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 together with reasonable optical activity.

The project consists of four groups – Yokohama national univ., Osaka univ., NTT, and NII. Each of them contributes different aspects as summarized below.

Subtheme 1: Quantum media conversion from a photon into a nuclear spin (Yokohama national univ.)
The main task of Yokohama national university group is to transfer the quantum state of a photon into a nuclear spin via an adjacent electron spin at an NV.
Subtheme 2: Enhancing Application Platform (Osaka univ.)
Osaka university group try to detect the entangled state stored in multiple nuclear spins.
Subtheme 3-1: Next Generation Quantum Key Distribution System Technology (NTT)
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.
Subtheme 3-2: : Long-term Operational Testing (NII)
NII group theoretically supports the cavity design which is ideal for a practical quantum repeater which consists of hybrid systems.
Theme drawing

For quantum entanglement purification between remote nodes, gate operation and entanglement detection between nuclear spins intermediated by an electron spin are needed besides the quantum media conversion. Furthermore, we have to solve the issue of fidelity degradation upon the system operation when we combine the quantum media conversion, gate operation, and entanglement detection.


Main result

Main result

Team 158B-T02 results summary

Task title Outcome Publications
1: Hybrid quantum repeater fundamental technology Development of quantum tomography technique based on initialization, manipulation, and readout of degenerate electron and nuclear spins in an NV center. Phys. Rev. Lett., 114, 053603 (2015).
Demonstration quantum state transfer from a photon to a nuclear spin via an electron spin with heralding function based on the quantum teleportation principle. Nature Photonics,10,507-511(2016).
Development of geometrical spin echo technique for enabling quantum media conversion and quantum gate operation with keeping quantum memory. Nature Communications, 7, 11668 (2016).
2: Hybrid quantum repeater purification technology Realization of 105 times gate operation within quantum memory lifetime. 28th International Conference on Defects in Semiconductors, (2015) [Invited]
Charge stabilization of NV center for faithful quantum non-demolition measurement towards complete Bell-state measurement. Physical Review B, 93, 081203 (R), 2016
Manipulation of three nuclear spin quantum entanglement Appl. Phys. Lett., 106, 153103 (2015).
3: Hybrid gate and optical module design Proposal of an expandable quantum repeater network with an optical module based on an NV center inside the optical cavity with optical input/output modes. New J. Phys., vol. 17, 103012 (2015)
Optimization of gate operations by considering the dynamics of the election and 15N & 13C nuclear spins in an NV center. New J. Phys., Vol. 16, 093043 (2014), Phys. Rev. A 89, 052317 (2014)
Design of the physical properties of three different module configurations with a cavity and a single NV center.  

Activity detail and results

1. Hybrid quantum repeater fundamental technology

(Yokohama National Univ.)



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2. Hybrid quantum repeater purification technology

(Osaka University)



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3. Hybrid gate and optical modulede sign



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Outlook (1/2)

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Outlook (2/2)

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