In the early seventies it was realized that the notion of particles depends on the specific details of the quantum measurement process used to detect them, and that the state of motion of the measuring device can determine whether or not particles are observed. This discovery has created a new viewpoint which was prompted by Fulling,Unruh and Hawking's work demonstrating that the number of particles found in a region depends on the acceleration of the measuring device. For example, the vacuum, i.e. a region that contains no particles at all, would be seen by an accelerated observer as aregion with particles. The number of particles and their energy would increase with increased acceleration. This effect is known as the Unruh effect. Since by general relativity acceleration and gravitation are equivalent, an analogical effect would be the black hole radiation.Einstein, Podolsky, and Rosen, introduced a Gedanken experiment in a 1935 paper to argue that quantum mechanics is not a complete physical theory. It is sometimes referred to as the EPR paradox. This thought experiment shows paradoxical features of quantum mechanics, demonstrating strange correlation sometimes referred to as spooky action from a distance. These correlations could be quantified. Various quantifications were suggested which are referred to as measures of entanglement.I propose to study entanglement using the view point introduced in the first paragraph. I am interested in studying the behavior of entanglement when it is probed by different observers. Especially, I would like to explore the experimental realization of these ideas.Since the Unruh effect was never measured due to experimental difficulties, I will study the realization of this effect in a Bose Einstein Condensate (BEC). A BEC is a macroscopic collection of atoms which are all located in the same state. BEC could be thought of as a macroscopic number of particles located at the same point, but this point, due to the rules of quantum mechanics could be quite big, due to uncertainty relations. It was found that this strange state, in some way, is very similar to the vacuum of light, i.e. if we think of the vacuum as some kind of ether which let the lightpropagate through, the BEC is a background in which information propagates.In this proposal I want to study the feasibility of the experimental realization of these effects in BEC. First I will study a scheme to measure the Unruh effect. I will propose a scheme in which an accelerated observer will find particles inside the vacuum, not thereal vacuum but its analogy, the BEC at very low temperature. Then I will propose experiments in which two observables which accelerate next to the vacuum would become entangled, i.e. would show EPR correlation. The experimental feasibility of this is important not only as a proof of physical theory which is believed to be true, butalso as a mean to study a scheme which cannot be calculated. The creation of entanglement by acceleration is a problem which cannot be solved analytically. The realization of this experiment would provide a numerical solution to this problem. It is important to note here, that this problem, in addition to not being analyticallysolvable can neither be checked numerically in a regular computer. A quantum computer could check this result, but unfortunately such a computer does not exist. Modeling experimentally problems that could be checked numerically only by using a quantum computer is just the idea behind the quantum simulator. The advance of this technology would serve as a major stepping stone to the creation of a quantumcomputer.

Cavity-mediated cooling has emerged as the only general technique with the potential to cool molecular species down to the microkelvin temperatures needed for quantum coherence and degeneracy. The EuroQUAM CMMC project will link leading theoreticians and experimentalists, including the technique's inventors and experimental pioneers, to develop it into a truly practical technique, reinforcing European leadership in this field. Four major experiments will explore a spectrum of complementary configurations and cavity-mediated cooling will be applied to molecules for the first time; a comprehensive theoretical programme will meanwhile examine the underlying mechanisms and identify the optimal route to practicality. The close connections between theory and experiment, and between pathfinding and underpinning studies, will allow each to guide and inform the others, ensuring that cavity-mediated cooling is swiftly developed as a broad enabling technology for new realms of quantum coherent molecular physics and chemistry.The Southampton component will address, both experimentally and theoretically, fundamental aspects of the cooling process that result from the retarded interaction of a trapped molecule with its reflection in a single mirror, and developments of this prototype scheme that exploit nanostructured mirror arrays that can be produced in our fabrication facilities, and which show both geometric and plasmonic resonances. Our particular aims are hence to understand and explore the most basic version of cavity-mediated cooling, and to develop new implementations suitable for nanoscale integration as a future technology.

Cavity-mediated cooling has emerged as the only general technique with the potential to cool molecular species down to the microkelvin temperatures needed for quantum coherence and degeneracy. The EuroQUAM CMMC project will link leading theoreticians and experimentalists, including the technique's inventors and experimental pioneers, to develop it into a truly practical technique, reinforcing European leadership in this field. Four major experiments will explore a spectrum of complementary configurations and cavity-mediated cooling will be applied to molecules for the first time; a comprehensive theoretical programme will meanwhile examine the underlying mechanisms and identify the optimal route to practicality. The close connections between theory and experiment, and between pathfinding and underpinning studies, will allow each to guide and inform the others, ensuring that cavity-mediated cooling is swiftly developed as a broad enabling technology for new realms of quantum coherent molecular physics and chemistry.Collective cooling schemes have already been proposed for the strong coupling regime. The aim of the Leeds research is to develop a detailed theory for the collective cooling of particles trapped inside a highly leaky optical cavity. The theoretical results obtained for this so-called bad-cavity regime will be compared with the still unexplained experimental studies reported elsewhere. Moreover, they will provide concrete input in the design of the physical setups used by the experimental groups in this network, who will operate their cavity in the so-called bad cavity limit.

Quantum systems are much more complex than classical ones. Therefore, they offer on the one hand the possibility to perform computations that classical computers cannot do. On the other hand, if they are large and composed of many particles, their description requires more data than a classical computer can handle. The investigation of large quantum many particle systems is thus very difficult as it is in general not possible to simulate a quantum many body system on a classical computer. To overcome this problem, scientists had to employ a different approach which makes use of the fact that the same physical mechanisms can inNature appear in various contexts. Hence one can use a system which can be well controlled and tuned in the laboratory to mimic other systems which are much more difficult to study. Those well controllable and tunablesystems are called quantum simulators . Due to their high precisioncontrollability and tuneability, quantum simulators are also suitable for creating entanglement, which is a key resource for quantum informationprocessing. If two or more particles are entangled, they share properties which cannot be attributed to one individual particle. These purely quantumcorrelations are responsible for the new possibilities quantum information processing offers compared to its classical counterpart. Several interesting candidates for a quantum simulator respectively entanglement production device have been studied in recent years. A very successful one is a lattice formed by standing waves of light with very cold atoms trapped in it. So far a very high degree of control and tunability has been achieved for global properties, but it still is very difficult to control and measure the individual constituent particles. In the proposed project we will investigate a new way to implement quantum simulators and create entanglement which would allow forexperimental access to properties of individual particles. Our approach makes use of arrays of micro-cavities, very small devices that can trap light for a long time. Atoms are trapped at each micro-cavity and interact with the light stored in it. The experimental realisation of such arrays of micro-cavities has seen some tremendous progress recently and the first arrays mounted on devices to trap the atoms in their vicinity have been realised. Within the proposed project, we will investigate thepossibilities for creation of various types of entangled states andeffective many particle systems in these newly built structures.

Coupling and coherent control of single photons and atoms are the key to quantum information physics, with atoms and photons acting as information carriers in scalable quantum networks. To reach this degree of control, we follow several routes. We will manipulate individual atoms in free space using an array of optical tweezers, and couple these atoms to nano-structured cavities, like photonic crystals. Furthermore, we will explore single-photon quantum memories, using either electromagnetically induced transparency to store a photon in an atomic ensemble, or a single atom coupled to an optical cavity to realise an atom-photon quantum interface.