Surface plasmon polariton excitation and manipulation by nanoparticle arrays

Using a vectorial dipolar model for multiple surface plasmon-polariton (SPP) scattering [T. Søndergaard, S.I. Bozhevolnyi, Phys. Rev. B 67 (2003) 165405], we investigate the possibility of simultaneous SPP excitation and in-plane manipulation with square-lattice arrays of nanoparticles. The SPP excitation followed by focusing and/or waveguiding of SPP waves is observed with nanoparticle arrays of different shapes, demonstrating the feasibility of the suggested approach.     

On the propagation characteristics of metal clad waveguides with a quantum well

The electromagnetic modes of planar metal clad dielectric waveguides containing an n-doped quantum well (QW) are studied theoretically. Special attention is paid on the coupling between metal surface plasmons and intersubband plasmons and the manifestation of this coupling in the propagation characteristics of metal/QW/dielectric and multimode metal/QW/dielectric/metal waveguide structures. The results obtained indicate that the modification of the propagation characteristic induced by the above-mentioned coupling is substantial only in the case of metal/QW/dielectric waveguide structures.     

Analysis of nonclassical behavior for a two-mode coupled-photon system

We consider a model two-mode coupled-photon system and verify that the photon distribution for this system is exactly super-Poissonian. We calculate the Glauber–Sudarshan diagonal P representation for both the individual photon subsystem and the complete photon–photon complex. We present the detailed analysis on the threshold temperature of the nonclassical behavior for the both cases. We discuss the effect of the interaction between two photons on the threshold temperature.     

Plasmon mechanism of light transmission through a metal film or a plasma layer

It is shown that a smooth metal film (or a plasma layer) can be made transparent for an electromagnetic wave when two identical subwavelength diffraction gratings are placed on both sides of the film. The electromagnetic wave transmission through the metal film is caused by excitation of evanescent surface waves (plasmons) and their transformation into propagating waves at the gratings. A model which is developed analytically shows that the problem of the wave transmission is physically equivalent to the problem of excitation of two coupled resonators of evanescent waves which are formed at the two film surfaces.     

Continuous Variable Entanglement and Violation of Bell Inequality for Two Modes in a Three-Level Cascade Atomic System

Continuous variable entanglement and violation of Bell inequality for two modes are investigated in a three-level cascade atomic system. Entanglement of the system is demonstrated according to the entanglement criterion [Phys. Rev. Lett. 84 （2000）2722]. Violation of Bell inequality is studied within the framework of a quantum theory of multiwave mixing. It is shown that there are some states that are entangled but do not violate the Bell inequality.     

Entanglement transfer from photon-subtracted and photon-added two-mode squeezed fields to a pair of qubits

We investigate the entanglement transfer from a bipartite non-Gaussian continuous-variable (CV) system to a pair of localized qubits. The non-Gaussian state is obtained by the de-Gaussification process involving subtracting photons from or adding photons to a Gaussian field. It is shown that such de-Gaussification process can improve the entanglement transfer.     

A simplified scheme for realizing multi-atom NOON state

We present a scheme for realizing a multi-atom NOON state via cavity QED system. The scheme bases on the Jaynes-Cumming mode with collective atomic bosonic mode. In the process, a series of control atoms are sent through two single mode cavities which are initially in vacuum states and have the same collective atoms. After the suitable interaction time, the collective atoms in two cavities are in the desired state.     

Effective generation of polarization-entangled photon pairs in a cavity-QED system

We propose a cavity-QED scheme to effectively generate Einstein-Podolsky-Rosen polarization-entangled photon pairs. Assisted by a classical π-polarized pump field, a tripod four-level atom successively couples to two high-Q optical cavities possessing polarization degeneracy. Through stimulated Raman adiabatic passage process the polarization-entangled photon pairs can be produced.     

Modulation of Splitting Beam Angle with Metal--Nonlinear Optical Material--Metal (M-NL-M) Array Structure

We demonstrate active manipulating plasmonic signals with metal--nonlinear optical material--metal (M-NL-M) arrays consisting of slits with variant widths. The parameters of the M-NL-M array structure are derived by theoretical analysis of dispersion relationship. The splitting angle can be modulated by the incident light intensity, and verified by a nonlinear two-dimensional finite difference time domain method. The physical principle of this phenomenon is analysed from the phase of surface plasmon polaritons and Fabry--Pérot (F-P) resonance in slits     

The generation of Entangled Qudits and their Application in Probabilistic Superdense Coding

A scheme of the generation of entangled qutrits is presented, and then is generalized to entangled ququads and entangled qudits. With the entangled qutrits, an experimental scheme of probability superdense coding with only linear optical elements is proposed. It is shown that this scheme will be suitable for the entangled ququads, even for the entangled qudits if some nonlinearity is used. This scheme is feasible in the laboratory with the current experimental technology.     

Enhanced squeezing and entanglement in a non-degenerate three-level cascade laser with injected squeezed light

We consider a non-degenerate three-level cascade laser coupled to a two-mode squeezed vacuum reservoir via the lossy single-port mirror. Applying the pertinent master equation, we analyze the effects of the injected squeezed light on the quadrature squeezing, entanglement and normalized intensity difference fluctuations. We show that the injected squeezed light considerably enhances the degree of squeezing and entanglement in the two-mode light for certain initial conditions. Moreover, the injected squeezed light increases the mean photon number where the squeezing and entanglement is significant. We also show that the presence of the injected squeezed light greatly reduces the noise in the intensity difference.     

Numerical Investigation of Surface Plasmons Associated Subwavelength Optical Single-Pass Effect

Surface plasmons （SPs） associated optical single-pass effect has been investigated in novel subwavelength metallic structures, including single slit and grating structures. With influence of SPs, these metallic structures can enhance transmission in incident direction and suppress it in the opposite direction, exhibiting a single-pass effect. The finite difference time domain method is employed to study the influences of structure parameters on far-field transmission, near-field electric field distribution and extinction ratio of the single-pass transmission effect. A maximal extinction ratio of 47.83dB is achieved in the grating structure.     

Entanglement between two atoms in two distant cavities connected by an optical fiber beyond strong fiber-cavity coupling

This paper investigates entanglement between two atoms in two distant cavities, which are connected by an optical fiber. We give an exact expression of the evolution of the whole system, and study the entanglement between the two atoms. We find that even the fiber-cavity coupling constant is smaller than the atom-cavity coupling constant, high degree entanglement between the two atoms is obtainable. This result gives a new prospect for experimental realization.     

Optical Realization of Deterministic Entanglement Concentration of Polarized Photons

We propose a scheme for optical realization of deterministic entanglement concentration of polarized photons. To overcome the difficulty due to the lack of sufficiently strong interactions between photons, teleportation is employed to transfer the polarization states of two photons onto the path and polarization states of a third photon, which is made possible by the recent experimental realization of the deterministic and complete Bell state measurement. Then the required positive operator-valued measurement and further operations can be implemented deterministically by using a linear optical setup. All these are within the reach of current technology.     

Generation of Multiple-Photon GHZ State via Cavity-Assisted Interaction

We propose a scheme for preparing multiple-photon GHZ state via cavity-assisted interaction. There are n-pair single-photon pulses successively injected and reflected from two sides of the cavity, which traps one atom. After the atomic state is measured, a 2n-photon GHZ state is produced. In the ideal case, the successful probability of the scheme is close to unity.     

Efficient atomic quantum memory for photonic qubits in cavity QED

We investigate a scheme of atomic quantum memory to store photonic qubits of polarization in cavity QED. It is observed that the quantum state swapping between a single-photon pulse and a Λ-type atom can be made via scattering in an optical cavity [T. W. Chen, C. K. Law, P. T. Leung, Phys. Rev. A 69 (2004) 063810]. This swapping operates limitedly in the strong coupling regime for Λ-type atoms with equal dipole couplings. We extend this scheme in cavity QED to present a more feasible and efficient method for quantum memory combined with projective measurement. This method works without requiring such a condition on the dipole couplings. The fidelity is significantly higher than that of the swapping, and even in the moderate coupling regime it reaches almost unity by narrowing sufficiently the photon-pulse spectrum. This high performance is rather unaffected by the atomic loss, cavity leakage or detunings, while a trade-off is paid in the success probability for projective measurement.     

Generation of multi-mode-entangled light

We propose a scheme to generate three-mode-entangled lights by means of the interaction between the four-level atoms and a three-mode cavity. We deduce the master equation of the cavity field and prove the existence of the three-mode entanglement by employing the criterion of positivity of partial transpose. We also discuss the effects of the initial atomic state and of the Rabi frequency of the classical pumping field on the entanglement and amplification.     

Preparation of Entanglement of Atoms and of Photons via Cavity Input-Output Process

We propose a method to prepare multipartite entangled states such as cluster states and graph states based on the cavity input-output process and single photon measurement. Two quantum gates, a controlled phase gate and a fusion gate between two atoms trapped in respective cavities, are proposed to prepare atomic cluster states and graph states with one and two dimensions. We also introduce a scheme that can generate an arbitrary multipartite photon duster state which uses two coherent states as a qubit basis.     

Teleporting an Unknown Two-qubit Entangled State via Ion-Trap Systems

We propose a scheme for teleportation of an unknown two-qubit entangled state via trapped ions. In this scheme, we use the GHZ state as a quantum channel and the success probability can reach 1. The distinct advantage of our scheme is insensitive to the heating of the vibrational mode. In addition, Bell-state measurement is not required.     

Tripartite Entanglement via Microwave Driven Atomic Coherence

We propose a new scheme to achieve the tripartite entanglement based on the standard criteria [Phys. Rev. A 67（2003） 052315] in a inverse-tripod atomic system. In our scheme, the atomic coherence is introduced by two microwave fields which drive the upper three levels of atom. By numerically simulating the dynamics of system, we investigate the generation and evolution of entanglement in the presence of atom and cavity decay. As a result, the present research provides an efficient approach to achieve fully tripartite entanglement with different frequencies and initial states for each entangled mode, which may have impact on the progress of multicolored multi-notes quantum information networks.