### Single-electron spin resonance in a quadruple quantum dot

**Introduction**

Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing.

Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two-qubit entanglement operations, and readout. Now it becomes crucial to demonstrate the scalability of this architecture by conducting spin operations on a scaled up system.

We demonstrate single-electron spin resonance in a quadruple quantum dot.

**Experiment**

The left picture shows a scanning electron micrograph of the device. A quadruple quantum dot is formed at the position of the four circles. We can detect the charge state by monitoring quantum dot sensors on the upper side.

The right graph shows a charge stability diagram. The quadruple quantum dot contains a few electrons.

We can detect the spin state as a change of the charge state by utilizing spin blockade.

We apply microwaves to induce the electron spin resonance. The microwave electric field and the magnetic field created by the micromagnet induce the rotation of the spin.

The upper graphs show the observed resonance lines. The four lines correspond to the electron spin resonance of the four quantum dot.

The upper graph shows the positions of the resonance dips. The four dips are not overlapped, and we can realize single-spin resonance by selecting the magnetic field of the frequency.

**Conclusion**

We have realized a quadruple quantum dot device and single-electron spin resonance in a quadruple quantum dot.

These results are important in scale-up of the qubit system and exploring multi-spin physics.

**Reference**

“Single-electron Spin Resonance in a Quadruple Quantum Dot”,

__Tomohiro Otsuka__, Takashi Nakajima, Matthieu R. Delbecq, Shinichi Amaha, Jun Yoneda, Kenta Takeda, Giles Allison, Takumi Ito, Retsu Sugawara, Akito Noiri, Arne Ludwig, Andreas D. Wieck, and Seigo Tarucha,