A trapped-ion local field probe

We introduce a measurement scheme that utilizes a single ion as a local field probe. The ion is confined in a segmented Paul trap and shuttled around to reach different probing sites. By the use of a single atom probe, it becomes possible characterizing fields with spatial resolution of a few nm within an extensive region of millimeters. We demonstrate the scheme by accurately investigating the electric fields providing the confinement for the ion. For this we present all theoretical and practical methods necessary to generate these potentials. We find sub-percent agreement between measured and calculated electric field values.     

Magneto-optical trapping of Stark-slowed metastable He atoms

We report on the first successful loading of a magneto-optical trap (MOT) with metastable He atoms from a Stark-slower. Thereby, deceleration of the atoms relies on laser-atom interaction in an inhomogeneous electric field. We show that the results obtained are comparable with early results from other groups achieved with a Zeeman slower. The Stark slower, which is able to fully control the final velocity of the atomic He beam, is the first step in achieving complete spin independent kinematic control based solely on electric fields. Received 2 October 2002 / Received in final form 20 January 2003 Published online 29 April 2003 RID="a" ID="a"e-mail: eichmann@mbi-berlin.de     

Simple and efficient photo-ionization loading of ions for precision ion-trapping experiments

We report a simple and efficient method to load a Paul trap with Ca⁺ ions. A beam of neutral atomic calcium is ionized in a two-step photo-ionization process using uv-diode lasers near 423 nm and 390 nm. Photo-ionization of a calcium beam for loading a Paul trap has first been demonstrated by Kjaergaard et al. The advantages of our method are the use of cheap and easily handled diode-laser systems and the large cross section for field ionization when exciting high-lying Rydberg states. Finally, we discuss the advantages of photo-ionization for ion generation compared to loading by electron bombardment. Received: 24 August 2001 / Revised version: 16 October 2001 / Published online: 23 November 2001     

First principles study of nuclear quadrupole interactions in the molecular solid BF3 and the nature of binding between the molecules

The LPCTrap facility is coupled to the low-energy beam line LIRAT of the SPIRAL source at GANIL (France). The facility comprises an RFQ trap for beam preparation and a transparent Paul trap for in-trap decay studies. The system has been tested for several ion species. The Paul trap has been fully characterized for ⁶Li⁺ and ²³Na⁺ ions. This characterization together with GEANT4 simulations of the in-trap decay setup (Paul trap and detection system) has permitted to predict the effect of the size of the ion cloud on the decay study of ⁶He⁺.     

An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems

Recent developments in the study of ultracold Rydberg gases demand an adwanced level of experimental sophistication, in which high atomic and optical densities must be combined with excellent control of external fields and sensitive Rydberg atom detection. We describe a tailored experimental system used to produce and study Rydberg-interacting atoms excited from dense ultracold atomic gases. The experiment has been optimized for fast duty cycles using a high flux cold atom source and a three beam optical dipole trap. The latter enables tuning of the atomic density and temperature over several orders of magnitude, all the way to the Bose--Einstein condensation transition. An elec- trode structure surrounding the atoms allows for precise control over electric fields and single-particle sensitive field ionization detection of Rydberg atoms. We review two experiments which highlight the influence of strong Rydberg---Rydberg interactions on different many-body systems. First, the Rydberg blockade effect is used to pre-structure an atomic gas prior to its spontaneous evolution into an ultracold plasma. Second, hybrid states of photons and atoms called dark-state polaritons are studied. By looking at the statistical distribution of Rydberg excited atoms we reveal correlations between dark-state polaritons. These experiments will ultimately provide a deeper understanding of many-body phenomena in strongly-interacting regimes, including the study of strongly-coupled plasmas and interfaces between atoms and light at the quantum level.     

All-optical realization of an atom laser

We demonstrate an atom laser using all-optical techniques. A Bose-Einstein condensate of rubidium atoms is created by direct evaporative cooling in a quasistatic dipole trap realized with a single, tightly focused CO2-laser beam. An applied magnetic field gradient allows the formation of the condensate in a field-insensitive m(F)=0 spin projection only, which suppresses fluctuations of the chemical potential from stray magnetic fields. A collimated and monoenergetic beam of atoms is extracted from the Bose-Einstein condensate by continuously lowering the dipole trapping potential in a controlled way to form a novel type of atom laser.     

Surface Planar Ion Chip for Linear Radio-Frequency Paul Traps

We propose a surface planar ion chip which forms a linear radio frequency Paul ion trap. The electrodes reside in the two planes of a chip, and the trap axis is located above the chip surface. Its electric field and potential distribution are similar to the standard linear radio frequency Paul ion trap. This ion trap geometry may be greatly meaningful for quantum information processing.     

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.     

Electrodynamic trapping of spinless neutral atoms with an atom chip

Three-dimensional electrodynamic trapping of neutral atoms has been demonstrated. By applying time-varying inhomogeneous electric fields with micron-sized electrodes, nearly 10(2) strontium atoms in the 1S0 state have been trapped with a lifetime of 80 ms. In order to design the electrodes, we numerically analyzed the electric field and simulated atomic trajectories in the trap, which showed reasonable agreement with the experiment.     

Paul阱中离子运动及稳定性分析

Paul离子阱由于没有外加磁场所引起的塞曼效应的影响,已成为离子存储及研究离子的重要装置.根据在实验中所采用的Paul离子阱结构及电场分布特点,列出阱内离子运动方程并进行求解,对其中各种运动进行分析,同时还分析了离子存储稳定性.最后对所作的研究进行总结,得到如下结论:阱中离子的运动为谐振运动、基频微运动和高阶微振动.     

Atomic beam guide by a one-dimensional magneto-optical trap

An atomic beam has been collimated, compressed, and deflected simultaneously by an atomic beam guide based on an inclined one-dimensional magneto-optical trap (1D-MOT). Isotope-selected rubidium atoms were extracted from the naturally-mixed thermal atomic beam with this method. We could manipulate the transverse displacement of the deflected beam precisely by adjusting the current in the copper rods to generate the quadrupole magnetic field. We could extract more than 50% of the incident atoms as a deflection beam when we combined this deflection technique with the atomic deceleration using a broadband spectral light. Received: 10 December 1998 / Published online: 24 June 1999     

High-resolution spectroscopy with laser-cooled and trapped calcium atoms

We report on high-resolution spectroscopy with two different samples of calcium atoms, in a laser-cooled and deflected beam and in a magneto-optical trap. The atomic beam was excited by spatially separated laser fields. For spectroscopy with stored atoms in a magneto-optical trap we used a multiple-pulse excitation scheme. The resolution as low as 2.5 kHz was limited by residual frequency fluctuations of our dye-laser spectrometer. The results should allow to establish a frequency standard with a relative uncertainty below 10^–14.     

抽运-检测型非线性磁光旋转铷原子磁力仪的研究

报道了一种抽运-检测型的非线性磁光旋转铷原子磁力仪.其原理是线偏振光通过处于外磁场环境中被极化的原子介质后,由于原子对线偏振光中左、右圆偏成分不同的吸收和色散,导致光的偏振方向会产生与磁场相关的转动.分析了该磁力仪的工作原理,并测试了它对不同磁场大小的响应.测试结果表明,磁力仪测量范围为100—100000 nT,极限灵敏度为0.2 p T/Hz~(1/2),磁场分辨率为0.1 p T.进一步研究了不同磁场下原子系综极化态的横向弛豫时间,讨论了原子磁力仪高磁场采样率的获得方法.本文的原子磁力仪在5000—100000 n T的磁场测量范围内磁场采样率可实现1—1000 Hz范围内可调,能够测量低频的微弱交变磁场.本文的研究内容为大磁场测量范围、高灵敏度、高磁场采样率的原子磁力仪研制提供了重要参考.     

Angular dependence of the dipole-dipole interaction in a nearly one-dimensional sample of Rydberg atoms

Atoms in an ultracold highly excited sample are strongly coupled through the dipole-dipole interaction. In an effort to understand and manipulate the complicated interactions in this system we are investigating their dependence on the relative orientation of the dipoles. By focusing a 480 nm beam from a tunable dye laser into a magneto-optical trap, we produce a nearly one-dimensional sample of Rydberg atoms. The trap lies at the center of four conducting rods with which we can vary the magnitude and direction of the electric field at the trap, thus controlling the orientation of the dipoles with respect to the sample axis. We have measured the strength of the interaction for a variety of relative orientations.     

Paul阱中存储离子的研究

根据Paul离子阱结构及电场分布特点,列出阱内离子运动方程并求解,对其中离子运动、硅团簇离子碰撞解离反应进行了分析.     

PYRAMIDAL-HOLLOW-BEAM DIPOLE TRAP FOR ALKALI ATOMS

We propose a dark gravito-optical dipole trap, for alkali atoms, consisting of a blue-detuned, pyramidal-hollow laser beam propagating upward and the gravity field. When cold atoms from a magneto-optical trap are loaded into the pyramidal-hollow beam and bounce inside the pyramidal-hollow beam, they experience efficient Sisyphus cooling and geometric cooling induced by the pyramidal-hollow beam and the weak repumping beam propagating downward. Our study shows that an ultracold and dense atomic sample with an equilibrium 3D momentum of ～3 \hbar k and an atomic density above the point of Bose-Einstein condensation may be obtained in this pure optical trap.     

RFQ冷却聚束器研究简介

详细论述了RFQ冷却聚束器相关的基本原理,简单介绍了国际上此方面的研究和我们的工作。The radiofrequency quadrupole （RFQ） cooler and buncher has been developed in many laboratories to improve the secondary radioactive ion beam quality. In this paper, the principles of the RFQ constraint, buffer gas cooling, axial electric field and Paul trap are discussed in detail. The studies around the world and our work are also briefly introduced.     

Trapping of neutral rubidium with a macroscopic three-phase electric trap

We trap neutral ground-state rubidium atoms in a macroscopic trap based on purely electric fields. For this, three electrostatic field configurations are alternated in a periodic manner. The rubidium is precooled in a magneto-optical trap, transferred into a magnetic trap, and then translated into the electric trap. The electric trap consists of six rod-shaped electrodes in cubic arrangement, giving ample optical access. Up to 10;{5} atoms have been trapped with an initial temperature of around 20 microkelvin in the three-phase electric trap. The observations are in good agreement with detailed numerical simulations.     

Effects of vacuum fluctuation suppression on atomic decay rates

The use of atomic decay rates as a probe of sub-vacuum phenomena will be studied. Because electromagnetic vacuum fluctuations are essential for radiative decay of excited atomic states, decay rates can serve as a measure of the suppression of vacuum fluctuations in non-classical states, such as squeezed vacua. In such states, the renormalized expectation value of the square of the electric field or the energy density can be periodically negative, representing suppression of vacuum fluctuations. We explore the extent to which atomic decays can be used to measure the mean squared electric field or energy density. We consider a scheme in which atoms in an excited state transit a closed cavity whose lowest mode contains photons in a non-classical state. A crucial feature of our analysis is that we do not employ the rotating wave approximation. The change in the decay probability of the atom in the cavity due to the non-classical state can, under certain circumstances, serve as a measure of the mean squared electric field or energy density in the cavity. We make some estimates of the magnitude of this effect, which indicate that an experimental test might be possible, although very challenging.     

Laser-cooled and trapped atoms as a precision target for heavy ion beams

We report on the development of a novel precision target for atomic physics with heavy ion beams, which consists of extremely cold and well localized, laser-cooled lithium atoms in a magneto-optical trap. First experiments are in preparation to study the collisional losses from the trap caused by the ion beam. The experimental set-up and the laser system, using exclusively 670 nm diode lasers, are described.