Researchers demonstrate high-speed electrical readout method for graphene nanodevices

a) Layer structure of the prepared device. (b) resonant circuit used for rf-reflectometry. Credit: Tomoya Johmen et al.

Graphene is known for its high electrical conductivity, mechanical strength and flexibility. By stacking two layers of graphene with the thickness of an atomic layer, bilayer graphene is created, which has excellent electrical, mechanical and optical properties. As such, bilayer graphene has attracted considerable attention and is used in many next-generation devices, including quantum computers.

But the complexity of their application in quantum computing comes in the form of obtaining precise measurements of quantum bit states. Most research has mainly used low frequency electronics to overcome this. However, for applications that require faster electronic measurements and insights into the fast dynamics of electronic states, the need for faster and more sensitive measurement tools has become apparent.

Now, a group of researchers at Tohoku University have outlined improvements to radio frequency (rf) reflectometry to achieve high-speed reading techniques. Notably, the breakthrough involves the use of graphene itself. Details of their study were reported in the journal A physical review was applied.

Rf reflectometry works by sending radio frequency signals down a transmission line, then measuring the reflected signals to obtain information about the samples. However, in devices using bilayer graphene, the presence of significant stray capacitance in the measurement circuit leads to rf leakage and suboptimal resonator properties. Although various methods have been explored to mitigate this, clear guidelines for device design are still awaited.

  • Researchers demonstrate high-speed electrical readout method for graphene nanodevices

    Dependence of Rf reflection characteristics on gate voltage, showing the change in conductivity. Credit: Tomoya Johmen et al.

  • Researchers demonstrate high-speed electrical readout method for graphene nanodevices

    Coulomb diamonds resulting from the formation of quantum dots are observed by monitoring the voltage reflected from the resonator. Credit: Tomoya Johmen et al.

“To circumvent this common shortcoming of RF reflectometry in bilayer graphene, we used a graphite back gate and an untreated silicon substrate,” said Tomohiro Otsuka, corresponding author of the paper and associate professor at Tohoku University’s Advanced Materials Research Institute (WPI). -AIMR).

“We successfully understood the good rf compliance conditions, numerically calculated the accuracy of the reading, and compared these measurements with direct current measurements to confirm its consistency. This allowed us to observe Coulomb diamonds by rf reflection, a phenomenon that indicates the formation of quantum dots in conduction. the wave due to the potential fluctuations of the bubbles’.

The improvements proposed by Otsuka and his team in measuring rf reflectance provide important contributions to the development of next-generation devices such as quantum computers and the study of physical properties using two-dimensional materials such as graphene.

Additional information:
Tomoya Johmen et al., Radio Frequency Reflectometry in Bilayer Graphene Devices Using Microscale Graphite Backgates, A physical review was applied (2023). DOI: 10.1103/PhysRevApplied.20.014035

Provided by Tohoku University

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