[ExI] Robust topological quantum computing

[John Clark]

In the July 21 2017 issue of the journal Science
​ ​
Qing Lin He
​  ​
reports he was able to move
​ ​
Majorana
​ ​
quasiparticles in a
​ ​
nanowire, their existence has been shown before but this is the first time
they could be moved around. Majorana quasiparticles
​ ​
(sometimes called Anyons)
​ ​
should obey something called
​ ​
non-Abelian statistics, which just means
​ ​
non-commutative. And that is
​a big deal​
 because something like that would be ideal for use
​ ​
as the working material
​ ​
in a Quantum Computer
​ ​
because they would be far more resistant to quantum decoherence, the
biggest enemy to
​practical ​
quantum computing.

​
The amount of conductance a nanowire containing Anyons has comes in
discrete jumps and is a function of the
​ ​
topological class
​ ​
(the number of times the spacetime worldlines
​ ​
of the Anyons cross over)
​,​
and
​ ​
it's not easy to change the
​ ​
topological class
​ ​
of entangled Anyons
​,​
and that makes them resistant to quantum decoherence.
​ ​
As a example you probably can't change the
​ ​
topological class
​ ​
of your shoelaces (nerd-speak for untie
​ ​
your shoelaces) with just any old random bump, a much more intricate
maneuver would be necessary. Another way of looking at it is that each
Anyon is really only half a particle so a single Qbit of information is
stored in both
​,​
so for it to be scrambled both Anyons would have to be hit at the same
time, and they can be as far apart as you like. The
​ ​
next
​ ​
step is to get the Anyons to actually perform a calculation and so far none
has even been able to add 1+1, however once that goal has been reached I
think it would be possible to scale up to something far larger much more
quickly than other approaches.

This certainly isn't the only approach to Quantum Computing, instead of
Anyons companies like IBM, and Google and D-wave are using other things
like ions and photons and superconducting junctions, and unlike Anyons they
have already been able to perform a few simple calculations. Only Microsoft
is betting entirely on the more radical topological approach, time will
tell which method is better but it would be ironic if a company with a
reputation for being plodding ends up being the most innovative of all. At
the very least you've got to give the
​m​
credit for taking the coolest path, and it might be the most lucrative too,

​ ​
John K Clark
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