Quantum
scientist Pan Jianwei works in the quantum lab of the Univerisity of
Science and Technology of China on April 20, 2017. [Photo/Xinhua]
Chinese scientists have achieved the world's first quantum key
distribution over 1,120 kilometers without relying on any intermediate
security relays, according to a study published in the journal Nature on
Monday. Experts said this represents a major milestone in building a
practical global-scale, ultra-secure quantum internet, but the actual
technology might still be years away. Quantum key distribution, known as QKD, is a technique used to
achieve secure communication that uses cryptographic protocols based on
the laws of quantum mechanics. Today's QKD is mostly conducted through
optical fibers on the ground, with few exceptions using quantum
satellites. These protocols can generate secret security keys that enable more
secured data transfer between devices by allowing authorities to spot
eavesdroppers trying to intercept communications. "QKD is theoretically highly secured. But in reality, imperfections
in equipment such as photon sources and detectors may lead to security
risks," said Pan Jianwei, noted quantum physicist and the lead scientist
behind the study. Moreover, QKD via optical fibers are susceptible to interference and
cannot be sent over ultralong distance without relying on intermediate
repeaters to boost the signals, he said. To tackle these issues, Pan and his team tested a new QKD protocol method that uses satellites instead of ground-based relays. They achieved this by using China's quantum science satellite Micius
to send a secret key at the rate of 0.12 bits per second between the
ground stations at Delingha and Urumqi, separated by around 1,120
kilometers. Peer-reviewed comments called the study a "groundbreaking
experiment", and a "significant step toward establishing a global
network for QKD, and more generally, a quantum internet for quantum
communication." Gilles Brassard, one of the founders of quantum cryptography, said if
the technology for secured, long distance quantum communication finally
arrives, "this would achieve the Holy Grail that all cryptographers
have been dreaming of for thousands of years." Wang Jianyu, a researcher from the Shanghai Institute of
Technological Physics of the Chinese Academy of Sciences, said now that
the study has proved that the new technique is technically feasible, the
next step should be increasing its communication capacity to make it
useful. "It is still too soon to say when the technology will reach the mass
market," he said. "But in the next three to five years, we might see
another leap in this method's efficiency, and that might be enough to
support a nation's financial and security communication needs."
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