Interference (excess noise) to quantum signals from sunlight has slowed down the creation of a global scale quantum communications network, but now physicists at Heriot-Watt University have proposed a way to tackle this ‘daylight noise’ issue, paving the way for all-day satellite transmission.
While satellite quantum key distribution (SatQKD) offers global connectivity, it struggles with ‘daylight noise’. At present, operations are therefore limited to night time, limiting applications and connectivity.
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.
Now a team at Heriot-Watt has proposed that using alternative encoding – the process by which data is converted into a quantum state – could allow SatQKD to operate, even at dawn and dusk.
Their newly published research proposes that using time and phase encoding could extend and enhance operations by three or four hours each day, a significant step.
Early simulations indicate that time and phase encoding unlocks the capability to filter in polarisation, yielding a reduction in detected daylight and allowing SatQKD to be performed at dawn and dusk due to the daylight noise being partially polarised.
“Current mitigation techniques are not yet sufficient to make daylight tolerable for SatQKD,” Dr Ross Donaldson, associate professor, School of Engineering and Physical Science, Institute of Photonics and Quantum Sciences, said.
“While all current SatQKD systems are polarisation-encoded, polarisation filtering has not been investigated – until now.
“We believe that by using time- and phase-encoded SatQKD, it is possible to filter in polarisation, allowing SatQKD to be performed at dawn and dusk, and paving the way for daylight SatQKD.
“One way to think about it is, if you put on a pair of polarising sunglasses, you’ll see some parts of the sky darker than others, because those parts are more polarised than others.
“We can use this filtering to overcome the issue of daylight ‘noise’ and eventually facilitate quantum communications via satellite, around the clock.”
The team will leverage their involvement in two missions (Quantum Communication hub’s Space Platform for Optical Quantum Communication (SPOQC) and Quantum Encryption and Science Satellite (QEYSSAT) being launched next year, to demonstrate their simulations experimentally.
Source: DIGIT