Researchers bounce polarized photons off satellites to show feasibility of space based quantum communications

June 30, 2014 by Bob Yirka report
Scheme of the Satellite QKD demonstration. Qubit pulses are sent at 100 Mhz repetition rate and are reflected back at the single photon level from the satellite, thus mimicking a QKD source on Space. Synchronization is performed by using the bright SLR pulses at repetition rate of 10 Hz. Credit: arXiv:1406.4051 [quant-ph]

( —A team of researchers working at the University of Padua in Italy has bounced polarized photons off of four in-flight satellites to show that quantum communications between such satellites and ground based stations is possible. The team has uploaded a paper they've written to the preprint server arXiv, describing their work and what it might mean for future quantum transmissions through space.

Scientists have figured out how to send quantum communications through fiber cables, but only for short distances as the tend to be absorbed by the glass at some point. Other scientists have successfully sent quantum communications directly through the air, but again only for short distances (the record is 144 kilometers) because of interference. In this latest experiment, the team in Italy bounced photons off satellites to show that quantum communications between ground based stations and satellites should be possible.

Up till now, most scientists have believed sending quantum messages between earth and space isn't feasible due to interference in the atmosphere—the error rate threshold has been found to be 11 percent. Above that limit, won't work. Holding up such research has been the lack of satellites that can be used for testing purposes. In this new effort, the researchers found a way to use existing satellites for their purposes.

The team singled out four currently orbiting satellites with metallic corner-cube retroreflectors—bouncing photons off them, the researchers concluded, would preserve polarization, making them suitable for testing quantum communications possibilities. They also selected another satellite also in orbit that has uncoated corner-cube retroreflectors as a control. They sent photons to all of the satellites from the Matera Laser Ranging Observatory when each was directly overhead (minimizing the distance the photons would have to travel through the atmosphere) and measured what was bounced back to them. In so doing, they found the control satellite had a high error rate, as expected—it was approximately 50 percent. But the other four, the team found, were all below the 11 percent threshold, indicating that satellites sent aloft with the capability of producing coherent photons, should be able to conduct perfectly secure quantum communications (using quantum key distribution) with ground based stations.

More progress is likely to come soon as China plans to send a into orbit in 2016 for the express purpose of conducting research. Other countries are working on their own programs as well, with many likely being conducted in secret.

Explore further: Secure Communication via Space

More information: Experimental Satellite Quantum Communications, arXiv:1406.4051 [quant-ph]

Quantum Communications on planetary scale require complementary channels including ground and satellite links. The former have progressed up to commercial stage using fiber-cables, while for satellite links, the absence of terminals in orbit has impaired theirs development. However, the demonstration of the feasibility of such links is crucial for designing space payloads and to eventually enable the realization of protocols such as quantum-key-distribution (QKD) and quantum teleportation along satellite-to-ground or intersatellite links. We demonstrated the faithful transmission of qubits from space to ground by exploiting satellite corner cube retroreflectors acting as transmitter in orbit, obtaining a low error rate suitable for QKD. We also propose a two-way QKD protocol exploiting modulated retroreflectors that necessitates a minimal payload on satellite, thus facilitating the expansion of Space Quantum Communications.

Related Stories

Secure Communication via Space

April 22, 2008

The exchange of information between distant sources is the basis of all communications, but quantum mechanics may open up this distant exchange as never before.

Space race under way to create quantum satellite

February 28, 2013

In this month's special edition of Physics World, focusing on quantum physics, Thomas Jennewein and Brendon Higgins from the Institute for Quantum Computing at the University of Waterloo, Canada, describe how a quantum space ...

Recommended for you

Innovations from the wild world of optics and photonics

August 2, 2015

Traditional computers manipulate electrons to turn our keystrokes and Google searches into meaningful actions. But as components of the computer processor shrink to only a few atoms across, those same electrons become unpredictable ...

New blow for 'supersymmetry' physics theory

July 27, 2015

In a new blow for the futuristic "supersymmetry" theory of the universe's basic anatomy, experts reported fresh evidence Monday of subatomic activity consistent with the mainstream Standard Model of particle physics.

Rogue wave theory to save ships

July 29, 2015

Physicists have found an explanation for rogue waves in the ocean and hope their theory will lead to devices to warn ships and save lives.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.