Quantum signal over the city
First quantum transmission of multi-bit photons through the air
Record-breaking: Researchers have transmitted a quantum signal with more than one data bit per photon for the first time - and this in a particularly difficult environment. For the quantum message was exchanged in the middle of the city of Ottawa over 300 meters between two houses. The double coding of the data made the quantum signal even legible despite the air turbulences, as the scientists report.
© University of Ottawa
Quantum cryptography is considered to be the encryption method of the future because it allows data to be sent almost "unbreakable". By interlacing photons, quantum signals also reach their receivers almost instantaneously - even over long distances. In the future, quantum communication could therefore make data exchange in urban fiber optic networks, but also with the orbit, safer and faster.
More than one bit per photon
Up to now, the simplest encoding is used to transmit quantum messages: A photon transmits one bit - a zero or one. However, by manipulating and reading out two or more properties of the photon, it is also possible to encode several bits per light particle. However, whether this so-called high-dimensional quantum fragmentation also functions in the case of transmission through the air, has so far remained open.
Ottawa intracity quantum communication link. © www.osapublishing.org
Now, Ebrahim Karimi from the University of Ottawa and his team have demonstrated this for the first time. For their experiment, they carried their laser equipment, normally used only in the laboratory, on two roofs, about 300 meters apart, on the university campus. The instruments produced entangled photons whose quantum states encoded two bits per particle. Each photon can carry four possible signals: 00,01,10 or 11. This technique is therefore also referred to as 4D quantum cryptography.
Quantum transmission through the city air
Would this quantum information outperform the turbulent city air? The problem is that the fragile state of the entanglement is relatively susceptible to interference. Especially in the atmosphere, turbulence and other disturbing influences can easily cancel the entanglement. As a result, only a few quantum signals are produced.
Colleagues thought our experiment was impossible, the researchers report.
But the experiment succeeded - even better than expected: the quantum message sent with the double-coded photons was still readable even after 300 meters of air transport.
For the first time, we successfully sent messages using high-dimensional quantum encryption under realistic city conditions, says Karimi.
Less glitchy
Simulated encryption of an image with structured photons.
© www.osapublishing.org
The reason for the physicists is that the 4D coding is less sensitive to interference.
This higher interference threshold means that the 4D quantum cryptography could be used wherever the conventional 2D transmission fails, says Karimi. The quantum communication demonstrated by us could be used to communicate with satellites or to transmit encrypted data between locations that can not be connected via fiber.
Even the airplanes could be sent with quantum signals.
Next, the researchers want to test their 4D quantum transfer on a longer distance. They are already planning a network of three stations, which are 5.6 kilometers apart. In the longer term, this test network is to be connected to an existing quantum communication network already in Ottawa.
Source: Optica, 2017, doi: 10.1364 / optica.4.001006
Makes me wonder if this technology could be adapted into SETI? Imagine a Massive Photon Antenna array listening off in space for these signals.
Hey.. shhh.... did you hear that?
Yes, I am sure there will be a lot of different scopes quantum technology could be applied on.
Check this out:
Watched the Vid, Read the blog. Non-scientist here, so what is faster a quantum bit or a photon carrying one quantum bit? Is the next computer going to be a photon computer?
Hey there, you are mixing up a few things here. A quantum bit or qubit is basically a unit of information. Quite similar to the classic bit which carries either the information 0 or 1. Now in a quantum computer a number of elemental particles (such as photons, electrons or even ions) can be used to carry this information, acting as a representation of 0 and/or 1. Each of this particles is known as a qubit.
The most relevant aspects of quantum physics are:
Superposition
This can get quite complex, but lets try to keep it simple. The special thing here is, that a qubit can take a so called superposition which means, that it can be 0 and 1 at the same time. Thus the number of computations that a quantum computer could undertake at the same time is 2^n, where n is the number of qubits used. So a computer with 1 qubit could perform 2^1 = 2 computations at once, which means true parallelism.
Entanglement
Particles can be in a state of entanglement. Knowing the state of one particle (up or down which basically is 0 or 1) allows one to know that the spin of its mate is in the opposite direction. A more amazing fact is, that the spin state of the particle is decided at the time of measurement and magically communicated to the correlated particle, which simultaneously assumes the opposite spin direction. Quantum entanglement allows qubits that are separated by incredible distances to interact with each other instantaneously (even faster then the speed of light).
The aspect of this article is more about sending (encrypting) information over the air in a reliable way (without too much loss) using more information (4D instead of 2D) to handle interference with regard to error correction.
Good explanation to a non-scientist. Thank you.
You are welcome!
Sounds cool
Indeed!
Awesome post. This is some groundbreaking futuristic stuff.
Thank you!
Intreasting 👌👌
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