Abstract
We present an electrostatically defined few-electron double quantum dot (QD) realized in a molecular beam epitaxially grown Si/SiGe heterostructure. Transport and charge spectroscopy with an additional QD as well as pulsed-gate measurements are demonstrated. We discuss technological challenges specific to silicon-based heterostructures and the effect of a comparably large effective electron mass on transport properties and tunability of the double QD. Charge noise, which might be intrinsically induced due to strain engineering, is proven not to affect the stable operation of our device as a spin qubit.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Single electrons that are electrostatically confined to semiconductor quantum dots are a promising architecture for the realization and investigation of a scalable set of quantum bits (qubits). In such an approach, the information can be encoded in the spin of an electron. To retain the information for logical operations, a qubit needs to be well isolated from its volatile solid-state environment. Using silicon as a host material for electron spin qubits provides an interesting alternative to conventional gallium-arsenide-based hosts because an electron spin in silicon is predicted to be sufficiently decoupled from typical mechanisms that lead to a loss of the fragile quantum information.
Main results. We present the characterization of an electrostatically defined double quantum dot device in the few-electron regime based on a silicon/silicon-germanium heterostructure. Stable operation of the device is demonstrated and it is found that electron transport properties are strongly affected by the comparatively large effective electron mass in silicon. In addition, we discuss technological challenges for the realization and stable operation of such devices.
Wider implications. Despite the remaining technological challenges, our study shows that such double quantum dot devices can serve as a fundamental building block for an electron-spin-based quantum computer. A major step forward will be the demonstration of coherent manipulation of electron spins harnessing the potential of silicon for much longer spin coherence times than those currently available in other material systems.
Figure. (left) AFM micrograph of a double quantum dot (DQD) structure on a Si/SiGe heterostructure. (right) Charge stability diagram of the DQD in the vicinity of two triple points. Different colors correspond to different numbers of electrons occupying the DQD.