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Quantum key distribution depends, if I don't err, on (irreversible) damages done by MITM's measurements on qbits. Now says:

"The Yale physicists successfully devised a new, non-destructive measurement system for observing, tracking and documenting all changes in a qubit’s state, thus preserving the qubit’s informational value."

Wouldn't the new technique, if not immediately practically, at least in long term render the security of QKD questionable?

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The article is pretty vague but I doubt that it intends to say that you can measure arbitrary qubits in a non destructive manner. It sounds like a highly specific form of measurement that allows you detect certain errors in quantum computing. – CodesInChaos Jan 20 '13 at 11:49

No. The Yale result describes a method of partial measurement that is not completely destructive to the quantum system's coherence, which is tied to its physical representation. It is not a refutation of quantum indeterminacy, which is the basis for (provably secure) quantum key exchange. In other words, the Yale team measured a qubit in such a way that it doesn't "fall apart" (decohere) when it's measured - in the author's words, "the measurement record faithfully reports the perturbation of the system after the fact." However, the act of measurement still affects the qubit's information content in accordance with the mathematics of quantum mechanics.

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There is a very recent paper by R. Anderson and R. Brady entitled "Why quantum computing is hard - and quantum cryptography is not provably secure". I should very much appreciate it, if some experts could evaluate that paper. – Mok-Kong Shen Feb 5 '13 at 12:25

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