Beam me up, Scotty? Not quite
Posted July 17
"Beam me up, Scotty" is a phrase that became iconic in the 1960s from its roots on the TV sci-fi show Star Trek. Although it was never said in exactly that way -- "Beam us up, Scotty" is the closest bit of dialogue in the show to the phrase that became famous -- it captured Star Trek's conception of "teleportation."
Captain James T. Kirk would radio his engineer to teleport Kirk from the surface of a planet to inside an orbiting star ship. Over the course of several seconds, he would be dematerialized in one location and reassembled hundreds or thousands of miles away.
It is therefore not surprising that the recent announcement that Chinese scientists teleported an object from the ground to a space satellite has engendered so much attention. Article headlines like "First object teleported to Earth's orbit" are pretty exciting. Taken literally, you could imagine not only visiting exotic locations across the globe in a blink of an eye, but also imagine an enormous advance in space technology.
If we were to develop the technology to transport materials to orbit, we could quickly build new satellites without the need to use expensive rockets to lift building materials into space. A large part of the mission of NASA, SpaceX, Virgin Galactic and a myriad of other rocketry-minded companies would be obsolete. These dreams, if realistic, would be a worldwide game changer.
There's only one problem. The reality of the accomplishment is quite different. The feat is still pretty cool, but it's not what the headlines would make you think.
What was really achieved was not teleportation in the Star Trek sense, but rather quantum teleportation. And that word, "teleportation," is quite misleading, because the process doesn't involve any physical transport or teleport of particles in the way you might think. It really should be called "quantum copying."
Quantum teleportation occurs when quantum information, which is to say the precise configuration of a photon, electron, or atom, is transmitted from one location to another. Now this doesn't sound like it is such a big deal. After all, you can imagine doing this by simply looking at, for example, an atom in one place and writing down its configuration. You then move that information to another place and arrange another atom in the same configuration. But that's not how it's done in quantum teleportation.
How does quantum teleportation work?
Quantum teleportation employs something called "quantum entanglement," which is a complicated name for a simple concept. In most experiments, quantum transportation begins with two photons, subatomic particles of ordinary light, which have their spin put in opposite configurations. If one photon -- call it photon #1 -- has a spin pointing left, the other is right. If #1 is up, then #2 is down. This is what is meant by "entangled."
The neat thing is that you don't know the direction of the spin of photon #1 or #2. The spin of photon #1 could be in any direction. All you really know is that the spin of photon #2 is opposite that of #1. You can separate the two photons by huge distances and the connection between the spin of two photons is unchanged.
So that's the first step. The second step is to generate a new particle -- call it A -- and have it interact with photon #1. If you do it the correct way, then the information of particle A will get transmitted to photon #2. Photons #1 and #2 will be destroyed and particle A will effectively be instantly transmitted from the location of photon #1 to photon #2. While the information is instantly transmitted, this doesn't mean faster-than-light communication, as the method requires communication using ordinary light or other slower methods.
Quantum teleportation was first proposed in 1992, and experiments demonstrating that it can happen have been performed many times. The two entangled photons are created at the same place and then separated. In the earliest experiments, photons #1 and #2 might have been separated by small distances, like being on opposite sides of the table. Over the years, the distance between the two entangled photons was increased, eventually approaching 100 miles. Separating the entangled photons by very large distances is actually very difficult, because it is very easy to disrupt the photon that is shot off to the distant location. If that photon interacts with anything during its journey, the photon's spin will be altered, which will break the entanglement. Quantum transportation is then impossible.
The recent transportation to a satellite smashes earlier distance records. Scientists were able to generate pairs of entangled photons using a titanium-doped sapphire laser and partially silvered mirrors, then transmitted one of the pairs from a location in Tibet to a satellite orbiting over 1,400 kilometers (875 miles) away. Both the emission and detection of this photon uses carefully aligned telescopes. This satellite, called Micius after an ancient Chinese philosopher, was designed and launched to perform this experiment.
Scientists transmitted the characteristics of photon A to the satellite and verified that they had successfully done so. Their success is in part due to the fact that the entangled photon shot to the orbiting satellite passed through a vacuum of space, which vastly minimized the probability that the photon would be disturbed in transit.
It's not Star Trek teleportation
So, what good is this new measurement? Well, first it is a daunting technical achievement -- but it also has some possible utility. Computer science is undergoing a slow revolution, where techniques are being developed not to do computing with the classical bits of ones and zeros, but rather quantum computing. Quantum computing will be enormously faster than ordinary computing and will also lead unbreakable ciphers. The researchers who performed this advance in quantum teleportation claim that this achievement is a step toward very long distance quantum teleportation, which is a necessary component for global-scale quantum internet.
This is an impressive achievement, no doubt about that. Quantum computing is a nascent technology that might revolutionize computers, although it is too soon to be sure that the technology will live up to its promise.
No matter how exciting these computational prospects are, there is a tinge of disappointment for Star Trek fans like me. Teleportation in the Star Trek sense is impossible. As Scotty said on Star Trek, "I can't change the laws of physics."
The technical announcement of this achievement can be found here.