2,284 research outputs found
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
The Role of Multilevel Landau-Zener Interference in Extreme Harmonic Generation
Motivated by the observation of multiphoton electric dipole spin resonance
processes in InAs nanowires, we theoretically study the transport dynamics of a
periodically driven five-level system, modeling the level structure of a
two-electron double quantum dot. We show that the observed multiphoton
resonances, which are dominant near interdot charge transitions, are due to
multilevel Landau-Zener-Stuckelberg-Majorana interference. Here a third energy
level serves as a shuttle that transfers population between the two resonant
spin states. By numerically integrating the master equation we replicate the
main features observed in the experiments: multiphoton resonances (as large as
8 photons), a robust odd-even dependence, and oscillations in the electric
dipole spin resonance signal as a function of energy level detuning
Field Tuning the G-Factor in InAs Nanowire Double Quantum Dots
We study the effects of magnetic and electric fields on the g-factors of
spins confined in a two-electron InAs nanowire double quantum dot. Spin
sensitive measurements are performed by monitoring the leakage current in the
Pauli blockade regime. Rotations of single spins are driven using
electric-dipole spin resonance. The g-factors are extracted from the spin
resonance condition as a function of the magnetic field direction, allowing
determination of the full g-tensor. Electric and magnetic field tuning can be
used to maximize the g-factor difference and in some cases altogether quench
the EDSR response, allowing selective single spin control.Comment: Related papers at http://pettagroup.princeton.ed
Radio frequency charge sensing in InAs nanowire double quantum dots
We demonstrate charge sensing of an InAs nanowire double quantum dot (DQD)
coupled to a radio frequency (rf) circuit. We measure the rf signal reflected
by the resonator using homodyne detection. Clear single dot and DQD behavior
are observed in the resonator response. rf-reflectometry allows measurements of
the DQD charge stability diagram in the few-electron regime even when the dc
current through the device is too small to be measured. For a signal-to-noise
ratio of one, we estimate a minimum charge detection time of 350 microseconds
at interdot charge transitions and 9 microseconds for charge transitions with
the leads.Comment: Related papers at http://pettagroup.princeton.ed
A Reconfigurable Gate Architecture for Si/SiGe Quantum Dots
We demonstrate a reconfigurable quantum dot gate architecture that
incorporates two interchangeable transport channels. One channel is used to
form quantum dots and the other is used for charge sensing. The quantum dot
transport channel can support either a single or a double quantum dot. We
demonstrate few-electron occupation in a single quantum dot and extract
charging energies as large as 6.6 meV. Magnetospectroscopy is used to measure
valley splittings in the range of 35-70 microeV. By energizing two additional
gates we form a few-electron double quantum dot and demonstrate tunable tunnel
coupling at the (1,0) to (0,1) interdot charge transition.Comment: Related papers at http://pettagroup.princeton.ed
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