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'Lazy' quantum ensembles

George Parfionov1 and Romàn Zapatrin2

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We compare different strategies aimed to prepare an ensemble with a given density matrix ρ. Preparing the ensemble of eigenstates of ρ with appropriate probabilities can be treated as 'generous' strategy: it provides maximal accessible information about the state. Another extremity is the so-called 'Scrooge' ensemble, which is mostly stingy in sharing the information. We introduce 'lazy' ensembles which require minimal effort to prepare the density matrix by selecting pure states with respect to completely random choice. We consider two parties, Alice and Bob, playing a kind of game. Bob wishes to guess which pure state is prepared by Alice. His null hypothesis, based on the lack of any information about Alice's intention, is that Alice prepares any pure state with equal probability. Then, the average quantum state measured by Bob turns out to be ρ, and he has to make a new hypothesis about Alice's intention solely based on the information that the observed density matrix is ρ. The arising 'lazy' ensemble is shown to be the alternative hypothesis which minimizes type I error.


PACS

03.65.Ta Foundations of quantum mechanics; measurement theory

42.50.Dv Quantum state engineering and measurements

MSC

81P15 Quantum measurement theory

81V80 Quantum optics

Subjects

Optics, quantum optics and lasers

Quantum information and quantum mechanics

Dates

Issue 34 (25 August 2006)

Received 7 March 2006, in final form 20 June 2006

Published 9 August 2006



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