Single neutral atoms trapped in an optical lattice form an ideal system for the investigation of coherent matter wave phenomena in a well controlled way. For this it is necessary to coherently manipulate and detect the system with a spatial resolution better than the periodicity of the optical lattice (λ/2 = 433 nm). We have realized such a system by trapping single laser cooled Caesium atoms in a spin dependent optical lattice. High resolution fluorescence imaging yields precise detection of atomic positions even down to nearest neighbors in the lattice [1].
Single neutral atoms trapped in an optical lattice form an ideal system for the investigation of coherent matter wave phenomena in a well controlled way. For this it is necessary to coherently manipulate and detect the system with a spatial resolution better than the periodicity of the optical lattice (λ/2 = 433 nm). We have realized such a system by trapping single laser cooled Caesium atoms in a spin dependent optical lattice. High resolution fluorescence imaging yields precise detection of atomic positions even down to nearest neighbors in the lattice [1].
Advances in the preparation and detection, but most importantly in the coherent manipulation of single neutral atoms have allowed the observation of intriguing phenomena of quantum physics in recent years. We discuss developments to prepare and detect single neutral atoms in a one-dimensional optical lattice potential with single site resolution. Moreover, using two different experimental techniques, a state-dependent optical lattice potential on the one hand and a high-finesse optical cavity on the other hand, we have obtained coherent control over single neutral atoms. The former has enabled us to observe the quantum walk of atoms in position space, and to coherently control the motion of trapped atoms via microwave radiation. The latter offers a means to non-destructively detect the atomic spin state, thereby revealing quantum jumps of single atoms, or the altered optical properties of single atoms when subject to electromagnetically-induced transparency.
The present work investigates the state-selective transport of single neutral cesium atoms in a one-dimensional optical lattice. It demonstrates experimental applications of this transport, including a single atom interferometer, a quantum walk and controlled two-atom collisions. The atoms are stored one by one in an optical lattice formed by a standing wave dipole trap. Their positions are determined with sub-micrometer precision, while atom pair separations are reliably inferred down to neighboring lattice sites using real-time numerical processing. Using microwave pulses in the presence of a magnetic field gradient, the internal qubit states, encoded in the hyperfine levels of the atoms, can be separately initialized and manipulated. This allows us to perform arbitrary single-qubit operations and prepare arbitrary patterns of atoms in the lattice with single-site precision. Chapter 1 presents the experimental setup for trapping a small number of cesium atoms in a one-dimensional optical lattice. Chapter 2 is devoted to fluorescence imaging of atoms, discussing the imaging setup, numeric methods and their performance in detail. Chapter 3 focuses on engineering of internal states of trapped atoms in the lattice using optical methods and microwave radiation. It provides a detailed investigation of coherence properties of our experimental system. Finally manipulation of individual atoms with almost single-site resolution and preparation of regular strings of atoms with predefined distances are presented. In Chapter 4, basic concepts, the experimental realization and the performance of the state-selective transport of neutral atoms over several lattice sites are presented and discussed in detail. Coherence properties of this transport are investigated in Chapter 5, using various two-arms single atom interferometer sequences in which atomic matter waves are split, delocalized, merged and recombined on the initial lattice site, while the interference contrast and the accumulated phase difference are measured. By delocalizing a single atom over several lattice sites, possible spatial inhomogeneities of fields along the lattice axis in the trapping region are probed. In Chapter 6, experimental realization of a discrete time quantum walk on a line with single optically trapped atoms is presented as an advanced application of multiple path quantum interference in the context of quantum information processing. Using this simple example of a quantum walk, fundamental properties of and differences between the quantum and classical regimes are investigated and discussed in detail. Finally, by combining preparation of atom strings, position-dependent manipulation of qubit states and state-selective transport, in Chapter 7, two atoms are deterministically brought together into contact, forming a starting point for investigating two-atom interactions on the most fundamental level. Future prospects and suggestions are finally presented in Chapter 8.
The imaging of neutral atoms confined in an optical lattice has been demonstrated by a number of groups, resolving single fluorescing atoms in samples of hundreds of atoms. To obtain a high signal the atoms remain confined in the wells of a deep optical lattice whilst fluorescence excitation light is applied for high resolution imaging. In most cases, the excitation light frequency is chosen so that there is a concomitant laser cooling effect. In existing implementations of an imaging lattice the preceding manipulation stage has used optical trapping and manipulation. In this thesis I describe work towards applying this imaging lattice technique on a magnetic trapping apparatus, in particular for carrying out quantum simulation experiments. An introduction to the specific challenge of performing a quantum simulation of the fractional quantum Hall effect is given, with the link to and nature of the imaging lattice technique explained. The existing quantum-gas machine that has been developed to produce Bose-Einstein condensates of 87Rb in this work is then described, including the new optical lattice subsystem and the associated diode laser system. An auxiliary project to develop a servo-control system for frequencies that are several GHz away from an atomic reference is presented. We implement an optical lattice using laser light with a frequency detuning of -20 GHz below the D1-resonance line. The construction and geometry of the individual dipole trapping beams in combination with our existing apparatus is discussed as well as the alignment methods used. We confirm the presence of three independent 1D lattices through diffraction, and observe the decay of a BEC loaded into a lattice using absorption imaging. We observe good long-term alignment and operational stability of the optical lattice. This system will enable us to ultimately detect single fluorescing atoms in the optical lattice, following the application of excitation light co-propogating with lattice beams, via an imaging system with a moderate numerical aperture of 0:27.
In this work we present the results of studies of one-dimensional (1D) and twodimensional (2D) optical lattices on a chip.We have developed a method to create 1D and 2D optical lattices above an optical waveguide.The method is based on the destructive interference of the evanescent waves of two modes of the waveguide, resulting in a periodic array of nodes above the waveguide surface.For blue-detuned light, this constitutes an array of optical dipole traps for neutral atoms.One pair of modes coupled into a ridge waveguide creates a 1D array of nodes in this manner, and two orthogonal pairs of modes in a slab waveguide result in a 2D array of nodes.Computational analysis of our method showed that these optical atom chips may be suitable for use as a quantum register, and for studies of atom-surface interactions between the trapped atoms and the waveguide surface.Using realistic waveguide materials and laboratory laser parameters we found that for a laser power of ~100 mW nodes can be created ~100 nm above the waveguide surface.The nodes constitute atom traps that are ~1mK deep, and have trap frequencies ~1MHz and ground state sizes of ~10 nm.The spacing between traps is ~1 µm enabling individual addressing with a focused laser beam.iii With the implementation of two-qubit gates in mind, initial investigations of extensions of the basic 2D optical lattice were conducted.Computational results for a counter-propagating 2D optical lattice with very close trap spacing (~λ/4) in one dimension, and for a 2D optical lattice with adjustable spacing between pairs of traps in one dimension are presented.An experimental setup for the realization of the proposed 2D optical lattices on a chip was designed and built.Several cooling and trapping steps necessary to prepare a cold atom sample for loading of the 2D optical lattice have been implemented successfully.In the course of previous studies of atom-surface interactions, a novel surfaceionization detector for 2D imaging of neutral atom samples was built and characterized.We find a detection efficiency ~50 %, a spatial resolution of 20 µm and a time response < 1/30 s. iv To my family.v ACKNOWLEDGMENTS First and foremost I would like to thank my advisor Greg Lafyatis for everything that he taught me.I also want to thank Frank DeLucia for always being there with his advice when I needed it.I appreciate Eric Herbst and Junko Shigemitsu for being willing to serve on
Neutral atoms trapped in optical lattices are promising candidates for quantum information processing and quantum simulation. Over the last decades, elegant tools for the manipulation of the internal and external states of optically trapped atoms have been developed. The crucial capability of scalable internal state readout in these systems, however, still relies on destructive methods. In spite of the important role of near-resonant illumination for the manipulation and detection of atoms in the lattice, there also exists a significant lack of studies on the heating and cooling dynamics of optically trapped atoms interacting with near-resonant light. An in-depth understanding of the heating and cooling processes is essential to finding the conditions of illumination that enable the non-destructive internal state readout of multiple atoms. This work presents an experimental system to cool, trap, manipulate, and detect the internal and external states of a small ensemble of 87Rb neutral atoms trapped in a one-dimensional optical lattice. A high photon detection efficiency in our experimental system allows for fast fluorescence imaging with acquisition times of 20 ms and fast position determination of atoms in the optical lattice with an accuracy of ∼ 40 nm. Using this experimental system, we investigate the heating dynamics of a neutral atom trapped in a standing wave dipole trap illuminated by a single near-resonant laser beam. A theoretical description to describe our measurements is provided in two experimentally relevant regimes. First, we consider the case of a weak near-resonant beam and later the case of off-resonant illumination. From this analysis, we find settings for the illumination light which allows an atom to scatter many photons before it is expelled from the trap. Building on these results we demonstrate simultaneous, non-destructive determination of the internal state of spatially resolved atoms trapped in a one-dimensional optical lattice with a fidelity of 98.6 ± 0.2% and a survival probability of 99.0 ± 0.2%. During the readout process, less than 2% of the atoms change their initial ground state. In order to determine the state of atoms that are not spatially resolved, a novel image analysis technique is presented. The technique uses Bayesian methods, which include the statistics of the detected photons as well as the response from the EMCCD camera. The Bayesian method is implemented on experimental data for atoms trapped in a one-dimensional optical lattice and its accuracy is tested by numerical simulations. In addition, an extension of this algorithm for atoms trapped in two-dimensional lattices is provided. Finally, the non-destructive state detection method is utilized as a tool for the state determination following the coherent control of the internal and external states of atoms in the optical trap. Here Raman sideband cooling is implemented and utilized in an atomic compression sequence for the creation of a small and dense atomic ensemble. These techniques will play an important role in experiments studying the collective light interaction of the atomic ensemble in a recently added optical fiber cavity.
Cooling and trapping of neutral atoms using laser techniques has enabled extensive progress in precise, coherent spectroscopy. In particular, trapping ultracold atoms in optical lattices in a tight confinement regime allows us to perform high-resolution spectroscopy unaffected by atomic motion. We report on the recent developments of optical lattice atomic clocks that have led to optical spectroscopy coherent at the one second timescale. The lattice clock techniques also open a promising pathway toward trapped ultracold molecules and the possible precision measurement opportunities such molecules offer.