
Getting the World Quantum Ready - zaphod_ibm
https://www.ibm.com/blogs/think/2017/12/getting-the-world-quantum-ready/
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ivan_ah
> What if everyone in the 1960s had a decade to prepare for PCs [...] while
> they were still prototypes? In hindsight, we can all see that jumping in
> early would have been the right call.

This is an interesting hypothetical based on the assumption that quantum
computers will be available in 10 years time. What if the first practical
quantum computers are still 50 years away? Using the same hypothetical, it
would be like someone preparing for the PC age in that 1920s. That might be
"jumping in" _too_ early.

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extide
Am I missing something because D-Wave has 1024 qubit machines available now
and 2000 qubit ones soon.

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archgoon
I'm going to repost from a year ago:

D-Wave isn't trying to build a general purpose quantum computer. As it stands,
they've been trying to optimize a computer that executes a particular
algorithm (and as it stands, it's not faster than optimized classical
algorithms). It is an open research question if D-Wave's architecture actually
utilizes any quantum effects to give it an advantage over classical
architectures. D-Wave hopes that it does, and that there will be enough
problems that their machine is good at that their approach will be justified.

D-Wave markets themselves as having hundreds or thousands of qubits, but these
qubits aren't easily controllable or measurable in ways that would allow
Shor's Algorithm to be executed on them (for example), so at the least, it
seems like dishonest marketing. In order to build a general quantum computer,
you need to be able to apply gates to arbitrary collections of qubits.

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extide
Ah, thanks

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omarforgotpwd
Can I run Shors algorithm on this? If not, how many qubits would I need for
that? If so, how do I short bitcoin?

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archgoon
According to this paper:

[https://arxiv.org/abs/quant-ph/0205095](https://arxiv.org/abs/quant-
ph/0205095)

You can implement Shor's algorithm to factor an N-bit number with just 2n+3
qubits. So the 20 qubit processor would be able to factor any 8 bit number
(not necessarily faster than a classical computer could, or even a human
could, mind you).

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garmaine
As the question was about bitcoin, I'm not sure how prime factoring is
relevant.

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archgoon
> Can I run Shors algorithm on this? If not, how many qubits would I need for
> that?

The question was about Shor's algorithm. The question relating to bitcoin
seemed like an aside.

[https://en.wikipedia.org/wiki/Shor%27s_algorithm](https://en.wikipedia.org/wiki/Shor%27s_algorithm)

Given that the original article was about Quantum Computing, I was more
interested in answering questions about Quantum Computing.

~~~
garmaine
Yes, but bitcoin's authentication is via ECDSA. Elliptic curve discrete log is
solvable with Shor's algorithm, but the qubit calculation would be different.

Wikipedia seems to indicate that 2330 qubits and 126 billion Toffoli gates
would be required for elliptic curves with 256-bit group size, although I
wonder if the endomorphism of secp256k1 gives an additional speedup.

