We propose a scheme to control the coupling between the charge qubit and the nitrogen-vacancy center ensemble (NVCE). The coupling is mediated by a large Josephson junction (JJ) and a flux qubit. The large JJ can be treated classically and behaves like an effective inductance to switch the coupling between the charge and flux qubits. The flux qubit serves as a bridge to couple the NVCE and the charge qubit, and quantum state transfer can be implemented, with the NVCE acting as a memory unit. The hybrid circuit can reinforce various advantages: controllability of the charge qubit and robust spin coherence of the NVCE.
The negatively charged nitrogen-vacancy defect (NV)
− in diamond has attracted much attention in recent years in qubit and biological applications. The negative charge is donated from nearby nitrogen donors that could limit or stem the successful application of (NV)
−. In this Letter, we unambiguously identify the \emph{neutral} nitrogen-vacancy defect (NV
0) by \emph{ab initio} supercell calculations. Our analysis shows that i) the spin state can be \emph{selectively} occupied optically, ii) the electron spin state can be manipulated by time-varying magnetic field, and iii) the spin state may be read out optically. Based on this NV
0 is a new hope for realizing qubit in diamond \emph{without} the need of nitrogen donors.
The negatively charged nitrogen-vacancy (NV) defect (NV center) in diamond is a leading candidate to realize solid-state qubits and ultrasensitive magnetometers in ambient conditions. A new interpretation of some of the properties of the center is presented. We show that the double peak in the absorption phonon sidebands may correspond to the local a 1 and e vibration modes of the defect that have very similar energies, and that tunneling of nitrogen atoms in the vacancy does not occur as had been previously suggested.