Posted on 10/09/2006 10:12:30 PM PDT by annie laurie
Even if quantum computers can be made to work, there will still be two big obstacles preventing quantum networks becoming a reality. First, quantum bits, or qubits, stored in matter will have to be transferred to photons to be transmitted over long distances. Secondly, errors that creep in during transmission have to be corrected. Two unrelated studies have now shown how to clear these hurdles.
Both studies use quantum entanglement, a spooky property that links particles however far apart they are. Measuring a quantum property on one particle immediately affects the other, and this effect can be used to “teleport” information between pairs of entangled particles.
To make quantum networks possible, qubits need to be held in atoms or ions, processed, and then transformed into qubits of light for transmission between computers, says Todd Brun of the University of Southern California, Los Angeles. One way to do this, he says, is to teleport the state between a photon and an atom.
Until now, quantum teleportation has only been done between similar objects – from light to light or matter to matter – but Eugene Polzik at the University of Copenhagen in Denmark and his colleagues have taken the first steps towards doing what Brun suggests.
They entangled photons with caesium atoms, transmitted the light and then teleported properties of the photons on to equivalent properties in the caesium atoms (Nature, vol 443, p 557). The information only travelled half a metre, but that distance can be increased, Polzik says. “Potentially, the only limit is how far light can travel without the signal becoming degraded,” he says.
That raises the second problem: “Quantum states are fragile and easily get distorted during transmission,” Polzik says. Quantum systems are prone to two types of errors: qubits can flip between values of 0 and 1, or they can change phase.
Trying to figure out which kind of error has occurred is difficult, because of Heisenberg’s uncertainty principle. “When you try to measure one type of error you can end up creating the other type of error,” says Brun. “You do more harm than good.”
Now Brun’s team has devised a way out. The solution is to first create several entangled pairs of particles and share them between the transmitter and receiver before any information is sent.
The transmitter then sends its entangled particles along with the quantum information. The team has shown, in theory, that when the receiver combines these particles with its entangled twins, it can detect both types of quantum error (Science, DOI: 10.1126/science.1131563).
Polzik is impressed. “Quantum teleportation between light and matter can be dramatically enhanced with the use of such efficient quantum error correction codes,” he says.
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Again, google DeBroglie, matter waves and his U=c^2/v equation.
Democrats: How we gonna tax 'em?
Sounds sorta like they've separated entangled particles by about a foot and a half and still can use the entanglement. Talk about needing tin (well, cesium) foil.
Can you give us a brief on the bottom line practicality, probable applications, common benefits and and a projected time line to all this?
Bottom line practicality is the transmission of information with particles/photons or quantum particle states instead of your normal on/off binary system. Think of it as broadband from information transmission. Instead of coding something with on/off I can just send you the whole kit and kiboodle.
But what can happen is when you try something like that, the subtle math that is quantum mechanics, creaps into the mix. So those errors have to be eliminated for quantum computing to be possible.
I'm only guessing at this, but if we use the exponential rule that has worked well in guessing growth in computer power, I am guessing 10 years for a prototype that proves the concept and 30 years for something that can do actual calculations.
every thing points to that, but it's confounding to alot of people that study it.
I enjoyed In Search of Schrodinger's Kittens by John Gribben in which this is detailed for at least half the book
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