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Imaging of Bose-Einstein condensates requires high-sensitivity detectors and images are often dominated by un-scattered light, complicating the detection of fine microscopic features such as quantised vortices and phonons (sound waves). Thanks to the Fourier transforming properties of optical diffraction there is a better way – throw away most of the unscattered light and keep the signal you want. Surprisingly, this spatial- frequency Fourier filter can be implemented with some simple optics, consisting of a couple of lenses and a small blocking mask. In effect, the concept is to produce a Photoshop-style edge detection filter, but rendered real-time and analogue by physical optics and a bench top optical system. This technique is known as darkground imaging.

The aim of this project is to explore and characterise the implementation of darkground imaging via a benchtop optical system, and determine its efficacy and capabilities. Opportunity to implement the system on the UQ Scalar BEC apparatus may arise towards the end of the project.

Atoms must be trapped to create a Bose-Einstein Condensate (BEC). This can be done either optically or magnetically. Optical trapping is insensitive to the magnetic sublevel of an atom, whereas in a magnetic trap, the degeneracy of these different states is lifted. Using optical traps one can create BECs in any internal state, allowing the spin of the atoms to be essentially a free parameter. Spinor condensates, which are multi-component condensates can be created in optical traps, where all magnetic sublevels of an internal state are populated. Adding spin freedom to our emulator increases parameter space which can be explored. The populations of these states can be altered passively through spin-exchange collisions or actively through time-varying magnetic fields (typically radio frequency or microwaves). By proper application of these fields, we can prepare the condensate in mixtures or superpositions of various internal states through spin flips.

This project will quantify and develop the methods, such as Rapid Adiabatic Passage, to couple and prepare desired internal state mixtures. This will then be applied to our condensates to study the dynamics and superfluid behaviour of spinor condensates in these systems.

Creating Bose-Einstein condensates requires lasers that are locked to particular atomic transitions. To do this, we typically scan the frequency of the laser and pass the light through a cell containing the a vapour of the atom of interest (in our case, rubidium). By measuring the light intensity on the other side of the cell, we can then detect the precise frequency at which the absorptions occur which correlate to these transitions.

An alternative approach to this method would be to instead, keep the laser locked to a particular frequency and apply an AC magnetic field to the absorption cell to scan the transition frequency through Zeeman shifting.

This project aims to setup the laser locking using these two methods and determine which one gives the most stable lock onto atomic transitions. The preferred setup will then be integrated into our Bose-Einstein condensate experiment.

Ultracold atoms are trapped in magnetic and optical traps. Trapping of ultracold atoms and condensing them into a Bose-Einstein condensate (BEC) allows us to study many quantum mechanical phenomena, such as the superfluid fountain effect and clustering of quantum vortices, leading to local negative absolute zero temperatures.

One method to optically trap ultracold atoms is in an optical lattice: Through interference of two optical beams, we create an accordion-shaped set of fringes in which we trap our atoms. While this method allows us to create very pure BECs, the downside of using optical interference is that it is very susceptible to phase fluctuations of the laser beams, mainly induced through vibrations. These vibrations shake the atoms inside the lattice heating them and reducing the lifetime of the BEC.

The aim of this project is to design and test a feedback system that is robust against any mechanical noise. The project includes a literature review of successful feedback schemes for optical lattices, programming a microcontroller to realise a feedback system, and setting up a proof-of-principle stabilised optical lattice in our lab.

Bose Einstein condensates (BECs) are used to study quantum effects at the macroscopic scale. This has allowed BEC systems to be developed into quantum simulators and extremely sensitive sensors for applications like the search for dark matter.

To do this, it is necessary to have a very high level of control over the parameter space of the atoms involved. In the UQ BEC lab, we achieve this control by projecting arbitrary light patterns onto the condensates and have managed to create optical potentials which trap the atoms with resolutions of about 1 μm (close to the diffraction limit of the light used). This does however mean that we are very susceptible to small changes in environmental conditions, leading to a lot of time being spent focussing optics to maintain this resolution.

The project aims to improve this process by implementing autofocusing of lenses that project these light potentials using computer interfaced lens stages. It will involve implementing the preexisting software to control these lenses, developing a way of determining when optimal focusing has been achieved and then feeding back to alter the lens position.