

QIP = PSPACE  - kvs
http://cacm.acm.org/magazines/2010/12/102144-qip-pspace-breakthrough/fulltext

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poet
A link to the actual paper for those interested:
[http://www.cs.cmu.edu/~odonnell/hits09/jain-ji-upadhay-
watro...](http://www.cs.cmu.edu/~odonnell/hits09/jain-ji-upadhay-watrous-QIP-
equals-PSPACE.pdf).

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DanielRibeiro
People wondering how IP = PSPACE can delve further into the free draft of this
great book on the subject:
<http://www.cs.princeton.edu/theory/index.php/Compbook/Draft>

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hypersoar
This news (although not this particular link) was posted over a year ago.

<http://news.ycombinator.com/item?id=729335>

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tocomment
Does this mean quantum computers can't do anything classical computers can't?
Does it let the air out of quantum computing? Or am I misreading?

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Dabacon
No. It means that for the complexity class of interactive proofs quantum and
classical are the same (when you ignore the number of rounds involved.) This
doesn't tell us anything about whether quantum polynomial time equals
classical polynomial time. The "IP" classes have problems that are very
intractable...this basically says that for these very intractable problems
quantum won't help (with the caveat that the quantum seems to allow fewer
rounds in the interactive proof.)

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palish
_the quantum seems to allow fewer rounds in the interactive proof_

This seems important. What if IP -> QIP is like O(N) -> O(log N)?

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Dabacon
The result, IIRC, is that all of QIP can be done in three rounds, whereas if
the same held in the classical world the polynomial hierarchy would collapse
(which is considered about as likely as P=NP). Not of practical value, but it
does point out that QIP is a slightly different beast than IP when you include
the number of rounds.

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Groxx
<http://en.wikipedia.org/wiki/IP_(complexity)>

Buh? Anyone care to explain what sort of problems would fall into this
description?

