Electrical gating of spin in InAs quantum dots

Full text: The choice of the electron spin degree of freedom for quantum information processing schemes requires a variety of architectures in which electrons can be trapped and coherently manipulated. The utilization of Quantum Dots (QDs) is the building block in many of these schemes as the need for individual electron assessment is necessary. An interesting aspect of QDs that are created by lattice-mismatched epitaxy and self-assembly concerns the ability of individual electron control, as well as relatively large lateral confining energies (∼50 m eV). In order to interact with the electronic spin, one needs to assess the Land e g-tensor. This can be carried out by capacitance spectroscopy for varying magnetic fields applied along the high symmetry directions of QDs. Orbital splitting, diamagnetic shift and spin splitting can be resolved for QD ensembles. Engineering g-factors can be implemented by modifying the spin-orbit coupling. That can be achieved by growing QDs of different compositions, capping the QDs with layers of different g-factors, or stressing QDs with layers of different equilibrium lattice parameters. g-tensor control can be implemented by spatially modulating the electronic wave function via an externally applied bias. These resources can be utilized for g-tensor modulation resonance (gTMR)[1]. Microwave modulation of the g-tensor induces frequency modulation of the spin precession, which at the Larmor frequency produces resonance. One of the interesting aspects of gTMR is the fact that one can obtain resonance without ac magnetic fields, consequently eliminating the need for cavities. Here a proposal for a gTMR experiment is shown and some preliminary results are presented. The sample consisted of In As QDs grown by Molecular Beam Epitaxy and embedded in a capacitor structure across which the microwave electric field was applied. Polarized electron and hole spin injection was carried out by a mode-locked 150 fs Ti:Saphire laser tuned at the wetting layer transition (830 nm). The mode-lock frequency was fed into a phase-locked oscillator generating integer multiples of 80 MHz as the microwave source. The QDs were loaded with electrons into each discrete shell, producing a magnetic field dependent, polarization modulated photocurrent signal. Preliminary analysis points in the direction of spin resonance, however at the wetting layer and/or GaAs electron injection contact g-factors. Further experiments are discussed aimed at the optimization of the resonance signal of the QDs electronic shell. 1] Y. Kato, R. C. Myers, D. C. Driscoll, A. C. Gossard, J. Levy, D. D. Awschalom, Science 299, 1201 (2003). (author)