
Quantum computers: 10-fold boost in stability achieved - upen
http://sciencebulletin.org/archives/6453.html
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ThePhysicist
While this is impressive compared to earlier systems, just citing the T1 & T2
values does not actually tell you much about the usability of the system as a
qubit. What really counts is the number of operations you can realize within
the coherence time of the qubit, and as far as I can see from the paper this
seems to be around 5-10 (which is two to three orders of magnitude below what
e.g superconducting qubits currently offer). Also, the next step would be to
show two-qubit operations with the system, which is another challenge that
isn't easy to overcome. So only after increasing the coherence time by another
two to three orders of magnitude and realizing a robust coupling mechanism
would it make sense to think about scaling the system and building an actual
quantum computer with it. Still, semiconductor qubits offer several
interesting possibilities as Silicon technology is something that is
significantly more robust and scalable than e.g. superconducting circuit
technology (currently at least).

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rubidium
arxiv link:
[https://arxiv.org/abs/1603.04800](https://arxiv.org/abs/1603.04800)

Short explanation: Qubits encode information needed for quantum computers.
Noise from the environment can destroy that information. By introducing a
driving field to the qubit they made the qubit+driving field the new qubit
("dressed" qubit) and it was more robust to noise.

It also gives some different levers to change the information (namely, the
driving field).

~~~
kefka
In other words, it gives a newfound impetus to follow through with converting
to Curve25519 cryptosystems.

It's what we believe to be quantum computer secure.

~~~
mil4n
can you explain this more? What is the affect on cryptography. Thanks a lot

~~~
IanCal
Lots of encryption is based on the prime factorisation being hard to do.
Specifically, that it scales significantly as you slightly increase the key
size.

There's a quantum algorithm (Shor's algorithm) that doesn't scale quite so
badly as the numbers get bigger. That means that with a fast quantum computer
you could solve this specific problem much _much_ more quickly than is
possible on a classical computer.

However, other crypto types (elliptical curve cryptography EDIT - ECC is _not_
a type that meets these criteria, see the responses to me below) doesn't
depend on prime factorisation, but other things. Those other things have no
known nice fast quantum algo. I'm not sure where this sits on "there's
provably no fast quantum algorithm" and "we don't currently know of one"
however (EDIT - ECC is in the "there is definitely a fast quantum algorithm"
category!).

Most generally, quantum computers are not just fast regular computers. For
some (not all) problems, they scale better for solving the problem. So for
example, finding an item in an unordered list. If you have 100 items, you need
to on average check 50 items to find it on a regular computer, and if you have
a million items you need to check 500,000 items. A quantum computer can run 10
iterations to solve find something out of 100, but just 1000 to find something
in a million. Other differences scale better or worse.

Quick simple overview: Some problems that we thought were intractable turn out
to be quite possible on quantum computers. But not every problem.

I tried to keep this simple as my understanding is also quite simple, and I
don't want to post things that are wrong.

~~~
wyager
> However, other crypto types (elliptical curve cryptography) doesn't depend
> on prime factorisation, but other things. Those other things have no known
> nice fast quantum algo.

This is wrong.
[https://en.m.wikipedia.org/wiki/Elliptic_curve_cryptography#...](https://en.m.wikipedia.org/wiki/Elliptic_curve_cryptography#Quantum_computing_attacks)

~~~
IanCal
Thank you, I didn't know this. I've updated my post to point out where I'm
wrong, hopefully that covers the important bits.

~~~
openasocket
For your clarification, Shor's algorithm just involves encoding every possible
value of a function (say f(x) for all values of x) into a bunch of qubits,
taking the fourier transform, and measuring, which will tell you the period of
that function (some r such that f(x + r) = f(x) for all x). Thus, you can find
the period of any function that you can define a fourier transform for. For
breaking RSA, your function is on the domain of integers modulo n, so you use
the discrete fourier transform. You can also define a fourier transform for
functions on the domain of an elliptic curve as well! In fact, any finite
abelian group has a unique definition of fourier transform (see
[https://en.wikipedia.org/wiki/Pontryagin_duality](https://en.wikipedia.org/wiki/Pontryagin_duality)
for some of the math behind it). That means we can't just upgrade our crypto
to some more complex curve space, because all of them will be vulnerable to
Shor's algorithm.

The mathematics behind Shor's algorithm is actually a really interesting read
if you enjoy pure, abstract algebra and topology.

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neom
General purpose QC + AI is going to be quite interesting indeed.

~~~
rubidium
Your comment seems to be a complete non-sequitur to this article.

Buzzword1+Buzzword2 = interesting.

Why? What part? What application?

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baq
with a proper algorithm which may well not exist it's in theory possible to
e.g. perform deep learning on all training examples in a single pass or
something like that.

~~~
Panoramix
But those hopes are not very much based on reality so why entertain them in
the first place?

It's a bit like saying that QC will be awesome because thanks to it people
could in theory find the cure for cancer, in some way, somehow.

~~~
neom
I didn't realize imagination was banned from HN now, my bad.

~~~
Dylan16807
Imagination that's not based on anything is generally considered to be off-
topic, sure.

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m3kw9
Tell me when there is actually a useful computer, otherwise it's all talk and
no action

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andrewljohnson
Talk precedes action in science. Imagine if Roosevelt had said tell me when
there is actually a useful bomb, or it's all talk and no action:
[https://en.wikipedia.org/wiki/Einstein%E2%80%93Szil%C3%A1rd_...](https://en.wikipedia.org/wiki/Einstein%E2%80%93Szil%C3%A1rd_letter)

