Nathan Rose

The influence of the measurement result of a qubit affecting the state of another, as happens in an entangled state, is called non-locality. This strange property was pointed out for the first time in a very influential paper, published in 1935, by Albert Einstein, Boris Podolsky and Nathan Rose [13]. The paper aimed to demonstrate that Quantum Mechanics was an incomplete theory. According to the authors, a theory to be considered complete should contain what they defined reality elements. A reality element would be, still according to the authors, any physical quantity whose value could be predicted before performing a measurement on the system. For example, when a measurement of the observable cty is performed on a qubit, in an entangled cat state, the result determines the state of the other qubit, which could then be predicted before a measurement. Hence the observable Uy is a reality element. However, before the measurement is performed on the first qubit. 

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