Missions scientist Ian D’Souza of Canadian satellite equipment firm Com Dev, wants to cover the planet with a swarm of microsatellites that will jump-start the quantum communications revolution. He just has to build one and get a launch date first.
Satellites capable of performing quantum cryptography, a form of communication that is theoretically unhackable, don’t even exist outside of the lab yet, but researchers at the Institute for Quantum Computing (IQC), in Waterloo, Ont., Canada, are engineering the technology as you read this, and they say they could have a working prototype this year. Com Dev, in Cambridge, Ont., would package the system as an inexpensive microsatellite and send it into orbit as a secondary payload on someone else’s rocket. If it works, Com Dev could refine the design and soon have more ready to go up with the next available launch. If the microsatellite fails, the company wouldn’t lose a boatload of money and years of time on an expensive piece of space junk.
Teams in Europe and Asia are working on the same problem, though not necessarily with the same cheap-and-dirty game plan. Com Dev’s strategy is alluring but also risky. Known as the microspace approach, it would use commercially available, off-the-shelf technologies that have not been designed for space. Of course, that doesn't mean Com Dev won't rigorously test its quantum satellite before launching it. The charm is in using off-the-shelf parts, which makes it easier to get cutting-edge technology. Technologies designed specifically for space tend to be of an older generation.
“It makes more sense to launch a low-cost satellite to prove the concept than to launch a very expensive satellite whose hardware works flawlessly—only to find out that the atmosphere does not allow quantum key distribution to work,” D’Souza says.
Quantum cryptography functions well in fiber, but a nascent quantum network in Vienna has shown that the photons that carry the encryption keys fade out after 200 kilometers or so. The signal should travel much farther in empty space, and a network of only six to eight satellites could cover the planet. But the air near the ground is turbulent, and researchers have so far been able to do delicate quantum communications tricks there only over a distance of about 140 km.
“The problem with quantum experiments is that…you need to carefully test everything in order to be successful. Otherwise you see nothing,” says Fabio Sciarrino, a quantum optics physicist at Sapienza Università di Roma.
Sciarrino is not exaggerating the difficulty. Quantum cryptography satellites must be able to detect a single photon beamed from Earth against a background flooded with photons. The photon must be aimed precisely, then travel through the turbulent lower levels of Earth’s atmosphere. Not only must the satellite detect the photon, it must also measure a quantum property of the photon: its polarization. The polarization will reveal whether the photon represents a zero or a one. And the satellite must do this over and over again for a stream of individual polarized photons. The stream represents a key for encrypting a message.
The satellite then transmits this key, photon by carefully aimed and polarized photon, to the recipient of the message. The message itself is sent via conventional wire and fiber. As long as it is encrypted with the satellite-distributed quantum key and the key is secure, the message is secure. And the sender and recipient know the key is secure, because if the photons had been intercepted or observed by a third party, they would be garbled owing to one of the basic tenets of quantum mechanics: If you measure it, you change it.
Measuring the photon’s polarization is one of the trickiest technical feats a quantum key distribution satellite must perform. The sender and satellite might both know that a polarization of zero degrees means zero, and a polarization of 90 degrees means one. But the satellite is moving and spinning with respect to Earth, so how can it know the correct frame of reference with which to measure the polarization?
Sciarrino’s group at Sapienza has proposed a solution. They have been testing a way to control not only the photon’s polarization but also its orbital angular momentum. As a photon with orbital angular momentum travels, the electromagnetic field will appear helical with an empty donut hole in the middle. Such a shape looks the same, no matter what the observer’s frame of reference.
The Canadian group is working on a different way to solve the frame-of-reference problem, by using a measurement feedback loop. Using signals from the satellite, the sender would shift the wave plates, the equipment that controls the photons’ polarization, to compensate for the satellite’s changing orientation.
China, the European Union, and Japan are also working to put experimental quantum key distribution satellites in orbit. China has said publicly that it plans to get a quantum key distribution satellite up by 2016.
It would be an incredible coup for Canada to beat China. The Canadian space agency is enthusiastic about the idea, and has already funded part of the research stage of the project. But no funds are allocated to the satellite part of the project as yet, and the agency hasn’t gotten approval to proceed with the mission.
Who wants to wait for government funding to start the quantum revolution? D’Souza of Com Dev hopes the space agency can be involved. But if that doesn’t work out, Com Dev, IQC, and their partners could still make it happen. Com Dev successfully launched a global ship-tracking business, exactEarth, in 2008, using a single inexpensive nanosatellite. The nanosat was engineered to last just four months, but it’s still going strong. So it’s easy to see why D’Souza is so tempted by the idea of a cheap and fast quantum key distribution satellite. A single, streamlined microsatellite the size of a dishwasher could be fabricated and launched into orbit for tens of millions of dollars, instead of the hundreds of millions for a conventional satellite. If it works, a team of Canadian researchers and companies could fundamentally alter the way banks, governments, and businesses think about secure communications.
When pressed, D’Souza admits it will probably take the Canadian team three years to do a “successful demonstration,” going as fast as they dare. So 2016 it is. We’re waiting.
A correction was made to this article on 8 May 2013.
About the Author
Kim Krieger is a freelance writer based in Norwalk, Conn. She has covered energy policy in Washington, D.C., commodities prices from the floor of the New York Mercantile Exchange, and telecommunications innovation everywhere.