It is possible to beam up quantum signals, scientists find

Quantum satellites currently beam entangled particles of light from space down to ground stations for ultra-secure communications. Now, researchers at the University of Technology Sydney (UTS) have found that it is also possible to send these signals upward, from Earth to a satellite — something once thought unfeasible.

Described in the journal Physical Review Research, the project brought together experts from the UTS Faculty of Engineering and IT and the Faculty of Science, combining strengths in quantum networking, systems modelling and photonics. It also paves the way for stronger quantum communication networks in future.

China launched the Micius satellite in 2016, which enabled the first experiments with the transmission of quantum-encrypted information from space. In 2025, the Jinan-1 microsatellite extended this progress with a 12,900 km quantum link between China and South Africa.

“Current quantum satellites create entangled pairs in space and then send each half of the pair down to two places on Earth — called a ‘downlink’,” said study co-author Professor Alexander Solntsev. “It’s mostly used for cryptography, where only a few photons (particles of light) are needed to generate a secret key.”

The reverse idea, where entangled photon pairs are created on the ground and sent upward to a satellite, hadn’t been taken seriously. This is because it was thought that an ‘uplink’ approach wouldn’t work due to signal loss, interference and scattering.

“The idea is to fire two single particles of light from separate ground stations to a satellite orbiting 500 km above Earth, travelling at about 20,000 km/h, so that they meet so perfectly as to undergo quantum interference. Is this even possible?” said study co-author Professor Simon Devitt.

“Surprisingly, our modelling showed that an uplink is feasible. We included real-world effects such as background light from the Earth and sunlight reflections from the Moon, atmospheric effects and the imperfect alignment of optical systems.”

The researchers suggested the uplink concept could be tested in the near future using drones or receivers on balloons, paving the way for future quantum networks across countries and continents using small low-orbit satellites.

“A quantum internet is a very different beast from current nascent cryptographic applications,” Devitt said. “It’s the same primary mechanism but you need significantly more photons — more bandwidth — to connect quantum computers.

“The uplink method could provide that bandwidth. The satellite only needs a compact optical unit to interfere incoming photons and report the result, rather than quantum hardware to produce the trillions upon trillions of photons per second needed to overcome losses to the ground, allowing for a high-bandwidth quantum link. That keeps costs and size down and makes the approach more practical.”

The work overcomes significant barriers to quantum satellite communications as ground station transmitters can access more power, are easier to maintain and could generate far stronger signals, enabling future quantum computer networks using satellite relays.

“In the future, quantum entanglement is going to be a bit like electricity: a commodity that we talk about that powers other things,” Devitt said. “It’s generated and transmitted in a way that is often invisible to the user; we just plug in our appliances and use it. This will ultimately be the same for large quantum entanglement networks. There will be quantum devices that plug into an entanglement source as well as a power source, utilising both to do something useful.”

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