Quantum Coherence and Correlated Transport in Quantum Dot Systems

The present thesis studies the electrical transport of two distinct quantum dot systems, providing insights into many-particle correlations, quantum dissipation and spin relaxation. The first part examines the third shell of a gate-defined single quantum dot formed in a two-dimensional electron gas within a GaAs/AlGaAs heterostructure. A quantum point contact, capacitively coupled to the quantum dot, serves as a sensitive charge detector to determine the exact number of electrons occupying the quantum dot. The addition energy of electrons in the third shell shows a triangular evolution with a maximum at half-filling, exceeding its value for shell transitions. This trend is described analytically with Hund’s rule exchange correlations. Zero-bias anomalies (ZBAs) are observed across all shell fillings, displaying similar trend, reflecting particle-hole symmetry of three degenerate orbitals with spin degeneracy. The unexpectedly broad ZBAs widths arise not only from the Kondo resonance but also from the contribution of excited Hund multiplets. The broad ZBA and, interestingly, the apparent addition energy both decrease with increasing temperature. The second part investigates asymmetrically coupled InAs double quantum dots in a GaAs/AlAs heterostructure. A strong temperature dependence is observed in both the coherent tunneling peaks and the background current. It is attributed to quantum dissipation from two different bosonic baths, originating from substrate phonons. The extracted system parameters are used to determine the charge qubit dephasing time. Under an applied magnetic field, the resonant peaks split into two, with one peak fading at lowtemperatures due to a spin-dependent blockade. This blockade is lifted by spin flips. For the upper channel, the spin flips occur via thermal excitaion and thus are suppressed at low temperature. The spin-flip rate is directly determined from the measured current, providing insights into the spin relaxation mechanism.