Quantum teleportation is not the easiest concept to understand, much less believe. Teleportation sounds like something out of Star Trek. It’s not; this is real. In what promises to be a milestone experiment led by Jian-Wei Pan and Cheng-Zhi Peng at the University of Science and Technology of China and Tsinghua University (Beijing, China), quantum information was ‘transmitted’ through the open air between two stations 16 kilometers (10 miles) apart. The previous record was a few hundred meters using fiber optic cable. At the distance of 10 or more kilometers, this almost mysterious form of communication, called “spooky action at a distance” by Einstein, becomes possible for Earth to orbiting satellites.
What’s so spooky is the nature of quantum entanglement…how separated particles can share quantum properties as if they were one particle. It’s one thing to imagine this kind of 2=1 condition for distances no bigger than an atom, but over kilometers?
The researchers set up two ‘stations:’ “Alice” located in a suburb of Beijing and 16 kilometers away on the other side of a reservoir was “Bob.” Alice and Bob each received one of a pair of entangled photons. Photons, the equivalent of electrons for light, are often used for entanglement experiments as they are good for transmission and can be manipulated by specialized lasers. At the Alice station, one entangled photon is measured in combination with an unknown qubit (a quantum unit of information), in a sense is charged-up by a maximally applied entangling force with both spatial and polarization (laser) methods. The result, a more highly entangled particle, is sent via telescope to Bob. At the Bob station, that photon then also projects the status of the unknown qubit as does Alice. The mumbo jumbo means that the state of one photon (Alice) is instantly reflected…is the state of…the other entangled photon (Bob). The qubit is the piece of quantum information that is passed, so this is a form of communication.
This experiment required a great deal of groundbreaking work, including specialized telescopes designed for the open air transfer, active feedback control for transmission stability, and synchronized real-time information transfer. The result was information fidelity approaching 90%. Good enough for a lot of quantum jazz.
That does not mean this is ready for real-world applications. It does mean that practical applications can be envisioned. Between now and the time when quantum teleportation is used for communication, there will need to be a lot of work done with the size, cost, and reliability of the equipment needed to generate and control the entanglement effect. The entangled photons will need better control. Charged electrons – ions – are easier to manipulate, for example to create encryption patterns; but something will be needed to achieve a similar level of manipulation for photons. Nevertheless, this is a mind-opening achievement.
In the present experiment, we demonstrate the transfer of a quantum state in the real scenario of public free space. The original quantum state was recovered following teleportation through a 16-km, noisy, free-space channel located on the ground. Active feed-forward technology was developed for the real-time transfer of quantum information. Importantly, the distance of 16 km is significantly greater than the effective aerosphere thickness (equivalent to 5–10 km of ground atmosphere)20. Such high-fidelity teleportation would pave the way for future space-based experiments, with links connecting a ground station and a satellite, or two ground stations with a satellite between acting as a relay; this has the potential for enabling quantum-communication applications on a global scale in the near future.
[Source: Nature - Photonics]
See also SciTechStory: Breakthrough will lead to further entanglements.