
Information teleported between two computer chips for the first time - dsr12
https://newatlas.com/quantum-computing/quantum-teleportation-computer-chips/
======
carlosdp
> Our current understanding of physics says that nothing can travel faster
> than the speed of light, and yet, with quantum teleportation, information
> appears to break that speed limit.

The word “information” could be interpreted to mean communication faster than
the speed of light, which is important to note is not made possible by
entanglement.

Entanglement can’t be used for faster-than-light communication because
although observing the spin of particle A affects the spin observed for
particle B, the spin you observe is effectively random, so there’s no way to
know that the results match up unless you compare them with another means of
communication, one that is at most the speed of light.

This article explains it way better:
[https://www.forbes.com/sites/chadorzel/2016/05/04/the-
real-r...](https://www.forbes.com/sites/chadorzel/2016/05/04/the-real-reasons-
quantum-entanglement-doesnt-allow-faster-than-light-communication/)

~~~
umvi
However, the article claims:

> Changing the properties of one particle will cause the other to instantly
> change too

Is this true? Doesn't that mean if we can control the spin of one particle on
command, the other will instantly change according to our control?

So basically, FTL communication is possible iff controlling the spin of a
particle is possible.

~~~
russdill
When you measure the spin of a particle, you can only get 2 possible answers,
up or down. The up or down is with respect to the angle you measure the spin.
You could measure it with respect to the z direction, the x direction, half
way in between, etc.

The important part about entangled particles is if you choose to measure two
entangled particles in the same direction you will always get the opposite
answer. Note that once you do such a measurement, the particles are no longer
entangled and you're gonna need another timmy.

Teleporting the quantum state involves transferring the entanglement of a
particle here to a particle over there. This is done by using another pair of
entangled particles. It's not possible to just transmit quantum state by
purely classical means.

I'll also note that the "transmitted instantly" part depends on your
interpretation of quantum physics.

~~~
umvi
> I'll also note that the "transmitted instantly" part depends on your
> interpretation of quantum physics.

Ok, the way I interpret it is that entangled particles are like 2 hard boiled
eggs that have collided.

It is well known that if you roll 2 hardboiled eggs into each other, only one
will crack.

So basically, if I roll two hardboiled eggs into each other and then hide them
in paper bags, the eggs are now "entangled" and if I separate the bags by 1
million miles, I can observe the state of my egg and know _instantly_ what the
state of the other egg is.

For example, if I peer into my bag and see my egg is not cracked, I know that
the other egg is indeed cracked! However, if I change the state of my egg
(crack it) then obviously nothing happens to the other egg because the eggs
are no longer "entangled".

There is no "instant transmission" happening here. All the properties of the
eggs were set in stone the moment the eggs collided and thus it doesn't matter
how far away you move them because the "entanglement" (collision) event
already happened.

This is not a very useful property of hardboiled eggs and so I fail to see how
this could be useful by scaling down the eggs to photons.

~~~
syrrim
That's the 'local hidden variable' model that was disproven by Bell in the
sixties.

~~~
umvi
Yeah, and I watched Veritasium's video on it, but I still don't really buy
"spooky action at a distance".

The way I understand it, particles have an "absolute orientation" in space
that is impossible to determine because currently we are limited to measuring
the orientation relative to another orientation and getting a yes/no
probabilistic outcome (also, we can only perform this measurement once because
the act of measurement changes the orientation of the particle).

Nevertheless, in reality the particle has an absolute, no-guesswork spin
orientation property that a theoretical godlike being running the universe
simulation would be able to observe in a "read only" fashion. (We mortals have
to use probability abstractions because we don't have sophisticated enough
methods of getting quantum information in a read-only fashion)

So basically, when you "entangle" two particles, the act of entanglement
affixes their absolute spin orientation to be polar opposites. Bell's theorem
doesn't disprove that, afaik, and it accounts for the "spooky action at a
distance".

~~~
russdill
Ok, let's say the absolute truth orientation is +x. What would you expect to
happen when you measure along the +y axis? You'd expect a completely random
result. But that isn't what you get when you measure both entangled particles
in +y. Yes the spin of either particle on it's own is completely random, but
their spin will always be opposite.

~~~
umvi
If you already know the absolute truth orientation, then there should be no
guesswork when it comes to measuring it

~~~
russdill
OK, so when you measure spin, you get two possible results. Either up or down.
Set up a particle so it it's spin is in the +z axis. Now measure it in the +x
axis. Will the detector return up or down?

------
umvi
I get the feeling this article is extremely inaccurate and that the author
doesn't understand quantum mechanics at all. I'm no expert either, but I've
heard over and over from experts that FTL information transfer is still
impossible even with "teleportation".

~~~
notfed
Articles like this come out once per week. And yes, the authors almost always
have very little physics experience. (Or are blatantly misleading for the
purpose of clickbait.)

It's also very tiring that people keep needing to be reminded of the fact that
no, faster-than-light communication is still not (and never will be) possible.

(Which really does leave us back at this question: if it doesn't get us faster
communication, then what advantages do we think quantum teleportation is going
to get us?)

~~~
umvi
> Which really does leave us back at this question: if it doesn't get us
> faster communication, then what advantages do we think quantum teleportation
> is going to get us?)

I believe currently its most useful property is its ability to detect
eavesdropping. With classical information, it is possible to make a copy of
information you observe without being detected. With quantum information, the
act of observing changes the state, so eavesdropping can be detected
somehow[1]

> An important and unique property of quantum key distribution is the ability
> of the two communicating users to detect the presence of any third party
> trying to gain knowledge of the key. This results from a fundamental aspect
> of quantum mechanics: the process of measuring a quantum system in general
> disturbs the system. A third party trying to eavesdrop on the key must in
> some way measure it, thus introducing detectable anomalies. By using quantum
> superpositions or quantum entanglement and transmitting information in
> quantum states, a communication system can be implemented that detects
> eavesdropping. If the level of eavesdropping is below a certain threshold, a
> key can be produced that is guaranteed to be secure (i.e., the eavesdropper
> has no information about it), otherwise no secure key is possible and
> communication is aborted.

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

------
api
Quantum entanglement can't transfer information because you have no way of
knowing whether the other end has "observed" their particle(s) yet. A
conventional signal is required to establish this.

But... as far as I recall there may be ways to have that conventional signal
only carry minimal (e.g. parity) information and thus to achieve not only much
higher data rates but physically un-snoopable communication. I wonder if you
could pair quantum entanglement with a slow ultra-long-range signal in the low
frequency range to achieve high speed perfectly secure long distance links? I
assume this sort of thing would be first of interest to military and
intelligence users.

~~~
akersten
Regarding the observation problem: Wouldn't you be able to set up a protocol
beforehand (e.g. sample the photon at X MHz) and then you know your window for
when the other side would have had the chance to observe? Isn't this how a lot
of time division multiplexing already works?

For me the bigger issue with quantum computing is that I just don't believe it
will ever be practical. Feels like we've been seeing this same article for the
last 30 years. I'll love to be proven wrong.

------
NSAID
>The team managed to send information from one chip to another instantly
without them being physically or electronically connected

Doesn't current quantum teleportation require optical connectivity because the
state transfers along photons?

The abstract says

>Here, we report the demonstration of chip-to-chip quantum teleportation and
genuine multipartite entanglement, the core functionalities in quantum
technologies, on silicon-photonic circuitry

So while there may not necessarily be a phsyical connection this does require
line-of-sight by my read, and "silicon-photonic circuitry" sounds like this is
all on one physical board.

I guess I don't understand how this is "two different chips" as the article
claims. Did they use two photomasks? Baby steps, I suppose.

~~~
krastanov
Any form of quantum "teleportation" requires that the two chips first share a
pair of entangles particles. Usually this is done by making the two entangled
particles on one of the chips and sending one of the particles to the other
chip. Usually the particles are photons for engineering reasons.

The quantum teleportation happens after that. Once the particles are
entangled, you can destroy yours in a very particular way that forces the
other particle to instantaneously become either a copy of the particle you
destroyed (i.e. its state is the same) or the opposite of the particle you
destroyed (i.e. its state is something like a boolean negation). Only you know
which one happened (you learn that when you destroy your particle) and need to
send one bit of classical information to the other chip in order for it to
know as well.

In other words, you can transmit one bit of classical information and
sacrifice one entangled pair to "teleport" one qubit of quantum information.

It is called teleportation because the quantum information never actually
physically moved, rather it instantaneously went to the other chip. To know
how to use it, you still need that classical bit to be transmitted in order to
know whether the quantum information underwent a boolean negation.

~~~
umvi
I'm still so confused. I understand what a photon is (ish... I understand it
can behave as a particle or wave, but in this case it is a "particle"). How do
you "observe" a single photon? How do you "destroy" a single photon "in a
particular way"? Heck, how to do keep something moving at the speed of light
stuck inside a chip? Create a fiber optic loop somehow? How is the photon
introduced into the loop?

~~~
fsh
Typically (for polarization qubits) a combination of waveplates, polarizing
beam splitters and single-photon detectors (avalanche photodiodes,
photomultipliers, or superconducting nano-wire detectors) are used to measure
the qubit state. These detectors absorb the photons and turn them into
detectable electrical signals. It is also possible to detect photons without
destroying them (non-demolition measurement). However, this is much more
difficult to do and leads to exactly the same results. After the measurement,
the photon is no longer in a superposition state and is no longer entangled
with the other one.

There is number of techniques for storing photon qubits. The easiest way is to
send the light through a very long optical fiber spool. However, the
achievable delay is limited due to absorption in the fiber. It is also
possible to transfer the photon state onto a different system, such as a
single ion or a superconducting qubit. Then the state of that system can later
be measured.

------
ibobev
As always with such articles, this is also misleading. They do not explain
that according to the "No-communication theorem" [1] it is not possible to use
quantum teleportation for faster than light information transfer.

This is becoming very common in popular science articles to be represented
some misleading propositions by avoiding to report a little, but important
part of the whole picture. In this way many people (sometimes including
myself) stayed with invalid picture for what is actually achieved or possible
to achieve.

[1] [https://en.wikipedia.org/wiki/No-
teleportation_theorem](https://en.wikipedia.org/wiki/No-teleportation_theorem)

------
secondo
Whereas we can’t send specific information between two entangled qubits would
we not be able to use it synchronize state (read seed) FTL? That state would
for instance allow the two systems to instantly be in sync with a newly
generated random seed?

------
khkjrhwer
One interesting theory of why a maximum speed of communication (speed of
light) exists is that it allows simulating the universe in a distributed way,
since it gives you a maximum effect range (light cone), thus you can shard
your simulation (of course, you still need to sync neighbor shards).

~~~
vjktyu
There is a simpler explanation. Assuming our world is discrete, like a
mathematical graph, every world state has one or a few next possible states.
If we imagine all possible states from past and future linked together by
causality links as a huge mathematical graph, any two states have a shortest
path between them. The length of this path is what we perceive as time or as
the speed of light. Same idea applies to chess: there is large, but finite,
number of chess board states and they are linked by moves allowed by the chess
rules; the number of moves on the shortest path connecting two positions is
what we'd call the speed of light in chess.

------
riku_iki
My bet is it will be first adapted by high-frequency traders.

~~~
kchamplewski
What advantages would it give them though?

It's no faster than any existing means of communication since you still need
to send classical information along with the quantum, though I guess it's nice
that it can be used for almost completely unbreakable encryption.

It feels like complete overkill for no practical advantage that I can see.

