Pulsed differential excitation of atoms

It is shown that differential excitation of similar atoms can be achieved by means of a spaced double π/2-pulse sequence in a shorter time than with a single π-pulse, with smaller relaxation degradation.     

Photoassociation of cold Ca atoms

We present the first measurement of a photoassociative spectrum of an alkaline earth element near the dissociation limit. The observed spectrum of Ca2 formed from cold atoms shows the regular vibrational series with the characteristic spacing of the 1/R3 asymptotic potential. The interpretation is in principle simplified compared to previous measurements on alkali metals by the nondegenerate ground state and the missing hyperfine structure of 40Ca. As an example, we derive the natural decay rate of the excited atomic 4p 1P1 state from the positions of the observed vibrational and rotational resonances with reduced uncertainty compared to previous measurements.     

Superradiance of several cold atoms

A method for calculating the spontaneous emission power of several immobile dipole-interacting two-level atoms located in a volume of about the wavelength of resonance radiation has been proposed in the Schrödinger representation. It has been shown that two atoms cannot, but four atoms can, emit a superradiance pulse under the conditions corresponding to experiments with cold atoms in dipole traps. Various methods for determining the quasistationary mixed atomic states, as well as the generalization of this method to other resonance emitting systems, are discussed.     

Pulsed standing wave deflection of sodium atoms

We study the deflection of sodium atoms by a resonantly tuned pulsed standing wave of high field intensity. The effects of the phase fluctuations of the pulsed laser field on the momentum distribution of the deflected atoms are experimentally determined. The results are explained using a theoretical model based on the generalized density matrix formalism of two-level atoms. Received 23 November 1998 and Received in final form 27 January 1999     

Gating ratchet for cold atoms

We demonstrate experimentally a gating ratchet with cold rubidium atoms in a driven near-resonant optical lattice. A single-harmonic periodic modulation of the optical potential depth is applied, together with a single-harmonic rocking force. Directed motion is observed as a result of the breaking of the symmetries of the system.     

Polarization squeezing with cold atoms

We study the interaction of a nearly resonant linearly polarized laser beam with a cloud of cold cesium atoms in a high finesse optical cavity. We show theoretically and experimentally that the cross-Kerr effect due to the saturation of the optical transition produces quadrature squeezing on both the mean field and the orthogonally polarized vacuum mode. An interpretation of this vacuum squeezing as polarization squeezing is given and a method for measuring quantum Stokes parameters for weak beams via a local oscillator is developed.     

Freezing light with cold atoms

The impact of disorder and localisation in electronic conduction was introduced more than half a century ago by Philip Anderson. In a much broader context of disorder-mediated wave dynamics it remains an important research area, and surprises abound. Meanwhile, research in ultracold atomic physics has led to phenomenally detailed elucidation of properties, including changes in phase, of quantum degenerate Bosonic and Fermionic gases. For example, beautiful experiments have recently demonstrated, in quasi one-dimensional systems, Anderson localisation of matter waves. In this brief essay, we describe and discuss research on wave localisation in the context of ultracold atomic physics, with a particular emphasis on light localisation in ultracold and high-density atomic gases. Essential ideas are reviewed, along with the current experimental status of the field, and promising avenues for future research are discussed.     

Efimov physics in cold atoms

Atoms with a large scattering length have universal low-energy properties that do not depend on the details of their structure or their interactions at short distances. In the 2-atom sector, the universal properties are familiar and depend only on the scattering length. In the 3-atom sector for identical bosons, the universal properties include the existence of a sequence of shallow triatomic molecules called Efimov trimers and log-periodic dependence of scattering observables on the energy and the scattering length. In this review, we summarize the universal results that are currently known. We also summarize the experimental information that is currently available with an emphasis on 3-atom loss processes.     

Andreev-like reflections with cold atoms

We propose a setup in which Andreev-like reflections predicted for 1D transport systems could be observed time dependently using cold atoms in a 1D optical lattice. Using time-dependent density matrix renormalization group methods we analyze the wave packet dynamics as a density excitation propagates across a boundary in the interaction strength. These phenomena exhibit good correspondence with predictions from Luttinger liquid models and could be observed in current experiments in the context of the Bose-Hubbard model.     

Microwave spectroscopy of cold rubidium atoms

The effect of microwave radiation on the resonance fluorescence of a cloud of cold ⁸⁵Rb atoms in a magnetooptical trap is studied. The radiation frequency was tuned near the hyperfine splitting frequency of rubidium atoms in the 5S ground state. The microwave field induced magnetic dipole transitions between the magnetic sublevels of the 5S (F=2) and 5S (F=3) states, resulting in a change in the fluorescence signal. The resonance fluorescence spectra were recorded by tuning the microwave radiation frequency. The observed spectra were found to be substantially dependent on the transition under study and the frequency of a repump laser used in the cooling scheme.     

自旋—轨道耦合下冷原子的双反射

随着中性冷原子气体的人造自旋-轨道耦合的实验实现,近年来人们开始关注与之相关的可能应用,其中包括自旋-轨道耦合下原子反射镜的研究.本文在前人研究的基础上,考虑一束自旋-轨道耦合的冷原子气体入射到有限高势垒的情形,通过将部分反射和全反射情况进行对比,发现了与之前研究不同的性质.我们发现,在全反射条件下,反射原子的极化率随入射角变化较大,而随自旋-轨道耦合强度和原子入射能量的变化较小.但在发生部分反射的情况下,反射原子的极化率不仅随入射角变化较大,随自旋-轨道耦合强度和原子的入射能量变化也十分明显.我们仔细研究了自旋-轨道耦合原子气体的反射性质并讨论了其可能的应用.     

Off-resonant defocus-contrast imaging of cold atoms

We demonstrate the retrieval of column-density images of cold atoms, using a noninterferometric phase-recovery technique based on a single off-resonant and defocused intensity image. The quantitative column density is retrieved via Fourier inversion and remains robust with respect to detuning and defocus. The technique offers excellent prospects for simple, nondestructive imaging of atoms in magnetic and optical traps and condensates.     

Topological quantum matter with cold atoms

This is an introductory review of the physics of topological quantum matter with cold atoms. Topological quantum phases, originally discovered and investigated in condensed matter physics, have recently been explored in a range of different systems, which produced both fascinating physics findings and exciting opportunities for applications. Among the physical systems that have been considered to realize and probe these intriguing phases, ultracold atoms become promising platforms due to their high flexibility and controllability. Quantum simulation of topological phases with cold atomic gases is a rapidly evolving field, and recent theoretical and experimental developments reveal that some toy models originally proposed in condensed matter physics have been realized with this artificial quantum system. The purpose of this article is to introduce these developments. The article begins with a tutorial review of topological invariants and the methods to control parameters in the Hamiltonians of neutral atoms. Next, topological quantum phases in optical lattices are introduced in some detail, especially several celebrated models, such as the Su–Schrieffer–Heeger model, the Hofstadter–Harper model, the Haldane model and the Kane–Mele model. The theoretical proposals and experimental implementations of these models are discussed. Notably, many of these models cannot be directly realized in conventional solid-state experiments. The newly developed methods for probing the intrinsic properties of the topological phases in cold-atom systems are also reviewed. Finally, some topological phases with cold atoms in the continuum and in the presence of interactions are discussed, and an outlook on future work is given.     

Gravity-sensitive quantum dynamics in cold atoms

We subject a falling cloud of cold cesium atoms to periodic kicks from a sinusoidal potential created by a vertical standing wave of laser light. By controllably accelerating the potential, we show quantum accelerator mode dynamics to be highly sensitive to the effective gravitational acceleration when close to specific, resonant values. This quantum sensitivity to a control parameter is reminiscent of that associated with classical chaos and promises techniques for precision measurement.     

Gauss sum factorization with cold atoms

We report the first implementation of a Gauss sum factorization algorithm by an internal state Ramsey interferometer using cold atoms. A sequence of appropriately designed light pulses interacts with an ensemble of cold rubidium atoms. The final population in the involved atomic levels determines a Gauss sum. With this technique we factor the number N=263193.     

Non-resonant magneto-optical effects in cold atoms

We report a novel nonresonant magneto-optical effect in cold atoms and present the optimized parameters of the biased magnetic field, the incident probe light intensity, and the probe detuning to obtain the maximal signal of the magneto-optical rotation. This detection scheme may further improve the stability of the cold atom clock.     

Quasiperiodically driven ratchets for cold atoms

We investigate experimentally the route to quasiperiodicity in a driven ratchet for cold atoms and examine the relationship between symmetries and transport while approaching the quasiperiodic limit. Depending on the specific form of driving, quasiperiodicity results in the complete suppression of transport, or in the restoration of the symmetries which hold for a periodic driving.     

Multi-dark-state resonances in cold multi-Zeeman-sublevel atoms

We present our experimental and theoretical studies of multi-dark-state resonances (MDSRs) generated in a unique cold rubidium atomic system with only one coupling laser beam. Such MDSRs are caused by different transition strengths of the strong coupling beam connecting different Zeeman sublevels. Controlling the transparency windows in such an electromagnetically induced transparency system can have potential applications in multiwavelength optical communication and quantum information processing.     

Continuous variable entanglement using cold atoms

We present an experimental demonstration of both quadrature and polarization entanglement generated via the interaction between a coherent linearly polarized field and cold atoms in a high finesse optical cavity. The nonlinear atom-field interaction produces two squeezed modes with orthogonal polarizations which are used to generate a pair of nonseparable beams, the entanglement of which is demonstrated by checking the inseparability criterion for continuous variables recently derived by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)]] and calculating the entanglement of formation [Phys. Rev. Lett. 91, 107901 (2003)]].     

Pulsed standing-wave mirror for neutral atoms and molecules

Reflection of neutral atoms and molecules by a pulsed standing wave with a duration on the order of nanoseconds is studied. It is shown that, with a suitable choice of the laser parameter values, each period of the standing-wave pattern functions as an independent mirror, thus providing a novel way to manipulate large samples of neutral gas-phase particles even with a single laser pulse. At moderate field intensities, the pulsed standing-wave mirror would be directly applicable, e.g., for the manipulation of buffer-gas cooled molecules.