NTT Research and Development 2012 Review of Activities

Overview

We have experimentally demonstrated a quantum memory operation in a superconductordiamond hybrid system. Quantum information manipulated in a superconducting flux qubit^*1 can be stored to and retrieved from an ensemble of nitrogen-vacancy (NV) centers^*2 in diamond. This technique holds the promise for a future implementation of an ultra-fast quantum processor equipped with a quantum memory that can maintain quantum states over a long time.

Features

• Diamond NV centers capable of long-term storage of quantum states (quantum memory).
• Superconducting flux qubits can be applied to quantum computation (quantum computing device).
• Gap-tunable superconducting flux qubits whose coupling to NV centers can be turned on and off.
• Quantum hybrid system that takes advantages of both systems.
• NV centers have transitions in both the microwave and optical bands.

Application scenarios

• Basic elements in the configuration of a quantum computer.
• Integration of a quantum computing device and a quantum memory for large-scale quantum computing.
• Quantum frequency conversion between the microwave and optical regimes.
• Quantum repeaters for long range quantum communication.

• *1 Superconducting flux qubit: A quantum bit for which the direction of current flow in a superconducting loop represents a 0 or 1 state.
• *2 Nitrogen-vacancy (NV) center: A complex defect in a diamond lattice formed by a vacancy (V) and by its neighboring nitrogen (N) replacing a carbon atom. The spin state of electrons captured by an NV center stores quantum information.