The issue of retrodiction in Bohm's theory

Izawa Ken'ichi, Taniguchi Tomonori

Basil J. Hiley, F. David Peat

Bohm's pathbreaking hidden variable theory of 1952 1 is often accused of artificiality and inelegance, and doubtless it is guilty of both. But to make such accusations, and to leave it at that, is to entirely miss the point. What Bohm was after in his theory was not elegance and not naturalness; Bohm's intentions were simply to produce a theory which, whatever its other characteristics, had logically clear foundations. It is for that clarity which Bohm's theory is highly and rightly praised.

Berthold‐Georg Englert, Marlan O. Scully, Georg Süssmann +1 more

Let us begin with a response to the summary of the Comment by D. Durr, W. Fusseder, S. Goldstein, and N. Zanghi [1]. We are accused to not stay inside orthodox quantum but to employ a naive, largely incoherent operationalism instead. We think that this charge is not justified, because we did apply standard quantum theory correctly and also followed the rules of Bohmian Mechanics (BM) carefully. In the following we react to the more essential points of the Comment in some detail. The Comment suggests that we have conceded many virtues to BM and that we have admitted that standard quantum theory is plagued by notorious conceptual difficulties. This is not the case. On the contrary, we maintain that BM is not needed to have the Schrodinger equation embedded into a physical theory. Standard quantum theory has already clarified the significance of Schrodinger's wave function as a tool used by theoreticians to arrive at probabalistic predictions. It is quite unnecessary, and indeed dangerous, to attribute any additional meaning to the (/^-function. The semantic difference between inconsistent and surrealistic is not the issue. It is the purpose of our paper to show clearly that the interpretation of the Bohm trajectory as the real retrodicted history of the atom observed on the screen is implausible, because this trajectory can be macroscopically at variance with the detected, actual way through the interferometer. And yes, we do have a framework to talk about path detection; it is based upon the local interaction of

Frederik Jozef Belinfante

John Jeffers, Daniel K. L. Oi, Thomas Brougham

Quantum retrodiction, in which the state of a quantum system prior to a measurement is assigned based on the results of that measurement, has had a long history and has been used in quantum optics research for decades. Here we summarize the theory and point out some of the more interesting results, before applying the theory to state identification from multiple shots of an experiment. One surprising result is that we show that a photodetector with low quantum efficiency can discriminate between photonic states better than a detector with a higher efficiency.This article is part of the theme issue 'The quantum theory of light'.

W. Michael Dickson