[Show abstract][Hide abstract] ABSTRACT: Spin qubits have been successfully realized in electrostatically defined,
lateral few-electron quantum dot circuits. Qubit readout typically involves
spin to charge information conversion, followed by a charge measurement made
using a nearby biased quantum point contact. It is critical to understand the
back-action disturbances resulting from such a measurement approach. Previous
studies have indicated that quantum point contact detectors emit phonons which
are then absorbed by nearby qubits. We report here the observation of a
pronounced back-action effect in multiple dot circuits where the absorption of
detector-generated phonons is strongly modified by a quantum interference
effect, and show that the phenomenon is well described by a theory
incorporating both the quantum point contact and coherent phonon absorption.
Our combined experimental and theoretical results suggest strategies to
suppress back-action during the qubit readout procedure.
[Show abstract][Hide abstract] ABSTRACT: Time resolved electronic dynamics in coupled quantum dots is directly obtained by a pulsed-gate technique. While individual gate voltages are modulated with periodic pulse trains average charge occupations are measured. A nearby quantum point contact serves as detector. A key component of our setup is a radio frequency sample holder based on impedance matched micro strip lines virtually free of cross-talk. It allows to observe displacements of single electrons on time scales well below a nanosecond. Microscopically resolved tunneling rates as well as relaxation times are obtained by using an adapted rate equation model.
[Show abstract][Hide abstract] ABSTRACT: Quantum point contacts (QPCs) are commonly employed to detect capacitively the charge state of coupled quantum dots (QDs). An indirect backaction of a biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure is observed. Energy is emitted by nonequilibrium charge carriers in the leads of the biased QPC. Part of this energy is absorbed by the double QD where it causes charge fluctuations that can be observed under certain conditions in its stability diagram. By investigating the spectrum of the absorbed energy, we find that both acoustic phonons and Coulomb interaction can be involved in the backaction, depending on the geometry and coupling constants.
Full-text · Article · May 2010 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: We report on the realization and top-gating of a two-dimensional electron system in a nuclear spin free environment using 28Si and 70Ge source material in molecular beam epitaxy. Electron spin decoherence is expected to be minimized in nuclear spin-free materials, making them promising hosts for solid-state based quantum information processing devices. The two-dimensional electron system exhibits a mobility of 18000 cm2/Vs at a sheet carrier density of 4.6E11 cm-2 at low temperatures. Feasibility of reliable gating is demonstrated by transport through split-gate structures realized with palladium Schottky top-gates which effectively control the two-dimensional electron system underneath. Our work forms the basis for the realization of an electrostatically defined quantum dot in a nuclear spin free environment.
Full-text · Article · Mar 2009 · physica status solidi (RRL) - Rapid Research Letters
[Show abstract][Hide abstract] ABSTRACT: Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed.
Full-text · Article · May 2008 · Physical Review Letters