A team of Chinese researchers say they have completed the first long-distance quantum secure direct communication, a critical step toward sending messages that are truly safe from eavesdropping.
The information traveled 2.7 kilometers along a quantum channel, the team said in a paper that was peer-reviewed by China’s Science Bulletin journal and placed online Oct. 22.
Here’s why that matters: The feat, if verified, marks a critical step forward in the pursuit of communication that does not require end-to-end encryption and cannot be secretly intercepted by a third party.
Today’s best encryption standards are nearly impossible to crack, but “nearly secure” is not “secure.” With enough computing power, they can be broken, just as Alan Turing’s Automatic Computing Engine penetrated Nazi Germany’s Enigma ciphers. But quantum secure direct communication doesn’t rely on codes that can be cracked, but rather on something far more secure: the laws of physics.
In classical computing, logic gates in integrated circuits convey pieces of information are called bits. These are detectable and interceptable by nature, hence the need for ciphers and encryption.
In quantum-scale communication — meaning on atomic sizes — information is conveyed by particles, rather than logic gates embedded in integrated circuitry. These particles, such as vertically or horizontally polarized photons, carry this information in their state of spin and other characteristics. Science has named those units of information: qubits. Two qubits sharing the same quantum state form a channel.
So why is quantum communicating more secure than the classical methods?
Subatomic particles behave differently than larger objects. As physicist Werner Heisenberg observed, merely attempting to keep tabs on subatomic particles using giant, crude, human-sized instruments changes their behavior. You can never be certain what you’re viewing. This is Heisenberg’s uncertainty principle.
If you can send information through a secure quantum channel, no one can intercept that communication without changing it in a way that both sender and receiver will detect. No fancy encryption is necessary. However, quantum communication in a way that’s comparable to traditional electronic communication will also requires quantum memory to store photonic quantum information. Quantum memory was discovered in 2010, but is very difficult to create at usable scale.
It’s an area of vital national security importance. Perfect information security gives a clear advantage over an adversary that lacks it. Quantum communication might even persuade an adversary to give up attempts to intercept secure messages, since such eavesdropping would be easily detected.
Both China and the United States have big investments in quantum communication. While U.S. investment was robust a few years ago, China has since demonstrated surprising expertise and ambition and has pulled ahead — in terms of investment, in new papers published in the field, big public projects such as a quantum communication satellite and long-range cable.
Chinese scientists demonstrated actual quantum secure direct communication — with quantum memory — in a tabletop experiment. The most recent breakthrough is another step toward secure quantum communication at meaningful distances. The researchers say that the method could be scaled up to send messages “tens of kilometers.” The U.S. has not achieved these milestones.
It’s another example of China vaulting ahead in an area where the U.S. was comfortably dominant not long ago. Chief among the reasons for this growing trend is that U.S. funding for basic science is unpredictable at best. Conversely, Chinese investment is strategic, sustained, and stable — particularly in quantum science, said Elsa Kania, an adjunct fellow in the Center for a New American Security’s Technology and National Security Program.
“The U.S. does not appear to be prioritizing investments in quantum sciences at comparable levels” to China, Kania told attendees at the U.S. Army Cyber Institute’s CyCon conference in Washington, D.C., on Wednesday.