[ExI] D-Wave's Quantum Computer

Giulio Prisco giulio at gmail.com
Thu May 23 07:11:02 UTC 2013

On Thu, May 23, 2013 at 8:17 AM, Anders Sandberg <anders at aleph.se> wrote:
> On 2013-05-22 22:22, Kelly Anderson wrote:

> As far as I understand, they can be general purpose. You just use gates that
> implement universal reversible operations. I don't think they would be
> amazingly effective, but they could do it.
> Incidentally, since we are talking quantum computation. I have been trying
> to track down a proper source on minimum energy dissipation for it. As far
> as I get it, by virtue of reversibility QCs can run with no dissipation -
> they do not erase bits, so the Landauer limit doesn't apply. But error
> correction will be necessary, and error correction schemes involve dirtying
> ancilla bits - these bits will have to be erased, at a thermodynamic cost.

Can't the extra bits be just stored?

BTW what do you guys think of this?
It seems sort of plausible that the universe may be optimally
energy-efficient. So it should be a reversible computer. But
apparently it isn't because information is irreversibly erased in
wavefunction collapse. But if the information is just stored away
instead of destroyed, the universe can still be a reversible computer.
Assuming the MWI interpretation, the lost information is, indeed,
still available. So the MWI follows from Landauer theorem with some
plausible assumptions.

I am sure somebody must have written about this in much more details.

> Does anybody know a paper placing bounds on how many ancillas are necessary?
> I know there are theorems stating that if the error probability per gate is
> under a certain constant in-the-large fault-tolerant computation is
> possible, but most of these constructions seem to have huge numbers of gates
> (literally millions per bit). Does anybody know a paper that instead
> minimizes the number of expected erasures?
> Oh, and while still quantum:
> http://news.sciencemag.org/sciencenow/2013/05/physicists-create-quantum-link-b.html?ref=hp
> Entanglement between particles separated in time. Unsurprising, yet totally
> rad.
> --
> Dr Anders Sandberg
> Future of Humanity Institute
> Oxford Martin School
> Oxford University
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