Storage of classical information in quantum spins

Digital magnetic recording is based on the storage of a bit of information in the orientation of a magnetic system with two stable ground states. Here we address two fundamental problems that arise when this is done on a quantized spin: quantum spin tunneling and backaction of the readout process. We show that fundamental differences exist between integer and semi-integer spins when it comes to both reading and recording classical information in a quantized spin. Our findings imply fundamental limits to the miniaturization of magnetic bits and are relevant to recent experiments where a spin-polarized scanning tunneling microscope reads and records a classical bit in the spin orientation of a single magnetic atom.

This work was supported by MEC-Spain (Grants No. MAT07-67845, and No. FIS2010-21883-C02-01, Grant No. JCI-2008-01885 and CONSOLIDER Grant No. CSD2007-00010) and Generalitat Valenciana (Grant No. ACOMP/2010/070).