The Atomic Force Microscope (AFM) is a key member of the Scanning Probe Microscope (SPM) family. Its versatility allows it to image and manipulate nanoscale features with high precision, making it one of the main instruments in nanotechnology for surface characterization. The aim of this thesis is to improve robustness, reproducibility, resolution and data interpretation in ambient conditions for dynamic AFM of heterogeneous samples. The AFM is particularly notorious for lack of reproducibility with apparent height and width being the two main measured parameters where accuracy is sought. Here i) the origins of reproducibility, or lack thereof, have been investigated experimentally via a systematic approach to imaging for the whole range of parameter space and relative humidity, ii) smooth and step-like transitions have been investigated both experimentally and with simulations, iii) a method to mechanically stabilise the tip radius and calculate the effective area of interaction in the dynamic mode has been developed and used to predict the number of eV dissipated per atom per cycle, iv) a method to predict the tip radius in situ has been developed, v) three types of dynamic behaviour have been categorised and distinguished (Type I, II and III) allowing to both predict the tip radius and noise patterns, vi) a general interpretation of a mechanism behind height reconstruction and vii) a novel high resolution and low wear imaging technique (SASS) have been developed, modelled, implemented and interpreted with the help of simulations. The most general outcome of this work is that the tip radius has to be well characterised since it plays a major role in any AFM experiment. The investigation is general for nano-mechanical forced oscillators in ambient conditions and the calculations will lead to mapping of local chemistry and mechanics at higher resolution.

The ability to make ultra-precise measurements is fundamentally important to science as it allows theories to be tested and refined. Interferometers offer unrivalled measurement precision and therefore form the basis of many metrology schemes. Research has shown that by using quantum states as inputs to interferometers, precisions better than anything possible classically can be achieved. Nevertheless, these states are difficult to produce and fragile to particle losses. Consequently, classical inputs, which are extremely robust, are used in experiments. Here, however, we propose experimentally accessible schemes to make quantum-limited measurements, in particular rotation measurements using Bose-Einstein condensates, that are robust to losses. We begin by describing how, by loading a Bose-Einstein condensate into an optical ring lattice, multiport beam splitters are created through a simple raising and lowering of potential barriers between sites. We then use these ‘splitters’ to create an atomic gyroscope. We demonstrate how to create several quantum states in the gyroscope, all capable of making rotation measurements. Whilst NOON states afford best precision in idealised set-ups, we find they are outperformed by ‘bat’ states for modest loss rates. However, bat states are not ideal as they are outperformed by classical states for large losses. A second gyroscope scheme is therefore developed. Using multiple momentum modes, rather than just two, we show quantum-limited precisions can be reached using states that have similar robustness to classical states. The final section focuses on the precision of linear interferometers. Recent work[1, 2] has calculated the theoretical optimum initial states for two-mode lossy interferometers. Here we present an experimental way to produce initial states that afford similar precisions to this optimum. We also consider lossy multimode interferometry and demonstrate a potential advantage over two-mode systems. It is thought with further investigation other advantages will be found.

We show that a Bose-Einstein condensate (BEC) interferometer on an atom chip is capable of making an absolute force measurement. We demonstrate this by making an absolute measurement of the gravitational acceleration g. We implement two interferometer arms by splitting a BEC into two symmetric wells using radio-frequency (rf) adiabatic potentials. The independent control of the rf currents running through the chip surface allows us to change the polarisation of the rf field and hence the orientation of the double well potential. Tilting of the system with respect to the horizontal introduces an energy difference Δ V and the relative phase between the BECs starts to evolve. After moving the atoms back to their initial position and overlapping the clouds in free fall we measure the resulting phase from the interference pattern. In order to derive a number for g from experimental results a detailed analysis and understanding of the interferometer scheme is essential. For this type of interferometer we have identified two main limitations to the accuracy of the measurement: a systematic error due to rf field gradients, and a statistical error due to phase spreading from atom-atom interactions. Taking all errors into account we expect a value for g to within 16%. The statistical uncertainty of the measurement is 5%. We have a strategy for reducing all systematic errors to less than 1%. In order to reduce the rate of phase spreading we want to squeeze the relative number of atoms between the wells in future experiments.

No description available.

This thesis introduces the first demonstration of a monolithic, micro-fabricated, multi-channel, optical-waveguide chip to measure ultra-cold atomic clouds. The optics consist of an array of 12 independent junctions, which are separated by only 10 μm and have large atom-photon coupling. The integrated and scalable design is presented, along with an atom chip for mounting the optical waveguide chip and magnetically trapping and handling ultra-cold atoms. The experimental apparatus which was built to accommodate this new chip set is described, along with a new experimental control programme which was developed to accommodate the scalability requirements of the new chip. The chip was optically, mechanically and magnetically characterised and cold atoms with densities up to 10-² μm-³, corresponding to 1 atom at a time inside the waveguide mode, were detected with this new kind of chip using absorption and fluorescence techniques. Subsequently, the atoms were utilised to diagnose light polarisation and intensity within the optical-waveguide chip. For future use, various detection methods adapted to the optical-waveguide chip were considered to minimise photon scattering and thus heating of a trapped ultra-cold sample of atoms.

No description available.

No description available.

No description available.

No description available.

No description available.