Theses

Full thesis can be accessed here.

Pulsar glitches are sudden increases in the rotational frequency of neutron stars and are widely believed to originate from the dynamics of quantized vortices in neutron-star superfluids. In this project, a rotating two-dimensional Bose–Einstein condensate (BEC) with programmable pinning sites is simulated using the dissipative Gross–Pitaevskii equation as a laboratory analogue of a neutron star superfluid. The simulations investigate vortex formation, pinning, depinning, and angular momentum transfer during spin-down. The results show that the equilibrium vortex number increases approximately linearly with rotation frequency, consistent with the Feynman relation, and that vortices relax into stable Abrikosov lattice configurations. During spin-down, pinned vortices initially remain locked to the rotating lattice before depinning and migrating outward. This outward vortex transport reduces the angular momentum stored in the condensate and produces a corresponding response in the inferred crust angular velocity. Sound-wave excitations generated by vortex motion are found to perturb neighbouring vortices and may contribute to collective depinning events. Comparison with a fully pinned control simulation demonstrates that vortex depinning is the primary mechanism responsible for angular momentum transfer in the model. These results reproduce several key ingredients of the vortex-avalanche interpretation of pulsar glitches and demonstrate how Bose–Einstein condensates can be used to investigate glitch-like dynamics in a controlled laboratory setting.

Full thesis can be accessed here.

Bose-Einstein condensates (BECs) are a type of superfluid that occurs when the majority of the population of a cloud of bosons is located in the ground state. This macroscopic occupation of the lowest energy state results in BECs exhibiting unique and unusual qualities consistent with superfluidity. These qualities permit the formation of quantum vortices which are points of zero atom density in the condensate with quantised circulation around the outside. The dynamics of quantum vortices facilitate a significant portion of BEC research. One of these BEC research applications is the characterisation and quantification of the mutual friction force. Mutual friction is a dissipative force that alters the dynamics of quantum vortices due to interactions with the normal (thermal cloud) component of the superfluid system. This force can be expressed as the sum of two components that act orthogonal to each other; the longitudinal coefficient α and the transverse coefficient α′. In an atomic BEC, the value of α′ has yet to be explicitly measured and quantified as existing research often assumes that it is close to, or equal to zero at very low temperatures. If this experiment produces a non-zero value for α′ it may suggest that there are some other dynamics in the system that we don’t yet understand. This thesis intends to officially quantify α′ in a quasi-2D BEC and contribute to our understanding of the mutual friction force in superfluids.

A variety of optical and magnetic trapping and cooling steps are used to create our BEC. Additionally, a digital micromirror device (DMD) is used for trapping in the x−y plane and for generating our initial system conditions. Our system consists of a vortex dipole pair with opposite charge, where one vortex is pinned at the centre of the condensate and the other is located slightly off-centre. This configuration is created in the DMD using the chopsticks technique where one beam splits into two separate beams that simultaneously move to the specified locations. This slow movement through the condensate is what creates vortices beneath the beams. By observing and tracking the orbital motion of the outer vortex around the centre vortex, we can extract the value of the mutual friction coefficients. Time-of-Flight and Faraday imaging is used to acquire clear images for analysis and a machine learning program is used to identify and extract the positions of vortices in each image.

Initial analysis of these vortex dynamics revealed that the appearance of spurious vortices in our images was significantly altering our results and preventing any accurate analysis.

To combat this issue, an additional blue-detuned optical dipole trap (ODT) was implemented into the apparatus. This trap uses a π-step phase plate which transforms the beam profile from a Gaussian to a TEM01 mode that has a region of zero intensity through the centre. By repulsively trapping atoms within this node, we aimed to reduce the presence of non-uniformities in our trap. Characterisation of this green sheet trap after implementation revealed a larger trap frequency in the axial direction and an improved trap uniformity across the entire x−y plane. These improvements to the final trap will allow for a more diverse range of experiments to be performed in the lab. The intensity profile, beam diameter and direct trap frequency also closely matched what we expected when computationally modelling an ideal TEM01 mode. There was not enough time after this implementation to resume our mutual friction analysis as the optimisation and alignment of this green sheet trap with the other components was very complex. However, the successful addition of the green sheet, which very accurately resembles an ideal TEM01 mode, ensures that future experiments involving the observation of vortex dynamics (including this mutual friction experiment) will now be seamless and unaffected by the presence of non-uniformities in the condensate.

Full thesis can be accessed here.

Superfluids differ fundamentally from classical fluids: viscous flows exhibit drag and dissipation at any nonzero velocity, whereas superfluids remain dissipationless until a geometry-dependent critical velocity is exceeded. Although dissipation emerges through quantum pressure, the resulting flows organise similarly. Universal drag laws reveal that superfluid flow is scale invariant under a superfluid Reynolds number. The onset of dissipation exhibits distinct geometric scaling: smooth, streamlined obstacles approach size-independent critical velocities, while sharp-edged geometries follow a power-law dependence on obstacle size. These results establish a unified picture of onset and scale-invariant dynamics in superfluid flow.

Full thesis can be accessed here.

Spinor Bose-Einstein condensates (sBECs) are quantum superfluids with a spin degree of freedom arising from interactions between atoms in different spin-1 magnetic states of 87Rb. These ultracold atomic systems exhibit magnetic order, tuneable interactions, and quantum phase transitions. This offers enhanced opportunities for exploring phenomena beyond those accessible in single state BECs, such as new classes of topological defects. This thesis is concerned with the experimental realities of controllably creating novel topological defects known as Polar-Core Vortices and Ferro-dark Solitons. These defects are proposed as stable spatial configurations of the transverse spin which exist in the so-called "Easy-Plane'' phase. Procedures are provided on how to produce a flexible apparatus hosting both 2D and 1D trapping geometries, reduce stray magnetic fields and minimise their noise using Ramsey interferometry, cross quantum phase transitions using detuned microwave fields, and develop techniques to image the transverse spin of the sBEC. The capstone of this project is the dual Digital Micromirror Device (DMD) setup we incorporated for the confinement of the sBECs and the creation of topological defects by spatially engineering the transverse spin in the EPP using tailored optical potentials at the tune-out wavelength. Engineering the transverse spin of a sBEC using techniques developed in this thesis constitutes the controllable creation of novel vortex and soliton structures which have not been realised in a controllable manner. This allows for significant experimental investigations into defects which have unique dynamics and interactions which insofar have only been described theoretically.

Full thesis can be accessed here.

Negative temperature equilibria and the formation of large-scale Onsager vortex clusters was predicted to be dependent on the energy of a turbulent system by Lars Onsager et al. using statistical model of 2D turbulence of superfluids known as the point vortex model. 70 years after their predictions, these predicted states were demonstrated experimentally. How the system would evolve from low to high energy remained unclear, but recent works in the field theorise negative temperature vortex clustering are achieved by evaporative heating of vortices. Despite this, how different 2D turbulent systems evolve to negative temperatures and what parameters affect the evolution are still largely unknown. I investigated the point vortex model on a disk and an annulus in the presence of pinned persistent current by performing statistical analysis of their phase space and looking at the dynamical evolution of the system. My work shows the system’s evolution is in agreement with the evaporative heating of vortices as a mechanism for driving to negative temperature equilibria, however the phase space, even in the wide annulus limit, implies approximating an annulus using a disc model may be unsuitable.

Full thesis can be accessed here.

Atomtronics is an emerging field that designs circuits using neutral atoms to take advantage of certain quantum properties, often defined by the geometry of the system. with promising use in atomic simulation and rotation measurement. An example of geometry defined system was given in recent articles by T. Bland et al., where their team numerically simulated systems of Bose-Einstein condensate (BEC) trapped in a pseudo-2D double-ring potential. The simulations demonstrated the localisation of quantized persistent current within their constituent rings, as well as a method to control the oscillation of such current using a barrier potential. Based on their work, we simulated similar double-ring systems using different physical parameters, as well as expanding up on their results by looking at states defined by the quantized vorticity of the current. Our findings show that a damped system will attempt to equalise its phase gradient, causing windings of persistent current to evenly distribute around a single ring. Additionally, we found that several process generates a well behaved phonon, such the annihilation of current, or a change in geometry due to the barrier potential. Using these simulations, we derived a method that can reproduce the oscillation of currents in a laboratory setting, using the equipment at UQ-BEC lab. This will enable us to study the properties of persistent current and potentially bring atomtronics one step closer to real-world applications.

Full thesis can be accessed here.

Bose-Einstein condensates are a state of matter that exist for dilute gases at sufficiently cold temperatures and high phase space densities, realising a superfluid. These systems are ideal for studying superfluids and with the use of different experimental techniques and technologies controlling these systems allows for studying different phenomena, such as persistent flow and quantum vortices. By using different experimental techniques and technologies to control these systems various phenomena can be studied, such as persistent flow and quantum vortices. In this thesis, building upon prior work we extend our system’s capabilities from scalar BECs of a single component, to multi-component BECs of different Zeeman states, allowing us to explore the interactions between two BECs of different miscibilities. To do so high levels of magnetic field stability are necessary, allowing us not only to create multi-component BECs but manipulate them with these fields.

With the use of spatial light modulator technologies, such as acousto-optical deflectors, we can create ring-shaped trapping potentials to confine our two-component condensates. The combination of magnetic Zeeman states yields different interspecies and intraspecies interaction strengths, resulting in various levels of miscibility. With this we explore how a miscible and immiscible two-component system respond under rotation in our ring geometry. The multiply connected nature allows for quantised rotation to occur in multiply connected condensates. This thesis provides preliminary results on an interesting regime, for an immiscible two-component system, where classical flow exists in a quantum system. Each state rotates with arbitrary angular momentum, due to the discontinuous density and phase for each component around the ring. Numerical simulations predict classical rigid body rotation for an immiscible two-component system. Experimentally, at finite temperature, this was not found to be the case, with the two condensates fragmenting and merging to overlap one another. Simulated and experimental data for the miscible two-component system showed a fast overlap between two densities.

This thesis then goes on to use spin-dependent optical tweezers to create and manipulate arbitrary spin patterns and magnetic domain structures in an immiscible two-component BEC. A detailed protocol is provided on how we produce these structures, using various high stability magnetic fields and RF pulses. The domain lifetime was found to have dependency on both temperature and initial size. We also explore the stability of the domain wall, through the application of a linear magnetic gradient field. Findings revealed a critical point in which flow from one state proceeds through the domain wall and through the other component, shedding vortices and soliton-like structures.

Finally, utilising the ultra-stable magnetic field control developed in this project, I describe experiments performed by periodically modulating a “see-saw” magnetic gradient field on a harmonically trapped BEC in an optical potential. A solvable analytical solution is produced for this system, which is rare in quantum mechanics for time-dependent potentials for a given Hamiltonian. This was found through Husimi’s solution to the Schrodinger equation for a single particle in a harmonic potential subject to periodic modulations, shown to apply for nonlinear many-body BEC systems. Such a driven system produces unique centre of mass trajectories, which we have shown experimentally, and fitted using the known analytical solution. An additional phenomenological damping term to compensate for the observed transition to driven oscillation is included in the analytical expression, with the damping arising from interactions with the thermal cloud. Finer features in the centre of mass motion are used for non-destructive measurements of the optical trapping frequencies. Combining our AOD technology with this driving scheme we have demonstrated a possible excitation-free way of transporting a BEC.

Full thesis can be accessed here.

The study of superfluids and their behaviour is of great interest due to their divergence from classical fluid behaviour, yet also due to the existence of some direct connections/analogs between the two. Perhaps even more interesting still is the overlap of these two possibilities as is investigated here. Bose-Einstein condensate (BEC) research has begun to delve into investigations of superfluidity due to the robustness and versatility of BEC superfluids in an experimental setting. BECs also enable direct resolution of turbulence phenomena. Recently developed methods additionally allow for almost arbitrary manipulation of BEC shape. Hence, BECs have the advantage that a multitude of shape and flow configurations can be investigated in an experimental setting with relative ease, allowing for a range of superfluid turbulence phenomena to be observed. This includes the study of Kelvin-Helmholtz (KH) instabilities which describe the transition to turbulent flow for a fluid system consisting of two parallel flowing streams. Specifically, KH instabilities predict a ``rolling up" effect of the interface between the streams. This project investigates the preliminary experimental investigation towards finding the KH instability in single-component BEC superfluids.

Full thesis can be accessed here.

Bose-Einstein condensates are superfluids which when engineered under suitable laboratory conditions support dissipationless flows and facilitate the development of quantum enhanced applications. Realising those suitable conditions requires experimental technologies which enable the complete dynamical control of the superfluid density and velocity profiles. This thesis conceives and demonstrates several dynamical controls using optical potentials formed using commercially available spatial-light-modulator technologies, and constitutes important progress toward many future experiments and the realisation of practical applications.

Experimental systems and control sequences are designed using complimentary acousto-optic deflection and digital micromirror spatial light modulator technologies, rather than magnetic field based approaches, given their inherently favourable spatial and temporal resolutions. An experimental apparatus which includes a time-averaged acousto-optic controlled potential is constructed to generate toroidal potentials suitable for developing inertial rotation sensors. Density and phase manipulation strategies are developed using that apparatus which prepare condensates with arbitrarily controllable wavefunctions. Complementary digital micromirror based adaptations are subsequently developed during this project.

Corrugations across the condensate density distributions are reduced using an iteratively corrected spatial light modulator configuration. Rigorous and generalised scan requirements are established for engineering time-averaged potentials; numerical methods are conceived which facilitate the simulation of these systems. The combination of the feedforward density control and time-averaging phase control enable the deterministic preparation of persistent currents around multiply connected condensates. These capabilities enable experiments into many-body groundstates, superfluid turbulence, atomtronics and metrology.

Spatial light modulator trapping sequences geared toward the study of Onsager vortices, vortex dipole optics, inertial rotation sensing and wake turbulence are specifically developed. Several upgraded experimental systems are finally designed using knowledge gained during this thesis, which enable these various applications in future. This thesis therefore constitutes significant progress toward several important experimental investigations using dynamically controllable optical trapping technologies.

Full thesis can be accessed here.

Optical dipole traps (ODTs) are among the most commonly used traps for confining Bose-Einstein condensates (BECs). A high degree of control of light allows for the realisation of a great variety of trapping geometries. The use of blue-detuned optical traps for BECs has many advantages over using red-detuned traps. As a blue-detuned trap acts as a repulsive potential, one of its main advantages is its ability to expel hot (thermal) atoms that introduce noise in measurements. We form our trap by creating an optical lattice of two interfering blue-detuned beams, and trap atoms vertically the nodal lattice planes. Another blue-detuned beam is used to trap atoms in the horizontal plane. This allows for creation of nearly uniform traps, closely resembling a finite-potential square well. The lattice spacing is easily adjusted, which provides stronger vertical confinement, making the trap a 2D box trap for BECs.

Full thesis can be accessed here.

Superfluidity has been exhibited in numerous systems including Bose-Einstein condensates (BECs) and liquid helium. Superfluids have many characterising features with a particularly striking one being the superfluid fountain effect. This effect is characterised by the flow of a superfluid from one cooler reservoir to another hotter one. Since the superfluid fountain effect has yet to be observed in BECs, the aim of this project is to experimentally look for the superfluid fountain effect in a BEC confined within a ‘dumbbell’ configuration. This thesis focuses on the technical and analytical steps needed to look for the fountain effect in a BEC, including determining an appropriate heating method for the BEC and accurate measurement technique of its temperature. Heating techniques of ‘bubbling’ and ‘shaking’ were tested and found to be appropriate ways to have control over partially heating the BEC or turning it entirely into a thermal cloud. Another intermediate test was to measure the superfluid transport in the newly implemented optical ‘box’ potential that provides optimal isolation of the two dumbbell reservoirs. Despite promising preliminary results, the search for the superfluid fountain effect was eventually halted by the experiment’s vacuum system failing after a number of other delays throughout the year. This thesis however makes progress towards looking for the superfluid fountain effect in a BEC to fill a gap in the demonstrations of a BEC as a superfluid and provides more knowledge as to how BECs transport when out of thermal equilibrium.

The full thesis can be accessed here.

The recent development of configurable optical trapping techniques for dilute atomic Bose- Einstein condensates, a macroscopically occupied quantum state and hence a superfluid, allow highly controllable experiments. The UQ BEC lab is capable of creating highly oblate BECs, ideal for experiments on two dimensional vortex dynamics. In this thesis, we present two experimental studies of the dynamics of these point vortices. In 1949 Lars Onsager predicated that point vortices in a bounded fluid must cluster at high energies, at a negative thermodynamic temperature. This was a very influential theory, explaining the stability of large two dimensional vortices, such as the Great Red Spot on Jupiter. The first section of this thesis investigates a system of same-signed vortices, known as the chiral system. This is predicted to have on-axis vortex equilibrium states at low energy, with a symmetry breaking transition to off-axis vortex clusters at high energies. We present the first observations of these equilibrium states, as well as the relaxation of a non-equilibrium state into an off- axis cluster. The data is very well described by our numerical calculations. These results answer some previously open theoretical questions such the relaxation time of vortices into equilibrium. The second experiment involves the dynamics of bound vortex-antivortex pairs, known as dipoles, the two dimensional equivalent of a smoke ring. As the dipoles carry linear momentum and energy, they obey a relation similar to Snell’s law in optics. Preliminary data shows qualitative agreement between the trajectories of the dipoles and simulations. Overall these results demonstrate the versatility of the apparatus, for investigating vortex dynamics, suggesting several future areas of experimental interest.

Full theses can be accessed here.

Turbulence, motion characterized by chaotic changes in pressure and flow velocity, is a challenging problem in physics. However, its underlying properties are found to be universal and do not depend on the host fluid. Meanwhile, transport phenomena, irreversible exchange processes due to the statistical continuous random motion of particles, although being complicated from a microscopic point of view, can often be modelled quite simply by tracking macroscopic quantities of interest in the system. In this thesis, using atomic Bose-Einstein condensates, we study both these phenomena inside a quantum fluid using a highly configurable BEC platform developed to provide arbitrary dynamic control over the 2D superfluid system. Furthermore, the experiments are modelled using the Gross-Pitaevskii equation, the
point vortex model and the hydrodynamic equations.

After theoretical background and introduction to the apparatus, the technique of direct imaging of a digital micromirror device is described, which achieves the highly versatile and dynamic 2D potentials that facilitate the experimental studies described. Superfluid transport through a mesoscopic channel of tuneable length and width is next described. By investigating low amplitude oscillations and their dependence on the system parameters, a resistor, capacitor, and inductor model is used to model the transport. Surprisingly, the “contact inductance” of the channel at the reservoirs is a dominant effect
for a significant portion of the parameter range. The resistive transport for high initial bias is also studied, showing an Ohmic resistive relationship over the broad parameter range. Next, the transport between two reservoirs initially prepared at different temperatures, but with similar particle number, was explored.

Our 2D superfluid system, with hard-wall confinement, provides an ideal experimental system for the study of 2D quantum turbulence. The system is utilized to demonstrate the first experimental realization of large Onsager vortex clusters in the negative absolute temperature regime, through the injection of high energy clusters into the 2D superfluid. The clusters are found to be surprisingly stable for long time periods. The vortex cluster energy loss rate is studied while changing the system parameters, suggesting thermal damping is the dominant loss mechanism. The techniques and results presented in this thesis open up new avenues for the study of quantum fluids, be it by providing a concise atomtronic model for predicting superfluid transport or expanding the accessible parameters space available to fundamental studies of turbulence. The realization of negative temperature vortex distributions, long ago predicted by Onsager, open up the experimental study of the full phase-diagram of 2D vortex matter. The refinement of optical trapping techniques for BECs presents new and promising directions for future BEC experiments in configured potentials.

Full thesis can be accessed here.

This thesis reports the final stages of construction and performance of a high atom number rubidium-87 Bose-Einstein condensate (BEC) apparatus, and the generation of timeaveraged optical potentials geared towards interferometric applications. A detailed description of the hybrid trap used in our experiment is given, which comprises magnetic confinement from a quadrupole field, and optical trapping from a focussed 1064 nm laser beam. We present the typical temperatures of atom clouds at all stages of cooling, from the 3D magneto-optical trap, through to the onset of condensation in the hybrid trap. Our trap typically realises nearly-pure BECs of 1.5–2.0 × 106 atoms, at temperatures of (217 ± 6) nK, over duty cycles of 16–25 s. The implementation of a time-averaged optical potential is also discussed, as a means of generating versatile, planar potentials for BECs. In this work, we focus on the generation of large, ring-shaped potentials, which have trapping frequencies in the ranges 2π × (110–140, 35–55)Hz vertically and radially, respectively. The details of a feedforward algorithm are presented, which allows for the realisation of smooth ring structures up to 150 µm in radius, which enclose areas ten times larger than optical ring traps created previously. These larger rings are promising candidates for interferometric measurements of the rotation-induced Sagnac phase, with the device sensitivity proportional to the enclosed area. We typically retain 2.5–3.0 × 106 atoms in these large traps, after evaporatively cooling to temperatures of (44 ± 9) nK. The measured lifetimes in the trap are on the order of 16 s. These ring condensates are expected to be fully phase coherent, despite their reduced dimensionality, as a result of high atom numbers, weak confinement, and low temperatures. We present preliminary data demonstrating these coherence properties, and outlay future plans for a comprehensive study of this coherence, probing both fully coherent rings, and those expected to fall within the phase-fluctuating regime. The control afforded using our time-averaged optical potentials is demonstrated through the generation of acoustic waves propagating around the ring condensates. The dispersion is linear for low driving frequencies, and allows for a determination of the speed of iv sound, and the chemical potential, found here to be cs = 1.34 mm. s−1 , and µ = kB ×18 nK respectively.

Full thesis can be accessed here.

The possibility to mould and control pure quantum systems has been offered by the experimental observation of Bose-Einstein condensation, a unique phase of matter when macroscopic quantities of a gas occupy the lowest quantum state. Techniques for creating these degenerate gases vary from laboratory to laboratory; each offers an unique test bed for studying quantum physics on a macroscopic scale. This thesis reports on the experimental design, construction and performance of an apparatus to create two-component 87Rb and 41K condensates for studies of non-equilibrium dynamics.

Full thesis can be accessed here.

Bose Einstein Condensates represent a valuable experimental medium for the study and application of fundamental atomic science. Within tailored trapping potentials, many exotic quantum phenomena may be probed or exploited, including Feshbach resonances, atomic clock measurements, Bragg spectroscopy, and superfluidity. While experimental condensates were first produced within magnetic traps, optical potentials are advantageous for interferometry, since they permit spin entangled sensitivity enhancement. Exploit- ing the strengths of each distinct approach, hybrid methods were proposed for the rapid production of large condensates within optical potentials. Following the work of, the present thesis aims to experimentally develop an optimised hybrid apparatus for the rapid production of condensates within optical potentials. Although condensates have not yet been produced, many preliminary trapping configurations have been demonstrated, representing substantial progress for the year available. We have successfully generated large Magneto- Optical Traps with 3 × 109 atoms, and Compressed Magneto-Optical Traps of 1.2 × 109 at temperatures of 32μK. Long lived Magnetic Traps with up to 3 × 108 atoms have been ad- ditionally formed. Transfer into the magnetic potential is however not yet optimised, with larger numbers expected once magnetic bias fields are employed to spatially overlap trap centres. Implementing a period of optical pumping should also increase loading into the magnetic potential. To form condensates it remains to firstly compress and evaporatively cool within the magnetic potential. An Optical Dipole Trap must then be overlapped and evaporative cooling continued to degeneracy.

Full thesis can be accessed here.

A new apparatus was built by the author and we report on the experimental details of the trapping of 87Rb atoms from a hot vapour and cooling them in a magneto-optical trap, and further evaporation to quantum degeneracy in a crossed optical dipole trap operating at a wavelength of λ = 1064nm, with accurate control of the power in both beams via a feedback loop. The evaporation of neutral atoms of 87Rb in far red detuned optical dipole traps using linearly polarised laser light is spin independent, and mixed spinor condensates of the F=1 manifold can be formed. As an empirical technique we found by applying a magnetic gradient field during the final evaporation that we can selectively populate mF spin states or prepare mixtures. This intriguing mechanism was found earlier as well by M. S. Chang, but is yet not fully understood and subject of our future research. We can now routinely prepare an almost pure condensate containing up to 7000 atoms in the condensed phase purely in the mF = 0 spin state.

Full thesis can be accessed here.

This thesis presents work on Bose-Einstein condensates in non-harmonic optical potentials. First, a new trap design developed at the University of Queensland is presented that allows the creation of nearly arbitrary two-dimensional potential landscapes by spatially scanning a far red-detuned laser beam using a two-dimensional acousto-optic modulator. In conjunction with a feed-forward technique this trap is capable of producing optical traps which have the necessary stability to be used in ultra-cold atom research. Different geometries are presented. In particular toroidal trap geometries are discussed which are interesting because they offer the possibility for a multiply connected Bose-Einstein condensate. The trap also offers the possibility of dynamic potentials which have been employed to measure the critical velocity of superfluidity in Bose-Einstein condensates. Secondly, measurements on condensation dynamics are presented which use an optical dim- ple potential superimposed upon a harmonic magnetic trap. In the experiments the dimple potential is ramped on slowly or turned on suddenly for a range of dimple depths and widths and the condensate fraction and temperature are measured as a function of hold times. Lastly, progress on experiments to measure the critical velocity of superfluidity in Bose- Einstein condensates is reported.