
What could the NSA do with a quantum computer? - jonbaer
http://www.newstatesman.com/sci-tech/2013/06/what-could-nsa-do-quantum-computer
======
jgrahamc
It's a pity that this article doesn't mention Shor's Algorithm
([http://en.wikipedia.org/wiki/Shor%27s_algorithm](http://en.wikipedia.org/wiki/Shor%27s_algorithm)).
Shor's algorithm would make integer factorization O((log n)^3).

But we have a way to go: "Also in 2012, the factorization of 21 was achieved,
setting the record for the largest number factored with a quantum computer."

~~~
mtp0101
The article actually does mention Shor's, just not explicitly. The author
introduces integer factorization as "a kind of reverse multiplication" (lol).
He then explains that quantum computers can factor numbers efficiently and
that this has implications for computer security.

------
uptown
Whenever somebody brings up what technology the NSA might have, now or in the
future, I think back to Apple's eventual response to "antenna-gate". The
speculation was that their antenna testing consisted of makings some phone
calls, and seeing if things worked. Then Apple released these photos:

[http://www.apple.com/lae/antenna/](http://www.apple.com/lae/antenna/)

I'd love to know what the NSA's version of this would be. Given their mission,
and the financials resources available to them - it's difficult for me to
imagine that they don't have technology at-their-disposal that blows most
people's minds in terms of power and capabilities.

~~~
mturmon
Another point of reference is the Keyhole satellites (e.g.,
[http://en.wikipedia.org/wiki/National_Reconnaissance_Office#...](http://en.wikipedia.org/wiki/National_Reconnaissance_Office#Spacecraft)),
which turned out to be larger than most people imagined.

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sp332
Um, _In certain conditions, atoms and subatomic particles can be in two places
at once, or spin clockwise and anticlockwise at the same time. That means you
can use a single atom to represent two binary digits._ No, that's not how that
works...

A qubit represents a single bit, in its two possible states: 1 and 0. Alone,
the qubit could hold the probabilities that the bit will be a 0 or a 1 when
you observe it. But for a quantum computer to be cool, you have to include
entanglement!

When 2 qubits are entangled, they represent the probabilities of _each_ of the
4 possibilities: 00, 01, 10, 11. If you only had the probability of each bit
separately, say 10%/90% and 40%/60%, then the state would just be the
multiplication of the two values: 4% for 00, 6% for 01, 36% for 10, 54% for
11. And if the first bit's probability changes, the second bit doesn't change.
A simple multiplication will give you the new answer.

But entanglement means the probabilities are dependent on the values of other
bits :) So say: if the first is a 0, the second has a 90% chance of also being
a 0. And if the first is 1, the second only has a 50% chance of being a 0 or a
1. So if the first has a 20% chance of being a 0, that gives us 18% for 00, 2%
for 01, 40% for 10 and 40% for 11. The values of the bits are linked to each
other. It's not limited to a simple linear percentage; it can get more
complicated by running the bits through various gates. So if the first bit's
probability changes, you have to recalculate the new probabilities of B
_given_ A. That's when it would take exponential time using a classical
computer, but it's all done instantaneously via entanglement.

~~~
xanmas
I think they were trying to explain super-dense coding [1].

[1]
[http://en.wikipedia.org/wiki/Superdense_coding](http://en.wikipedia.org/wiki/Superdense_coding)

~~~
sp332
Maybe. But even that requires 2 qubits.

------
Zarathust
"A report leaked to the Guardian suggests that the NSA can get three billion
pieces of information a month from computer records alone.".

3 billion records doesn't seem to be that much. I mean, even with a desktop
computer, having a month to compute something meaningful out of that doesn't
seem far fetched. I really don't think they need sci-fi computers for all of
that. 3B/month * 12months * 5 years = 180 billion records. That's a lot but
large tech companies seem to deal with those kinds of numbers all year long.

------
jstalin
For those of us who are not mathematicians, what would quantum computing
practically mean? Compare current math capabilities of computers and quantum
computing in layman's terms, please.

~~~
darth_aardvark
Quantum computers are not just super-fast versions of normal computers. They
allow the running of some algorithms that normal computers can't physically
run. One particularly important algorithm is Shor's algorithm.

Shor's algorithm allows quick factorization of primes. RSA encryption, the
main way that things are encrypted today, relies on the assumption that
factoring large primes is computationally infeasible. So quantum computers
would allow the NSA to read RSA-encrypted data.

~~~
weinzierl
From a computer science standpoint this incorrect. Regarding computability,
quantum computers have exactly the same power as traditional computers.

~~~
bo1024
I'm not sure what you're referring to; everything in the parent post is
correct. You are right that quantum and classical computers have the same
"power" in terms of problems that can be solved, but it is also true that
quantum computers may be able to computer certain functions _faster_ than
classical computers (using faster algorithms that don't run on classical
computers).

~~~
weinzierl
I'm referring to "They allow the running of some algorithms that normal
computers can't physically run."

I understood this as, it's impossible to run some algorithms on a traditional
computer. You can run Shor's algorithm on a Turing machine, albeit requiring a
simulation of qbits. You can run it in javascript and in your browser if you
like.

~~~
mtp0101
True, you can simulate the qbits, so the more precise statement would be they
can execute some algorithms in a way that classical computers cannot and this
gives them superior efficiency in some situations.

------
jzelinskie
Isn't this article pretty much fear mongering? There's no way the NSA has a
reasonably powerful quantum computer and the proper algorithms to do anything.
However, the question still remains once these devices are feasible and
popular: how can they use it to process the data they've already collected?

~~~
ryandvm
I don't know about that. _If_ a quantum computer is possible, you can rest
assured that the U.S. defense complex has procured themselves one with their
unfathomable budget.

~~~
jzelinskie
Quantum computers are very well __possible __; whether they are feasible to
data mine our large amounts of data is the actual question. You don 't think
the corporate entities in the tech industry would be just as invested? This is
an area of research far too large to be concealed within the government. I
wonder what the NSA program would look like if it wasn't for the surge in "big
data" tooling after Google's MapReduce/GFS/BigTable papers.

------
Xcelerate
If the NSA wanted to do something really interesting with a quantum computer,
they would invest in scientific research instead.

Quantum computing allows specific types of quantum simulations to be performed
in polynomial time instead of exponential time. The most powerful classical
computers cannot get around what is known as the fermion sign problem.

I think super-accurate simulations would be very exciting; imagine a world
where experiments are conducted using computers, but give the same exact
results as their "real-life" counterparts.

~~~
mturmon
"they would invest in scientific research instead"

They already are, and have been for many years now. Here's one example from a
couple of years ago
([https://www.fbo.gov/index?s=opportunity&mode=form&tab=core&i...](https://www.fbo.gov/index?s=opportunity&mode=form&tab=core&id=637e87ac1274d030ce2ab69339ccf93c))
but there have been much larger-scale investments too.

Because of its coding and codebreaking relevance, this stuff is squarely
within their charter. They are all over it.

------
nissimk
What's the deal with this Dwave device?? Is it the real thing?

According to wikipedia there is a "history of controversy." [1] Can anyone
here provide more details?

[http://en.wikipedia.org/wiki/D-Wave_Systems#History_of_contr...](http://en.wikipedia.org/wiki/D-Wave_Systems#History_of_controversy)

~~~
izend
The Dwave device is definitely real, it is a specific type of quantum computer
which is called adiabatic quantum computer and can be used to efficiently
solve optimization problems [1].

Some people believe the Dwave device shouldn't be labeled as a "Quantum
Computer" because the general community typically uses the Quantum Computer
label for a device which could compute NP-Complete problems in linear time
instead of exponential time, the Dwave device cannot do this.

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

~~~
arjunnarayan
Quantum computing is not known to allow you to compute NP hard problems in
linear (or polynomial) time. Specifically, the relationship between BQP and NP
is open, but widely believed to be not equal (just as the general community's
priors are biased towards P \neq NP). Here's a hint as to why:
[http://en.wikipedia.org/wiki/Grover%27s_algorithm#Optimality](http://en.wikipedia.org/wiki/Grover%27s_algorithm#Optimality)

If you are interested in what exactly the D-Wave computer is doing,
[http://www.scottaaronson.com/blog/?p=1400](http://www.scottaaronson.com/blog/?p=1400)
is a good source.

------
lucb1e
This might sound conspiracy-theory-like, but I think we should assume they
have technology a few years ahead of what we know. It might be best to assume
they do actually have a working quantum computer, perhaps not breaking all
existing crypto yet, but certainly something powerful.

------
mtgx
NSA with classic computers - analyzing what has already happened.

NSA with quantum computers - pre-crime analysis

CIA is already working on this with Recorded Future, and NYPD created a system
with the help of Microsoft to create statistics to see where most crime is
"likely" to happen and when.

I think we'll see a lot of very powerful technologies (quantum computers,
mosquito-drones that can poison you in your sleep, etc) that can be so easily
abused by governments, because they won't resist using them to get rid of
people they don't like, especially if these technologies step on legal gray
areas, but even if they don't (not like "mass spying of citizens" is anywhere
close to gray area), or if they think they can keep their usage secret.

This is why it's going to be extremely important that the people get very
outraged at such abuses as soon as even small ones happen using these
technologies in the next few decades, to find balance in the law and
government, before it's too late (these things will be moving fast).

~~~
tptacek
I've read this comment 3 times right now and, respectfully --- I mean this in
a dry, analytical sense --- I can't understand the claim here.

Can you be specific as to how quantum algorithms are going to allow NSA to do
"pre-crime analysis"? Could you talk a little bit more about the applicability
of quantum algorithms to big data statistics problems?

You were very quick to comment on this thread, so I'm asking expecting that
you have some interesting thoughts about quantum computing.

~~~
bad_user
Quantum computing could be used for solving systems of linear equations more
efficiently for example, having applications in image/video processing,
weather predictions and all kinds of analysis - solving such equations with
classic computers is done in something like O(n^3) or O(Cn^2) with a huge C,
but quantum computers could reduce this to O(log n) or something like that.
This is really cool, because doing simulations of complex systems, like
weather modelling, involves a huge number number of equations and variables
(think billions, or even trillions).

It isn't far fetched to think of evolved quantum algorithms for making better
predictions than we currently do. On the other hand, some people kind of have
the impression that with quantum computers suddenly NP won't be an issue
anymore. Which is simply not true. Most problems we have will simply go
unsolved and quantum computers will introduce problems of their own.

~~~
gizmo686
>quantum computers could reduce this to O(log n)

I doubt it. It would take O(n) just to copy that data into your quantum
computer.

~~~
drkevorkian
He might be referring to this:
[http://arxiv.org/pdf/0811.3171v3.pdf](http://arxiv.org/pdf/0811.3171v3.pdf)

So, if the question you want to ask is "what is some property of the solution
of the (sparse) set of linear equations" rather than wanting to know the
(inherently O(n)) solution itself, you can get exponential speedup.

