Erin Marshall Seroka, Ana Valdés Curiel, Dimitrios Trypogeorgos, Nathan Lundblad, Ian B. Spielman
2019-07-11
We demonstrate partial-transfer absorption imaging as a technique for repeatedly imaging an ultracold atomic ensemble with minimal perturbation. We prepare an atomic cloud in a state that is dark to the imaging light. We then use a microwave pulse to coherently transfer a small fraction of the ensemble to a bright state, which we image using in situ absorption imaging. The amplitude or duration of the microwave pulse controls the fractional transfer from the dark to the bright state. For small transfer fractions, we can image the atomic cloud up to 50 times before it is depleted. As a sample application, we repeatedly image an atomic cloud oscillating in a dipole trap to measure the trap frequency.
Simon Ragg, Chiara Decaroli, Thomas Lutz, Jonathan P. Home
2019-07-11
We describe the use of laser-enhanced etching of fused silica in order to build multi-layer ion traps. This technique offers high precision of both machining and alignment of adjacent wafers. As examples of designs taking advantage of this possibility, we describe traps for realizing two key elements of scaling trapped ion systems. The first is a trap for a cavity-QED interface between single ions and photons, in which the fabrication allows shapes that provide good electro-static shielding of the ion from charge build-up on the mirror surfaces. The second incorporates two X-junctions allowing two-dimensional shuttling of ions. Here we are able to investigate designs which explore a trade-off between pseudo-potential barriers and confinement at the junction center. In both cases we illustrate the design constraints arising from the fabrication.
B. Dubetsky
2019-07-07
An analytical expression for the gravitational field of a homogeneous cylinder is derived. The phase of the atom interferometer produced by the gravity field of the set of cylinders has been calculated. The optimal values of the initial positions and velocities of atomic clouds were obtained. It is shown that at equal sizes of the atomic cloud in the vertical and transverse directions, as well as at equal atomic vertical and transverse temperatures, systematic errors due to the finite size and temperature of the cloud disappear. It is shown that, although the gravitational field of the Earth does not affect the phase double difference, it continues to affect the measurement accuracy of this signal. To overcome this influence, it is proposed to use the technique of eliminating gravity-gradient terms. Nonlinear dependences of the phase on the uncertainties of atomic positions and velocities required us to modify the expression for the standard phase deviation. Moreover, such dependencies lead to a phase shift, which was also calculated. The relative accuracy of measurements of Newtonian gravitational constant 10^{-4} and 2*10^{-5} is predicted for sets of 24 and 630 cylinders, respectively.
Graeme Harvie, Adam Butcher, Jon Goldwin
2019-06-13
We study optical gain in a gas of cold 39K atoms. The gain is observed during operation of a conventional magneto-optical trap without the need for additional fields. Measurements of transmission spectra from a weak probe show that the gain is due to stimulated Raman scattering between hyperfine ground states. The experimental results are reproduced by a simplified six-level model, which also helps explain why such gain is not observed in similar experiments with rubidium or cesium.
Igor M. Sokolov, William Guerin
2019-02-12
Collective effects in atom-light interaction is of great importance for cold-atom-based quantum devices or fundamental studies on light transport in complex media. Here we discuss and compare three different approaches to light scattering by dilute cold atomic ensembles. The first approach is a coupled-dipole model, valid at low intensity, which includes cooperative effects, like superradiance, and other coherent properties. The second one is a random-walk model, which includes classical multiple scattering and neglects coherence effects. The third approach is a crude approximation only based on the attenuation of the excitation beam inside the medium, the so-called "shadow effect". We show that in the case of a low-density sample, the random walk approach is an excellent approximation for steady-state light scattering, and that the shadow effect surprisingly gives rather accurate results at least up to optical depths on the order of 15.
K. N. Lyashchenko, D. M. Vasileva, O. Yu. Andreev, A. B. Voitkiv
2019-07-11
We develop {\it ab initio} relativistic QED theory for elastic electron scattering on hydrogen-like highly charged ions for impact energies where, in addition to direct (Coulomb) scattering, the process can also proceed via formation and consequent Auger decay of autoionizing states of the corresponding helium-like ions. Even so the primary goal of the theory is to treat electron scattering on highly charged ions, a comparison with experiment shows that it can also be applied for relatively light ions covering thus a very broad range of the scattering systems. Using the theory we performed calculations for elastic electron scattering on B
, Ca , Fe , Kr , and Xe . The theory was also generalized for collisions of hydrogen-like highly charged ions with atoms considering the latter as a source of (quasi-) free electrons.
Mariusz Pawlak, Piotr S. Żuchowski, Nimrod Moiseyev, Piotr Jankowski
2019-07-11
Cold collisions serve as a very sensitive probe of the interaction potential. In the recent study of Klein et al. (Nature Phys. 13, 35-38 (2017)) the one-parameter scaling of the interaction potential was necessary to obtain agreement between theoretical and observed patterns of the orbiting resonances for excited metastable helium atoms colliding with hydrogen molecules. Here we show that the effect of nonrigidity of the H
molecule on the resonant structure, absent in the previous study, is critical to predict correct positions of the resonances in that case. We have complemented the theoretical description of the interaction potential and revised reaction rate coefficients by proper inclusion of the flexibility of the molecule. The calculated reaction rate coefficients are in remarkable agreement with the experimental data without empirical adjustment of the interaction potential. We have shown that even state-of-the-art calculations of the interaction energy cannot ensure agreement with the experiment if such an important physical effect as flexibility of the interacting molecule is neglected. Our findings about the significance of the nonrigidity effects can be especially crucial in cold chemistry, where the quantum nature of molecules is pronounced.
Vladimir I. Korobov
2019-05-20
The Bethe logarithm for a large set of states of the helium atom is calculated with a precision of 12-14 significant digits. The numerical data is obtained for the case of infinite mass of a nucleus. Then we study the mass dependence and provide coefficients of the
expansion, which allows us to calculate accurate values for the Bethe logarithm for any finite mass. An asymptotic expansion for the Rydberg states is analyzed and a high-quality numerical approximation is found, which ensures 7-8 digit accuracy for the , , and states of the helium atom.
Huayu Hu
2019-07-08
Researches on the electron-positron pair production in the presence of the intense laser field are reviewed, motivated by the theoretical importance of the nonperturbative QED problem and the worldwide development of the strong laser facilities. According to distinct experimental requirements and theoretical methods, two types of pair production are elaborated, which are respectively the pair production in the combination of a seed particle and the strong laser, and vacuum pair production without a seed particle. The origin of the nonperturbative problem caused by the strong field is analyzed. The main ideas, realization, achievements, validity, challenges and bottleneck problems of the nonperturbative methods developed for each type of the pair production problem are discussed.
Kevin C. Cox, David H. Meyer, Zachary A. Castillo, Fredrik K. Fatemi, Paul D. Kunz
2019-07-10
Significant resources are now being devoted to develop intermediate scale quantum systems with tens of quantum bits, tunable interactions, and independent control of each element. Ion traps, superconducting circuits, tweezer arrays of neutral atoms, and other systems have made exciting recent advances, but scaling precise quantum dynamics from few-body to many-body remains as a primary challenge in quantum science. Instead of building up qubit-by-qubit, like the aforementioned platforms, here we focus on a system where quantum information is stored as patterns or images inside a single cavity-coupled atomic ensemble containing up to
atoms. This scalability more closely resembles, for example, that of a neural network, where data is stored and manipulated as patterns and images rather than binary bits. We demonstrate cavity electrodynamics between multiplexed excitations stored in a laser-cooled and trapped ensemble of atoms coupled to an optical ring cavity. Multiplexing is achieved by applying multiple dressing laser beams, creating cavity-coupled spin-wave excitations, that are holographic in nature. We demonstrate strong cavity interactions with multiple spin waves and measure cavity-mediated interactions between pairs of spin waves as a function of their holographic and spectral overlap. The current optics configuration allows rapid, interchangeable cavity-coupling to 4 profiles with an overlap parameter of less than 10%, enough to demonstrate, for example, a quantum repeater network simulation in the cavity. With further improvements to the optical multiplexing setup, we infer the ability to access more than independent spin-wave profiles.
