Time-Resolved Dynamics of a Double Quantum Dot Charge Qubit Probed by Dispersive Readout

We study the dynamics of a GaAs based double quantum dot (DQD) charge qubit with a dephasing rate of γ₂ ~ 4 MHz which is strongly coupled to a high impedance SQUID array resonator. In time-resolved measurements, realized in the dispersive regime, we discriminate between contributions of relaxation and dephasing to the decoherence rate. We realize measurements of Rabi-oscillations, Ramsey-fringes, charge relaxation and Hahn-echo for a DQD charge qubit, with timescales T₂^* ~ 25 ns, T₁ ~ 100 ns and T_2,echo ~ 50 ns extracted for interdot detuning δ = 0 and tunnel rate 2t ~ 4 GHz. Furthermore, we investigate the dependence of these time scales on the interdot tunnel rate 2t at δ = 0 and on the detuning δ ≠ 0 for 2t ~ 4 GHz. We conclude that T₁ and T₂^* are dominated by the interaction with phonons and by charge noise, respectively. We extract a standard deviation of the detuning noise more than an order of magnitude lower than reported previously in literature for semiconductor DQDs.