有心结构耦合腔系统中的几何量子失谐（英文）

引入了由N+1个单模腔构成的有心结构耦合腔物理模型.其中,中心腔起耦合器作用,其余N个腔通过N条光纤与中心腔耦合,并且每个腔囚禁1个二能级原子.在系统激发数等于1的情况下,给出了系统态矢的演化规律,研究了两原子间和两腔场间的几何量子失谐.通过数值计算,讨论了耦合腔数目和原子与腔场间耦合强度对几何量子失谐的影响.研究结果表明:随着腔数目的增加两原子间和两腔场间的几何量子失谐都减弱;随着原子与腔场间耦合系数增大,两原子间几何量子失谐减弱,但两腔场间几何量子失谐却加强.     

Λ型和V型三能级原子与耦合腔相互作用系统中的纠缠特性

研究了由一个Λ型三能级原子、一个V型三能级原子和光纤连接的双模腔构成的系统,给出了系统态矢的演化. 采用部分转置密度矩阵的负本征值来描述两个子系统间的纠缠,利用数值计算方法研究了原子与原子之间和腔场与腔场之间的纠缠特性. 讨论了光纤模与腔场间的耦合强度对纠缠特性的影响. 研究结果表明:随光纤模与腔场间的耦合强度增强,原子间的纠缠和腔场间的纠缠均增强. 关键词： 量子光学 原子-腔-光纤复合系统 三能级原子 量子纠缠     

Entanglement Properties in a Star Structure Coupled Cavities System

In this paper, the star structure coupled cavities system is composed of six single-mode cavities. One of them is at the center of the star structure, and other five cavities are at the five vertices of the star structure, respectively. The center cavity is connected with other five cavities by optical fibers. The situation is considered that six identical two-level atoms are separately trapped in six single-mode optical cavities, each atom resonantly interacts with cavity via a one-photon hopping, and the total excitation number of the system equals one. Negativity is adopted to quantify the degree of entanglement between two subsystems. The entanglement properties between atoms and that between cavities are investigated. The influences of atom-cavity coupling coefficient on the entanglement properties between two subsystems are studied. The results obtained using the numerical method show that the atom-atom entanglement is weakened, and the cavity-cavity entanglement is strengthened with the increase of atom-cavity coupling coefficient.

     

Geometrical Quantum Discord in the Coupled Cavities System with Tetrahedral Structure

In this paper we consider the situation that four identical two-level atoms are separately trapped in four single-mode optical cavities, which are placed at the vertices of a tetrahedron and coupled by six fibers. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the schrödinger equation when the total excitation number of the system equals one. The geometrical quantum discords between atoms and between cavities are investigated. The effects of cavity-fiber coupling coefficient on the geometrical quantum discords between atoms and between cavities are discussed. The results obtained using the numerical method indicate that the geometrical quantum discords between atoms and between cavities are all weakened with increase of cavity-fiber coupling coefficient.

     

大型LTD装置功率源可靠性初步分析

产生脉冲电流约50 MA的大型LTD装置功率源由数十万个电容器、开关和触发器组成。规模庞大的功率源采用串联系统可靠性模型,其可靠度想要达到一个较高的水平,存在所要求的开关可靠度难以实现的情况。大型LTD装置功率源的主要故障模式为开关自击穿和触发器故障,开关自击穿将导致其所在的模块故障,而触发器一对多的触发方式,使其故障时引起更多的模块故障。在LTD装置输出性能满足要求的前提下,允许存在一定数量的模块故障,并且控制故障模块分布,是实现功率源高可靠度的关键。基于概念设计的大型LTD装置功率源构成框架,分别建立了在功率源、支路、分层上控制故障模块数量的可靠性模型。采用蒙特卡罗方法对该模型进行仿真计算,得出了在给定的功率源可靠度条件下开关和触发器需要达到的可靠度。为实现该可靠性模型,使故障模块不对其他部分产生影响,还对故障模块隔离技术进行了分析。     

Dynamical Properties of Two Coupled Dissipative QED Cavities Driven by Coherent Fields

When two identical QED cavities driven by the coherent fields are located in a uniform environment, in addition to dissipation, there appears an indirect coupling between the two cavities induced by the background fields. We investigate the effects of the coherent fields, the dissipation as well as the incoherent coupling on the following dynamical properties of the system: photon transfer, reversible decoherence, and quantum state transfer, etc. We find that the photons in the cavities do not leak completely into the environment due to the collective coupling between the cavities and the enviroment, and the photons are transferred irreversibly from the cavity with more photons to the cavity with less ones due to the incoherent coupling so that they are equally distributed among the two cavities. The coherent field pumping on the two cavities increases the mean photons, complements the revived magnitude of the reversible decoherence, but hinders the quantum state transfer between the two cavities. The above phenomena may find applications in quantum communication and other basic fields.     

Dynamical Properties of Two Coupled Dissipative QED Cavities Driven by Coherent Fields

When two identical QED cavities driven by the coherent fields are located in a uniform environment, in addition to dissipation, there appears an indirect coupling between the two cavities induced by the background fields. We investigate the effects of the coherent fields, the dissipation as well as the incoherent coupling on the following dynamical properties of the system： photon transfer, reversible decoherence, and quantum state transfer, etc. We find that the photons in the cavities do not leak completely into the environment due to the collective coupling between the cavities and the enviroment, and the photons are transferred irreversibly from the cavity with more photons to the cavity with less ones due to the incoherent coupling so that they are equally distributed among the two cavities. The coherent field pumping on the two cavities increases the mean photons, complements the revived magnitude of the reversible decoherence, but hinders the quantum state transfer between the two cavities. The above phenomena may find applications in quantum communication and other basic fields.     

Triple optomechanical induced transparency in a two-cavity system

We theoretically investigate the optomechanical induced transparency(OMIT) phenomenon in a two-cavity system which is composed of two optomechanical cavities. Both of the cavities consist of a fixed mirror and a high-Q mechanical resonator, and they couple to each other via a common waveguide. We show that in the presence of a strong pump field applied to one cavity and a weak probe field applied to the other, a triple-OMIT can be observed in the output field at the probe frequency. The two mechanical resonators in the two cavities are identical, but they lead to different quantum interference pathways. The transparency windows are induced by the coupling of the two cavities and the optical pressure radiated to the mechanical resonators, which can be controlled via the power of the pump field and the coupling strength of the two cavities.     

Photonic spectral density of coupled optical cavities

We study a pair of anharmonic optical cavities that is connected by an optical fiber. The photonic spectral density characterizes the evolution of the coupled cavities after the system has been prepared in a Fock or N00N state. We evaluate the photonic spectral density within the recursive projection method and find that the anharmonicity leads to a collapse of the low-energy spectrum. The level spacing of the remaining spectrum agrees quite well with that of the harmonic cavities, whereas the spectral weights are strongly affected by the anharmonicity.     

原子与耦合腔相互作用系统中的量子失协

本文研究由两个全同的二能级原子和耦合腔构成的系统,利用Dakic等提出的几何量子失协的度量方法,采用数值计算方法计算了系统中两原子间和两腔场间量子失协的演化.讨论了原子间初始纠缠度和腔场间耦合系数变化对几何量子失协演化的影响.研究发现:随腔场间耦合系数的增大,量子失协周期性演化的频率增大;随原子间初始纠缠度的增大,两原子间的关联增强,两腔场间的关联减弱.     

Adjustable quantum coherence effects in a hybrid optomechanical system

We propose a system for achieving some adjustable quantum coherence effects, including the normal-mode splitting(NMS), the optomechanically induced transparency(OMIT), and the optomechanically induced absorption(OMIA). In this system, two tunnel-coupled optomechanical cavities are each driven by a coupling field and coupled to an atomic ensemble.Besides, one of the cavities is also injected with a probe field. When the system works under different conditions, we can obtain the NMS, the OMIT, and the OMIA, respectively. These effects can be flexibly adjusted by the tunnel coupling between the two cavities, the power of the coupling lasers, and the coupling strength between the atomic ensembles and the cavity fields. Furthermore, we can realize the OMIT even if the oscillating mirrors have relatively larger decay rates.     

Fabrication and characterization of high-quality-factor silicon nitride nanobeam cavities

We present the fabrication and characterization of high-quality-factor (Q) Si3N4 photonic crystal nanobeam cavities at visible wavelengths for coupling to nitrogen-vacancy centers in a cavity QED system. Confocal microphotoluminescence analysis of the nanobeam cavities demonstrates quality factors up to Q ~ 55,000, which are limited by the resolution of our grating spectrometer. This is a 1-order-of-magnitude improvement over previous SiNx cavities at this important wavelength range. We also demonstrate coarse tuning of cavity resonances across 600-700?nm by lithographically scaling the size of fabricated devices.     

Protection of entanglement between two V-atoms in a multi-cavity coupling system

The protection of the entanglement between two V-atoms(EBTVA)in a multi-cavity coupling system is studied.The whole system consists of two V-atoms.The two V-atoms are initially in the maximum entangled state and interacts locally with its own dissipative cavity which is coupled to the external cavities with high quality factor(ECWHQF).The results show that,when there is no ECWHQF,the EBTVA can be protected effectively in the case where the V-atom and the dissipative cavity are weak coupled in large detuning,while when there are different numbers n of ECWHQF coupled to two dissipative cavities,by adjusting the parameters of the number n of ECWHQF and the coupling strength k between cavities,the EBTVA can be protected perfectly and continuously.Our result provides an effective method for protecting entanglement resources of three-level system.     

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.     

原子与耦合腔相互作用系统中的纠缠特性

研究了耦合腔A和B中各囚禁一个二能级原子的情况,给出了总激发数为2时系统态矢的演化.利用Negativity熵度量两子系统间的纠缠,采用数值计算方法研究了两个原子之间、腔内原子与腔场之间和两个腔场之间的纠缠性质.讨论了腔场间的耦合强度对纠缠特性的影响.研究结果表明:原子1和原子2处于分离态.另一方面,随腔场间耦合系数增大腔场间的纠缠和原子与腔场间的纠缠减小.     

原子与耦合腔相互作用系统中的纠缠特性

研究了耦合腔A和B中各囚禁一个二能级原子的情况,给出了总激发数为2时系统态矢的演化.利用Negativity熵度量两子系统间的纠缠,采用数值计算方法研究了两个原子之间、腔内原子与腔场之间和两个腔场之间的纠缠性质.讨论了腔场间的耦合强度对纠缠特性的影响.研究结果表明:原子1和原子2处于分离态.另一方面,随腔场间耦合系数增大腔场间的纠缠和原子与腔场间的纠缠减小.     

Remote entanglement for quantum networks

Quantum networks are distributed many-body quantum systems with tailored topology and controlled information exchange. We present two schemes to generate remote entanglement, in atomic external degrees of freedom and between cavities. In the first scheme, we entangle two atoms with their cavities in momentum space through Bragg diffraction. Thereafter, in order to trace out the cavities, we let resonantly interact an auxiliary atom with each cavity. In the last, we perform quantum measurement on two auxiliary atoms and get remote entangled state in atomic external degrees of freedom. In the second scheme, we have a three cavities system. The other two cavities, A and B, are entangled with indistinguishable modes of cavity, C. Performing quantum measurement on third cavity, C, we disentangle it from the system and the cavities, A and B, become entangled.     

Nuclear electric quadrupole interactions in liquids entrapped in cavities

Liquids entrapped in cavities and containing quadrupole nuclei are considered. The interaction of the quadrupole moment of a nucleus with the electric field gradient is studied. In such a system, molecules are in both rotational and translational Brownian motions which are described by the diffusion equation. Solving this equation, we show that the intra- and intermolecular nuclear quadrupole interactions are averaged to zero in cavities with the size larger than several angstroms.     

Entanglement Generation Between Two Mechanical Resonators in Two Optomechanical Cavities

A standard model is suggested to explore correlation features of two spatially separated optomechanical cavities. The cavities are coupled through the photon-hopping process. In particular, we investigate the generation of entanglement between mechanical resonators in the strong coupling regime and the two cavities are assumed to be driven by a coherent laser field. In order to quantify entanglement we use the logarithmic negativity. The analytical solutions are presented for the system in a parameter regime very close to the current experimental results. We show that in the presence of the photon hopping process between the cavities, the two mechanical resonators and the field modes can be entangled. This shows clearly that the entanglement can be transfer via radiation pressure of a photon hopping coupling from the intracavity photon-phonon entanglements to an inter-cavity photon-photon or phonon-phonon entanglement.     

Radiation noise in a three-mirror system

The effect of noise on the output parameters of a three-mirror system is investigated under the conditions when one of the cavities is filled with an amplifying medium and the other is empty. For weak coupling between the cavities, the amplitude noise at the outlet of the empty cavity decreases sharply, and the emission band becomes narrower than the natural bandwidth. Expressions are given for analyzing a more general problem on the statistical characteristics of laser radiation emitted by the three-mirror system with a weak noise.