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SUMMARY:Quantum annealing on Ising spin glasses - Troels Frimodt Rønnow (
 NRC Cambridge)
DTSTART:20141121T120000Z
DTEND:20141121T130000Z
UID:TALK56373@talks.cam.ac.uk
CONTACT:Sergii Strelchuk
DESCRIPTION:While a universal quantum computing is not yet within our reac
 h\, quantum computing technology has matured to the point where certain qu
 antum algorithms and simulators can be realized in laboratories. One examp
 le of this is quantum annealing which is realized in D-Wave One and Two. I
 n this talk\, we review some aspects of the recent development of quantum 
 annealing with focus on D-Wave One and Two. First we discuss various model
 s which potentially could explain the behaviour of D-Wave (DW) machines an
 d we demonstrate that the statistics of DW are well explained using path-i
 ntegral quantum Monte Carlo quantum annealing (SQA).  Next\, we look at th
 e scaling of DW and compare this to simulated thermal annealing (SA). For 
 the chosen problems\, we show that SA is always superior to DW when lookin
 g at the scaling\, and that the two approaches are about equally fast if o
 ne looks at total time to solution. That SA should scale better than SQA/D
 W is in contrast to a theory formulated in 2002 where it was shown that SQ
 A is more efficient than SA in finding low-energy states. To resolve this 
 discrepancy we revisit the work by Santoro. Studying thousands of problems
 \, we show the better scaling report by Santoro et al. is a result of cert
 ain assumptions in the derivation of SQA. The consequence of these assumpt
 ions is that the theory does not apply to physical systems\, and in partic
 ular not to DW. To further support the claim that SQA should scale worse t
 han SA\, we look at the distributions of time-to-solution. We demonstrate 
 that the SQA distributions are dominated by long fat tails. In turn\, this
  means that the mean time-to-solution for a large problem set is expected 
 to be worse for SQA than SA. Finally\, we discuss some of the open questio
 ns.
LOCATION:MR13\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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