P_(3/2)(F′=5)激发态和nP_(3/2)(n=70—94)里德伯态构成的V型三能级系统,通过频率锁定于铯原子6S_(1/2)(F=4)—6P_(3/2)(F′=5)超精细跃迁的852.3 nm探测光束的吸收减弱信号获得了里德伯态的信息,并利用高精度波长计测量了铯原子nP_(3/2)(n=70—94)里德伯态的量子亏损值.经过与理论计算值的变化趋势进行对比,我们认为由于原子气室的里德伯屏蔽效应并不能完全屏蔽外部直流电场,铯原子气室内存在残余的直流电场,影响了对里德伯态的量子亏损值的实验测量.利用残余直流电场的Stark效应理论模型及其与有效主量子数n*的依赖关系,对铯原子里德伯态的量子亏损实验测量值进行了修正.修正后的铯原子nP_(3/2)(n=70—94)态量子亏损测量值为3.5591±0.0007,与理论计算值相吻合.     

Controlling ultracold Rydberg atoms in the quantum regime

We discuss the properties of Rydberg atoms in a magnetic Ioffe-Pritchard trap being commonly used in ultracold atomic physics experiments. The Hamiltonian is derived, and it is demonstrated how tight traps alter the coupling of the atom to the magnetic field. We solve the underlying Schr?dinger equation of the system within a given n manifold and show that for a sufficiently large Ioffe field strength the 2n;{2}-dimensional system of coupled Schr?dinger equations decays into several decoupled multicomponent equations governing the center of mass motion. An analysis of the fully quantized center of mass and electronic states is undertaken. In particular, we discuss the situation of tight center of mass confinement outlining the procedure to generate a low-dimensional ultracold Rydberg gas.     

Local blockade of Rydberg excitation in an ultracold gas

In the laser excitation of ultracold atoms to Rydberg states, we observe a dramatic suppression caused by van der Waals interactions. This behavior is interpreted as a local excitation blockade: Rydberg atoms strongly inhibit excitation of their neighbors. We measure suppression, relative to isolated atom excitation, by up to a factor of 6.4. The dependences of this suppression on both laser irradiance and atomic density are in good agreement with a mean-field model. These results are an important step towards using ultracold Rydberg atoms in quantum information processing.     

The Stability of Matter in Quantum Mechanics,by E.H. Lieb and R. Seiringer

Laser spectroscopy of atomic hydrogen has been important in the recent development of Doppler-free laser techniques and offers stringent tests of atomic theory together with precise measurements of fundamental atomic constants. In this review we outline the theory of the structure of atomic hydrogen and describe the techniques of Doppler-free laser spectroscopy. This field has been extremely active in recent years and we bring together the most recent results of measurements of the Rydberg constant and the ground-state Lamb shift.     

Continuous wave field ionization laser spectroscopy

A new technique is described which allows Doppler-free, isotope-selective excitation of atoms by continuous wave laser radiation and continuous ionization of the atoms by an electric field. The atoms are excited to high Rydberg states in an electric-field-free region of a collimated atomic beam. Because the lifetimes of Rydberg atoms are long they can reach a spatially separated region of the atomic beam where they are ionized by a continuous electric field with a probability of unity. In the case of lithium we obtained a 10³ times larger ion signal by field ionization of Rydberg atoms than by direct photoionization from low excited states.     

超冷铯(60D5/2)2 Rydberg分子的双色光缔合光谱

本文主要从理论和实验上研究超冷铯（60D_5/2）₂ Rydberg分子的双色光缔合光谱.数值计算了铯60D_5/2 Rydberg原子对态的长程电多极相互作用和（60D_5/2）₂ Rydberg分子的绝热势能曲线,获得了（60D_5/2）₂ Rydberg分子的势阱深度和平衡间距.实验上利用双色光缔合超冷铯原子的方法制备了（60D_5/2）₂ Rydberg分子.其中,第一色激光（pulse-A）双光子共振激发种子Rydberg原子A;第二色激光（pulse-B,失谐于分子的束缚能）共振激发第二个Rydberg原子B,原子A与B由分子势阱束缚形成超冷（60D_5/2）₂ Rydberg分子.由脉冲场电离探测技术获得Rydberg分子的光缔合光谱,测量的Rydberg分子的势阱深度与理论计算结果相一致.     

Quantum simulation of quantum many-body systems with ultracold two-electron atoms in an optical lattice

Ultracold atoms in an optical lattice provide a unique approach to study quantum many-body systems, previously only possible by using condensed-matter experimental systems. This new approach, often called quantum simulation, becomes possible because of the high controllability of the system parameters and the inherent cleanness without lattice defects and impurities. In this article, we review recent developments in this rapidly growing field of ultracold atoms in an optical lattice, with special focus on quantum simulations using our newly created quantum many-body system of two-electron atoms of ytterbium. In addition, we also mention other interesting possibilities offered by this novel experimental platform, such as applications to precision measurements for studying fundamental physics and a Rydberg atom quantum computation.     

基于Rydberg原子天线的太赫兹测量

Rydberg原子在微波和太赫兹频段具有极大的电偶极矩,利用量子干涉效应可实现对该频段电磁波场强的高灵敏探测,理论上灵敏度可达到远高于现有探测技术的水平.基于Rydberg原子量子效应的电磁场探测及精密测量技术在太赫兹的场强和功率计量、太赫兹通信和太赫兹成像等方面有着巨大的应用前景.本文回顾了基于Rydberg原子量子干涉效应实现电磁波电场自校准和可溯源测量的基本理论和实验技术,详细介绍了基于Rydberg原子的高灵敏太赫兹场强测量、太赫兹近场高速成像和太赫兹数字通信的基本原理和技术方案.最后简单介绍了本研究团队正在开展的基于Rydberg原子的太赫兹探测工作.     

Optogalvanic spectroscopy of sputtered atoms

Optogalvanic Spectroscopy (OGS) is finding wide ranging applications in atomic structure studies, laser wavelength calibration, intensity and frequency stabilization of lasers and analytical chemistry. Sputtered atoms produced in a hollow cathode lamp by the bombardment of a rare gas discharge is a convenient source for optogalvanic spectroscopy work. Here, we discuss the sputtered ion/atom optogalvanic spectroscopy applications to low resolution atomic spectroscopy, laser wavelength calibration, studies of radioactive samples available in limited quantities, studies of atoms in highly excited states and Rydberg atoms and high resolution laser spectroscopy. For the sake of completeness, we list other applications of OGS without going into details.     

New applications of atomic physics to the study of nuclear properties

The hyperfine interaction couples the atomic electrons and the nucleus, and because of this interaction, there is a fundamental link between the fields of atomic physics and nuclear physics. Of course, information flows in both directions through this link. This paper reviews in broad terms the previous applications of atomic physics methods to the study of nuclear properties and fundamental interactions, and then focuses on the possible applications of atom trapping methods to nuclear physics problems.Supported in part by the National Science Foundation.     

Lee–Yang zeros in the Rydberg atoms

Lee–Yang (LY) zeros play a fundamental role in the formulation of statistical physics in terms of (grand) partition functions, and assume theoretical significance for the phenomenon of phase transitions. In this paper, motivated by recent progress in cold Rydberg atom experiments, we explore the LY zeros in classical Rydberg blockade models. We find that the distribution of zeros of partition functions for these models in one dimension (1d) can be obtained analytically. We prove that all the LY zeros are real and negative for such models with arbitrary blockade radii. Therefore, no phase transitions happen in 1d classical Rydberg chains. We investigate how the zeros redistribute as one interpolates between different blockade radii. We also discuss possible experimental measurements of these zeros.     

镓原子的Stark能级结构

里德堡原子的Stark效应在偶极偶极相互作用、量子信息和量子调控等方面具有潜在的应用前景. 本文首先根据零场时镓原子的能级数据, 通过非线性拟合方法获得了镓原子各态的量子亏损, 仔细分析了量子亏损随主量子数的变化特征; 然后利用Numerov算法计算了镓原子的径向波函数; 最后采用矩阵对角化方法, 数值计算了镓原子高里德堡态在场强范围F=0-3000 V·cm^{- 1}时n=7和n=18附近的Stark能级结构. 结果显示在主量子数n=7多重态以上的能级结构中, (n+1)P态的能级接近并大于nD态的能级, 在n=7多重态以下的能级结构中, (n+1)P态的能级接近并小于nD态的能级. 这一现象不同于通常的碱金属原子的Stark结构, 论文对该现象及其他Stark能级结构特征进行了详细分析, 为相关研究工作提供了重要参考价值.     

自旋极化扫描隧道显微镜的研究进展

自旋极化扫描隧道显微镜(spin-polarized scanning tunneling microscope,SP-STM)将扫描隧道显微镜(scanning tunneling microscope,STM)的实空间分辨率和对自旋敏感的磁成像技术结合起来,已经成为人们研究纳米磁性物理的最有效工具之一.文章介绍了SP-STM的工作原理及其在低维磁性物理领域的应用和最新进展,如对磁性薄膜、磁性纳米岛、磁性原子及不共线结构的研究等,并对我国在这一领域的研究现状和发展前景进行简要评述.     

同步辐射在原子、分子物理中的应用

同步辐射(S.R.)的独特性质(在10-100μ波长内的可调谐性和高度的线偏振性)使它在原子、分子物理的研究中显示了超过一般实验室光源的巨大优越性。本文在介绍了与S.R.应用相关的几种重要的实验技术后,评述了近年来S.R.在原子物理、分子物理和光化学反应中的典型应用。     

以Ne原子为联合原子的系列分子里德伯能级结构

本文在独立电子近似的基础上,利用多重散射自洽场理论方法,系统地计算了含10个电子的分子B₂,HF,H₂O,NH₃,CH₄的里德伯能级结构,通过分析这些分子量子数亏损的变化规律,阐明了其激发态的电子能级结构,根据分子电子组态的联合原子极限,确定了各里德伯初始态的主量子数,量子数亏损的计算值与已有的实验值符合良好。 关键词：