Space race under way to create quantum satellite

Feb 28, 2013

In this month's special edition of Physics World, focusing on quantum physics, Thomas Jennewein and Brendon Higgins from the Institute for Quantum Computing at the University of Waterloo, Canada, describe how a quantum space race is under way to create the world's first global quantum-communication network.

The field of – the science of transmitting quantum states from one place to another – has received significant attention in the last few years owing to the discovery of .

Quantum cryptography exploits a unique property of single particles, such as photons: they can exist in two separate states – such as vertically polarized or horizontally polarized – or something in-between, known as a . Upon measuring the state of a particle you instantly change this state, meaning an made of photons can be passed between two parties safe in the knowledge that if an eavesdropper intercepts it, this would be noticed.

Quantum cryptography has been described as a way of creating "unbreakable" messages and has attracted the attention of major technology companies, governments, banks and other security-focused clients.

The transmission of encryption keys over long distances still remains a significant challenge for scientists, however, as the intensity of signals tends to weaken as they travel further because photons get absorbed or scattered off molecules.

Up until now, the furthest that quantum- have been sent is a few hundred kilometres, which would realistically enable communication between just one or two cities.

There is one place, however, where scattering doesn't appear to happen – empty space. Jennewein and Higgins lead just one of several teams around the world looking to take advantage of this by pursuing the concept of a quantum satellite.

A signal travelling from a ground station on Earth to a satellite would spend most of its time in the empty vacuum of space – rather than in Earth's atmosphere, which is crowded with gas molecules – so the signal would travel a lot further without weakening.

A satellite orbiting at around 32,000 km above Earth would act as a kind of relay between two ground stations in a way that allows them to establish a secure link by sharing an encryption key made of photons.

In addition to the basic mass and power of the satellite itself, the team led by Jennewein and Higgins has been studying the overall design features of the satellite and ground stations and has emphasized the need for them both to be precisely aligned so they can be certain that what they are measuring correctly corresponds to the photons that are prepared.

"With the prospect of global-scale quantum communications and fundamental quantum science within new, unexplored regimes, the next few years are sure to be exciting," Jennewein and Higgins write.

Explore further: New experiment provides route to macroscopic high-mass superpositions

Related Stories

Secure Communication via Space

Apr 22, 2008

The exchange of information between distant sources is the basis of all communications, but quantum mechanics may open up this distant exchange as never before.

Not 1, not 2, not 3, but 4 clones!

Nov 04, 2011

Xi-Jun Ren and Yang Xiang from Henan Universities in China, in collaboration with Heng Fan at the Institute of Physics of the Chinese Academy of Sciences, have produced a theory for a quantum cloning machine able to produce ...

Recommended for you

Scientists develop compact medical imaging device

7 hours ago

Scientists at the MIRA research institute, in collaboration with various companies, have developed a prototype of a handy device that combines echoscopy (ultrasound) with photoacoustics. Combining these two ...

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

Tausch
3.7 / 5 (3) Feb 28, 2013
Quantum states are transferred. Not transmitted.
The journalistic wording is forgivable.
Those able will make the distinction.
antialias_physorg
3 / 5 (6) Mar 01, 2013
Quantum states are transferred. Not transmitted.

Good call. Transmission would indicate infomation exchange (which doesn't happen with a quantum encryption process - or any encryption process in general).
Infinum
2.5 / 5 (2) Mar 01, 2013
Transmission would indicate infomation exchange (which doesn't happen with a quantum encryption process - or any encryption process in general).


Well, it actually does.

The information is send with the speed of light before the measurement. It is the measurement i.e. entanglement that is instant, but the information itself has to be transmitted/propagated through space beforehand.
antialias_physorg
2.3 / 5 (3) Mar 01, 2013
You have to distinguish between the information transmission (the message) and the encryption process (the transformation of the message into another form)

The transmission of the message conveys information (and is therefore limited to the speed of light), the encryption process does not (and is therefore not limited to the speed of light).

Read:
While you need to convey the entangled photons at the speed of light for the encryption/decryption you don't need to use them immediately. So you can start sending the message way after the encryption/decryption process is in place (i.e. the encryption process itself is instant accross any distance).
dbsi
3 / 5 (1) Mar 01, 2013
What needs to be relayed through the satellites are just the photons to construct the keys. The protocol how the receiving site has to make the measurements and construct the keys out of the measurements can be transmitted using conventional technology using a second channel. The encryption and decryption of any "payload" information can be done, using the constructed keys, by standard cryptographic methods, the transmission of the encrypted payload information could also be done by conventional methods.
Tausch
2.3 / 5 (3) Mar 02, 2013
I pointed out an incorrect usage of words. This led to discourse.

Everyone hopes that discourse leads to understanding.
To an understanding that when distinctions are made the motivations behind making distinctions can be understood by eventually everyone/anyone.

I forgive anyone who does not grasp the understanding behind the motivation to make a choice between words.

An incorrect choice of words leads to discourse. And to understanding.
A correct choice of words leads to acceptance without discourse.

Jitterbewegung
1 / 5 (1) Mar 02, 2013

"Quantum cryptography exploits a unique property of single particles, such as photons: they can exist in two separate states – such as vertically polarized or horizontally polarized – or something in-between, known as a quantum superposition."

That's just plain wrong and misleading. A photon's polarization can be linear, circular or elliptical.

http://en.m.wikip...rization
antialias_physorg
2.3 / 5 (3) Mar 02, 2013
That's just plain wrong and misleading. A photon's polarization can be linear, circular or elliptical.

Why is that misleading? The 'such as' is a dead giveaway that those are not the only possibilities.