High-resolution microscopy of two-dimensional dipolar quantum gases requires selecting individual atomic layers, a task complicated for strongly magnetic lanthanide atoms by the limited applicability of standard magnetic-gradient techniques. We present an all-optical method for the deterministic spatial selection of single- and bilayer samples of cold dipolar atoms using spatially selective parametric heating within a beat-note superlattice. By utilizing a high-resolution microscope objective as a common retroreflector for both optical frequency components, the lattice planes are passively stabilized. This renders their positions exceptionally robust against experimental drifts and structure-borne vibrations, even eliminating the need for active laser stabilization over millimeter-scale separations from the reflecting surface. We validate this approach by demonstrating the robust isolation of one or two atomic layers in precise coincidence with the focal plane of our objective. This enables future single-atom-resolved studies of long-range interacting systems.
High-resolution microscopy of two-dimensional dipolar quantum gases requires selecting individual atomic layers, a task complicated for strongly magnetic lanthanide atoms by the limited applicability of standard magnetic-gradient techniques. We present an all-optical method for the deterministic spatial selection of single- and bilayer samples of cold dipolar atoms using spatially selective parametric heating within a beat-note superlattice. By utilizing a high-resolution microscope objective as a common retroreflector for both optical frequency components, the lattice planes are passively stabilized. This renders their positions exceptionally robust against experimental drifts and structure-borne vibrations, even eliminating the need for active laser stabilization over millimeter-scale separations from the reflecting surface. We validate this approach by demonstrating the robust isolation of one or two atomic layers in precise coincidence with the focal plane of our objective. This enables future single-atom-resolved studies of long-range interacting systems.
Quantum gas microscopy has enabled the study on intriguing properties of ultracold atoms in optical lattices. It provides the cutting-edge technology for manipulating quantum many-body systems. In such experiments, atoms have to be prepared into a two-dimensional (2D) system for being resolved by microscopes with limited depth of focus. Here we report an experiment on slicing a single layer of the atoms trapped in a few layers of pancake-shaped optical traps to create a 2D system. This technique is implemented with a microwave “knife”, i.e., a microwave field with a frequency defined by the resonant condition with the Zeeman-shifted atomic levels related to a gradient magnetic field. It is crucial to keep a stable preparation of the desired layer to create the 2D quantum gas for future experimental applications. To achieve this, the most important point is to provide a gradient magnetic field with low noises and slow drift in combination with a properly optimized microwave pulse. Monitoring the electric current source and the environmental magnetic field, we applied an actively stabilizing circuit and realized a field drift of 0.042(3) mG/hour. This guarantees creating the single layer of atoms with an efficiency of 99.92(3)% while atoms are hardly seen in other layers within 48 hours, satisfying future experimental demands on studying quantum many-body physics.
We report the experimental realization of a new kind of optical lattice for ultracold atoms where arbitrarily large separation between the sites can be achieved without renouncing to the stability of ordinary lattices. Two collinear lasers, with slightly different commensurate wavelengths and retroreflected on a mirror, generate a superlattice potential with a periodic "beat-note" profile where the regions with large amplitude modulation provide the effective potential minima for the atoms. To prove the analogy with a standard large spacing optical lattice we study Bloch oscillations of a Bose Einstein condensate with negligible interactions in the presence of a small force. The observed dynamics between sites separated by ten microns for times exceeding one second proves the high stability of the potential. This novel lattice is the ideal candidate for the coherent manipulation of atomic samples at large spatial separations and might find direct application in atom-based technologies like trapped-atom interferometers and quantum simulators.
Our knowledge on ultracold quantum gases is strongly influenced by our ability to probe these objects. In situ imaging combined with single atom sensitivity is an especially appealing scenario as it can provide direct information on the structure and the correlations of such systems. For a precise characterization a high spatial resolution is mandatory. In particular, the perspective to study quantum gases in optical lattices makes a resolution well below one micrometer highly desirable. Here, we report on a novel microscopy technique which is based on scanning electron microscopy and allows for the detection of single atoms inside a quantum gas with a spatial resolution of better than 150 nm. Imaging a Bose-Einstein condensate in a one-dimensional optical lattice with 600 nm period we demonstrate single site addressability in a sub-um optical lattice. The technique offers exciting possibilities for the preparation, manipulation and analysis of quantum gases.
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.
Atomic physics has greatly advanced quantum science, mainly due to the ability to control the position and internal quantum state of atoms with high precision, often at the quantum limit. The dominant tool for this is laser light, which can structure and localize atoms in space (e.g., in optical tweezers, optical lattices, 1D tubes or 2D planes). Due to the diffraction limit of light, the natural length scale for most experiments with atoms is on the order of 500 nm or larger. Here we implement a new super-resolution technique which localizes and arranges atoms on a sub-50 nm scale, without any fundamental limit in resolution. We demonstrate this technique by creating a bilayer of dysprosium atoms, mapping out the atomic density distribution with sub-10 nm resolution, and observing dipolar interactions between two physically separated layers via interlayer sympathetic cooling and coupled collective excitations. At 50 nm, dipolar interactions are 1,000 times stronger than at 500 nm. For two atoms in optical tweezers, this should enable purely magnetic dipolar gates with kHz speed.
We present a method for preparing a single two-dimensional sample of a two-spin mixture of fermionic potassium in a single antinode of an optical lattice, in a quantum-gas microscope apparatus. Our technique relies on spatially-selective microwave transitions in a magnetic field gradient. Adiabatic transfer pulses were optimized for high efficiency and minimal atom loss and heating due to spin-changing collisions. We have measured the dynamics of those loss processes, which are more pronounced in the presence of a spin mixture. As the efficient preparation of atoms in a single antinode requires a homogeneous transverse magnetic field, we developed a method to image and minimize the magnetic field gradients in the focal plane of the microscope.