document: Quantum retrodiction in open systems Quantum retrodiction involves finding the probabilities for various preparation events given a measurement event . This theory has been studied for some time but mainly as an interesting concept associated with time asymmetry in quantum mechanics . Recent interest in quantum communications and cryptography , however , has provided retrodiction with a potential practical application . For this purpose quantum retrodiction in open systems should be more relevant than in closed systems isolated from the environment . In this paper we study retrodiction in open systems and develop a general master equation for the backward time evolution of the measured state , which can be used for calculating preparation probabilities . We solve the master equation , by way of example , for the driven two-level atom coupled to the electromagnetic field
doc_bio_tags: B I O B I B I O O O B O O B I O O B I O O O O O O O O O O O O O O O O O B I O B I O O O O B I O B O O O O O O O O O O O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I I O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O
extractive_keyphrases: quantum retrodiction probabilities preparation events measurement event time asymmetry quantum mechanics quantum communications cryptography backward time evolution open systems
abstractive_keyphrases: retrodictive master equation preparation probabilities driven two level atom-electromagnetic field coupling