Qiong Chen

Entanglement dynamics for three nitrogen-vacancy centers coupled to a whispering-gallery-mode microcavity

The solid-state qubits based on diamond nitrogen-vacancy centers (NVC) are promising for future quantum information processing. We investigate the dynamics of entanglement among three NVCs coupled to a microtoroidal cavity supporting two counter-propagating whispering-gallery-modes (WGMs) in the presence of Rayleigh scattering. Our results indicate that the maximal entanglement among all the NVCs could be achieved through adjusting several key parameters, such as the scattering-induced coupling between the WGMs, the distance between the NVCs, and the NVC-WGM coupling strengths, as well as the frequency detuning between the NVC and cavity. We show that entanglement of the NVCs displays a series of damped oscillations under various experimental situations, which reflects the intricate interplay and competition between the Rayleigh scattering and the NVC-WGM coupling. The quantum dynamics of the system is obtained via solutions to the corresponding microscopic master equation, which agrees well with the numerical simulation results using the phenomenological master equation. The feasibility of our proposal is supported by the application of currently available experimental techniques.

Nonlinear coupling between a nitrogen-vacancy-center ensemble and a superconducting qubit

By exchange of virtual microwave photon induced by a transmission line resonator, the nonlinear interaction between a nitrogen-vacancy-center ensemble (NVE) and a superconducting charge qubit is achieved in circuit quantum electrodynamics, where the nonlinear coupling results from the second order of the coupling between the magnetic field of the transmission line resonator and the charge qubit. In our case, the nonlinear coupling can be much enhanced by a factor of the total spin number in the NVE. As an application, we present a potentially practical scheme to realize the squeezing of the NVE using the nonlinear coupling, which is within reach of the currently available technology.

Grover search in decoherence-free subspace with low-Q cavities

By virtue of the single-photon input-output process, we present a potentially practical scheme for realization of a multi-qubit Grover search algorithm in decoherence-free subspace (DFS) with low-Q cavities. Our treatment considers the decay of the cavity, which favours the input and output of the single photons, and the DFS encoding suppresses the collective dephasing errors. We show that our scheme for the three-qubit Grover search in DFS would work using near-future available techniques.