
On the Leaked Google/NASA Quantum Supremacy Paper - tosh
https://twitter.com/isislovecruft/status/1175557089067823104
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reikonomusha
> however, despite other interesting finds in the paper (such as being able to
> collapse state and read output from multiple qubits at once), claiming
> quantum supremacy feels to me to be somewhat aggrandising and disingenuous,
> given what the quantum circuit was actually computing

As the person says, they have been out of the field. For better or for worse,
this is the term the field settled on years ago to mean showing that a quantum
computer can sample from the Porter-Thomas distribution more quickly than a
classical computer, “beyond reasonable doubt.” (What I mean by the last bit is
that it must be an empirical demonstration that matches the very well
established theory.)

It’s maybe worth repeating: “Quantum supremacy” isn’t some gimmick made up by
the authors of this paper. It was used as early as 2012 [0] by John Preskill,
a well known scientist in the field. It has well-defined meaning in the
research community: a specific experimental verification of a mathematical
result which shows plausible rejection of the extended Church-Turing thesis.

This result may not seem like much to the average reader, but—provided it
passes the muster of peer review—it’s a huge step of progress in the
development of quantum computers.

[0] [https://arxiv.org/abs/1203.5813](https://arxiv.org/abs/1203.5813)

~~~
johnfactorial
Thank you. There was too much left-of-dunning-kruger-peak anger in the thread
to give me any sense that the tweeter knew what they were talking about.

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jebej
Quantum physicist here: just to correct the mistaken claims in this,
interference is definitely a feature of quantum computing, and not a bug.

Interference is also NOT why there are are no error corrected quantum
computers. The reason there are no error corrected quantum computers is
because we need way (way way) many more physical qubits, and they would need
to be of better quality (less decoherence).

~~~
reikonomusha
I don’t think it’s a mistaken claim so much as a misused term-of-art by
conflating it with its layman meaning. If you replace “interference” with
“noise”, what’s being said makes sense.

However, the second bit you said is true, even after correcting the term.

~~~
jebej
They seem to know about decoherence, and in a later post associate
interference with probabilities, so I don't think that was the issue. Maybe a
typo?

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lallysingh
From the discussion:
[https://twitter.com/_gregmeyer/status/1175812382209167361?s=...](https://twitter.com/_gregmeyer/status/1175812382209167361?s=09)
supremacy is doing any computation that's provably hard on classical machines.

~~~
excalibur
If this is accurate, it is a poor naming convention. This is the exact
opposite of the way these concepts should be labeled to make intuitive sense.

~~~
marcosdumay
What term fits better the mark where quantum computers become better than
classical computers at something?

~~~
excalibur
_Quantum advantage_ may not be the perfect term, but it seems to be a better
fit than _quantum supremacy_. The former term conveys a sense that it has a
limited scope, while the latter seems to imply that it beats classical across
the board, or in the majority of cases, or even just in the ones we care
about.

I get that the term _quantum supremacy_ was coined long ago, by people who
were most likely not looking at the event with the degree of granularity that
our present technologies require. It's just unfortunate that what made sense
on a macro level becomes illogical when looking at the minutiae.

Although I suppose this IS fitting in a way, since it parallels quantum
mechanics itself.

~~~
marcosdumay
From now on, quantum computers will beat classical computers, one problem at a
time, until they are the only viable option for all the quantum easy problems
(no we don't know exactly what those are). Supremacy seems quite fitting.

~~~
excalibur
I think you overestimate the accomplishment at hand.

~~~
marcosdumay
You are only looking at one accomplishment, when the name is meant to apply to
an entire period.

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prpl
A real reason for papers such as this, even with seemingly bombastic claims as
"supremacy" with modest improvements, is to prove real progress at a time
where QIS funding is sharply ramping up by DOE/DOD/(NSA/CIA) while also
identifying core areas for improvement (where to spend that money).

$300MM has been set aside for DOE QIS alone (with more of a focus on
simulation), and that is likely to ramp up with papers like this, probably
somewhere over $1B over the next 5 years for DOE Science alone. Throw in
DOD/NSA and the number is easily going to be in the $5-10B total over the next
5-10 years, assuming there's no quantum winter.

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cthalupa
I'm not a quantum physicist, but I pretend that copious amounts of reading and
watching PBS Space Time and Infinite has made me somewhat knowledgeable on
this. The author looks to have previously been a theoretical physicist, so I
might be very off base here, but... this thread doesn't square up with my
understanding of things at all.

>QUANTUM INTERFERENCE IS JUST WHAT QUANTUM PROCESSORS DO, ITS A BUG, NOT A
FEATURE

This sort of throws the whole series of tweets into question for me. Of course
interference is a feature - you want to create a pattern of interference where
paths leading to the wrong answer interfere with each other and cancel out!
Without interference I don't understand how quantum computers could even work,
what they would look like, and why we would want to use them for anything.

>which, to me, is an infuriating thing to label “quantum supremacy” because
quantum interference is EXACTLY WHY WE CAN’T USE CURRENT QUANTUM PROCESSORS TO
“BREAK ALL CRYPTO” IN THE FIRST PLACE BECAUSE WE CANNOT DO EFFICIENT QUANTUM
ERROR CORRECTING CODES

Error correction requires more qubits to do the error correction. We need the
current qubits just to do the calculations, leaving us no qubits to use for
error correction. Quantum interference certainly isn't the reason we can't do
error correction.

If the author is confusing decoherence and interference, then I can understand
why they believe what they do, though that confusion ultimately removes a
significant portion of their point. Decoherence is what takes something in
superposition and puts it back into the realm of classical physics - we lose
the ability to utilize that quantum interference and entangled qubits.
Ultimately to get a result we have to de-cohere the qubit, because we have to
observe it, so not all decoherence is bad. The problem is all sorts of things
besides our desired observation can cause decoherence, which results in
errors, and avoiding this requires implementing error correction, which takes
additional physical qubits. We need a lot more physical qubits, qubits that
are more resistant to decohering when we don't want them to, and/or for
someone to come through with a breakthrough that does error correcting much
more efficiently than the methods Shor came up with.

Of course, I might be the one that's confused here.

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q_eng_anon
Is she getting 'interference' and 'de-coherence' mixed up..?

~~~
mrfox321
No. Interference is what makes quantum computers work. Decoherence destroys
superposition.

~~~
reikonomusha
The person FTA is saying interference is what causes issues, so I believe
there is a mix up.

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tromp
The paper claims that a classical supercomputer is MUCH slower at simulating a
noiseless 53 logical qubit system, but doesn't exclude the possibility of a
classical supercomputer simulating an approximation of the actual noisy 53 bit
physical qubit system, that still gives sufficiently decent estimates of the
observed final state probabilities. Such a simulation would compute orders of
magnitude fewer than 2^53 amplitudes, and use whatever shortcuts are available
to get approximately correct results.

Quantum supremacy cannot be claimed until this possibility is ruled out.

~~~
reikonomusha
To folks in the field, it is my impression that this is about as minor as
assuming P != NP. Conjectured, unproven, but the world would be a _lot_ more
interesting if wrong.

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abdullahkhalids
TLDR; I don't think this twitter thread is good public science communication,
and should not appear on the HN frontpage.

As a quantum computing researcher, I can't make head and tail of what OP is
saying after and including tweet 7. I don't think OP understands interference
correctly. As someone points out elsewhere in the comment section, she might
mean decoherence, but I can only evaluate what she has written.

She also makes light of the theoretical computational complexity results
underlying the demonstration of quantum supremacy using random circuits. This
experiment's results and interpretation might be iffy at best, but the
underlying strategy of the quantum computing community in this matter are
sound. We don't want to keep asking for funding for the next 20 years without
proofs of principles in between, and this experiment is one step along the
way.

------
magneticnorth
The paper is here (link from further down in their discussion):
[https://drive.google.com/file/d/19lv8p1fB47z1pEZVlfDXhop082L...](https://drive.google.com/file/d/19lv8p1fB47z1pEZVlfDXhop082Lc-
kdD/view)

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imvetri
Binary is a no-show to the Quantum, Both shouldn't be a circus show to which
realm?

Let the computation power grow exponentially, Until one day, computation faces
its vulnerability.

Let all be known, beautiful dawn holds its crown.

Computation is a growing pyramid, da da da, dancing on a brittle tip.

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vectorEQ
marketingleaks :')

~~~
nocturnial
You think this "leak"/leak is related to the recent IBM announcement?

[https://news.ycombinator.com/item?id=21004615](https://news.ycombinator.com/item?id=21004615)

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exabrial
> tl;dr: no crypto is broken, some people just did some tricks with misusing
> fancy big words in an otherwise alright but now-retracted paper, and i’m
> Very Mad On Line about it, also everyone should give me shells on their
> supercomputers

~~~
h4t
`give`

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wmnwmn
Commentator appears to have a layman's understanding of quantum mechanics.

