This PITP-CQIQC workshop will address various aspects of decoherence, which is showing itself to be one of the most interesting and enigmatic physical processes in physics, quite apart from its role in the emergence of theclassical world from quantum theory.

Given that decoherence is currently of interest in almost every field of physics, we have had to make a choice between different areas- this workshop will be concentrating on the following areas and questions:

(i) The PHYSICAL MECHANISMS of DECOHERENCE: These clearly vary depending on the the nature of the physical system- in solid-state systems one has to deal with phonens, photons, spin and charge excitations, and also localised excitations ranging from nuclear spins to topological and other defects. In quantum optical systems, and in quantum chemistry it is typically photons and phonons that are of main interest. In atomic systems, decoherence is involved in the study of delocalisation in optical lattices, and the physics of phase fluctuations and quasicondensates. One of the most important questions is whether there exist other decoherence mechanisms, as yet undiscovered, perhaps of an 'intrinsic' nature, which will bear on fundamental tests fo quantum mechanics.

(ii) QUANTUM INFORMATION PROCESSING: Decoherence is the main problem confronting any practical implementation of quantum computing and related information processing techniques. Progress in the theory of quantum error correction, and various schemes for suppressing decoherence, along wioth experimental demonstrations of some of these, offer great hope for the future. In addition new theoretical results on decoherence in various schemes, ranging from topological quantum computing to quantum walks, show how much more remains to be discovered. Related questions are obviously of deep importance it all areas of "quantum control", as well as in quantum communication.

(iii) EXPERIMENTAL ASPECTS of DECOHERENCE: Experiments in a wide variety of systems are capable of probing decoherence- it can be looked upon as a pest or a tool, depending on what one is doing. There are strong disagreements between theory and experiment in a number of systems- the elucidation of the various decoherence mechanisms is a very active field right now, with experiments on magnetic, superconducting, and quantum dot systems, as well as cavities and other quantum optical devices, and in cold atoms systems. The workshop will examine some of what is known about decoherence in experiments, how it can be manipulated, suppressed, or explored, and what interesting future experiments might be done.