### Detection and control of charge states in a quintuple 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 realizing larger systems.

We demonstrate detection and control of charge states in a quintuple quantum dot.

**Experiment**

The left picture shows a scanning electron micrograph of the device and a schematics of the measurement setup. A quintuple quantum dot is formed at the position of the five circles. We detect the charge state by monitoring quantum dot sensors on the upper side.

We use the two quantum dot sensors because it becomes difficult to detect the charge state of the all five quantum dots with high sensitivity by only one sensor.

The right graphs show that the two sensors can be measured at the same time.

We form the quintuple quantum dot and measure the charge state.

The upper graphs show the observed signals by sensor 1 and sensor 2. Sensor 1 (Sensor 2) mainly detects the charge state of the tree quantum dots on the left (right) side.

We extract the charge transition points from the upper two graphs. The lower left graph shows the extracted charge state of the quintuple quantum dot.

We can observe five kinds of slopes corresponding to the five quantum dots.

The charge state can be reproduced by numerical calculations shown on the lower right.

We can also tune the charge state by gate voltages and monitor the change by the sensors.

**Conclusion**

We have realized a quintuple quantum dot device and demonstrated detection and control of the charge state.

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

**Reference**

“Detection and control of charge states in a quintuple quantum dot”,

Takumi Ito*, __Tomohiro Otsuka__*, Shinichi Amaha, Matthieu R. Delbecq, Takashi Nakajima, Jun Yoneda, Kenta Takeda, Giles Allison, Akito Noiri, Kento Kawasaki, and Seigo Tarucha,

Scientific Reports 6, 39113(2016), arXiv:1604.04426, (*equal contribution).