Spin dynamics explain geomagnetic reception in certain organisms

Ever wondered how certain migratory birds traverse half of the world and make periodic short term visits? It turns out the interactions between the earth's magnetic field and certain molecules present in these birds' eyes play the key role. Over the past few decades, scientists have been analysing these traits in a wide variety of organisms. There are two main models that explain this behaviour – a magnetite based model and a radical pair (RP) based model. Prof. Swaroop Ganguly and his team at IITBNF have been working on the dynamics of radical pair model to explain magnetic sensing in birds.

The radical pair theory suggests that the magnetic sensing happens through short lived radical species which are generated when light falls on certain molecules. They carry unpaired electrons that either have the same spin (singlet) or opposite spin (triplet). The magnetic state of their surrounding nuclei and the external magnetic field of earth together create a local magnetic field for these radicals. The spins of the unpaired electrons are therefore continuously modified by this local magnetic field. The net collection of these states helps birds to “see” the magnetic field.

Using Matlab software, the team has illustrated variation in yield of spin states for different magnetic strengths. They have also studied the impacts of environmental noise and nuclear spin on the spin dynamics of the system. A detailed understanding of this biological system could help in recreating this effect using semiconductor devices and circuits. They can be used for navigation assisted by the earth’s magnetic field and also for biomimetic applications.

- Reshma Krishnan

Published paper : Vishvendra Singh Punia, Dipankar Saha, and Swaroop Ganguly, “State Transitions and Decoherence in the Avian Compass” APS Physical Review E 91, 052709, 21 May 2015