

A Baby Quantum Internet Was Born Today - eplanit
http://news.discovery.com/tech/quantum-internet-120412.html

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pranjalv123
The cool thing about quantum mechanics is that a man-in-the-middle attach
won't work!

The reason for this is the Heisenberg Uncertainty Principle, which states that
there are certain attributes of a particle where we can't know both of them
perfectly. The classic example of this is position and energy.

The relevant attributes here, though, are angular momentum (spin) in the
"left/right" and "up/down" directions. Think of a particle as two arrows, one
pointed either left or right, and the other pointed either up or down. The
Heisenberg Uncertainty Principle states that if I know with 100% accuracy that
a particle is pointed left (or right), I can't know anything about if it's
pointed up or down, and vice versa. In fact, if I measure the left/rightness
of a particle, the up/downness gets set randomly to be either of them.

So quantum communication works more or less like this: We agree that left and
up correspond to a 1, and right and down correspond to a zero. So if I want to
send a 1, I randomly choose a either a left or an up, and send it to you.
Then, on your end, you randomly choose an axis to measure on, and after I've
measured, we tell each other (through a public channel) which axis we measured
on. If we agree, we use the bit, otherwise, we throw it away.

Ok, so now, what if Eve comes in the middle and steals our electron, reads it,
and sends it again. Well, she doesn't know what axis to measure on! So if I
send it on the up/down axis, Eve measures it on the right/left axis, and you
measure it on the up/down axis, you have a 50% chance of getting a wrong
answer. So if we take a few bits at random and publish them, we can get a
pretty good idea if someone's snooping.

Also, Eve can't copy our particle, because if she could, she could read one
axis from one particle and the second from the other, which would violate the
Uncertainty Principle (this result is known as the No-Cloning theorem).

~~~
comex
That only works if the public channel is trustworthy. If Eve can man-in-the-
middle it too, she can just conduct separate instances of the protocol with
Alice and Bob, forwarding on the classical data.

~~~
MarkPNeyer
this is true of any form of communication.

if you go far enough into crypto theory, you become so skeptical that even
hume looks naive. how do you know you aren't a brain in a jar, subject to a
cruel experiment to explore how people respond to boring philosophical
rebuttals to their posts on social networks?

~~~
adrianbg
Pretty harsh considering comex is right and pranjalv123 is wrong.
Authentication is still necessary in quantum communication channels. MIM is no
less possible on a quantum channel than a classical one. Eavesdropping is
harder but the no-cloning theorem doesn't prevent attackers from learning
information about what you and your buddies are saying to each other.
[http://en.wikipedia.org/wiki/No-
cloning_theorem#Imperfect_cl...](http://en.wikipedia.org/wiki/No-
cloning_theorem#Imperfect_cloning)

------
stewie2
I don't understand.

If the two atoms are linked via entanglement, why are they also connected by
optical fiber?

if aiming a laser at the first atom will change its state, then shouldn't the
state of the second atom change too at the same time?

" That photon zooms along the optical fiber to other optical cavity containing
the other atom."

photon zooms? that means on the other side of the optical fiber, the second
atom absorbs more than just one photon?

~~~
jean-
The atoms are not initially entangled. They become entangled once a photon
from one atom travels along the fiber and interacts with the second atom.

I believe that "zoom" means "to travel very quickly" in the sentence you
quote.

~~~
stewie2
Thank you. I'm not native English speaker.

------
powertower
> That photon zooms along the optical fiber to other optical cavity containing
> the other atom.

Wouldn’t this break the entanglement?

That photon is going to be absorbed/re-emitted countless amounts of times as
it "travels" though the optical fiber.

Every time this happens, the wave function is collapsed.

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mjjones0
Wouldn't the man-in-the-middle attack still work in this scheme?

------
wicknicks
Previous discussion on the topic here:
<http://news.ycombinator.com/item?id=3830746>

------
pfraze
I like to think that we'll uncover a new phenomena for communication, but be
troubled the the incredible amount of noise in the medium, only to discover
it's the channel for intergalactic WiFi.

Browsing the UWW will be crazy.

------
indiecore
>never be hacked

May I be the first to say, challenge accepted.

~~~
pranjalv123
Actually, a bunch of commercial quantum crypto systems were hacked a few years
ago, in spite of being "theoretically unhackable". The details are at
[http://www.techrepublic.com/blog/security/quantum-hacking-
cr...](http://www.techrepublic.com/blog/security/quantum-hacking-cracks-
quantum-crypto/4371), but basically you can convince avalanche diodes that
they're only receiving one photon by blinding them, and this lets you bypass
the security inherent to the No-Cloning theorem and the Uncertainty Principle
that quantum crypto relies on .

~~~
EthanHeilman
Untappable is not the same as unhackable. Using the term "unhackable =
untappable" is really bad way to talk about computer security since it ignores
every other security bad other than the ability to capture photons traveling
down a fiber.

