Entangling quantum copiers: an application to improving detection efficiency

Summary form only given. Copying machines in general use two approaches. One of the extreme cases is a classical copying machine, where measurements (destructive or non-destructive) are made on the original state, the results of which are then fed as parameters into some state preparation scheme which attempts to construct a copy of the original. The opposite extreme is a fully quantum copying machine which by some process that is unseen by external observers, creates a fixed number of copies, usually destroying the original in the process. Naturally in a realistic situation, noise will additionally degrade the quality of the copies, and copiers which utilise both of the processes above are obviously also possible. While quantum copying promises the possibility of many applications in the future, few specific examples of uses for a quantum copier have been considered so far. When discussing practical applications, quantum copiers have mainly been put forward as something to be defended against by quantum cryptography schemes. This talk presents a analysis of a possible application of quantum copiers: using them to improve detection efficiencies.