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Fast electrical control of single-electron spins in quantum dots

Introduction

Electron spins in semiconductor quantum dots have relatively long coherence time in solids and are good candidates of quantum bits for quantum information processing.

The electron spins can be controlled by electron spin resonances. We enhanced the operation speed and realized good operation fidelity by improving the technique. We also realized another approach to rotate the spin without electron spin resonances.


Experiment

The left picture shows a scanning electron micrograph of the device. We utilize the micro-magnet and the microwave to induce the electron spin resonances. The operation speed is enhanced by optimizing the shape of the micro-magnet.

The obtained electron spin resonance signals are shown in the right figure. The resonance field changes linearly with the frequency of the microwave.





We measured Rabi oscillations to evaluate the rotation speed. The realized Rabi frequency is as fast as 127 MHz in the left figure. 

With this fast Rabi oscillations, the effect of the fluctuating nuclear spins in the device is suppressed and we can observe the characteristic chevron pattern. 












Another way of rotating spins around z axis can be realized by switching the magnetic field with the micro-magnet and the voltage pulses.

We demonstrated this operation as fast as 54 MHz as shown in the right figure.











Conclusion

We have improved the operation speed of the spin rotation by the electron spin resonances utilizing the micro magnet. We have also demonstrated a new way of spin rotation by switching  the magnetic field directly.

These results will be important towards realization of quantum information processing utilizing quantum dots.


Reference

 Fast Electrical Control of Single Electron Spins in Quantum Dots with Vanishing Influence from Nuclear Spins”, Jun Yoneda*, Tomohiro Otsuka*, Takashi Nakajima, Tatsuki Takakura, Toshiaki Obata, Michel Pioro-Ladrière, Hong Lu, Christopher Palmstrøm, Arthur C. Gossard, and Seigo Tarucha, Physical Review Letters 113, 267601 (2014)arXiv:1411.6738, (*equal contribution).