Wang Hong-Fu

Two-qubit and three-qubit controlled gates with cross-Kerr nonlinearity

Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper. The probability of the success of these gates can be increased by quantum nondemolition detectors, which are used to judge which paths the signal photons pass through. These schemes are almost deterministic and require no ancilla photon. The advantages of these gates over the existing ones include less resource consumption and a higher probability of success, which make our schemes more feasible with current technology.

Scheme for generating a cluster-type entangled squeezed vacuum state via cavity QED

A scheme is proposed to generate an N-qubit cluster-type entangled squeezed vacuum state (CTESVS) based on the two-photon interaction between a two-level atom and the cavity fields with the cavity QED system. The CTESVS in N separate cavities can be effectively obtained after performing a simple one-qubit measurement on the atom. The influence of cavity decay on the CTESVS is also discussed.

Generating a four-photon polarization-entangled cluster state with homodyne measurement via cross-Kerr nonlinearity

We propose a protocol to generate a four-photon polarization-entangled cluster state with cross-Kerr nonlinearity by using the interference of polarized photons. The protocol is based on optical elements, cross-Kerr nonlinearity, and homodyne measurement, therefore it is feasible with current experimental technology. The success probability of our protocol is optimal, this property makes our protocol more efficient than others in the applications of quantum communication.

Quantum superdense coding based on hyperentanglement

We present a scheme for quantum superdense coding with hyperentanglement, in which the sender can transfer four bits of classical information by sending only one photon. The important device in the scheme is the hyperentangled Bell-state analyzer in both polarization and frequency degrees of freedom, which is also constructed in the paper by using a quantum nondemolition detector assisted by cross-Kerr nonlinearity. Our scheme can transfer more information with less resources than the existing schemes and is nearly deterministic and nondestructive.

Universal quantum computation using all-optical hybrid encoding

By employing displacement operations, single-photon subtractions, and weak cross-Kerr nonlinearity, we propose an alternative way of implementing several universal quantum logical gates for all-optical hybrid qubits encoded in both single-photon polarization state and coherent state. Since these schemes can be straightforwardly implemented only using local operations without teleportation procedure, therefore, less physical resources and simpler operations are required than the existing schemes. With the help of displacement operations, a large phase shift of the coherent state can be obtained via currently available tiny cross-Kerr nonlinearity. Thus, all of these schemes are nearly deterministic and feasible under current technology conditions, which makes them suitable for large-scale quantum computing.By employing displacement operations, single-photon subtractions, and weak cross-Kerr nonlinearity, we propose an alternative way of implementing several universal quantum logical gates for all-optical hybrid qubits encoded in both single-photon polarization state and coherent state. Since these schemes can be straightforwardly implemented only using local operations without teleportation procedure, therefore, less physical resources and simpler operations are required than the existing schemes. With the help of displacement operations, a large phase shift of the coherent state can be obtained via currently available tiny cross-Kerr nonlinearity. Thus, all of these schemes are nearly deterministic and feasible under current technology conditions, which makes them suitable for large-scale quantum computing.

Dissipative preparation of a steady three-dimensional entangled state via quantum-jump-based feedback

A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a Λ-type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.

Implementation of nonlocal Bell-state measurement and quantum information transfer with weak Kerr nonlinearity

We propose a protocol to implement the nonlocal Bell-state measurement, which is nearly determinate with the help of weak cross-Kerr nonlinearities and quantum non-destructive photon number resolving detection. Based on the nonlocal Bell-state measurement, we implement the quantum information transfer from one place to another. The process is different from conventional teleportation but can be regarded as a novel form of teleportation without entangled channel and classic communication.

Time-bin-encoding-based remote states generation of nitrogen-vacancy centers through noisy channels*

We design proposals to generate a remote Greenberger–Horne–Zeilinger (GHZ) state and a W state of nitrogen-vacancy (NV) centers coupled to microtoroidal resonators (MTRs) through noisy channels by utilizing time-bin encoding processes and fast-optical-switch-based polarization rotation operations. The polarization and phase noise induced by noisy channels generally affect the time of state generation but not its success probability and fidelity. Besides, the above proposals can be generalized to n-qubit between two or among n remote nodes with success probability unity under ideal conditions. Furthermore, the proposals are robust for regular noise-changeable channels for the n-node case. This method is also useful in other remote quantum information processing tasks through noisy channels.

Implementation of unambiguous comparison for unknown pure quantum states with cavity-assisted interaction

We propose two effective schemes for local and remote unknown atomic state comparisons with a cavity-assisted single photon input—output process without any initial entanglement or auxiliary resource. The unambiguous state discrimination is considered using the state comparison process as the basic module. All the implementation schemes here just involve common quantum logic gates and the single qubit measurement. The analysis shows that our schemes are feasible under the current experimental conditions.

Deterministic implementations of fermionic quantum SWAP and Fredkin gates for spin qubits based on charge detection

We propose a scheme to implement fermionic quantum SWAP and Fredkin gates for spin qubits with the aid of charge detection. The scheme is deterministic without the need of qubit—qubit interaction, and the proposed setups consist of simple polarizing beam splitters, single-spin rotations, and charge detectors. Compared with linear optics quantum computation, this charge-measurement-based qubit scheme greatly enhances the success probability for implementing quantum SWAP and Fredkin gates and greatly simplifies the experimental realization of scalable quantum computers with noninteracting electrons.