Sympathetic and swap cooling of trapped ions by cold atoms in a MOT

A mixed system of cooled and trapped, ions and atoms, paves the way for ion assisted cold chemistry and novel many body studies. Due to the different individual trapping mechanisms, trapped atoms are significantly colder than trapped ions, therefore in the combined system, the strong binary ion$-$atom interaction results in heat flow from ions to atoms. Conversely, trapped ions can also get collisionally heated by the cold atoms, making the resulting equilibrium between ions and atoms intriguing. Here we experimentally demonstrate, Rubidium ions (Rb$^+$) cool in contact with magneto-optically trapped (MOT) Rb atoms, contrary to the general expectation of ion heating for equal ion and atom masses. The cooling mechanism is explained theoretically and substantiated with numerical simulations. The importance of resonant charge exchange (RCx) collisions, which allows swap cooling of ions with atoms, wherein a single glancing collision event brings a fast ion to rest, is discussed.Comment: 10 pages, 3 figure

Multi-photon ionisation spectroscopy for rotational state preparation of N+2

In this paper we investigate the 2 + 1′ resonance enhanced multi-photon ionisation (REMPI) of molecular nitrogen via the a1Πg(v = 6) intermediate state and analyse its feasibility to generate molecular nitrogen ions in a well defined ro-vibrational state. This is an important tool for high precision experiments based on trapped molecular ions, and is crucial for studying the time variation of the fundamental constant mp/me using N+2. The transition is not reported in the literature and detailed spectral analysis has been conducted to extract the molecular constants of the intermediate state. By carefully choosing the intermediate ro-vibrational state, the ionisation laser wavelength and controlling the excitation laser pulse energy, unwanted formation of rotationally excited molecular ions can be suppressed and ro-vibrational ground state ions can be generated with high purity

Precision spectroscopy technique for dipole-allowed transitions in laser-cooled ions

In this paper , we present a technique for the precise measurement of electric dipole-allowed transitions in trapped ions. By applying a probe and a cooling laser in quick succession, the full transition can be probed without causing distortion from heating the ion. In addition, two probes can be utilized to measure a dispersion-like signal, which is well suited to stabilizing the laser to the transition. We have fully characterized the parameters for the measurement and find that it is possible to measure the line center to better than 100 kHz with an interrogation time of 30 s. The long-term stability of the spectroscopy signal is determined by employing two independent ion trap systems. The first ion trap is used to stabilize the spectroscopy laser. The second ion trap is then employed to measure the stability by continuously probing the transition at two frequencies. From the Allan variance, we obtained a frequency instability of 1⋅10⁻¹⁰ for an interrogation time of 1,000 s

The structure of a micro-bat community in relation to gradients of environmental variation in a tropical urban area

We investigated patterns of community structure (species composition, foraging activity, and nightly foraging patterns) of bats in relation to gradients of environmental variation in a tropical urban area. A total of 32 sites spread equally across eight habitat types were sampled in the city of Townsville, North Queensland, Australia. Each site was sampled on 3 non-consecutive occasions using automated AnaBat systems. Eleven species were confidently identified while a possible four more were identified only to the genus level. Ordination of environmental variables measured at these sites identified two distinct environmental gradients reflecting the degree of urbanisation and foliage density. With increasing urbanisation there was a decline in species richness and total foraging activity. We used regression trees to characterise foraging preferences of each species. This analysis suggested that only one species of Mormopterus was able to exploit the resources provided by urbanisation. This species foraged in areas with higher numbers of white streetlights. The remaining species of bats preferred to forage within close proximity to natural vegetation and with low numbers of streetlights. The density of vegetation in long-established suburbs did not substantially reverse the trend for urban areas to have fewer bat species than original habitats