Synopsis: Flights of fancy

Quantum Control and Entanglement in a Chemical Compass

Jianming Cai, Gian Giacomo Guerreschi, and Hans J. Briegel

Published June 4, 2010

Could quantum entanglement help a flock of birds fly south for the winter? A team of scientists at the Akademie der Wissenschaften and the Universität Innsbruck, both in Austria, is looking at how concepts central to the field of quantum information—entanglement and coherence—play a role in the chemistry of magnetodetection that animals use for navigation.

Writing in Physical Review Letters, Jianming Cai, Gian Giacomo Guerreschi, and Hans Briegel study a model for magnetodetection called radical pair mechanism. Here, light activates two unpaired electrons on a molecule to form a zero-spin singlet state. The interaction between the electrons and nuclei (the hyperfine interaction) mixes the singlet state with the finite-spin triplet state—making the pair sensitive to a particular magnetic field direction and, ultimately, causing decoherence.

In contrast to the rule of thumb that coherence is essential to quantum information storage, Cai et al. find that it is not enough to explain the high magnetic field sensitivity of certain radical pair reactions. Entanglement, instead, appears to play a more positive role in some magnetically sensitive molecules—but perhaps not for the specific molecule believed to be important in avian magnetic navigation, where Cai et al. find the entanglement between paired spins lasts for only a fraction of the pair’s lifetime.

The study may not affect the flight path of geese in the near future, but it does tie into the ongoing dialogue about quantum versus classical descriptions of what we observe. – Jessica Thomas

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