Precise determination of the structure factor and contact in a unitary Fermi gas

We present a high-precision determination of the universal contact parameter in a strongly interacting Fermi gas. In a trapped gas at unitarity we find the contact to be $3.06 \pm 0.08$ at a temperature of 0.08 of the Fermi temperature in a harmonic trap. The contact governs the high-momentum (short-range) properties of these systems and this low temperature measurement provides a new benchmark for the zero temperature homogeneous contact. The experimental measurement utilises Bragg spectroscopy to obtain the dynamic and static structure factors of ultracold Fermi gases at high momentum in the unitarity and molecular Bose-Einstein condensate (BEC) regimes. We have also performed quantum Monte Carlo calculations of the static properties, extending from the weakly coupled Bardeen-Cooper-Schrieffer (BCS) regime to the strongly coupled BEC case, which show agreement with experiment at the level of a few percent.Comment: Replaced with accepted versio

Adaptive optics tracking and pushing system for space debris manoeuvre

As space debris in lower Earth orbits are accumulating, techniques to lower the risk of space debris collisions must be developed. Within the context of the Space Environment Research Centre (SERC), the Australian National University (ANU) is developing an adaptive optics system for tracking and pushing space debris. The strategy is to pre-condition a laser launched from a 1.8 m telescope operated by Electro Optics Systems (EOS) on Mount Stromlo, Canberra and direct it at an object to perturb its orbit. Current progress towards implementing this experiment, which will ensure automated operation between the telescope and the adaptive optics system, will be presented.The authors would like to acknowledge the support of the Cooperative Research Centre for Space Environment Management (SERC Limited) through the Australian Government’s Cooperative Research Centre Programm

Site characterisation at Mount Stromlo: results with a single-detector stereo-SCIDAR

We present the status of the site-characterisation campaign at Mount Stromlo Observatory. The main goal of the project is to aid the development and operation of new adaptive optics (AO) systems for space debris tracking and pushing as well as satellite imaging. The main method we use for the characterisation is based on the SCIntillation Detection And Ranging (SCIDAR) technique. We have designed a unique version of the SCIDAR instrument: a stereo-SCIDAR system that uses a roof prism to separate beams from a double-star system to obtain two isolated pupil images on a single detector. The instrument is installed on the 1.8 m telescope of Electro-Optic Systems (EOS), sharing facilities with the adaptive optics systems we are currently building. The SCIDAR instrument will be operated intermittently, weather and availability permitting, until sufficient amount of data has been collected to characterise the site. This paper reports the current status of the project: we have recently started the commissioning phase and obtained first measurements with the instrument.James Osborn is grateful to the Science and Technology Facilities Committee (STFC) for financial support (grant reference ST/J001236/1 and the research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2013-2016) under grant agreement number 312430 (OPTICON)

High level adaptive optics supervision software for fast transition to optimal performance

Space debris in low Earth orbit (LEO) below 1500 km is becoming an increasing threat to spacecrafts. To manage the threat, we are developing systems to improve the ground-based tracking and imaging of space debris and satellites. We also intend to demonstrate that it is possible to launch a high-power laser that modifies the orbits of the debris. However, atmospheric turbulence makes it necessary to use adaptive optics with such systems. When engaging with objects in LEO, the objects are available only a limited amount of time. During the observation window, the object has to be acquired and performance of all adaptive optics feedback loops optimised. We have implemented a high-level adaptive optics supervision tool to automatise time-consuming tasks related to calibration and performance monitoring. This paper describes in detail the current features of our software