Thursday 26 March 2015

Now you see it: Real-space observation of many-body proton tunneling in water nanocluster

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There's more to quantum tunneling than meets the eye – or rather, the visualization technique. Most quantum tunneling discussion focus on incoherent single-particle tunneling; on the other hand, quantum tunneling in the context of proton dynamics usually involves many hydrogen bonds at once, which leads to what is known as correlated many-body tunneling. (The many-body problem refers to the properties of microscopic systems that are described by quantum mechanics, comprising a large number of interacting particles – that is, ≥ 3 – which can become entangled.) The downside is that while single-particle tunneling is well understood, many-body tunneling is still shrouded in mystery. Recently, however, scientists at Peking University, Beijing reported the real-space observation of concerted proton tunneling in a cyclic water tetramer – a macromolecular nanocluster consisting of four water molecules arranged in a loop or ring – by using a cryogenic scanning tunneling microscope (STM). The scientists found that the presence of the Cl- chlorine anion (a negatively charged chlorine ion) at the STM tip apex may either enhance or suppress the concerted tunneling process based on the coupling symmetry between the ion and the protons, adding that their work may allow the control the quantum states of protons with atomic-scale precision.



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