(Invited) Silicon Quantum Dot Single-Electron Pumps for the Closure of the Quantum Metrology Triangle
Authors: Fujiwara Akira , Yamahata Gento , Johnson Nathan , Nakamura Shuji , Kaneko Nobuhisa 
Published: February 2024

Si quantum dot (QD) devices fabricated by MOSFET technology are promising for future and ultimate quantum electronics such as quantum electrical standards and quantum computers. We have developed Si tunable-barrier QD devices with a quasi-gate-all-around (GAA) nanowire [1], which are designed to be used as basic elements such as single-electron (SE) transfer devices and qubits; the precise manipulation of charges and their states are realized in the QDs. The device is especially suitable for high-speed tunable-barrier SE pumps driven at GHz frequencies [2,3] which can generate an electric current via a single QD precisely equal to the elementary charge times the driving frequency and thereby are promising for quantum current standards [4].
To achieve a high accuracy using tunable-barrier SE pumps [5-7], proper designs of device structures are required to secure robust charge quantization. The potential shape of the QD and the entrance tunnel barrier [8] are critical parameters to dictate the pump accuracy because they determine the charging energy and energy filtering effect during SE capture into the QD. Furthermore, deep understanding of electron dynamics such as mechanism crossover of the dynamical charge quantization process [9] and quantum nonadiabatic excitation [10]/electron-phonon relaxation inside the QD are important to get optimal accuracy and extend the frequency breakdown of SE pumps. We have recently developed a device simulator of Si GAA-nanowire SE pumps [11], which is a useful tool to find optimal design and control parameters in all the above-mentioned respects.
One of the long-desired targets of SE pumps is to close the quantum metrology triangle (QMT) [12] by checking the consistency among three quantum electrical standards: the SE current standard, the quantum Hall resistance standard, and Josephson voltage standard (JVS). The Japanese QMT project [13] has aimed to conduct the QMT experiment with sub-ppm uncertainty in a single dilution refrigerator by placing all the quantum electric standards inside it. Our key approaches are to use quantum Hall array resistance (QHAR) [14] and parallelized Si SE pumps, which provide higher resistance and current respectively, making the generated voltage more easily compared to JVS. In the project we have succeeded in developing a current-reversal technique with electromechanical relays to cancel out the drift and low frequency noise from various sources in the measurement setup, and applying it to high accuracy measurement of current delivered by a Si SE pump [15]. We have also recently performed a comparison measurement of two Si SE pump operated in parallel and thereby have confirmed a sub-ppm level accuracy [16]. All these progresses will lead to a more precise closure of QMT at deep sub-ppm level in the new future. Si MOSFET technology continues to expand its versatility into quantum electronics technology. This work was supported by JSPS KAKENHI Grant Number JP18H05258.

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