Liu-Yong Cheng

Quantum state engineering with nitrogen-vacancy centers coupled to low-Q microresonator

We demonstrate efficient schemes of deterministic entanglement generation and quantum state transfer (QST) with the nitrogen-vacancy (NV) centers in diamond confined in separated microtoroidal resonators via single-photon input-output process. Assisted by the polarization of input photon pulse and the electron spin state of NV center, high fidelity NV center entangled states and photonic entangled states can be generated, respectively. The analyses of experimental feasibility show that our schemes work well with low quality resonators and weak coupling between qubits, which may be beneficial for exploring large-scale quantum information processing with diamond-based solid-state devices.

Counterfactual entanglement distribution without transmitting any particles.

To date, all schemes for entanglement distribution needed to send entangled particles or a separable mediating particle among distant participants. Here, we propose a counterfactual protocol for entanglement distribution against the traditional forms, that is, two distant particles can be entangled with no physical particles travel between the two remote participants. We also present an alternative scheme for realizing the counterfactual photonic entangled state distribution using Michelson-type interferometer and self-assembled GaAs/InAs quantum dot embedded in a optical microcavity. The numerical analysis about the effect of experimental imperfections on the performance of the scheme shows that the entanglement distribution may be implementable with high fidelity.

Simple schemes for universal quantum gates with nitrogen-vacancy centers in diamond

We propose efficient schemes for universal quantum gates with the photon polarization states and electron spin states of nitrogen-vacancy (NV) centers in diamond embedded in optical microcavity. A hybrid polarization-spin controlled-NOT gate and a two-qubit controlled phase gate between NV centers in separated cavities are demonstrated in the weak-coupling regime without complex devices or interaction. The gates presented here are deterministic and can be applied directly to a variety of quantum information processing tasks. The feasibility analyses show that our schemes can be accomplished with high fidelity under current technologies and have wide potential applications in quantum communication and computation fields.

Generation of two-atom Knill–Laflamme–Milburn states with cavity quantum electrodynamics

This paper proposes two schemes to generate the two-atom Knill–Laflamme–Milburn states with a strong coupling cavity-fiber system and the cavity-assisted single-photon input-output process, respectively. The significant logical operations for the generation are constructed accurately. The resonant interactions between atoms and photons in the two schemes imply a relatively short operation time, and the probabilities of successful generation are near to unity under the current experimental conditions.

Realization of nondestructive multi-atom cluster state analyzer via the cavity input---output process

We propose a deterministic scheme to realize four-atom and five-atom cluster state analyzers based on the cavity input–output process. In the scheme, we construct a multi-qubit parity analyzer and two cluster state phase analyzers and show that all the orthogonal multi-atom cluster states can be completely identified in a nondestructive way by combining these two kinds of analyzers. The fidelities of analyzers are also calculated, which show that our scheme has a high performance in the intermediate coupling region. Furthermore, the scheme opens promising perspectives for large-scale Bell-state-measurement-based and cluster-state-measurement-based quantum communication and quantum information processing networks.

Quantum state manipulation of dipole emitters with a plasmonic double-bar resonator

We demonstrate efficient processes of entanglement generation and quantum state transfer (QST) with dipole emitters coupled to a plasmonic double-bar resonator. The bipartite and multipartite maximal entanglement and complete QST can be deterministically achieved by selecting appropriate coupling strength between individual emitters and the resonator mode. Moreover, the entanglement dynamics show that high fidelities of entanglement generation and QST can be realized even under imprecise coupling strength and the system decay. The feasibility analysis and practical implementation are discussed, which manifest that our schemes may be meaningful for exploring solid-state quantum information processing with the metal plasmonic mode.