Quantum Teleportation Achieved Over 100 Km in Optical Fiber

[Guest_Jim_*]

To one day build a quantum Internet, it will be necessary to have the ability to reliably transmit or teleport quantum information over large distances. Researchers at NIST have recently set a new record for quantum teleportation distance through fiber optic lines of over 100 Km. This more than quadruples the previous record.

Quantum teleportation is not like the teleporters found in science fiction, because it is not that something physical has been relocated, but that the quantum state of something has been transferred or reconstructed somewhere else. In this case the quantum state of one photon was teleported onto another that ran through the 102 Km long fiber optic coil. The state in question was the position a photon had in a series of time slots just one nanosecond long. First the photon was sent through either a long or short fiber coil to put it into a superposition, as the coil length would determine its temporal position. This photon is then split by a special crystal into two identical and entangled photons, with one going on to the 100 Km coil. The other, helper photon would head to a beam splitter where it and another input photon each have a fifty-fifty chance of going through the splitter or being reflected. This input photon's state can be set to be early, late, or in a superposition. Detectors are set up to record the helper and input photons, and if one detects a photon before the other, that means they were in opposite states. Because the output photon and the helper photon are entangled and in identical states, we can know that the output photon will also have the opposite state of the input photon, meaning the opposite state of the input photon has been teleported to the output photon, that just traveled through some 100 Km of fiber optic line.

To make this experiment work, it was very important that the researchers use new single-photons detectors made at NIST that are very sensitive. After traveling through 100 Km of fiber optic cable, only 1% of photons survive, hence why those detectors are so important. On top of that, the teleportation is only successful 25% of the time, at best, but with those detectors it was successful 83% of that maximum, proving it was quantum teleportation that was happening, and not just coincidence. Potentially this work could lead to quantum repeaters for building a quantum Internet or advancing quantum computing.

Source: NIST

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