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Metal-based additive manufacturing (AM) represents a paradigm change in engineering and production methods across multiple industries and sectors. AM methods enable mass reduction and performance optimisation well beyond that achievable via conventional manufacturing, thereby impacting significantly on aerospace and space technologies. Technologies relying on high and ultra-high vacuum (UHV), such as x-ray photo-electron spectroscopy, photo-sensors, cameras and cryostats, could also benefit greatly from AM. Despite recent advances in AM processing of metals, additively manufactured UHV chambers have so far not been achieved. Reducing the mass of UHV equipment is particularly critical for the development of portable cold atom systems, which are expected to underpin the next generation of sensing and timekeeping technologies and to allow novel space-based sensors for fundamental research. We demonstrate here an additively manufactured UHV chamber reaching a pressure below $10^{-10}$ mbar, enabling a cloud of cold $^{85}$Rb atoms to be trapped - the starting point for many precision timekeeping and sensing devices. The chamber is manufactured from aluminium alloy AlSi10Mg by laser powder bed fusion and has a mass of less than a third of a commercially-available equivalent. Outgassing analysis based on mass spectrometry was performed and it was demonstrated that even without active pumping the system remains in the $10^{-9}$ mbar regime for up to 48 hours.

Recent advances in the preparation, control and measurement of atomic gases have led to new insights into the quantum world and unprecedented metrological sensitivities, e.g. in measuring gravitational forces and magnetic fields. The full potential of applying such capabilities to areas as diverse as biomedical imaging, non-invasive underground mapping, and GPS-free navigation can only be realised with the scalable production of efficient, robust and portable devices. Here we introduce additive manufacturing as a production technique of quantum device components with unrivalled design freedom, providing a step change in efficiency, compactness and facilitating systems integration. As a demonstrator we present a compact ultracold atom source using less than ten milliwatts power to produce large samples of cold rubidium gases in an ultrahigh vacuum environment. This disruptive technology opens the door to drastically improved integrated structures, which will further reduce power consumption, size and assembly complexity in scalable series manufacture of bespoke quantum devices., Comment: 7 pages, 6 figures

A combination of molecular-dynamics simulations, theoretical predictions, and previous experiments are used in a two-part study to determine the role of the Knudsen layer in rapid granular flows. First, a robust criterion for the identification of the thickness of the Knudsen layer is established: a rapid deterioration in Navier-Stokes-order prediction of the heat flux is found to occur in the Knudsen layer. For (experimental) systems in which heat flux measurements are not easily obtained, a rule-of-thumb for estimating the Knudsen layer thickness follows, namely that such effects are evident within 2.5 (local) mean free paths of a given boundary. Second, comparisons of simulation and experimental data with Navier-Stokes order theory are used to provide a measure as to when Knudsen layer effects become non-negligible. Specifically, predictions that do not account for the presence of a Knudsen layer appear reliable for Knudsen layers collectively composing up to 20% of the domain, whereas deterioration of such predictions becomes apparent when the domain is fully comprised of the Knudsen layer., Comment: 9 figures, accepted to Journal of Fluid Mechanics