CHINA has sent an “unbreakable” code from a satellite to Earth, the first time space-to-ground quantum key distribution technology has been realized.
China launched the world’s first quantum satellite in August last year, to help establish “hack-proof” communications.
The latest experiment was published in the journal Nature yesterday, where reviewers called it a “milestone.”
The satellite sent quantum keys to ground stations in China up to 1,200 kilometers away at a transmission rate up to 20 times more efficient than optical fiber, said Pan Jianwei, lead scientist on the experiment.
“That, for instance, can meet the demand of making an absolutely safe phone call or transmitting a large amount of bank data,” Pan said.
Any attempt to eavesdrop on the quantum channel would introduce detectable disturbances to the system, Pan said.
Once intercepted or measured, the quantum state of the key will change, and the information intercepted will self-destruct.
Pan said quantum teleportation allows faithful transfer of unknown quantum states from one object to another over a long distance, without physical travel of the object itself.
Previous experiments between locations were limited to a distance of about 100 kilometers. An outstanding challenge for building a global-scale “quantum Internet” is to significantly extend the range, Pan said.
A promising solution to this problem is exploiting satellite platforms and space-based links, which can conveniently connect two remote points on Earth while greatly reducing channel loss, because most of the transmission path is in empty space, Pan said.
In their experiment, scientists transmitted quantum states of photons from a ground station about 5,100 meters above sea level in southwest China’s Tibet Autonomous Region to the satellite 500km above the Earth.
To optimize the link’s efficiency and overcome atmospheric turbulence, a series of techniques were developed, according to Pan.
This work established the first ground-to-satellite uplink for faithful and ultra-long-distance quantum teleportation, an essential step toward a global-scale quantum Internet, Pan said.
Quantum physics is the study of the universe’s basic building blocks at a scale smaller than atoms. These tiny particles behave in a way that could overturn assumptions of how the world works.
Entanglement is one of the strange properties of quantum physics.
It so confounded Albert Einstein he described it as “spooky action at a distance” in 1948.
Scientists found that when two entangled particles are separated, one particle can somehow affect the action of the far-off twin at a speed faster than light.
This magic-like connection inspired the idea of quantum teleportation.
The first paper expounding the idea of quantum teleportation was published in 1993.
In 1997, Austrian quantum physicist Anton Zeilinger, Pan’s tutor, succeeded in the first experimental verification of quantum teleportation. Since then, scientists have demonstrated quantum teleportation with different physical systems such as atoms, ions, electrons and superconducting circuits.
The limit for quantum teleportation is constantly expanding.
Pan’s research team was awarded the Physics World 2015 Breakthrough of the Year “for being the first to achieve the simultaneous quantum teleportation of two inherent properties of a fundamental particle — the photon,” according to PhysicsWorld.com.
Pan regards the achievement as a step toward the teleportation of more complex quantum systems.
Despite such progress, Pan said, the prospect of using it to beam people, as in “Star Trek” and other works of science fiction, is still a distant dream.
But like most sci-fi fans, Pan hopes that day will come: “It’s a common dream to see what’s beyond our solar system. However, our life is limited, and we could grow old before we get out of the solar system in a spacecraft.”
But as a vehicle to the stars, quantum teleportation might carry generations to come, Pan said.