
VW Solves Quantum Chemistry Problems on a D-Wave Machine - saligne
https://spectrum.ieee.org/tech-talk/computing/hardware/vw-tackles-chemistry-problems-with-a-dwave-quantum-computer
======
twtw
... and couldn't get the correct answers for LiH. Interesting that the article
didn't mention this.

From the paper:

> For lithium hydride, LiH, we were not able to reproduce closely the ground
> state energy with the currently available hardware. When accounting for 3
> orbitals and using a scaling factor of r = 4, we already had to use 1558
> qubits, which is a large fraction of available qubits. To summarize: the
> investigated method in general works, but it might be difficult to apply it
> to larger systems.

~~~
jf-
Presumably because that’s just a matter of scale. The calculation didn’t turn
out wrong, the machine just isn’t powerful enough to calculate it. All of this
work is proof of concept for more powerful devices down the road, the point
isn’t that it’s better than a classical computer right now.

~~~
williamscales
Is there any evidence it will ever be better than a classical computer?

~~~
FeepingCreature
For the record, the concept is called Quantum Supremacy [1]. So far, there is
no demonstration of quantum supremacy, but it seems like it may just be a
matter of time.

[1]
[https://en.wikipedia.org/wiki/Quantum_supremacy](https://en.wikipedia.org/wiki/Quantum_supremacy)

~~~
stochastic_monk
It’s related, but quantum supremacy is about asymptotic speedups rather than
actual speed differences.

Additionally, it’s worth keeping in mind that D-Wave machines aren’t true
quantum computers in the sense that they can’t perform Grover’s or Shor’s
algorithms.

~~~
garmaine
It’s not clear what “true quantum computer” means. There are many different
types of quantum computers, and quantum annealing, what D-wave does, is one.
It’s just the least interesting of the bunch...

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sampo
> The researchers did not run a similar algorithm on a conventional computer
> system to see whether the D-Wave computation was faster.

~~~
philipkglass
Standard quantum chemical methods for this sort of problem would finish in a
fraction of a second on a Raspberry Pi. Calculating the ground state energy of
a tiny system like LiH was tractable way back in the 1960s. I'd need to see
their actual numbers to determine when a conventional computer first reached
their level of accuracy on LiH but I'm sure it is several decades back.

EDIT: according to the paper, the initial energy at each point was found using
the Hartree-Fock method with a minimal STO-3G basis set. This is one of the
simplest and oldest approaches to this sort of calculation on a conventional
computer. For these starting calculations they used Psi4 [1] by way of
OpenFermion [2]. For the H2 molecule, their additional DWave calculations
improved the accuracy of the distance-energy curve over the baseline Hartree-
Fock/STO-3G calculations. For LiH, there was no improvement (Figure 3). The
total runtime of their approach was therefore that of the conventional
approach _plus_ an additional series of calculations that did not yield
improvements in the case of LiH.

[1] [http://www.psicode.org/](http://www.psicode.org/)

[2]
[https://github.com/quantumlib/OpenFermion](https://github.com/quantumlib/OpenFermion)

------
zaroth
I appreciated the rudimentary presentation of the capabilities and limitations
of the machine and calling out the connectivity of the qubits versus a
universal quantum machine which would have full connectivity between all the
bits.

I’d be curious is there a simple formula for calculating the “effective
universal qubits” of the D-Wave?

2,048 indeed sounds like a lot of qubits based on my extremely limited
knowledge of quantum, but with only ~6k connections versus fully connected
which would be n(n-1)/2 = ~2mil is it just a marketing gimmick?

Why is it useful to push the bit count so high if the connectivity is so
limited?

~~~
tbabej
It's important to note here that the current gate-based quantum processors
also suffer from the connectivity problems. It's not just annealers suffering.

In those architectures, the limited connectivity enforces usage of SWAP gates,
which increases the circuit depth.

Circuit depth, with imperfect qubits and gates, is currently the limiting
factor - we don't have practical error-correction for the chips of today's
size. Hence one can only perform a certain number of operations before his
computation decoheres and becomes useless.

------
martinlaz
The paper:
[https://arxiv.org/abs/1811.05256](https://arxiv.org/abs/1811.05256)

------
Havoc
>For beginners, he says, an actual D-Wave device isn’t even necessary.

I find this somewhat surprising.

If you think of AI code designed for GPUs, there I can see "yeah you can
practice on a CPU". It'll suck but it'll work.

For quantum tech the entire sales pitch is that it's fundamentally
different...doing what's near impossible on conventional hardware.

Yes I realise he's talking about the library so annealing on a CPU I guess but
still seems like a very strange comment in this context.

~~~
ben_w
If I understand correctly (which is a big if given it is quantum mechanics),
any quantum algorithm can be stimulated on a non-quantum computer, but doing
so has an exponential penalty.

~~~
lisper
Exactly right.

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AlexCoventry
What's the business motivation of this research, for VW?

~~~
pas
Batteries? Fuel efficiency? Better catalytic emission filter?

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iamgopal
VW also does science ? Nice to know. Is it related to battery technology etc ?
Or such companies usually invest in fundamental research ?

~~~
iamlucaswolf
They do. As an annecdote, the professor who formerly held the "Machine
Learning" course at TU Munich left for VW's AI research group
([https://argmax.ai](https://argmax.ai)) a few years ago. Whether that
qualifies as "science" may be debatable, but the larger players in the
automotive space are definitely invested in this kind of research.

------
nickpsecurity
Wouldnt these potential customers of D-Wave be better off just buying a HPC
cluster with lots of CPU's, GPU's, and FPGA's? Probably more opportunities for
hardware reuse, too.

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crb002
Curious to see Aaronson's criticism.

~~~
jackfraser
Aaronson is unfortunately in a sunk-cost position when it comes to D-Wave -
he's been so against them for so long that even if they start to produce good
results his bias is going to make it difficult for him to fairly evaluate
them, especially if it means reaching different conclusions about their past
work than he did previously.

Probably better to look to other commentators on this one, at least until he
has enough time to emotionally process the situation and come around to it.
It's not so easy admitting you're wrong in the shtetl.

~~~
Dylan16807
Your first paragraph is fine.

But your second says "process the situation and come around to it" as if
they've already proven anything.

Nobody has ever seriously claimed that the machine can't _calculate things_.
Proof of it doing a calculation doesn't change the status quo.

