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| QUESS sattelite, Credit: Xinhua |
Quantum
Experiments at Space Scale (QUESS) spacecraft lifted off atop a Long
March-2D rocket from the Jiuquan Satellite Launch Center in the Gobi
Desert on Monday, August 15, 2016. Its objective is to test whether it is
possible to develop a large capacity, unhackable communication network. It
uses curious features of quantum particles, photons: superposition and quantum
entanglement. The satellite will circle the Earth at an altitude of about 600 kilometres
trying to teleport confidential information over 2000 kilometres away which is
fifteen times more than the current record held by the European and American
scientists. In collaboration with Europe, China intends to develop European and
Asian quantum telecommunication network by the year 2020 and a worldwide
quantum telecommunication network by the year 2030.
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| Long March-2D Launch, Credit: China Daily |
The Chinese
experimental satellite will test out the possibility to teleport quantum
cryptographic keys for a considerably longer distance that it was achieved
on the Earth´s surface. You may be surprised; however the quantum distribution
of cryptographic keys is a service commercially available on the Earth´s
surface. It is expensive, slow, for short distances only but incredibly safe. At
present, there are at least four companies that are able to provide the quantum
cryptographic network as a turnkey delivery. The most powerful quantum
communication network is currently being tested in Japan.
Then why
does China want to develop a quantum network infrastructure at the Earth´s
orbit? It is related to the principle on which the quantum communication works.
Let us
imagine that Alice wants to send a confidential message to Bob. At first
she encrypts the message by a cryptographic key representing a chain
of some hundreds of random letters and digits. And somehow she has to deliver
the key to Bob. Since then Bob is able to read any kind of message encrypted by
Alice. Delivery of the cryptographic keys is performed by the quantum
communication networks.
But why
should such expensive devices be used when this issue is reliably solved by the
current cryptographic algorithms using private and public cryptographic keys?
It is because the quantum communication networks are promising a unique feature.
Alice and Bod are able to find out whether their cryptographic key has not been
read by a third person along the way. How is that possible?
As I have already
mentioned before, the quantum cryptographic communication uses mostly photons
to teleport information. Actually, their features. For example polarization. To
make it more simple, let us assume that each photon can be present in three
states only: in the state of horizontal polarization, in the state of vertical
polarization and in the state of superposition. Each “newly born” photon is
present in the state of superposition, e.g. it exists in both states:
horizontal and vertical simultaneously. How can we imagine that? Take
a coin, place it on its edge and flip it. It will be flipping on its edge.
And it would flip forever if no friction of the air and desk surface. What
would you say which side is the flipping coin on: heads or tails? Weird but the
true answer would be: neither of them but both sides at the same time.
It is exactly
the same with a photon being in superposition. Unless we start to measure it,
we have no chance to know what state it is. If we try, it will end up in
a stable state: horizontal or vertical polarization. As if we covered the
flipping coin with a hand in one moment, move the hand away to see what
side is the coin: heads or tails.
Moreover,
the Chinese satellite uses another weird feature of the quantum world: quantum entanglement.
I would say that it is the most curious characteristic that I have
ever come across in my entire life. It is so curious that neither Einstein could
believe it.
What is the
quantum entanglement all about? Imagine we have a laser generating
a stream of photons passing through a special crystal. Approximately one
out of a billion splits into two - being quantum entangled. Since that
moment they are going to behave as “twins”. Even if they were on the other side
of the universe they will know everything about each other. Immediately.
Example. A
collapse of one entangled photon to the horizontal polarization will cause
the other end to be immediately programmed to collapse to the vertical
polarization. Immediately. As if no law of the maximum speed of light applied
to them. How is that possible?
Just
imagine that both of the entangled photons are two “ends” of the same quantum formation
passing through a wormhole. If one end collapses to a stable state,
the other has to collapse to a compatible state. Otherwise it would violate
the momentum conservation law. And, since they are in the wormhole
a totally different space-time applies to them than to us. It is twisted
to microscopic space.
A wormhole
is a hypothetical physical feature predicted by Einstein´s theory of
general relativity. It is a space-time tunnel, shortcut for long journeys
across the universe. Wormholes are widely used in science fiction.
If you are
already feeling dizzy from the quantum and relativistic terms which I have
used - get used to it. It is nothing in comparison to what is about to come in
near future. The world´s greatest masterminds of physics are right now
feverishly verifying the previously mentioned hypothesis. The hypothesis of the
century:
ER=EPR.
The
abbreviation ER refers to Einstein, Rosen who described the phenomenon of
wormholes in 1935. The abbreviation EPR refers to Einstein, Podolsky, Rosen who
in the same year theorized about the phenomenon of quantum entanglement.
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| Credit: www.physics-astronomy.com |
Please
remember this “Einstein´s equation”. It is going to be as important as his E=mc2.
This hypothesis claims that wormholes and quantum entanglement are expression
of the same natural phenomenon. In case it proves to be correct, something
amazing will happen. We will discover a unified physical theory of
everything: quantum theory of gravity. This theory would, for example, allow us
something what is beyond our imagination: targeted manipulation with space and
time.
Let us go back
to the quantum communication. Alice wants to send a cryptographic key to
Bob using the Chinese satellite. How will she do that? The satellite will send
two entangled photons to Earth. Both in the superposition state. One will be
received by Alice, the other by Bob. At first, Alice will “encrypt” the first
bit of the cryptographic key to its photon. At that moment Bob´s photon “knows“
to which state it will collapse once Bob is reading it. This procedure is being
repeated, bit by bit, for the whole cryptographic key.
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| Credit: Xinhua |
Okay, but
how is the resistance against eavesdrop being assured? Let us imagine that
Bob´s photon would be eavesdropped by a third party - Eva. Of course, she
would be able to read the information from Alice. As well as Bob. However, the
photon once read will no longer be entangled and in state of superposition. Eva
can no longer use it for communication. She has to send a false one
bringing a statistic error to the communication which can be detected by
Alice or Bob.
And why do
the Chinese bring the quantum communication to the orbit? As you can imagine
from the previous text, quantum communication is dependent on delivery of every
single photon. Even though the photon is rather resistant to “damage”, as every
particle, it can sometimes collide with something on its journey: electron,
other photon, atomic core. Each of these “dates” means loss of communication.
The same as if Eva had read the message.
This
significantly decelerates the quantum communication and makes it more
expensive. So far, the scientists have been able to teleport a photon over 150 kilometres
away. To teleport a photon over 2000 kilometres away assumes using a pretty
brute force. For example, a large quantity of photons transmitted in parallel of
which only a few will cross the finish line. In addition, the Chinese want to
make use of the fact that with an ascending altitude the number of atmospheric
gas molecules decreases. So when a photon is shot off from a sufficient
altitude above the Earth´s surface it might meet fewer obstacles on its journey
than a photon flying only a few meters above the Earth. And that is what the
Chinese satellite is going to test and measure.
After GPS, permanently
testing correctness of the theory of time deformation, the space quantum
communication is going to be another technology that is going to test out even
more curious features of the quantum world on a massive level.
For all skeptics this is going to be a clear evidence that reality is rather weird than
normal, that we are headed to success by open mind rather than prejudice, and a
change eventually brings more advantages than hides dangers.
Quite a
decent contribution of the Chinese quantum satellite, don’t you think?
