Evolution of nonclassical light propagating through passive optical coupled waveguides: Entanglement dynamic

In this paper, nonclassical light propagation through passive optical coupler is investigated. On the other hand, passive optical device design for nonclassical light is analyzed in this work. Effect of mode mismatching including mismatching in propagation constant on operation of the considered device is studied. We investigate different separable and entangled input excitations with single photons in this case. We specially study the measure of entanglement and effect of propagation constant mismatch on it. The simultaneous effect of loss and mismatch is also studied. Obtained results for different excitation states illustrate that there is a possibility to design such that the system operation can be immune versus fabrication imperfections.     

Photon Correlations from the Mollow Triplet

Photon correlations between the photoluminescence peaks of the Mollow triplet have been known for a long time, and recently hailed as a resource for heralded single‐photon sources. Here, we provide the full picture of photon‐correlations at all orders (we deal explicitly with up to four photons) and with no restriction to the peculiar frequency windows that enclose the peaks. We show that a rich multi‐photon physics lies between the peaks, due to transitions involving virtual photons, and thereby much more strongly correlated than those transiting through the real states. Specifically, we show that such emissions occur in bundles of photons rather than as successive, albeit correlated, photons. We provide the recipe to frequency‐filter the emission of the Mollow triplet to turn it into a versatile and tunable photon source, allowing in principle all scenarios of photon emission, with advantages already at the one‐photon level, i.e., providing more strongly correlated heralded single‐photon sources than those already known.     

Propagation of quantum states of light through absorbing and amplifying media

We describe how quantum features of light fields become modified upon propagation through absorbing and amplifying media. Both absorption and amplification add noise to a beam of light. We examine the extent to which quantum features remain after this noise is added. We also examine the question of whether certain quantum states are more robust than others against degradation due to loss. Quantum states of this sort would constitute an important resource for use in quantum information processing. We quantify this thought by determining how the integration time required to achieve a specified signal-to-noise ratio increases in the presence of transmission losses. We find that under certain circumstances the required integration time increases more rapidly with transmission loss for measurement strategies based on coincidence detection of entangled photons than for strategies based on the properties of squeezed light.     

Ghost images without the background based on Bell states

When observing a ghost image, information on an object is obtained by measuring the spatial correlation between photons propagating in the object and reconstruction channels. In the traditional schemes involving two-mode entangled quantum states or quasithermal light sources, the correlation function of photons has a background associated with the average number of photons in the channels. It has been shown in this work that the use of polarization-entangled states, e.g., Bell states, allows removing this background and, thereby, obtaining a higher quality reconstructed image.     

Energy-time entanglement preservation in plasmon-assisted light transmission

We report on experimental evidence of the preservation of the energy-time entanglement of a pair of photons after a photon-plasmon-photon conversion. This preservation is observed in two different plasmon conversion experiments, namely, extraordinary optical transmission through subwavelength metallic hole arrays and long range surface plasmon propagation in metallic waveguides. Plasmons are shown to coherently exist at two different times separated by much more than their lifetimes. This kind of entanglement involving light and matter is expected to be useful for future processing and storing of quantum information.     

Random walk of polarized light in turbid media

We study the propagation of polarized light in turbid media as a random walk of vector photons. Both propagation and polarization directions of light are found to isotropize, following a power law of the number of scattering events. The characteristic length scale governing light isotropization and linear depolarization, the isotropization length , is derived using the exact Mie scattering for spherical particles. A simple relation is obtained for Rayleigh-Gans scatterers where is the transport mean free path and is the mean cosine of scattering angles.     

Negative refraction in photonic crystals

We demonstrate that light propagation in strongly modulated 2D/3D photonic crystals (PhCs) becomes refraction-like in the vicinity of the photonic bandgap, which is contrary to the fact that light propagation in weakly modulated PhCs is very different from refraction and thus the definition of refraction index becomes meaningless. Such a crystal behaves like a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. The propagation states having a negative effective index exhibit unusual properties, such as mirror-like imaging effect, image-transfer effect. These properties are confirmed by finite-difference time-domain simulations.     

Putting mechanics into circuit quantum electrodynamics

We review the use of mechanical oscillators in circuit quantum electrodynamics. The capacitive coupling of nano-electromechanical systems with quantum bits and superconducting microwave resonators gives rise to a rich quantum physics involving electrons, photons and phonons. We focus in particular on the linear coupling between a mechanical oscillator and a microwave resonator and present the quantum dynamics that stems from the phonotonic Josephson junction. The microwave cavity turns out to be a powerful device to detect quantum phonon states and manipulate entangled states between phonons and photons.     

Ray Modes in Random Gap Systems

A disordered photonic crystal with spectral degeneracies in the form of Dirac nodes is considered. Disorder can create a random gap at the Dirac nodes, which leads to the formation of random edge modes. We study the distribution of these edge modes and find from symmetry considerations that the discrete anisotropy of the photonic crystal is spontaneously broken for the propagation of photons from a local photon source. This effect can be understood as the spontaneous creation of a ray mode or as the creation of a one‐dimensional waveguide in a two‐dimensional photonic crystal through strong random scattering. The phenomenon must be distinguished from Anderson localization of photons in a single band crystal and can be considered as angular localization, since it creates geometric states rather than confining the photons to an area of the size of the localization length. The propagation of the photon intensity is described by a Fokker‐Planck equation, whose drift term is determined by the spectrum of the photonic crystal near the Dirac node.     

Quantum routing of few photons using a nonlinear cavity coupled to two chiral waveguides

We investigate few-photon scattering properties in two one-dimensional waveguides chirally coupled to a nonlinear cavity. The quantum states of scattered few photons are solved analytically via a real-space approach, and the solution indicates the few-photon reflection and transmission properties. When inputting two photons of equal energy to resonate with the cavity, the propagation characteristics of the two photons will be interesting, which is different from the previous anti-bunching effects with a quantum emitter. More importantly, when the total energy of the two incident photons equals the energy of a nonlinear cavity accommodating two photons, influence of the bound state will become larger to result in disappearance of antibunching effect. However, the bound state has no effect on probability of routing to another waveguide.     

Propagation characteristics of biphotons in cold atomic vapor

We investigate the propagation characteristics of the narrowband Stokes/anti-Stokes photons in cold atomic vapor. The four-wave mixing process results from parametric amplification of the anti-Stokes photons. We find that the process of parametric amplification is very similar to the light pulse propagating through an anomalous dispersion gain medium. Finally, we obtain the general solutions of the Glauber biphoton correlation functions, which are in good agreement with the experiment results.     

Pulse propagation of photon-added coherent states in waveguides with side-coupled nonlinear cavities

We present a theoretical analysis of pulse propagation in a waveguide with a side-coupled Kerr nonlinear cavity. As a specific application, we demonstrate how the nonlinearity has a profound influence on transport properties of a photon-added coherent state. We find that the fields provided by the coherent states facilitate a tunable nonlinearity on the few-photon level, allowing for a robust gating of single photons.     

Exafs like oscillations in X-ray excited autoionization spectra assisted by compton process

Oscillating features have been observed in the background of the inelastic electrons excited by high energy monochromatic X-ray photons at kinetic energy above the Cr M_2,3VV Auger transition. These structures are absent when X-ray photons of are used. We suggest that these extended features are due to an autoionization process experienced by the 3p core electron assisted by a Compton scattering with the X-ray photons. Through the inelastic Compton process the incoming photons excite the core electrons towards empty states above the Fermi level in a continuous manner up to a maximum energy, which strongly depends on the incident photon energy. These excited states are modulated in energy by the crystalline structure as it has been shown by means of the EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy. These oscillating structures are compared with those obtained through electron excitation for the same Auger transition in the Extended Fine Auger Structure (EXFAS) spectroscopy.     

Entanglement of atomic ensembles by trapping correlated photon states

We describe a general technique that allows for an ideal transfer of quantum correlations between light fields and metastable states of matter. The technique is based on trapping quantum states of photons in coherently driven atomic media, in which the group velocity is adiabatically reduced to zero. We discuss possible applications such as quantum state memories, generation of squeezed atomic states, preparation of entangled atomic ensembles, quantum information processing, and quantum networking.     

Imaging in turbid media using quasi-ballistic photons

We study by means of experiments and Monte Carlo simulations, the scattering of light in random media, to determine the distance up to which photons travel along almost undeviated paths within a scattering medium, and are therefore capable of casting a shadow of an opaque inclusion embedded within the medium. Such photons are isolated by polarisation discrimination wherein the plane of linear polarisation of the input light is continuously rotated and the polarisation preserving component of the emerging light is extracted by means of a Fourier transform. This technique is a software implementation of lock-in detection. We find that images may be recovered to a depth far in excess of that predicted by the diffusion theory of photon propagation. To understand our experimental results, we perform Monte Carlo simulations to model the random walk behaviour of the multiply scattered photons. We present a new definition of a diffusing photon in terms of the memory of its initial direction of propagation, which we then quantify in terms of an angular correlation function. This redefinition yields the penetration depth of the polarisation preserving photons. Based on these results, we have formulated a model to understand shadow formation in a turbid medium, the predictions of which are in good agreement with our experimental results.     

Quantum communication without alignment using multiple-qubit single-photon states

We propose a scheme for encoding logical qubits in a subspace protected against collective rotations around the propagation axis using the polarization and transverse spatial degrees of freedom of single photons. This encoding allows for quantum key distribution without the need of a shared reference frame. We present methods to generate entangled states of two logical qubits using present day down-conversion sources and linear optics, and show that the application of these entangled logical states to quantum information schemes allows for alignment-free tests of Bell's inequalities, quantum dense coding, and quantum teleportation.     

基于光子轨道角动量的密码通信方案研究

设计了一个基于两个正交的光子轨道角动量态的量子密码通信方案.在该方案中,Alice使用具有独特设计的激光器,随机发送有确定轨道角动量的光子;Bob采用由两个达夫棱镜组成的光束旋转器,对光子的轨道角动量态进行测量.对系统安全性的讨论表明,Eve采用截获重发、攻击单臂等攻击手段,其窃听行为都会被发现.理论证明,该方案不需要通信双方实时监测和调整参考系,同时避免了BB84,B92协议因发送基和测量基不一致而丢弃一半信息的问题,从而提高了密钥生成效率. 关键词： 量子保密通信 轨道角动量     

Simulation of propagating EAS Cherenkov radiation over the ocean surface

We present computing results of the Cherenkov light propagation in the air and water from an extensive air shower (EAS) over the ocean. Limits on the zenith angles of the showers, for which the registration of the flash of reflected photons by the space-detector is possible, are analyzed with consideration for waves on the ocean surface.     

Bound states of a photon and optical reflectivity in a monolayer of dielectric spheres

In a monolayer of arrayed macroscopic spheres of dielectric, it is shown that the localized states of photons appear as sharp peaks in the line shape of reflectivity of light. They are confirmed as such by calculating the integrated density of states of photons and the dependence of the reflectivity on the radius of spheres. The condition for their existence and the possibility of their detection are also discussed.     

等离激元增强的石墨烯光吸收

石墨烯中等离激元具有特殊的光电性质,其和入射光的强烈耦合可以引起光吸收的增强.本文基于时域有限差分法和多体自洽场理论研究了等离激元对处于光学谐振腔中的石墨烯光吸收的影响.由于石墨烯中等离激元与入射光动量和能量不匹配而不能直接相互作用,因此石墨烯上施加了金属光栅结构.研究发现光栅结构能够对入射光进行动量补偿并且能够引起其下石墨烯中的电场强度产生很大程度增强,从而导致在该石墨烯结构中太赫兹等离激元和入射光发生强烈耦合而产生太赫兹等离极化激元,同时引起石墨烯光吸收的增强.希望本文能够加深对石墨烯光电特性的理解以及可以为基于石墨烯的太赫兹光电装置提供一定的理论依据.