A schematic shows how China’s Micius satellite could theoretically enable secure quantum communications. (SMOC Graphic)
Chinese researchers report that they’ve set a new distance record for quantum teleportation through space, the phenomenon that Albert Einstein once scoffed at as “spooky action at a distance.”
The technology isn’t yet ready for prime time, but eventually it could open the way for a new type of unbreakable encryption scheme based on the weirdness of quantum physics.
The Chinese experiment involved transmitting pairs of entangled photons from China’s orbiting Micius satellite to two ground stations in the mountains of Tibet, separated by more than 745 miles (1,200 kilometers).
When the polarizations of more than 1,000 photon pairs were compared, the researchers found that the photons stayed entangled more often than would be expected by chance.
That achievement outdid the previous record of 89 miles (143 kilometers).
Quantum entanglement and teleportation sound like science-fictiony terms, but it’s a real phenomenon. Quantum physics allows for two particles to be linked in such a way that you can immediately determine the state of one particle – for example, its polarization – by measuring the state of the other particle.
That would hold true even if the two entangled particles end up being separated by light-years. That’s what led Einstein to complain about the “spooky” nature of entanglement.
Over the past couple of decades, a series of experiments have verified that photons and electrons can indeed become entangled, but it’s not easy. Scientists have found that the entangled pairs can degrade and become disentangled as they pass through air or optical fiber.
That shouldn’t be as much of a problem in the near-vacuum of space, and China’s space agency launched the Micius satellite last August to find out. The Micius mission, which is named after an ancient Chinese philosopher, is part of the country’s $100 million Quantum Experiments at Space Scale program, or QUESS.
Aboard the satellite, a light beam was passed through a crystal of potassium titanyl phosphate, which emitted pairs of entangled photons. One of the photons was sent to a ground station in Delingha, and the other to Lijiang, more than 745 miles away. The mountain locations were chosen to minimize the distance traveled through the atmosphere.
When the pairs of photons were measured and compared via a ground-based link, the researchers found that the polarizations were opposite more often than not.
The technology is tricky, because quantum signals can’t be amplified by classical means. Only about one photon out of every 6 million could be recovered. But it’s a start.
If researchers can find ways to boost the quantum signal’s strength and reliability, that could open the way for quantum-based transmission of encryption keys. Such a mode of communication is considered super-secure, because any attempt to eavesdrop on transmissions en route would basically result in the collapse of the signal.