Tomohiro Kambara

Key capacitive parameters for designing single-electron transistor charge sensors

Single-electron transistors (SETs) are efficient charge sensors for reading out spin or charge qubits confined in quantum dots (QDs). To investigate their capacitive parameters, which are related to the signal-to-noise ratio (SNR) during qubit readout, twin silicon single QDs were fabricated using a lithographic process on a silicon-on-insulator substrate. Since the configuration and dimensions of the QDs could be determined by direct imaging, the theoretical capacitive parameters could be compared to the measured values. Good agreement was found between the calculated and measured values, which confirms the validity of the calculation method. The results indicated that decreasing the SET diameter reduces the capacitive coupling between qubits but increases the signal-to-noise ratio for both dc and radio frequency single-shot measurements. Since these results are independent of the device materials, they are useful for establishing guidelines for the design of SET charge sensors in lateral QD-SET structur...

Fabrication and characterization of p-channel Si double quantum dots

Lithographically defined p-channel Si single hole transistors (SHTs) and double quantum dot (DQD) devices are fabricated and characterized. Coulomb oscillations are clearly evident at a temperature of 4.2 K. The charging energy and the diameter of the SHT are estimated from the Coulomb diamonds. Honeycomb-like charge stability diagrams are observed from measurements of the DQD devices. Single hole transitions through the DQD are detected using an integrated SHT as a charge sensor, and a few-hole regime of the DQD is observed.

Realization of Lithographically‐Defined Silicon Quantum Dots without Unintentional Localized Potentials

We have fabricated lithographically‐defined Si quantum dots (QDs) within a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) structure. In this architecture, the top gate is used to tune the carrier density whereas side gates control the potentials of the QDs and tunneling barriers. These lithographically‐defined and electrically‐tunable Si QDs were successfully realized without unintentional localized potentials.

Manipulation of silicon quantum dots and isolated structures using GHz photons

We demonstrate that microwave photons can be used to remotely manipulate electron tunneling across a tunnel barrier at 4.2 K. A similar method is used to successfully modify the charges states of an electrically isolated doped silicon double quantum dot with potential coherence time of the order of a few μs.

Microwave manipulation of electrons in silicon quantum dots

Here we present the results of an investigation on microwave-induced effects that we have observed in silicon devices, including phosphorous doped and Metal-Oxide-Semiconductor Single Electron Transistors (SET) as well as IDQD. Continuous pulsed microwave and single shot measurements are used to demonstrate that photons in the range of 10-15 GHz allow manipulation of the electron number in the island of a doped SET, despite the high value for the charging energy and in a regime where photon assisted tunnelling is not observable. The method is applied to a device made of a SET with a capacitively coupled IDQD. Partial control of the qubit is obtained and results in the possibility of manipulating charge states in an isolated structure with GHz photons.

Fabrication and Characterization of p-Channel Si Double-Quantum-Dot Structures

1 Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan 2 Institute for Nano Quantum Information Electronics, The Univ. of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 Japan 3 PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan *Phone: +81-3-5734-2542, Fax: +81-3-5734-2542, E-mail: yamada.k.av@m.titech.ac.jp

Dual Function of Charge Sensor: Charge Sensing and Gating

1 Quantum Nanoelectronics Research Center, Tokyo Inst itute of Technology, 2-12-1 O-okayama, Megro-ku, Tokyo 152-8550, Japan 2 Institute for Nano Quantum Information Electronics , The Univ. of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 Japan 3 PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, Japan *Phone: +81-3-5734-2542, Fax: +81-3-5734-2542, E-ma il: k mbara@neo.pe.titech.ac.jp

Spin-related tunneling in lithographically-defined silicon quantum dots

We realized lithographically-defined electrically-tunable silicon quantum dots (Si QDs) without unintentional localized potentials by improving device structures and fabrication techniques. Carrier density was tuned with a top gate and QD-potentials were controlled with the side gates. We succeeded in observing spin-related tunneling phenomena using the double QD device.