Friday, December 12, 2014

Simple teleportation over-hyped again

LiveScience reports:
A new distance record has been set in the strange world of quantum teleportation.

In a recent experiment, the quantum state (the direction it was spinning) of a light particle instantly traveled 15.5 miles (25 kilometers) across an optical fiber, becoming the farthest successful quantum teleportation feat yet. Advances in quantum teleportation could lead to better Internet and communication security, and get scientists closer to developing quantum computers.
No, almost every part of this story is wrong. There is no such thing as teleportation. The quantum state is not just the direction a particle is spinning. Nothing traveled instantly. This cannot lead to better Internet and communication security, or get scientists closer to developing quantum computers.

All they did was to split a laser beam into two identical light pulses, send one 15 miles thru optical fiber, and detect the polarization at both ends to see that they match.

The light pulse goes at the speed of light, not instantly. The only teleportation is that a bit of info is being conveyed by the polarization to the detection device at the other end of the fiber.

The application to cryptography and quantum computers is all a big hoax. It does not exist.
Quantum teleportation doesn't mean it's possible for a person to instantly pop from New York to London, or be instantly beamed aboard a spacecraft like in television's "Star Trek." Physicists can't instantly transport matter, but they can instantly transport information through quantum teleportation. This works thanks to a bizarre quantum mechanics property called entanglement.
It is not that bizarre. As you read this, you got the info as light pulses were transmitted over fiber in massive internet trunk lines.

The only addition in the new experiment is that a copy of the polarized light pulse is at both ends. This is a cute demonstration of quantum mechanics, but the effect has been well understood for decades and there are no practical applications.
Quantum entanglement happens when two subatomic particles stay connected no matter how far apart they are. When one particle is disturbed, it instantly affects the entangled partner. It's impossible to tell the state of either particle until one is directly measured, but measuring one particle instantly determines the state of its partner.
They are only connected in the sense that they were produced in a way that produces equal and opposite light pulses. No one has ever done an experiment to prove that disturbing one particle has any effect on the other.

That last sentence may surprise you if you read popularizations of quantum mechanics. But I fully accept quantum mechanics, as described by the textbooks. I assure you that Nobel prizes would be given if anyone did such an experiment.

What we do know is that it is possible to put two particles in an entangled state such that measurements give equal (or opposite) results. Measuring one might tell you what the other measurement is going to be, but there is no causal effect.
Physicists think quantum teleportation will lead to secure wireless communication — something that is extremely difficult but important in an increasingly digital world. Advances in quantum teleportation could also help make online banking more secure.
We already have secure online communication for banking. Confidential and authenticated messages can be sent all over the world using the internet.

The above technology, if perfected, might be able to send a few bits confidentially from one router to another. It cannot send messages across routers, and it cannot authenticate messages. It is commercially worthless.

1 comment:

  1. Quantum teleportation = H (hype) + LOM (lots of money) / DSLFW (Desperate Scientists Looking For Work)

    Of course this is all part of the greater endeavor to properly fund
    .... their acronym slips my mind at just this moment, but I'm sure it will come to me later.