Research and Development

To make a practical quantum repeater, we need to have a long-lived quantum memory at the nodes. Our target is to make an interface between a photon as a transmission qubit and a nuclear spin as a memory qubit intermediated by an electron spin as a gate qubit.

Toward this purpose, we have several candidates such as semiconductor quantum dots, NV centers in diamond, and rare-earth impurities in non-linear crystal. Among those candidates this project focuses on NV centers in diamond which provide longest memory time and reasonable optical activity.

The project consists of four groups - Tohoku univ., Osaka univ., NTT, and NII. Each of them contributes different aspects as summarized bellow. The main task of Tohoku university group is to transfer the quantum state of a photon into a nuclear spin via an adjacent electron spin at an NV center. Osaka university group try to detect the entangled state stored in multiple nuclear spins. NTT group theoretically supports this entanglement detection by solving the decoupling problem between an electron spin and nuclear spins during the state transfer and gate operation. NII group theoretically supports the cavity design which is ideal for a practical quantum repeater which consists of hybrid systems.