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To be, or not to be? What is a quantum state?

How would you unscramble what you see through a kaleidoscope? Now try it without knowing about optics or even the existence of objects.  Interpreting the underlying nature of the universe through the lens of quantum mechanics (QM) is at least as challenging.

While enabling physical calculations of stunning accuracy, the QM view of the universe is so strange that, as Feynman said, \Nobody knows how it can be like that.\" What is reality, and how do we know what we know?  What does that even mean?

A new ArXiv paper has been attracting a great deal of attention from the theoretical physics community.  The paper ('The quantum state cannot be interpreted statistically,' M.F. Pusey et al., ArXiv 1111.3328v1) demonstrates that a quantum state is a physical property of the system it describes by showing that a statistical interpretation leads to a contradiction. 

Take as an example the infamous Schrödinger's Cat paradox.  A cat is placed in a box with a vial of poison, an apparatus which can be triggered to smash the vial, and a random timer based on observing radioactive decay.  After a period of time t, QM says there are equal chances to observe a live cat or a dead cat.  A question about interpretation of QM might ask if the probabilistic QM description reflects an underlying ontic reality, if the statement of probability is the only reality, or if the quantum state itself is 'real'. The paper lends support to the notion of an underlying reality. 

Although no result of a QM calculation will be changed by this tension between ontic and epistemic quantum realities, refining our view of reality by nibbling away at the edges of QM is both satisfying and may lead to a more complete view of reality.

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