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Old Aug 11th 2009, 02:06 PM   #1
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Resolving an 82-year-old quantum paradox

Resolving an 82-year-old quantum paradox

By Physics Today on August 4, 2009 9:40 AM


In 1927, during the formative years of quantum mechanics, Friedrich Hund posed a paradox: Why is a chiral molecule found in either its left-handed or right-handed isomeric forms and not in a superposition of the two? After all, both isomers are equally likely. At first glance, the answer seems clear. If the tunneling time between the two isomers is long, their superposition is unlikely to arise. That answer might hold for a sugar, protein, or other large chiral molecule, whose tunneling time may exceed the age of the universe, but it fails for small molecules. Nor can it explain why the habitual states of a molecule, large or small, are its left-handed and right-handed isomers and not its energy or parity eigenstates. Now, Klaus Hornberger and Johannes Trost of Ludwig-Maximilians University in Munich have resolved Hund's venerable paradox. The two theoreticians analyzed the case of one of the smallest chiral molecules, deuterium disulphide (shown here), tumbling in and buffeted by a monoatomic gas. The calculation uncovered a surprisingly large phase-dependence in the scattering amplitude that distinguishes the two isomers. Thanks to the phase difference, the ambient gas atoms can pick out the states that correspond to the molecule's left-handed and right-handed isomers far more readily than the molecule’s other states. When the first few atoms strike a molecule, it's knocked into either its left-handed or right-handed configurational state. Further atomic bombardment acts on the molecule like repeated quantum measurements, keeping it in its chiral state. (J. Trost, K. Hornberger, Phys. Rev. Lett. 103, 023202, 2009.) —Charles Day

From Resolving an 82-year-old quantum paradox - Physics Update.
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Old Aug 24th 2009, 11:14 PM   #2
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Very nice

Good..............
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