Sensitive Absorption Imaging of Single Atoms in Front of a Mirror

In this paper we show that the sensitivity of absorption imaging of ultracold atoms can be significantly improved by imaging in a standing-wave configuration. We present simulations of single-atom absorption imaging both for a travelling-wave and a standing-wave imaging setup, based on a scattering approach to calculate the optical density of a single atom. We find that the optical density of a single atom is determined only by the numerical aperture of the imaging system. We determine optimum imaging parameters, taking all relevant sources of noise into account. For reflective imaging we find an improvement of 1.7 in the maximum signal-to-noise ratio can be achieved. This is particularly useful for imaging in the vicinity of an atom chip, where a reflective surface is naturally present

Off-axis dipole forces in optical tweezers by an optical analog of the {Magnus} effect

It is shown that a circular dipole can deflect the focused laser beam that induces it, and will experience a corresponding transverse force. Quantitative expressions are derived for Gaussian and angular tophat beams, while the effects vanish in the plane-wave limit. The phenomena are analogous to the Magnus effect pushing a spinning ball onto a curved trajectory. The optical case originates in the coupling of spin and orbital angular momentum of the dipole and the light. In optical tweezers the force causes off-axis displacement of the trapping position of an atom by a spin-dependent amount up to $\lambda/2\pi$, set by the direction of a magnetic field. This suggests direct methods to demonstrate and explore these effects, for instance to induce spin-dependent motion.Comment: 5 pages, 3 figures; plus 3 pages Supplemental Material (accepted version

Classical wave-optics analogy of quantum information processing

An analogous model system for quantum information processing is discussed, based on classical wave optics. The model system is applied to three examples that involve three qubits: ({\em i}) three-particle Greenberger-Horne-Zeilinger entanglement, ({\em ii}) quantum teleportation, and ({\em iii}) a simple quantum error correction network. It is found that the model system can successfully simulate most features of entanglement, but fails to simulate quantum nonlocality. Investigations of how far the classical simulation can be pushed show that {\em quantum nonlocality} is the essential ingredient of a quantum computer, even more so than entanglement. The well known problem of exponential resources required for a classical simulation of a quantum computer, is also linked to the nonlocal nature of entanglement, rather than to the nonfactorizability of the state vector.Comment: 9 pages, 6 figure

Collective suppression of optical hyperfine pumping in dense clouds of atoms in microtraps

We observe a density-dependent collective suppression of optical pumping between the hyperfine ground states in an array of submicrometer-sized clouds of dense and cold rubidium atoms. The suppressed Raman transition rate can be explained by strong resonant dipole-dipole interactions that are enhanced by increasing atom density, and are already significant at densities of ﰀ0.1k3, where k denotes the resonance wave number. The observations are consistent with stochastic electrodynamics simulations that incorporate the effects of population transfer via internal atomic levels embedded in a coupled-dipole model

Permanent magnet atom chips for BEC and microtrap arrays

Abstract not available

The LOFAR Transients Key Project

International audienc

The LOFAR Transients Key Project

International audienc