Entangling the spatial properties of laser beams

Abstract

The use of non-classical states of light, such as squeezed states, have allowed the exploration of quantum mechanical effects that had previously been the subject of speculation only. One of the more interesting aspects of quantum mechanics is when two objects become linked in a process known as quantum entanglement. This property has been the focus of much research due to the potential applications that are expected to emerge from entangled systems. This thesis focuses on the various spatial properties of continuous variable entangled systems, and on simplifying entanglement experiments for a given set of resources. We begin by reviewing the required background quantum optics, and introducing the quantum optics tools that we will be using in the series of experiments. The rest of the thesis details the experiments performed and the implications of the results that were obtained. Firstly, the spatial entanglement experiment is presented. This experiment involved the observation of Einstein-Podolsky-Rosen entanglement for the position and momentum of two laser beams. The position and momentum observables for laser beams manifest themselves as the displacement and tilt of the beams, and entanglement relies on the used of squeezed TEM?? laser modes, mixed with a TEM?? reference mode. The result of the EPR measure for the system was found to be 0.62{u00B1}0.03. The next section deals with a multimode entanglement experiment, where two spatial modes are entangled in a single beam of light. The experiment offers several simplifications upon more standard entanglement layouts, including the use of a single quadrant detector for the measurements, and a single squeezer that was used to produce two independent squeezed spatial modes. The observed Inseparability of the system was found to be 0.79{u00B1}0.02. Lastly, the effect of asymmetries in entangled systems was investigated. The possibility of changing the beamsplitter ratio in biased entanglement experiments in order to improve the measurements made was shown to be a useful approach in some circumstances. An experiment was performed, and showed that by changing the beamsplitter ratio, the value from the EPR criterion can be optimised, and in some cases can show entanglement when it would otherwise not be possible.