Microwave spectroscopy of a double quantum dot in the low- and high-power regime

Microwave experiments on an artificial two-level system formed by a double quantum dot, are discussed for different coupling and microwave power regim es. When the inter-dot coupling, T, is weak, an ionic-like bonding is obser ved. The current through the double dot is power dependent. In the strong c oupling regime, a covalent-like bonding is formed and the energy separation between the symmetric and anti-symmetric eigenstates, Delta E*, becomes po wer dependent as well. It is given by Delta E* = root{Delta E}(2) + {2J(0) (eV(AC)/hf)T}(2), where Delta E is the uncoupled energy splitting, J(0) the zeroth-order Bessel function of the first kind, V-AC the microwave amplitu de, and f the frequency. We show that in the case of strong coupling and lo w microwave power (eV(AC) much less than hf, J(0) approximate to 1), the ob served energy separation is well described by Delta E* = J{Delta E}(2) + {2 T}(2). For larger microwave powers (eV(AC) greater than or similar to hf) i t is shown that the energy separation is modified according to the Bessel f unction term. (C) 1999 Published by Elsevier Science B.V. All rights reserv ed.