AI and Adaptive Optics propel free-space quantum communication into a new era

In the quest for ultra-secure, long-range quantum communication, two major challenges stand in the way: the unpredictable nature of atmospheric turbulence and the limitations of current optical wavefront correction techniques. Researchers at the University of Ottawa, under the supervision of Professor Ebrahim Karimi, the director of Nexus for Quantum Technologies, in collaboration with the National Research Council Canada (NRC) and the Max Planck Institute for the Science of Light (Germany), have made significant advances in overcoming both obstacles. Their two latest breakthroughs—an AI-powered turbulence forecasting tool called TAROQQO and a high-speed Adaptive Optics (AO) system for correcting turbulence in quantum channels—represent a turning point in developing free-space quantum networks.

These advancements, published in Optics Express and Communication Physics, offer complementary solutions to the fundamental issue of atmospheric turbulence that distorts and diminishes photonic quantum states as they traverse through the air. While TAROQQO facilitates real-time turbulence forecasting to optimise experimental conditions, the fast adaptive optics system actively rectifies turbulence-induced errors, ensuring dependable, high-dimensional quantum communication even under adverse conditions.

TAROQQO and AI-Driven Turbulence Forecasting: One key challenge in free-space quantum communication—particularly in satellite-based and intra-city networks—is the constant fluctuation of the atmosphere. This can unpredictably disrupt the quantum states of light used for secure communication. To address this, PhD students Tareq Jaouni, Lukas Scarfe, and Dr. Francesco Di Colandrea developed TAROQQO, a turbulence prediction tool based on Recurrent Neural Networks (RNNs).

By employing real-time weather data—including humidity, solar radiation, temperature, pressure, and a turbulence parameter known as Cn²—TAROQQO can accurately predict turbulence strength up to 12 hours in advance, offering a time resolution as precise as one minute. This enables researchers to anticipate atmospheric conditions and plan their quantum experiments at optimal times, thereby avoiding unnecessary losses and maximising the efficiency of free-space quantum links.

Beyond simple forecasting, TAROQQO also allows scientists to simulate the effects of turbulence on different quantum experiments, helping optimise quantum network deployment strategies. The complete TAROQQO software is now publicly available on GitHub – TAROQQO, enabling the global scientific community to integrate turbulence forecasting into their own quantum research and communication networks.

“By enhancing efficiency, cutting costs, and ensuring improved resource allocation, TAROQQO will serve as an invaluable tool for experimental physicists,” stated Dr. Francesco Di Colandrea.

While TAROQQO anticipates turbulence, a second breakthrough from the University of Ottawa team directly combats its effect on photonic quantum states in real-time.

Fighting Turbulence with Speed and Precision: Even with turbulence forecasting, certain quantum communication scenarios—such as free-space links and satellite-based quantum channels—necessitate immediate correction of optical distortions. To achieve this, the research team has successfully implemented a rapid and accurate adaptive optics system to restore the photons’ quantum state in real-time.

Quantum Key Distribution (QKD) is a cryptographic technique rooted in the principles of quantum mechanics, allowing two parties to securely generate a random encryption key while simultaneously detecting any potential eavesdropping. If an unauthorised entity attempts to intercept the transmission, the very act of measurement disturbs the quantum states, introducing noise and immediately revealing the presence of an intruder. When conducting high-dimensional QKD (encryption beyond 0 and 1) in free space, atmospheric turbulence introduces noise that reduces efficiency and, in extreme circumstances, renders the channel unsecure since any noise is assigned to eavesdroppers.

The University of Ottawa researchers have now demonstrated that adaptive optics (AO) can correct these distortions in real time, restoring the channel’s security and enabling high-dimensional quantum information transfer. AO works by using a custom deformable mirror that can change its shape up to 3000 times per second to compensate for fast turbulence effects before the measurement of quantum signals is performed.

“In our controlled laboratory experiment, we simulated a turbulent free-space quantum channel to evaluate the effectiveness of our adaptive optics system. The results were striking,” said PhD student Lukas Scarfe. “Without adaptive optics, turbulence introduced errors that exceeded the security threshold, making quantum key distribution impossible. However, with adaptive optics enabled, we successfully restored the channel, performing high-dimensional QKD and encoding up to three bits per photon—significantly boosting the key generation rate.”

These findings illustrate that adaptive optics presents a viable solution for practical quantum experiments and quantum networks, allowing secure communication even under extreme atmospheric conditions.

The University of Ottawa’s pioneering efforts in turbulence prediction (TAROQQO) and real-time turbulence correction (AO for QKD) provide complementary solutions that, when combined, pave the way for robust and scalable free-space quantum communication. Indeed, TAROQQO enables pre-emptive scheduling of quantum communication sessions to minimise disruptions, and Adaptive Optics actively corrects real-time turbulence distortions, ensuring reliable quantum key distribution.

These breakthroughs are crucial for the next generation of ground-to-satellite, underwater and free-space quantum communications and the deployment of global-scale quantum networks.

For more information:

The study “Predicting Atmospheric Turbulence for Secure Quantum Communications in Free Space,” by Tareq Jaouni, Lukas Scarfe, Frédéric Bouchard, Mario Krenn, Khabat Heshami, Francesco Di Colandrea, Ebrahim Karimi was published in Optics Express.

The study “Fast Adaptive Optics for High-Dimensional Quantum Communications in Turbulent Channels” by Lukas Scarfe, Felix Hufnagel, Manuel F. Ferrer-Garcia, Alessio D’Errico, Khabat Heshami, and Ebrahim Karimi was published in Communications Physics.