Is the quantum state real? An extended review of $\psi$ontology theorems
Abstract
Towards the end of 2011, Pusey, Barrett and Rudolph derived a theorem that aimed to show that the quantum state must be ontic (a state of reality) in a broad class of realist approaches to quantum theory. This result attracted a lot of attention and controversy. The aim of this review article is to review the background to the PuseyBarrettRudolph Theorem, to provide a clear presentation of the theorem itself, and to review related work that has appeared since the publication of the PuseyBarrettRudolph paper. In particular, this review: Explains what it means for the quantum state to be ontic or epistemic (a state of knowledge); Reviews arguments for and against an ontic interpretation of the quantum state as they existed prior to the PuseyBarrettRudolph Theorem; Explains why proving the reality of the quantum state is a very strong constraint on realist theories in that it would imply many of the known nogo theorems, such as Bell's Theorem and the need for an exponentially large ontic state space; Provides a comprehensive presentation of the PuseyBarrettRudolph Theorem itself, along with subsequent improvements and criticisms of its assumptions; Reviews two other arguments for the reality of the quantum state: the first due to Hardy and the second due to Colbeck and Renner, and explains why their assumptions are less compelling than those of the PuseyBarrettRudolph Theorem; Reviews subsequent work aimed at ruling out stronger notions of what it means for the quantum state to be epistemic and points out open questions in this area. The overall aim is not only to provide the background needed for the novice in this area to understand the current status, but also to discuss often overlooked subtleties that should be of interest to the experts.
 Publication:

arXiv eprints
 Pub Date:
 September 2014
 arXiv:
 arXiv:1409.1570
 Bibcode:
 2014arXiv1409.1570L
 Keywords:

 Quantum Physics
 EPrint:
 88 pages, 15 figures, and a lot of sleepless nights. v2 is the journal version. Reformatted in journal format, references updated, many typo corrections and other minor updates. TeX source had to be modified slightly to compile using the arXiv autocompiler, so I recommend downloading the journal version from http://quanta.ws/ojs/index.php/quanta/article/view/22