Automated tuning of inter-dot tunnel couplings in quantum dot arrays

Semiconductor quantum dot arrays defined electrostatically in a 2D electron gas provide a scalable platform for quantum information processing and quantum simulations. For the operation of quantum dot arrays, appropriate voltages need to be applied to the gate electrodes that define the quantum dot potential landscape. Tuning the gate voltages has proven to be a time-consuming task, because of initial electrostatic disorder and capacitive cross-talk effects. Here, we report on the automated tuning of the inter-dot tunnel coupling in a linear array of gate-defined semiconductor quantum dots. The automation of the tuning of the inter-dot tunnel coupling is the next step forward in scalable and efficient control of larger quantum dot arrays. This work greatly reduces the effort of tuning semiconductor quantum dots for quantum information processing and quantum simulation

Coulomb effects in semiconductor quantum dots

Coulomb correlations in the optical spectra of semiconductor quantum dots are investigated using a full-diagonalization approach. The resulting multi-exciton spectra are discussed in terms of the symmetry of the involved states. Characteristic features of the spectra like the nearly equidistantly spaced s-shell emission lines and the approximately constant p-shell transition energies are explained using simplified Hamiltonians that are derived taking into account the relative importance of various interaction contributions. Comparisons with previous results in the literature and their interpretation are made.Comment: 7 pages, 2 figure

Spin relaxation in semiconductor quantum dots

We have studied the physical processes responsible for the spin -flip in GaAs quantum dots. We have calculated the rates for different mechanisms which are related to spin-orbit coupling and cause a spin-flip during the inelastic relaxation of the electron in the dot both with and without a magnetic field. We have shown that the zero-dimensional character of the problem when electron wave functions are localized in all directions leads to freezing out of the most effective spin-flip mechanisms related to the absence of the inversion centers in the elementary crystal cell and at the heterointerface and, as a result, to unusually low spin-flip rates.Comment: 6 pages, RevTe

Competing interactions in semiconductor quantum dots

We introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.Comment: 10 pages, 5 figures [v2: subsection and references added

Optical spectra of quantum dots: effects of non-adiabaticity

It is shown that in many cases an adequate description of optical spectra of semiconductor quantum dots requires a treatment beyond the commonly used adiabatic approximation. We have developed a theory of phonon-assisted optical transitions in semiconductor quantum dots, which takes into account non-adiabaticity of the exciton-phonon system. Effects of non-adiabaticity lead to a mixing of different exciton and phonon states that provides a key to the understanding of surprisingly high intensities of phonon satellites observed in photoluminescence spectra of quantum dots. A breakdown of the adiabatic approximation gives an explanation also for discrepancies between the serial law, observed in multi-phonon optical spectra of some quantum dots, and the Franck-Condon progression, prescribed by the adiabatic approach.Comment: 4 pages, 3 figures, E-mail addresses: [email protected], [email protected], [email protected], [email protected], [email protected]

Intrinsic spin dynamics in semiconductor quantum dots

We investigate the characteristic spin dynamics corresponding to semiconductor quantum dots within the multiband envelope function approximation (EFA). By numerically solving an $8\times8$ $k\cdot p$ Hamiltonian we treat systems based on different III-V semiconductor materials.It is shown that, even in the absence of an applied magnetic field, these systems show intrinsic spin dynamics governed by intraband and interband transitions leading to characteristic spin frequencies ranging from the THz to optical frequencies.Comment: to be published in Nanotechnology. Separated figure file