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Are quantum states the real thing?

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19:00 – 20:00 28 Feb 2012
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Chichester I, Lecture Theatre, University of Sussex

Speakers: Dr Terry Rudolph

What is the quantum state? There is no widely agreed answer to this question, despite the ubiquitous and crucial role this mathematical object plays in our lives.
Two broad schools of thought can be identified. The "ontic view" is that the quantum state describes (partially or completely) the real physical state of affairs.
The "epistemic view" is that it instead represents some agent's knowledge or information about the physical system in question.
The existence of entangled quantum states trivially implies, under the ontic view, that reality is drastically nonlocal.
To show reality is still necessarily nonlocal under the epistemic view, known as Bell's Theorem, is hard - it involves an argument regarding making multiple measurements on entangled systems and invoking an extra assumption of free will - and the complexity of this argument could be taken as indirect support for some sort of (nonlocal) epistemic view of quantum states.
Further support for the epistemic view comes from many other close analogies between quantum states and classical probability distributions, these latter being unarguably epistemic.
While the ontic view is severely nonlocal when dealing with entangled states, it is compatible with local realism if one applies it only to unentangled quantum states: preparations of independent quantum states at separated locations requires no nonlocal effects, even if the remotely prepared systems are subsequently brought together and measured.
What I will show here is the remarkable fact that the same is not true if the quantum state is epistemic. Specifically I will explain a new result, namely that local realism for product states is only compatible with the ontic view of quantum states.
This result will hopefully leave you as uncomfortable about the status of the quantum state as I am, and perhaps, like me, after the talk you will find yourself requiring some fortification before having the courage to step out into reality...
Free entry, no need to reserve a place. Everybody welcome, especially non-scientists!

Event type: Lecture/Talk
Organised by: South Central Branch
Contact details: Dr Simon JM Peeters
Email: S.J.M.Peeters@sussex.ac.uk

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Location icon
Chichester I, Lecture Theatre, University of Sussex
Clock icon
19:00 – 20:00 28 Feb 2012
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