Quantum memory may topple Heisenberg's uncertainty principle
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From: Yousuf Khan on 2 Aug 2010 11:59 Quantum memory may topple Heisenberg's uncertainty principle "A quantum memory may be all scientists need to beat the limit of Heisenberg's uncertainty principle, according to a paper published in Nature Physics. According to a group of researchers, maximally entangling a particle with a quantum memory and measuring one of the particle's variables, like its position, should snap the quantum memory in a corresponding state, which could then be measured. This would allow them to do something long thought verboten by the laws of physics: figure out the state of certain pairs of variables at the exact same time with an unprecedented amount of certainty. " http://arstechnica.com/science/news/2010/08/quantum-memory-may-topple-heisenbergs-uncertainty-principle.ars
From: Yevgen Barsukov on 2 Aug 2010 17:46 Yousuf Khan <bbb...(a)spammenot.yahoo.com> wrote: > Quantum memory may topple Heisenberg's uncertainty principle > "A quantum memory may be all scientists need to beat the limit of > Heisenberg's uncertainty principle, according to a paper published in > Nature Physics. According to a group of researchers, maximally > entangling a particle with a quantum memory and measuring one of the > particle's variables, like its position, should snap the quantum memory > in a corresponding state, which could then be measured. This would allow > them to do something long thought verboten by the laws of physics: > figure out the state of certain pairs of variables at the exact same > time with an unprecedented amount of certainty. "http://arstechnica.com/science/news/2010/08/quantum-memory-may-topple... This is just a "media" statement, that does not make any sense but makes for a nice sound-bite. Heisenberg uncertainty principle should be applied to the entire ansamble that includes QM memory itself, and would in this case would not be violated, it would be just much more complex to calculate. If overall system is large enough, you would also need to use Dirac equation (instead of Schredinger equation that Heisenberg used to derive his principle) to account for relativistic effects in information exchange between its parts. This still does not invalidate Heisenberg "principle", but just makes particular equation commonly used in text books not applicable. Regards, Yevgen -- Tune in to "Strange Drawing of the Day" buzz: http://www.google.com/profiles/100679771837661030957#buzz
From: Yousuf Khan on 2 Aug 2010 19:53 On 02/08/2010 5:46 PM, Yevgen Barsukov wrote: > This is just a "media" statement, that does not make any sense but > makes for a nice sound-bite. > Heisenberg uncertainty principle should be applied to the entire > ansamble > that includes QM memory itself, and would in this case would not be > violated, it would be just much more complex to calculate. > > If overall system is large enough, you would also need to use Dirac > equation (instead > of Schredinger equation that Heisenberg used to derive his principle) > to > account for relativistic effects in information exchange between its > parts. > This still does not invalidate Heisenberg "principle", but just makes > particular equation commonly used in text books not applicable. > > Regards, > Yevgen It's not a direct recantation of the uncertainty principle, it's more of a bypass of it. Yousuf Khan
From: Sam Wormley on 2 Aug 2010 22:59
On 8/2/10 10:59 AM, Yousuf Khan wrote: > Quantum memory may topple Heisenberg's uncertainty principle > "A quantum memory may be all scientists need to beat the limit of > Heisenberg's uncertainty principle, according to a paper published in > Nature Physics. According to a group of researchers, maximally > entangling a particle with a quantum memory and measuring one of the > particle's variables, like its position, should snap the quantum memory > in a corresponding state, which could then be measured. This would allow > them to do something long thought verboten by the laws of physics: > figure out the state of certain pairs of variables at the exact same > time with an unprecedented amount of certainty. " > http://arstechnica.com/science/news/2010/08/quantum-memory-may-topple-heisenbergs-uncertainty-principle.ars > Letter abstract Nature Physics Published online: 25 July 2010 | doi:10.1038/nphys1734 The uncertainty principle in the presence of quantum memory Mario Berta, Matthias Christandl, Roger Colbeck, Joseph M. Renes & Renato Renner "The uncertainty principle, originally formulated by Heisenberg1, clearly illustrates the difference between classical and quantum mechanics. The principle bounds the uncertainties about the outcomes of two incompatible measurements, such as position and momentum, on a particle. It implies that one cannot predict the outcomes for both possible choices of measurement to arbitrary precision, even if information about the preparation of the particle is available in a classical memory. However, if the particle is prepared entangled with a quantum memory, a device that might be available in the not-too-distant future2, it is possible to predict the outcomes for both measurement choices precisely. Here, we extend the uncertainty principle to incorporate this case, providing a lower bound on the uncertainties, which depends on the amount of entanglement between the particle and the quantum memory. We detail the application of our result to witnessing entanglement and to quantum key distribution". |