Seigo Tarucha, University of Tokyo

Manipulation of Quantum Entanglement with Quantum Dots

Department of Applied Physics, The University of Tokyo

Manipulation of quantum entanglement is the core of quantum information processing. In this talk I will review our approach to manipulate local and non-local spin entanglement with quantum dots. The local entanglement is typically the case for spin singlet coupling in single or multiple quantum dots, and its manipulation enables to prepare universal sets of logical gates in quantum computing. We have used a micro-magnet technique to prepare two spin qubits with a double quantum dot and performed combined operation of spin rotation and spin exchange coupling to control the degree of spin entanglement as a function of exchange coupling operation time.

The concept of non-local entanglement is well established for correlated photon pairs and provides a technique of quantum teleportation. However, it has never been established in solid state systems because of the technical difficulty. We use a double dot Josephson junction to study the non-local entanglement. The splitting of Cooper pairs into both dots may contribute to generate supercurrent, because Cooper pair tunnelling through the same dot is strongly suppressed by the electron-electron interaction. We observe the supercurrent depending on the double dot charge state and discuss the contribution from the split Cooper pair tunnelling to the supercurrent.