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 regimes. When the inter-dot coupling, T, is weak, an ionic-like bonding is observed. The current through the double dot is power dependent. In the strong coupling regime, a covalent-like bonding is formed and the energy separation between the symmetric and anti-symmetric eigenstates, Delta E*, becomes power 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 amplitude, and f the frequency. We show that in the case of strong coupling and low microwave power (eV(AC) much less than hf, J(0) approximate to 1), the observed energy separation is well described by Delta E* = J{Delta E}(2) + {2T}(2). For larger microwave powers (eV(AC) greater than or similar to hf) it is shown that the energy separation is modified according to the Bessel function term. (C) 1999 Published by Elsevier Science B.V. All rights reserved.