Condensed-Matter Physics & Materials Science Seminar

Semiconductor nanowires are a new class of materials with promising applications to spin-based quantum information processing. We use nanowires made of indium arsenide (InAs), material with the strong spin-orbit interaction, to realize spin-orbit qubits. When the spin and orbital degree of freedom are strongly coupled, the eigenstates of a single electron confined to a nanowire quantum dot become a spin-orbital doublet. The transitions between the eigenstates can be driven using high frequency electric fields which couple to the orbital part of the electron wavefunction.

In order to initialize and detect the spin-orbit eigenstates, we use double quantum dot configuration tuned to the Pauli blockade regime.
Blockade between triplet and singlet states is used to initialize the two electrons in the triplet configuration and to distinguish the states during the detection stage. We demonstrate coherent Rabi oscillations using electric dipole spin resonance (EDSR) mediated by spin-orbit interaction. The highest Rabi frequency achieved is ~57MHz, an order of magnitude faster compared to the EDSR in GaAs/AlGaAs 2d electron gas. We show universal qubit control and study qubit dephasing in a Ramsey type experiment. We apply spin-echo and dynamical decoupling techniques to extend the coherence time. Finally, we show that qubits in two quantum dots can be selectively addressed due to the difference in Landé g-factors.