Population switching and charge sensing
in quantum dots:
A case for quantum phase transitions
Moshe Goldstein
Department of Physics,
``Population switching'' is a phenomenon involving
a steep filling of a narrow level in a quantum dot at the expense of a wide one
as a common gate voltage is varied. This effect has been discussed in several
contexts, including charge sensing by means of a current-carrying quantum point
contact (QPC), as well as in relation with lapses of the transmission phase of
a quantum dot. Is the switching involved abrupt, in which case one is facing a
first order quantum phase transition? Mapping this problem onto a two-species
Coulomb gas representation, we demonstrate that it is equivalent to an orbital
Kondo model, and find that the switching is steep but not abrupt; however, when
one tries to measure this behavior by electrostatically
coupling one of the levels to a charge detecting QPC, one may render the
switching abrupt. We show that this quantum phase transition is triggered by a
change in physics from a Mahan exciton controlled
dynamics to an