Quantum signals can travel from Earth to space, opening new network possibilities

For years, scientists assumed sending quantum signals upward from Earth to a satellite was impractical—too much atmospheric interference, too many losses, too difficult to pull off. A team at the University of Technology Sydney just proved that assumption wrong.

The finding matters because it flips how we might build future quantum networks. Current satellite systems work one way: a satellite in orbit creates entangled particles of light and beams them down to ground stations. It's elegant, but it has real constraints. The satellite has to do all the heavy lifting—generating trillions of photons per second to overcome losses as the signal travels through atmosphere and clouds.

Sending the signal the other way changes the economics. Ground stations can be more powerful, easier to maintain, and produce much stronger signals. A satellite only needs a compact optical unit to receive the incoming photons and measure them, rather than quantum hardware the size of a refrigerator. That's the kind of shift that could make quantum networks actually scalable.

The "Impossible" Becomes Feasible

Professor Simon Devitt and his team at UTS modeled what would happen if two single particles of light were fired from separate ground stations toward a satellite orbiting 500 kilometers above Earth—moving at about 20,000 kilometers per hour. The particles would need to meet with such precision that they undergo quantum interference. On paper, it seemed impossible.

But the modeling included real-world messiness: background light from cities, sunlight bouncing off the Moon, atmospheric distortion, misaligned optical systems. All of it. And the answer came back: yes, it works. The research, published in Physical Review Research, removes a major barrier that's been holding back quantum satellite development.

Context matters here. China's Micius satellite, launched in 2016, proved quantum communication from space was real. Last year, the Jinan-1 microsatellite established a 12,900-kilometer quantum connection between China and South Africa. These are working systems. What UTS has done is show there's a simpler path forward.

Why This Matters Beyond the Lab

Quantum entanglement has two very different futures. One is quantum cryptography—using entangled particles to create unbreakable encryption keys. That's happening now, and it only needs a few photons. The other is quantum computing networks, where distant quantum computers need to share information through satellites acting as relays. That requires significantly more bandwidth, more photons flowing through the system.

The uplink method could provide that bandwidth without the cost and complexity of launching satellites packed with quantum hardware. Instead, ground stations do the work. The satellite becomes a relay point rather than a factory.

Devitt describes the long-term vision this way: quantum entanglement becomes like electricity. You don't think about where your power comes from when you plug in a lamp. In the same way, quantum devices would eventually connect to an entanglement source the way they connect to a power source—invisible infrastructure that just works.

The next step is testing. The team plans to use drones or balloon-mounted receivers to validate the concept before moving to actual satellites. It's the kind of incremental progress that doesn't make headlines but builds toward something larger: networks that span continents, connecting quantum computers in ways that weren't possible a year ago.