QDev Seminar: Akito Noiri – University of Copenhagen

QDev Seminar: Akito Noiri

Tarucha-Yamamoto Laboratory
University of Tokyo

Implementation of three spin qubits in a lateral triple quantum dot

Multiple quantum dots (QDs) are fascinating systems to explore the physics of electron interactions. The confined electron spins in QDs can be addressed both electrically and optically, which makes QDs highly promising building blocks for quantum information processing [1]. Recent experiments on GaAs QDs have demonstrated the necessary ingredients of universal quantum gate operations: single-spin rotations by electron spin resonance (ESR) [2,3] and pulsed control of two-spin entanglement [4]. Single-spin manipulation with fidelity up to 96% was achieved [5] by employing a magnetic field gradient induced by a specially designed micro-magnet (MM) [3]. The next step to implement quantum algorithms is to scale up this system to three or more. The number of qubits, however, has so far been limited to two.

In this presentation, I will mainly talk about addressable initialization/control/readout of single spins in a laterally coupled triple QD (TQD) based on GaAs defined by gate electrodes. Initialization of individual spins is performed by pulse operation of detuning energies between two adjacent QDs. Also, spin-state readout is realized by Pauli spin blockade with detuning pulse operation. Each spin state can be manipulated individually by frequency-selectable ESR with a maximum Rabi frequency up to 25MHz. The spin in the right QD shows the largest Rabi frequency in agreement with the simulated local magnetic field property created by the MM.

In the last of the presentation, I will also briefly talk about our recent project focusing on the two-dimensional (2D) arrangement of tunnel-coupled QDs. It is very intriguing for studies on complex spin correlations as well as applications to fault tolerant scalable quantum computing. A triangle and a square with a QD at each apex are the fundamental basis for the 2D arrangement. At this moment, we are working with a triangular-shaped TQD and successfully demonstrated TQD with a finite inter-dot tunnel coupling between all pair of the QDs.


[1] D. Loss et al., Phys. Rev. A. 57, 120 (1998).

[2] F. H. L. Koppens et al., Nature 442, 766 (2006).

[3] M. Pioro-Ladrière et al., Nat. Phys. 4, 776 (2008).

[4] J. R. Petta et al., Science 309, 2180 (2005).

[5] J. Yoneda et al., Phys. Rev. Lett. 113, 267601 (2014).