1,772 research outputs found
Dispersive readout of valley splittings in cavity-coupled silicon quantum dots
The bandstructure of bulk silicon has a six-fold valley degeneracy. Strain in
the Si/SiGe quantum well system partially lifts the valley degeneracy, but the
materials factors that set the splitting of the two lowest lying valleys are
still under intense investigation. We propose a method for accurately
determining the valley splitting in Si/SiGe double quantum dots embedded into a
superconducting microwave resonator. We show that low lying valley states in
the double quantum dot energy level spectrum lead to readily observable
features in the cavity transmission. These features generate a "fingerprint" of
the microscopic energy level structure of a semiconductor double quantum dot,
providing useful information on valley splittings and intervalley coupling
rates.Comment: 8 pages, 4 figure
High-quality quantum point contact in two-dimensional GaAs (311)A hole system
We studied ballistic transport across a quantum point contact (QPC) defined
in a high-quality, GaAs (311)A two-dimensional (2D) hole system using shallow
etching and top-gating. The QPC conductance exhibits up to 11 quantized
plateaus. The ballistic one-dimensional subbands are tuned by changing the
lateral confinement and the Fermi energy of the holes in the QPC. We
demonstrate that the positions of the plateaus (in gate-voltage), the
source-drain data, and the negative magneto-resistance data can be understood
in a simple model that takes into account the variation, with gate bias, of the
hole density and the width of the QPC conducting channel
Interplay of charge and spin coherence in Landau-Zener-St\"uckelberg-Majorana interferometry
We study Landau-Zener dynamics in a double quantum dot filled with two
electrons, where the spin states can become correlated with charge states and
the level velocity can be tuned in a time-dependent fashion. We show that a
correct interpretation of experimental data is only possible when finite-time
effects are taken into account. In addition, our formalism allows the study of
partial adiabatic dynamics in the presence of phonon-mediated hyperfine
relaxation and charge-noise-induced dephasing. Our findings demonstrate that
charge noise severely impacts the visibility of
Landau-Zener-St\"uckelberg-Majorana interference fringes. This indicates that
charge coherence must be treated on an equal footing with spin coherence.Comment: 13 pages, 9 figure
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