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International Affairs Students Current Students Alumni Faculty/Staff Careers--> TOHOKU UNIVERSITYCREATING GLOBAL EXCELLENCE Search 日本語 Contact Tohoku University --> About Facts & Figures Facilities Organization Chart History President's Message Top Global University Project Designated National University Global Network Promotional Videos Academics Undergraduate Graduate Courses in English Exchange Programs Summer Programs Double Degree Programs Academic Calendar Syllabus Admissions Undergraduate Admissions Graduate Admissions Fees and Expenses Financial Aid Research Feature Highlights Research Releases University Research News Research Institutes Visitor Research Center Research Profiles Academic Research Staff Campus Life International Support Office IT Services Facilities Dining & Shops Campus Bus Clubs & Circles News University News Research--> Arts & Culture Health & Sports Campus & Community Press Release--> International Visit Alumni Careers Events Exhibits Music Special Event Lecture Alumni--> Map & Directions Campus Maps & Bus--> Facilities Map--> TOHOKUUNIVERSITY About Academics Admissions Research Campus Life News Events International Affairs Students Current Students Alumni Faculty/Staff Promotional Videos Subscribe to our Newsletter Map & Directions Contact Jobs & Vacancies Emergency Information Site Map 日本語 Close Home Research News Researchers Demonstrate a High-speed Electrical Readout Method for Graphene Nanodevices Research News Researchers Demonstrate a High-speed Electrical Readout Method for Graphene Nanodevices 2023-10-20 The 'wonder material' graphene is well-known for its high electrical conductivity, mechanical strength, and flexibility. Stacking two layers of graphene with atomic layer thickness produces bilayer graphene, which possesses excellent electrical, mechanical, and optical properties. As such, bilayer graphene has attracted significant attention and is being utilized in a host of next-generation devices, including quantum computers. But complicating their application in quantum computing comes in the form of gaining accurate measurements of the quantum bit states. Most research has primarily used low-frequency electronics to overcome this. However, for applications that demand faster electronic measurements and insights into the rapid dynamics of electronic states, the need for quicker and more sensitive measurement tools has become evident. Now, a group of researchers from Tohoku University have outlined improvements to radio-frequency (rf) reflectometry to achieve a high-speed readout technique. Remarkably, the breakthrough involves the use of graphene itself. (a) The layer structure of the fabricated device. (b) The resonant circuit used for rf-reflectometry. ©Tomoya Johmen et al. Rf reflectometry works by sending radio frequency signals into a transmission line and then measuring the reflected signals to obtain information about samples. But in devices employing bilayer graphene, the presence of significant stray capacitance in the measurement circuit leads to rf leakage and less-than-optimal resonator properties. Whilst various techniques have been explored to mitigate this, clear device design guidelines are still awaited. The dependence of rf reflection characteristics on gate voltage, showing the change in conductance. ©Tomoya Johmen et al. "To circumvent this common shortfall of rf reflectometry in bilayer graphene, we employed a microscale graphite back-gate and an undoped silicon substrate," says Tomohiro Otsuka, corresponding author of the paper and associate professor at Tohoku University's Advanced Institute for Materials Research (WPI-AIMR). "We successfully realized good rf matching conditions, calculated the readout accuracy numerically, and compared these measurements with direct current measurements to confirm its consistency. This allowed us to observe Coulomb diamonds through rf reflectometry, a phenomenon indicating the formation of quantum dots in the conduction channel, driven by potential fluctuations caused by bubbles." Coulomb diamonds originating from the formation of quantum dots are observed by monitoring the reflected voltage from the resonator. ©Tomoya Johmen et al. Otsuka and his team's proposed improvements to rf reflectometry provide important contributions to the development of next-generation devices such as quantum computers, and the exploration of physical properties using two-dimensional materials, such as graphene. The details of their study were reported in the journal Physical Review Applied. Publication Details: Title: Radio-Frequency Reflectometry in Bilayer Graphene Devices Utilizing Microscale Graphite Back-GatesAuthors: Tomoya Johmen, Motoya Shinozaki, Yoshihiro Fujiwara, Takumi Aizawa, and Tomohiro OtsukaJournal: Physical Review AppliedDOI: 10.1103/PhysRevApplied.20.014035 Press release in Japanese Contact: Tomohiro Otsuka, WPI-AIMR, Tohoku UniversityEmail: tomohiro.otsukatohoku.ac.jpWebsite: https://en.qd.riec.tohoku.ac.jp/ --> Archives 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 Page Top About Tohoku University Academics Admissions Research Campus Life News Events International Affairs Students Alumni Promotional Videos Subscribe to our Newsletter Map & Directions Contact Tohoku University Jobs & Vacancies Emergency Information Site Map Media Enquiries Parent & Family Support Public Facilities Contact Tohoku University