Nowadays most of researches are being carried out in cross-disciplinary field with collaboration between various schools and departments of universities. For example computational biology is cross-disciplinary program encompassing skills of life science, mathematics, statistics and computer science. Similarly, quantum information technology uses skills of physics, mathematics and computer science. Recently, lots of new field have emerged as a result of newer approach developed for solving most difficult problems of science and engineering.
If somebody wants switch from pure science/mathematics or computer science to a cross-disciplinary field, then how should he/she craft the statement of purpose to suit to the program of his/her choice? What are the points that need to emphasized in his/her essay?