All photons are equal but some photons are more equal than others

31.10.2012, 16:51

Newsletter 5


Although particle indistinguishability (PI) has long been a central tenet of quantum mechanics, it is still not well understood; the large literature on the subject lies mostly at the interface between physics and philosophy. Despite lively research activity, some misconceptions still remain. For example, it is commonly thought that "... quantum mechanical particles … don’t have enough degrees of freedom to enable one to mark each particle differently" [G. Baym: Lectures on Quantum Mechanics, (Westview Press, Boulder, 1990), p. 387]. We demonstrate that, contrary to popular belief, photons do have enough degrees of freedom to be marked. From an analysis of Hong-Ou-Mandel interference we were able to introduce a novel parameter called the "rate of distinguishability", which furnishes a quantitative measure of the indistinguishability of photons prepared in a given state. Our results suggest that the strong concept of "PI" may need to be replaced with the weaker concept of "PI with respect to a given degree of freedom".


Contact: falk.toeppel(at)mpl.mpg(dot)de
Group: Leuchs Division
Reference: F. Töppel et al., New J. Phys. 14 093051 (2012).