Archive for quantum states

Are Quantum States “Real”?

Posted in The Universe and Stuff with tags , , on November 20, 2011 by telescoper

Busy day today, despite it being a Sunday, so I’ve only got time for a quick post, by way of a diversion while I take a break for a cup of tea.

There’s been an attack of the hyperbolics this week arising from a paper entitled “The quantum state cannot be interpreted statistically”.  The abstract of the paper reads:

Quantum states are the key mathematical objects in quantum theory. It is therefore surprising that physicists have been unable to agree on what a quantum state represents. There are at least two opposing schools of thought, each almost as old as quantum theory itself. One is that a pure state is a physical property of system, much like position and momentum in classical mechanics. Another is that even a pure state has only a statistical significance, akin to a probability distribution in statistical mechanics. Here we show that, given only very mild assumptions, the statistical interpretation of the quantum state is inconsistent with the predictions of quantum theory. This result holds even in the presence of small amounts of experimental noise, and is therefore amenable to experimental test using present or near-future technology. If the predictions of quantum theory are confirmed, such a test would show that distinct quantum states must correspond to physically distinct states of reality.

According to a commentary published in the journal Nature, this paper could “rock quantum theory to the core” and a number of quantum physicists have reacted, e.g.:

“I don’t like to sound hyperbolic, but I think the word ‘seismic’ is likely to apply to this paper,” says Antony Valentini, a theoretical physicist specializing in quantum foundations at Clemson University in South Carolina.

I have to admit I haven’t had time to read the paper in detail yet, so I’m just passing this on as something fresh that may be of wider interest, rather than something I’ve got particularly strong views about. I have to admit, though, that I find the way quantum theorists use words, especially what is meant by “physically real” and what “states of reality” could be. Can a mathematical theorem ever prove itself to be applicable to the physical world anyway? You’ll see that ontology was never my strong suit.

However, if anyone out there in blogland has read this paper and would like to pass on their thoughts for the edification of me and my readers I’d be delighted. I might return to it in a longer post if and when I’ve been able to digest it fully.

Now, back to reality…