

Inside the D-Wave Fridge [video] - jonbaer
https://www.youtube.com/watch?v=VfxNdBTH8wY

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efangs
First off, this is not a "quantum computer" as defined by the field. Instead
it is a "quantum annealer" that relies on the quantum adiabatic theorem,
though it's pretty clear it is impossible for these spins devices to remain
completely adiabatic.

They look at mostly combinatorial optimization problems, and largely they can
not do anything faster than a classical (non-quantum) computer (i.e. a single
laptop).

I read in future versions they may embed classical chips into their D-wave
black box. Benchmarks at that point will be sort of silly.

~~~
gradi3nt
But if they call it a quantum computer enough times it's almost like it is
one, right?

Troyer's group has done some great work looking for any quantum speedup from
one of these annealers, for example:
[http://www.sciencemag.org/content/345/6195/420](http://www.sciencemag.org/content/345/6195/420)

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DalekBaldwin
I've taken courses in quantum mechanics and quantum computing, and I put in
the effort to try and actually develop some intuition as to how they work, but
I still don't have the slightest clue as to how you could build the actual
physical substrate for performing those kinds of computations.

Then again, I don't feel like I understand classical computers all the way
down to the metal, even after taking courses that supposedly explained that.
No matter how much I learn, my mental model of real-world computing is not all
that different from what it would be if I had simply decided to believe that,
at the bottom, code just runs on magic.

~~~
lmm
Have you built an adder out of logic gates? For me that was a good exercise in
bridging the gap between "piece of electronics that I understand" and
"component that does computation".

Quantum computation is the same. You figure out how to build gates (there are
dozens of competing ideas), and then it's just plugging them together in the
right way.

~~~
tagrun
> Quantum computation is the same. You figure out how to build gates (there
> are dozens of competing ideas), and then it's just plugging them together in
> the right way.

Not exactly. Quantum computers are a kind of analog computers based on quantum
mechanics and there are several different models for doing quantum computation
---only one of them is based on gates. Annealers such as D-Wave aren't based
on quantum gates.

They instead slowly anneal the system to its ground state (while avoiding
states corresponding to a local minima in energy), and the usefulness of this
lies in the fact that calculation of ground state of a system is often an
extremely difficult problem, and that you can map your NP problem onto
calculation of the ground state in certain cases.

~~~
lmm
Most of the models I've seen have been gate-based; there are certainly a wide
variety of physical implementations for the same logical gates. You're right
that the D-Wave system (if it's real) is different, but are there really that
many other non-gate models?

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callesgg
I would like to know what type of stuff they are able to run/use one the
thing.

------
solve
Electrons have a temperature? Didn't know that.

~~~
raverbashing
Yes.
[https://en.wikipedia.org/wiki/Fermi%E2%80%93Dirac_statistics...](https://en.wikipedia.org/wiki/Fermi%E2%80%93Dirac_statistics#Fermi.E2.80.93Dirac_distribution)

~~~
ashmud
Do any particles not have a temperature?

~~~
gradi3nt
Anything that has an energy can be turned into a temperature by dividing by
the Boltzman constant k_b (units: Joules/Kelvin).

The meaning of that temperature can be hard to interpret, though. Temperatures
make the most sense when you are thinking about thermodynamics, not when you
consider a single isolated particle.

