Breakthrough Could Make Quantum Data Transmission a Reality

Imagine sending data over the air in the form of light rather than radio waves, a method that eliminates the restriction on spectrum availability in wireless networks.

Researchers at the University of Ottawa in Canada have taken a step forward towards this goal by sending a secure quantum message containing more than one bit of information per photon into the air over a city. It may sound esoteric, but sending multiple bits per photon is a critical requirement for this technology to move from theoretical to real applications.

As the Optical company details in his academic journal, Optica, quantum encryption uses photons to encode information.

“In its simplest form, known as 2D encryption, each photon encodes a bit: either a one or a zero. Scientists have shown that a single photon can encode even more information – a concept known as high-dimensional quantum encryption – but so far this has never been demonstrated with optical communication in free space. under real conditions. With eight bits needed to encode a single letter, for example, putting more information together in each photon would significantly speed up data transmission.

If high-capacity, free-space quantum communications become practical, it will pave the way for the creation of highly secure links between ground networks and satellites, and possibly a global quantum encryption network.

“Our work is the first to send messages securely using high-dimensional quantum encryption under realistic urban conditions, including turbulence,” said Ebrahim Karimi, head of the research team. “The secure free-space communication scheme we have demonstrated could potentially link Earth to satellites, securely connect places where it is too expensive to install fiber, or be used for encrypted communication with a moving object,” such as an airplane. “

Researchers were able to demonstrate 4D quantum encryption (meaning that each photon encodes two bits of information instead of one) on a free-space optical network spanning two buildings 0.3 km apart at the University of Ottawa. By taking optical lab setups to two different rooftops and covering them with wooden boxes to protect them from the elements, through trial and error, they finally succeeded in transmitting 4D. The messages had an error rate of 11%, below the threshold of 19% needed to maintain a secure connection. And compared to 2D encryption, they were able to transmit 1.6 times more information per photon.

“After bringing equipment that would normally be used in a clean, isolated laboratory environment on a roof exposed to the elements and without vibration isolation, it has been very gratifying to see results showing that we can transmit data securely,” said Alicia Sit. , an undergraduate student in Karimi’s lab.

As a next step, the researchers plan to implement their project in a network comprising three links approximately 5.6 kilometers apart and using technology known as adaptive optics to compensate for turbulence. Ultimately, they will extend to the whole city. One of the main issues with any free space experiment is dealing with air turbulence, which distorts the optical signal, so future testing will focus on how to mitigate this.

“Our long-term goal is to implement a quantum communication network with multiple links but using more than four dimensions while trying to work around the turbulence,” Sit said.

Implementing the technology globally will require transmissions to be sent between ground stations and quantum satellite communications networks, which would then link cities and countries. To test the feasibility of a global network, researchers will focus on horizontal tests to simulate satellite uplinks, with about three horizontal kilometers roughly equivalent to sending a signal through Earth’s atmosphere to a satellite.

In addition to what this 4D breakthrough means for the future of data transmission, it is also a big step forward in security; these links are by nature almost bulletproof.

Encrypted communications today, for things like text messages, banking transactions, and health information, are activated by mathematical algorithms. However, these algorithms are hackable and crackable, especially in the age of artificial intelligence and machine learning. 4D quantum encryption, on the other hand, uses quantum key distribution, which uses the properties of light particles called quantum states to encode and send the key needed to decrypt the encoded data.