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Interactive proofs — mathematical games that underlie much modern cryptography — work even if players try to use quantum information to cheat.Interactive proofs, which MIT researchers helped pioneer, have emerged as one of the major research topics in theoretical computer science. In the classic interactive proof, a questioner with limited computational power tries to extract reliable information from a computationally powerful but unreliable respondent. Interactive proofs are the basis of cryptographic systems now in wide use, but for computer scientists, they’re just as important for the insight they provide into the complexity of computational problems. Twenty years ago, researchers showed...

Scientists have linked two diamonds in a mysterious process called entanglement that is normally only seen on the quantum scale. Entanglement is so weird that Einstein dubbed it "spooky action at a distance." It's a strange effect where one object gets connected to another so that even if they are separated by large distances, an action performed on one will affect the other. Entanglement usually occurs with subatomic particles, and was predicted by the theory of quantum mechanics, which governs the realm of the very small... Because energy must be conserved in closed systems (where there's no input of outside...

Britain buckles before Saudi threats Financial Times 12/19/2006 Author: Philip Stephens Consider the dry explanation of Britain's most senior law officer: "It has been necessary to balance the need to maintain the rule of law against the wider public interest." Now translate: "Faced with serious threats to the nation's security from the rulers of Saudi Arabia, I have decided to put aside the fundamental principles at the heart of our democratic system of government." Little wonder that Lord Goldsmith, the attorney-general, sounded almost contrite when he called a halt to the long-running criminal investigation into whether a British defence company...

Building upon recent studies on optomechanical entanglement with lasers and mirrors, a group of scientists has developed a theoretical model using entanglement swapping in order to entangle two micromechanical oscillators. This ability could lead to advances in information processing, as well as other applications that use micromechanical resonators, such as electrometers, displacement detectors, and radio frequency signal processors, wrote scientists Stefano Pirandola et al. in a recent Physical Review Letters. "Until now, entanglement has been observed only for optical modes, i.e., photons (which are massless particles)," Pirandola told PhysOrg.com. "The significance of purely mechanical entanglement would be that it involves...

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”...

Physicists seek to put one thing in two placesSept. 25, 2006 Special to World Science  Physi­cists say they have made an ob­ject move just by watch­ing it. This is in­spir­ing them to a still bold­er proj­ect: put­ting a small, or­di­nary thing in­to two places at once. It may be a “fan­ta­sy,” ad­mits Keith Schwab of Cor­nell Uni­ver­si­ty in Ith­a­ca, N.Y., one of the re­search­ers. Then again, the first ef­fect seemed that way not long ago, and the sec­ond is re­lat­ed. The gray sliv­er reach­ing from top to bot­tom, slanted in the im­age, is a na­no­me­chan­i­cal re­s­o­na­tor, a sub-mi­c­ro­s­co­pic de­vice...

December 27, 2005 Quantum Trickery: Testing Einstein's Strangest Theory By DENNIS OVERBYE Einstein said there would be days like this.This fall scientists announced that they had put a half dozen beryllium atoms into a "cat state."No, they were not sprawled along a sunny windowsill. To a physicist, a "cat state" is the condition of being two diametrically opposed conditions at once, like black and white, up and down, or dead and alive.These atoms were each spinning clockwise and counterclockwise at the same time. Moreover, like miniature Rockettes they were all doing whatever it was they were doing together, in...