Constructing Robust Entangled Coherent GHZ and W States via a Cavity QED System

Using a system of three distant cavities, we propose a method for constructing tripartite entangled coherent GHZ and W states which are robust due to the photon losses in the cavities. Each of cavities is doped with a semiconductor quantum dot. By the dynamics, the excitonic modes of quantum dots are enabled to exhibit entangled coherent GHZ and W states. Apart from the exciton losses, the master equation approach shows that when the populations of the field modes in the cavities are negligible the destruction of entanglement due to dissipation arises from photon losses, is effectively suppressed.     

矩阵理论在半导体激光器耦合中的应用

傍轴近似下的光学矩阵理论,可以简化光束传输计算过程,使光学系统设计更为方便。将ABCD变换矩阵方法引入到耦合光学系统的设计中,运用高斯光束的ABCD法则,详尽地给出了某一耦合方式下的半导体激光器耦合入单模光纤系统的设计;另一方面,对系统的耦合损耗与耦合距离的关系进行了理论计算,并把计算结果与最近的实验报道做了比较,它们基本相吻合,说明此方法是可行的、合理的。从整个设计及理论计算来看,ABCD矩阵方法减少了复杂的计算,从而简化了设计过程,与通常的衍射计算相比,它不失为一种方便、有效的方法,同时它对生产半导体激光耦合器也有实际指导意义。     

Spatial modal control of two-dimensional photonic crystal Bragg lasers

We investigate the modal losses and field distributions of different order transverse modes supported by the photonic crystal Bragg structure using a transfer matrix method. We find that only the fundamental transverse mode has a single-lobed near field and far field and there exists a trade-off between ensuring lasing in the fundamental transverse mode and reducing the threshold. Employing these design principles, we experimentally demonstrate a large-area, edge-emitting, and single-mode semiconductor photonic crystal Bragg laser with a single-lobed, diffraction-limited far field under continuous wave condition.     

Stable spatial solitons in semiconductor optical amplifiers

The existence of stable dissipative spatial solitons at low intensities in patterned electrode semiconductor optical amplifiers (SOAs) is predicted theoretically. In contrast to conventional SOAs, this system may support stable solitons because the inherent saturating losses provide subcritical bifurcations for both the plane-wave and the soliton solution.     

用楔形柱面光纤微透镜耦合的1.3μm SOA组件

运用激光模式耦合理论分析了半导体光放大器(SOA)与单模通信光纤的连接损耗,并设计制作了楔形柱面光纤微透镜用来实现两者的模斑匹配,有效地降低了器件的光耦合损耗.本文介绍了楔形柱面光纤微透镜耦合的1.3 μm半导体光放大器(SOA)组件及其制作方法.该组件的最大增益不小于14 dB,其偏振灵敏度小于1 dB,增益波动不大于0.5 dB.     

New method for calculating the spectra and radiation losses of leaky waves in multilayer optical waveguides

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties of which are determined by antiresonant reflection from the multilayer cladding (antiresonant reflecting optical waveguides) rather than by total internal reflection from the core-cladding interface as in standard optical waveguides. The new method applies to calculation of both electromagnetic modes in dielectric waveguides and electron quantum states in multibarrier semiconductor heterostructures. The characteristics of multilayer waveguides calculated by the new method are compared with published data obtained from a complex dispersion relation by the transfer matrix method. As an example, the wavelength dependence of the radiation losses for the first TE mode of a planar optical waveguide containing 52 pairs of layers is calculated.     

Toward low-loss photonic crystal waveguides in InP/InGaAsP heterostructures

Line-defect photonic crystal waveguides exhibit severe propagation losses if they are implemented in semiconductor heterostructures with a weak refractive index contrast. We present, for what we believe is the first time, experimental structures for which we have evidence that fabrication imperfections are not the limiting factor in terms of propagation losses. We demonstrate a loss figure of 335±5 dB/cm, which is an improvement by a factor of about 2 with respect to state-of-the-art values. Simulations show that even lower losses can be obtained with different waveguide geometries. In other words, the dominant loss mechanism is related to the waveguide design, and losses are not expected to decrease upon further optimization of the fabrication process.     

Realization of temperature in semiconductor using optical principle

Owing to temperature is important for both elemental and compound semiconductor to study various properties, this paper presents a novel technique to measure the temperature in semiconductor at wavelength, 10.59 μm using optical principle. Here both reflection and absorption losses are considered to find out temperature in semiconductor. Reflectance is found using plane wave expansion method, where absorption factor is determined using Maxwell's curl equations. Simulation result reveals that reflectance and transmitted intensity vary linearly with respect to different temperatures. Apart from this, it is also seen that absorbance is zero for all semiconductor at wavelength 10.59 μm. The excellent linear variation of transmitted intensity gives an accurate measurement of temperature in semiconductors at aforementioned wavelength.     

Emergence of Anderson localization in plasmonic waveguides

The propagation of surface plasmon polaritons in dielectric loaded waveguides with randomly placed scatterers is studied using both numerical simulations and a simplified transfer matrix framework. Despite the importance of losses in this system, we find fingerprints of the localized behavior of one-dimensional disordered systems. Furthermore, losses amplify the impact of the necklace states on the transport properties for systems not much larger than the localization length. The system presented here also offers the possibility to use localization effects for engineering purposes by means of deliberately introduced disorder.     

Complex-envelope alternating-direction-implicit FDTD method for simulating active photonic devices with semiconductor/solid-state media

A complex-envelope (CE) alternating-direction-implicit (ADI) finite-difference time-domain (FDTD) approach to treat light-matter interaction self-consistently with electromagnetic field evolution for efficient simulations of active photonic devices is presented for the first time (to our best knowledge). The active medium (AM) is modeled using an efficient multilevel system of carrier rate equations to yield the correct carrier distributions, suitable for modeling semiconductor/solid-state media accurately. To include the AM in the CE-ADI-FDTD method, a first-order differential system involving CE fields in the AM is first set up. The system matrix that includes AM parameters is then split into two time-dependent submatrices that are then used in an efficient ADI splitting formula. The proposed CE-ADI-FDTD approach with AM takes 22% of the time as the approach of the corresponding explicit FDTD, as validated by semiconductor microdisk laser simulations.     

Exact solution in the damped Cummings-Tavis model and entanglement

An exact analytical expression is found for the density matrix of a system composed of a photon mode and two two-level dipole-dipole interacting atoms in a cavity with losses. The behavior of the atom-atom entanglement has been investigated on the basis of the Peres-Horodecki criterion.     

Waveguide modulated non-local optical interaction of semiconductor microdisks

The non-local optical interaction of two semiconductor microdisks with a waveguide bridged at radial direction is proposed and studied by three dimensional finite-difference time-domain （FDTD） electromagnetic simulations. The strong and weak optical interactions between two microdisks are observed and ascribed to the internal coupled modes with different coupling ratios. The vertical radiation losses and the related mode quality factors are modulated by waveguide length and present oscillation characteristics for the resonant modes. In addition, the optical leakage of coupling system is affected by the etching depth of disks due to tile emission of minor components of electric field.     

Density matrix tomography through sequential coherent optical rotations of an exciton qubit in a single quantum dot

We demonstrate single qubit density matrix tomography in a single semiconductor quantum dot system through consecutive phase sensitive rotations of the qubit via ultrafast coherent optical excitations. The result is important for quantifying gate operations in quantum information processing in the quantum dot systems as well as demonstrating consecutive arbitrary qubit rotations.     

Surface electromagnetic waves at the interface between dissipative porous nanocomposite and hypercrystal under different temperatures

In the current paper the properties of surface plasmon polaritons as well as hybrid polarized surface electromagnetic waves at the plane interface of a porous semiconductor nanomaterial and a hypercrystal are studied theoretically and numerically. The nanomaterial, as well as the hypercrystal, is made of n-type doped indium antimonide (n-InSb) semiconductor layers. The losses which inherent to the semiconductor materials are taken into account. To describe the properties of the constituent semiconductor layers the approximate analytical temperature models for concentration and mobility of conduction electrons are applied. This allows to consider the effect of electron scattering on the properties of supported electromagnetic modes in the wide frequency range. The contacting materials are considered in the subwavelength approximation when it is possible to introduce the effective permittivity components. It is shown that taking into account dissipation processes in the semiconductor constituent layers result in the appearance of additional surface modes branches, changes in the surface waves penetration depth, frequency and angular existence domains.     

Closed-loop design of a semiconductor laser

We provide what we believe is the first closed-loop prediction of a semiconductor laser performance using fully microscopic many-body models for the spontaneous emission, gain, and carrier recombination losses due to Auger processes without having to resort to phenomenological adjustable fit parameters.     

AC losses in multifilamentary Bi(2223) tapes with an interfilamentary resistive carbonate barrier

For the most common AC application frequencies, the main component of the AC losses in multifilamentary Bi(2223) tapes are caused by hysteresis- and coupling losses. These losses can be reduced enhancing the matrix resistivity and applying a twist to the filaments. We report on the AC loss properties of 37-filament tapes with AgAu (8 wt.%) matrix, and novel 19-filament tapes with SrCO₃ barriers between the filaments. We performed transport AC loss and magnetic AC loss measurements in parallel and perpendicular magnetic fields. Both kinds of tapes were also prepared with filament twists below a twist pitch of 20 mm. The influence of the different tape modifications on the AC loss behaviour is presented and compared with theoretical models to understand the effect of the resistive matrix. In the case of magnetic AC loss measurements, reduced AC losses due to decoupled filaments were observed for the twisted tapes with a resistive matrix in low parallel fields.     

Quantum information transmission between two qubits through an intermediary photon gas

The theory of the quantum information transmission between two semiconductor two-level quantum dots as two qubits through an intermediary photon gas in a cavity is presented. The reduced density matrix of each two-level quantum dot is the quantum information encoded into this qubit. The quantum information exchange between two distant qubits imbedded in the photon gas is performed in the form of the mutual dependence of their reduced density matrices due to the interaction between the electrons in the qubits and the photon gas. The system of rate equations for the reduced density matrix of the two-qubit system is derived. From the solution of this system of equations it follows the mutual dependence of the reduced density matrices of two distant qubits.