A team of researchers, including a University of Calgary scientist and two former PhD students, says satellites are the only viable path to a secure global quantum internet.
The conclusion is part of a recent review published in Optica Quantum, an open-access journal committed to high-impact results in quantum information science and technology. It was highlighted on the cover of the journal.
The paper notes that academia, governments and industry around the world are on a quest to build long-distance quantum communication networks for a future quantum internet.
"If they succeed in making quantum computers, which they're working very hard on, one of the things that will happen that is not so good is that our current ways of secure communication won't be secure anymore, because quantum computers would be able to break that," says Dr. Christoph Simon, PhD, a professor in the Department of Physics and Astronomy and co-author of the paper.
That would include secure communications used for banking, health care, government services and critical infrastructure.
It would be solved with quantum communication, technically known as quantum key distribution.
Dr. Sumit Goswami, PhD'22, lead author of the review, says the research team has concluded that the only way to secure global quantum networks is through satellites.
"In the next five to 10 years, whatever will happen in global-scale quantum networks is going to happen through satellites," says Goswami, now with the Institute of Atomic and Molecular Sciences at Academia Sinica in Taiwan.
Dr. Neil Sinclair, MSc'10, PhD'16, was also involved in the paper and now works as a research scientist at Harvard University.
The problem with ground networks
The dream of a quantum internet, which relies on fragile fundamental light particles (single photons) to transmit information, would be constrained by distance on Earth.
The problem is that in standard fibre optic cables, like the internet we use today, photons are absorbed and then lost after travelling a few hundred kilometres. This can be solved by amplifying (i.e., copying) them every so often along the way. However, quantum signals can't be copied or cloned due to a quirk of quantum mechanics called the no-cloning theorem.
Scientists invented quantum repeaters to solve this and send quantum information through Star Trek-like teleportation through one or more intermediate nodes. The review, however, argues that the loss in fibres is still too big and memories are low performance at this time.
The space solution
Goswami says the solution lies in taking the signal out of the atmosphere and into space.
Photons beamed from a satellite fly through a near-perfect vacuum, where they face no exponential loss, the paper notes.
In 2017, a single Chinese satellite called Micius successfully shared quantum connections over more than 1,200 km, but the paper notes one single satellite may not be able to achieve much farther distance.
The paper suggests that's why global quantum links will rely on satellite chains or networks, which are becoming more realistic as satellites become smaller and cheaper. Launches are also becoming more affordable, the researchers note.
"The satellite chains can be made either with a repeater protocol over satellite links with memories on the ground or in satellite, or with memoryless satellites just reflecting the photon along the chain," explains Goswami.
The satellite repeater idea was first proposed by Simon's group in 2015 while the satellite reflection idea was proposed by Goswami in 2023.
