2008, Vol.11, No.2, pp.141-148

Quantum Information Theory is the extension of Classical Information Theory when the quantum nature of the physical devices plays a key role. All the information storage and processing systems, to work in the desired quantum mechanical way, must be isolated from environmental perturbations and classical interactions with other systems. This isolation protects entanglement (the fundamental resource of quantum information) from decoherence (the deterioration of quantum coherence). But in order to prepare the initial state of a quantum system, to control its evolution, and measure its final state, we must interact with it with big classical systems and thus induce unavoidable perturbations. This is the main problem for the scalability of all proposed architectures for quantum computers. In the search for design optimizations it has been natural to ask whether the classical properties of quantum systems play any role either helping in the protection of entanglement or inducing specific undesired behavior. Thus the question of the influence of classical chaos or integrability has been posed and studied extensively. While there exist many results based on specific models of quantum systems, the picture is not definite since one can see chaos in some cases to accelerate decoherence but in many cases to help entanglement. In this talk we present two different results. The first is an inequality, which holds, under certain conditions, for general systems. The proof is based on Random Matrix Theory. The second result is an analysis of the influence of the existence of the scars on decoherence and of the role of bifurcation points. This study is based on the comparison of Classical and Quantum Kicked Tops, the latter used as a model of a system of many qubits.
Key words: entanglement, quantum chaos, Calogero-Moser model, quantum kicked top, scars, bifurcations, upper bounds

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