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

Abstract

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, Δ E ∗ , becomes power dependent as well. It is given by Δ E ∗= { ΔE} 2+{2J 0(eV AC /hf )T} 2 , where Δ 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 ⪡hf, J 0≈1 ), the observed energy separation is well described by Δ E ∗= { ΔE} 2+{2T} 2 . For larger microwave powers ( eV AC≳ hf) it is shown that the energy separation is modified according to the Bessel function term.