Physicists at Heriot-Watt University have proposed a novel approach to overcome the significant hurdle of “daylight noise” that has hindered the development of a global scale quantum communications network.
Currently, satellite-based quantum key distribution (SatQKD) systems are limited to nighttime operations due to interference from sunlight. However, by using alternative encoding methods, such as time and phase encoding, researchers believe they can extend SatQKD operations by three to four hours each day, paving the way for all-day satellite transmission.
According to Dr. Ross Donaldson, Associate Professor at Heriot-Watt University’s Institute of Photonics and Quantum Sciences, current mitigation techniques are insufficient to make daylight tolerable for SatQKD. The team’s research, published in Optica Quantum, suggests that time- and phase-encoded SatQKD can filter out polarized daylight noise, allowing for secure communication over long distances even during dawn and dusk.
The proposed solution has significant implications for the development of global quantum networks, and the researchers will test their simulations experimentally through involvement in two upcoming satellite missions: the Space Platform for Optical Quantum Communication (SPOQC) and the Quantum Encryption and Science Satellite (QEYSSAT).
Overcoming the Barriers to Global Scale Quantum Networks
One of the significant challenges in creating a global scale quantum communications network is the interference caused by sunlight, also known as “daylight noise.” This excess noise has limited the operation of satellite-based quantum key distribution (SatQKD) systems to nighttime only, restricting their applications and connectivity. However, physicists at Heriot-Watt University have proposed a novel approach to tackle this issue, paving the way for all-day satellite transmission.
The team’s research, published in the journal Optica Quantum, focuses on using alternative encoding methods to filter out the daylight noise. Currently, SatQKD systems rely on polarization-encoded quantum states, which are susceptible to interference from sunlight. By employing time and phase encoding, the researchers believe they can extend and enhance operations by three or four hours each day, allowing for SatQKD to be performed during dawn and dusk.
The proposed approach takes advantage of the partial polarization of daylight noise. Early simulations indicate that time and phase encoding can unlock the capability to filter in polarization, yielding a reduction in detected daylight. This would enable SatQKD systems to operate reliably even during periods of high solar activity. Dr. Ross Donaldson, Associate Professor at Heriot-Watt University, explains that current mitigation techniques are not yet sufficient to make daylight tolerable for SatQKD and that their approach offers a promising solution.
The Importance of Filtering Daylight Noise
Filtering out the daylight noise is essential to allow quantum systems to operate reliably, especially for applications like SatQKD that aim to secure communication over long distances. The excess noise caused by sunlight can overwhelm the sensitive quantum signals, making it challenging to maintain the fragile quantum states required for secure communication. By developing effective filtering techniques, researchers can unlock the full potential of SatQKD and enable global connectivity.
The use of polarization-encoded quantum states in current SatQKD systems is a significant limitation. While these systems are designed to operate at night, they are not equipped to handle the high levels of daylight noise during dawn and dusk. The proposed time and phase encoding approach offers a promising solution by allowing for the filtering of polarization, which can reduce the impact of daylight noise.
The Role of Polarization in Daylight Noise
Polarization plays a crucial role in understanding the behavior of daylight noise. When sunlight passes through the Earth’s atmosphere, it becomes partially polarized, with some parts of the sky appearing darker than others when viewed through polarizing sunglasses. This property can be leveraged to filter out the daylight noise and enable SatQKD systems to operate during periods of high solar activity.
The researchers’ approach takes advantage of this phenomenon by using time and phase encoding to filter in polarization. By doing so, they can reduce the impact of daylight noise and enable SatQKD systems to operate reliably even during dawn and dusk. This breakthrough has significant implications for the development of global scale quantum networks, enabling secure communication over long distances.
Experimental Demonstration and Future Directions
The team’s research is set to be experimentally demonstrated through their involvement in two upcoming missions: the Space Platform for Optical Quantum Communication (SPOQC) and the Quantum Encryption and Science Satellite (QEYSSAT). These missions, scheduled to launch next year, will provide a platform to test the proposed approach in a real-world setting.
The successful demonstration of this technology could pave the way for the development of global scale quantum networks that can operate around the clock. This would have significant implications for secure communication, enabling governments, organizations, and individuals to exchange sensitive information with unprecedented security. As researchers continue to push the boundaries of quantum communication, it is clear that overcoming the barriers posed by daylight noise will be a critical step towards realizing the full potential of this technology.
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