Effect of spontaneous Raman scattering on quantum channel wavelength-multiplexed with classical channel

We quantitatively estimate the effect of spontaneous Raman scattering on a quantum channel wavelength-multiplexed with a classical channel. Based on an experiment that measured the generation power of spontaneous Raman scattering in a fiber, the performance of wavelength-multiplexed quantum key distribution (QKD) systems using the differential-phase-shift protocol is evaluated for various system conditions.     

Research on co-propagation of QKD and classical communication by reducing the classical optical power

We investigate the crosstalk noise, especially the spontaneous Raman scattering, in the optical fiber of a copropagation system between quantum key distribution(QKD) and classical communications. Although many methods have been proposed, such as increasing the wavelength spacing and narrowband filtering technique, to suppress Raman scattering noise, these methods greatly affect the performance of QKD. One way to solve the obstacle restricting the coexistence is to decrease the classical signal power. Based on the high gain of the gated avalanche photodiode and pulse position modulation, we demonstrate that the co-propagation system works effectively with only a small effect on long-haul fibers, which has great significance for the practical widespread commercialization of QKD.     

受激拉曼增益介质中的量子噪声特性研究

研究了三能级原子系综与相干控制场以及量子探测场的相互作用下的受激拉曼系统.运用量子理论推导出了该受激拉曼系统中由于量子场真空涨落引起的量子噪声以及受激散射的量子化光场噪声谱,并且数值计算了注入拥有非经典涨落的量子探测场,真空涨落所引起的量子噪声谱. 关键词： 受激拉曼增益 量子噪声 噪声谱     

Theory on the optical-phonon Raman scattering in GaAs/AlAs heterostructures

A microscopic theory of Raman scattering by optical phonons in GaAs/GaAlAs heterostructures is worked out systematically, on the basis of recent advances in our knowledge of the electronic structure and the optical-phonon modes in superlattices and quantum wells. Theories have shown that specific features of the intermediate states are of special importance for a quantitative theory. Thus, the heavy and light hole mixing effect, and the angular momentum state of the four-component excitons, can play a decisive role in determining the predominant scattering channels. Special attention has been paid to the Frolich-interaction induced scattering, which is dipole forbidden in bulk materials but allowed in multiple quantum wells owing to the barrier penetration and the hole mixing. Based on the microscopic theory, explanations are provided for such experimental facts as the asymmetry between the incoming and the outgoing resonance, the line shape of Raman spectra and the features of two-phonon Raman scattering in quantum well systems.     

Quantum interference in Mössbauer scattering spectra

The role of quantum interference in the formation of the resonance scattering spectra of Mössbauer photons is studied. A resonant rf field mixing the spin levels of the excited state of a nucleus is considered to be the mechanism ensuring the conditions for quantum interference. A considerable intensity redistribution of the elastic and Raman scattering channels is shown to occur as a result of quantum interference.     

Reprint of : Correlated voltage probe model of relaxation in two Coulomb-coupled edge channels

A phenomenological correlated voltage probe model is introduced to mimic the effects of inelastic scattering between particles in different conduction channels of a phase coherent conductor. As an illustration, the non-equilibrium distribution functions of two noisy co-propagating chiral edge channels of the integer quantum Hall effect are calculated and compared with recent experiments. The method is further applied to calculate the linear response current noise through an interacting Mach–Zehnder interferometer.     

Correlated voltage probe model of relaxation in two Coulomb-coupled edge channels

A phenomenological correlated voltage probe model is introduced to mimic the effects of inelastic scattering between particles in different conduction channels of a phase coherent conductor. As an illustration, the non-equilibrium distribution functions of two noisy co-propagating chiral edge channels of the integer quantum Hall effect are calculated and compared with recent experiments. The method is further applied to calculate the linear response current noise through an interacting Mach–Zehnder interferometer.     

Surface enhanced Raman scattering by CdS quantum dots

Surface enhanced Raman scattering is studied in nanostructures with CdS quantum dots formed using the Langmuir-Blodgett technology. Features due to quantum dot longitudinal optical phonons are observed in the Raman spectra of both free CdS quantum dots and such dots distributed in an organic matrix. The surface enhanced Raman scattering by nanostructures with CdS quantum dots covered by an Ag cluster film is observed experimentally. Applying Ag clusters onto the nanostructure surfaces results in a sharp (40-fold) increase in the intensity of Raman scattering by optical phonons in the quantum dots. It is shown that the dependence of surface enhanced Raman scattering on the excitation energy is resonant with a maximum at the energy corresponding to the maximum absorption coefficient of Ag clusters.     

Quantum stochastic differential equation for squeezed light

In this paper, the quantum stochastic differential equation (QSDE) is derived which is based on explanatory for interaction of open quantum system with squeezed quantum noise. This equation describes the stochastic evolution of unitary operator and is used to compute the evolution of quantum observable and output field. Our QSDE has complete form with respect to previous QSDE for squeezed light, because it bears three fundamental quantum noises for its evolution and the scattering between quantum channels is included. Meanwhile, when squeezed noise reduces to vacuum noise, our QSDE reveals the famous Hudson-Parthasarathy QSDE. Our equations may have application for quantum network analysis of squeezed noise interferometer for gravitational wave detection.     

Fundamental noise limitations to supercontinuum generation in microstructure fiber

Broadband noise on supercontinuum spectra generated in microstructure fiber is shown to lead to amplitude fluctuations as large as 50% for certain input laser pulse parameters. We study this noise using both experimental measurements and numerical simulations with a generalized stochastic nonlinear Schr?dinger equation, finding good quantitative agreement over a range of input-pulse energies and chirp values. This noise is shown to arise from nonlinear amplification of two quantum noise inputs: the input-pulse shot noise and the spontaneous Raman scattering down the fiber.     

压电晶体拉曼散射的统一量子论

发展了拉曼散射的一个广义量子理论，它能同时说明非极性模和极性模的作用.在场论中， 光被纵光学和横光学模的拉曼散射能在一个统一的理论框架内描述. 关键词： 拉曼散射 声子 量子场论     

Generation of photon pairs in dispersion shift fibers through spontaneous four wave mixing: Influence of self-phase modulation

Correlated signal and idler photon pairs with small detuning in the telecom band can be generated through spontaneous four-wave mixing in dispersion shift fibers. However, photons originated from other nonlinear processes in optical fibers, such as Raman scattering and self-phase modulation, may contaminate the photon pairs. It has been proved that photons produced by Raman scattering are the background noise of photon pairs. Here we show that photons induced by self-phase modulation of pump pulses are another origin of background noise. After studying the dependence of self-phase modulation induced photons in signal and idler bands, we demonstrate that the quantum correlation of photon pairs can be degraded by the self-phase modulation effect. The investigations are useful for characterizing and optimizing an all fiber source of photon pairs.     

High transparency of a two-photon scattering channel in triple-barrier structures

An analytical solution of the Schrödinger equation with open boundary conditions in all scattering channels has been found for asymmetric triple-barrier resonance-tunneling structures with thin high barriers. This solution describes resonance transitions between three quantum levels in a high rf electric field. It is found that, under certain conditions, most electrons incident on the upper resonance level can emit two photons and leave a structure through the lower level without intermediate interaction with phonons. The structure appears to be almost absolutely transparent in a wide range of the rf field amplitude. This behavior fundamentally distinguishes the multiphoton scattering process from previously considered single-photon scattering processes and the quantum efficiency of such transitions can be twice as high as the maximum quantum efficiency of the transitions between neighboring levels and can reach a value of 160% in the limiting case.     

Modulation of optical pulses under electromagnetically induced transparency conditions: transfer of the Rabi oscillations manifestation from the radiofrequency to the optical range

The relative intensities of lines in resonance Raman scattering spectra of isolated skatole and skatole-water complex have been calculated quantum mechanically. The influence of the intermolecular interaction on these spectra has been considered. Particular features of the intensity distribution in the resonance Raman scattering spectra of indole and skatole have been compared.     

A simple analytic model for noise shaping by an optical fiber Raman generator

An analytic model for first Stokes–Raman generation in optical fiber is used to evaluate the relative importance of quantum initiation noise and amplified classical pump noise in recent experiments on noise shaping. The model accounts for pump depletion and for fluctuations arising from the spontaneous generation of the first Stokes pulse, but not for scattering into higher-order Stokes pulses. The model reproduces the qualitative features of the measured first Stokes pulse energy statistics using realistic parameter values.     

Reduced quantum noise in waveguide coherent Raman scattering spectroscopy

Waveguide regimes of nonlinear-optical interactions allow a reduction of quantum noise in spectra of coherent Raman scattering (CRS). We will find the optimal waveguide length providing the maximum quantum limit for the signal-to-noise ratio in waveguide CRS and assess this ratio for laser intensities right below the optical breakdown threshold. This analysis shows that the quantum-limit signal-to-noise ratio of coherent femtosecond CRS spectroscopy of the gas phase can be increased in the waveguide regime by more than four orders of magnitude relative to the regime of tight focusing.     

Higher-order squeezing and sub-poissonian photon statistics in CARS and CAHRS

The Squeezing and sub-poissonian photon statistics of an optical field are a purely quantum mechanical phenomenon and has been accepted as means of achieving noise below the quantum shot-noise limit. The effect of higher-order squeezing and sub-poissonian nature of an optical field in coherent anti-Stokes Raman scattering (CARS) and coherent anti-Stokes hyper Raman scattering (CAHRS) are investigated under short-time approximation. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators are established and solved under short-time scale. The dependence of squeezing on the number of photons is also investigated. It is also shown that higher-order squeezing allows a much larger fractional noise reduction than lower-order squeezing. The occurrence of amplitude squeezing effects of the radiation field in the fundamental mode is investigated in both the processes. The present work shows that squeezing is greater in CAHRS than the corresponding squeezing in CARS. It is also shown that squeezing is greater in stimulated process than corresponding squeezing in spontaneous interaction. The conditions for obtaining maximum and minimum squeezing are obtained. The photon statistics of the pump mode in the processes has also been investigated and found to be sub-poissonian in nature.     

Noise performance analysis of bi-directionally pumped distributed fiber Raman amplifiers with consideration of fiber nonlinearity and its impact on EDFA output OSNR

Under small-signal assumption, equivalent noise figure normalized by fiber nonlinearities (NENF) of bi-directionally pumped distributed fiber Raman amplifiers (BiDFRA) is derived. Amplified spontaneous Raman scattering noise and double Rayleigh scattering noise are both included. The relation between NENF and Raman gain, forward Raman gain percentage is investigated under different polarization factor and Rayleigh scattering coefficient. It agrees well with numerical simulation results. Based on the analytical expression, the optical signal-to-nose ratio (OSNR) improvement of hybrid pre-BiDFRA/erbium-doped fiber amplifier (EDFA) compared with sole EDFA is studied. It is shown that there is an optimum Raman gain and forward Raman gain percentage to maximize the OSNR improvement. Finally, some guidelines on BiDFRA design are proposed.     

Vibrational density of states of hen egg white lysozyme

The resonant Raman scattering in GeSi/Si structures with GeSi quantum dots has been analyzed. These structures were formed at various temperatures in the process of molecular-beam epitaxy. It has been shown that Raman scattering spectra recorded near resonances with the E₀ and E₁ electronic transitions exhibit the lines of Ge optical phonons whose frequencies differ significantly from the corresponding values in bulk germanium. In the structures grown at low temperatures (300–400°C), the phonon frequency decreases with increasing excitation energy. This behavior is attributed to Raman scattering, which is sensitive to the size of quantum dots, and shows that quantum dots are inhomogeneous in size. In the structures grown at a higher temperature (500°C), the opposite dependence of the frequency of Ge phonons on excitation energy is observed. This behavior is attributed to the competitive effect of internal mechanical stresses in quantum dots, the localization of optical photons, and the mixing of Ge and Si atoms in structures with a bimodal size distribution of quantum dots.