Algorithms for the D-Wave – A Physics Perspective
A talk by Dr. Raina Olsen from the Army Research Lab
Thursday, March 9, 2017 · 1:30 - 2:30 PM
The spin ½ chain
is often used as an example problem that is particularly ill suited for
the quantum annealing (QA) technique used by the D-Wave computer.
Sometimes QA produces a correct classical ground state, but other times
it produces a classical state which is only nearly correct. The thing
that makes this spin chain problem ill suited for QA is degeneracy – the
fact that the quantum ground state contains many classical states with
the same or similar energy.
Dr.
Olsen will discuss two problems in condensed matter physics. One is the
well known damping of heat conduction by phonons in a disordered
lattice. This damping occurs because disorder tends to spatially
localize the phonons, equivalent to reducing the degeneracy in the spin
chain problem. The second is an experimental system which is not yet
fully understood, but which suggests that entangled particles can remain
strongly correlated even in the presence of decoherence. Dr. Olsen will
then return to the spin 1⁄2 chain. She will demonstrate the entirely
expected result that addition of disorder reduces the degeneracy of the
solution. But shealso shows that introducing correlations in the
disorder is more effective at reducing the degeneracy, thus making the
problem much better suited for QA.