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.     

Squeezed States of Magnons and Phonons in a Cavity Magnomechanical System with a Microwave Parametric Amplifier

The cavity magnomechanical system has become a promising platform for preparing macroscopic quantum states. In this work, a scheme for generating the steady-state quadrature squeezing of the magnon and phonon modes in a cavity magnomechanical system is presented. This scheme uses a degenerate microwave parametric amplifier (PA) inside the microwave cavity. It is found that the squeezing of the cavity mode produced by the PA can be transferred to the magnon mode due to the cavity-magnon beamsplitter-like interaction, and the squeezing of the magnon mode can be further transferred to the phonon mode due to the magnon-phonon beamsplitter-like interaction induced by driving the magnon mode with a red-detuned microwave field. The effects of the parametric gain and phase of the PA, the magnon-cavity coupling strength, the power of the magnon drive, and the temperature of the environment on the squeezing of the magnon and phonon modes have been evaluated. The results show that the squeezing of the magnon and phonon modes is robust against the temperature of the environment.     

Nonclassicality in off-resonant Raman process

The detuning parameter in experimentally feasible off-resonant Raman process is shown as a control parameter to probe and enhance the nonclassicality generated in the output of the process. Specifically, the normal characteristic function is obtained for the process as a function of detuning parameters in Stokes and anti-Stokes generation processes using more general solution than the conventional short-time solution under complete quantum treatment, which remains in the multimode Gaussian form. Single- and two-mode squeezing and antibunching as well as intermodal entanglement are reported in terms of experimentally accessible quantum noise fluctuations considering either phonon mode coherent or chaotic. Further, the joint photon-phonon number and integrated intensity distributions reveal a higher number of Stokes-phonon (pump-phonon) pair generation for the lower (higher) values of detuning parameter in Stokes generation. Pump-phonon pair generation is also supported by the lower values of detuning parameter in anti-Stokes generation.     

Double resonance Raman scattering of second-order Raman modes from an individual graphite whisker

Resonant Raman scattering of second-order Raman modes from an individual graphite whisker synthesized by a high-temperature heat-treatment method at a special pressure was discussed here. The dependence of phonon frequencies on the incoming laser light and the frequency difference between Stokes and anti-Stokes scattering show their origin from double resonance Raman scattering. Our results show that all the experimental results of second-order Raman modes in graphite whiskers, such as the excitation-energy dependence on the mode frequency, the frequency shift between a second-order Raman mode and its fundamentals, and the frequency discrepancy between Stokes and anti-Stokes components of a second-order Raman mode can be well understood by double resonance Raman scattering.     

Raman spectroscopic evidence for hot-phonon generation in electrically biased carbon nanotubes

We provide spectroscopic evidence for hot-phonon generation in biased single-walled carbon nanotubes by measuring simultaneously the Stokes and anti-Stokes Raman lines of the G mode and of the radial-breathing mode as a function of current bias. Using Bose-Einstein statistics we can directly calculate the phonon temperature from the intensity ratio of the anti-Stokes to Stokes lines. Upon nanotube biasing we observe (i) an increase of the G mode phonon temperature in contrast to the radial-breathing mode phonons that remain thermalized at room temperature, and (ii) no softening of the G mode. Based on these observations, we exclude current-induced thermal heating of the nanotube.     

Superradiance regime of laser cooling in extended solids

The kinetics of the extended crystal doped by rare-earth ions in the regime of anti-Stokes laser cooling has been considered taking into account the collective radiation effects. The system of Markovian equations for impurities and pseudolocal phonons has been obtained. As would be expected, the collective radiation effects cause an acceleration in relaxation depletion of the phonon mode and, therefore, an increase in crystal cooling efficiency. The text was submitted by the author in English.     

Raman光激射器

本文从哈密顿量出发,导出描写受激Raman过程的方程式:Laser光、一级Stokes与反Stokes光及相干的声子场的耦合方程,并唯象地引入弛豫耗散。在分子属于远共振情形及比介电常数近似更高一级的近似下,分析了方程的性质。由平衡点稳定性的讨论给出了Raman光激射器的阈值,发现反Stokes激射光的产生并不要求附加的阈条件,即在受激Raman效应中,反Stokes光总是必然出现的。对于Raman光激射器诸工作点的性质及工作过程也作了进一步的讨论,发现在一定条件下,在强激射光源辐照下,存在着Stokes与反Stokes成分几乎各占一半的唯一的稳定平衡点(Raman光激射器的工作点)。文中也顺便讨论了声子弛豫所起的作用及有长寿命的声子时Raman光激射器的行为。     

QUANTUM NONDEMOLITION MEASUREMENTS OF TO PHONONS VIA DETECTING ANTI-STOKES FIELD

A scheme of quantum nondemolition measurement of transverse optical phonons in a Raman crystal is presented through detecting an anti-Stokes field. The exact solutions of the system is obtained. According to the calculation of the criteria for quantum nondemolition measurements, it is shown that under certain conditions the amplitude quadrature component of the phonon mode can be measured without demolition by the phase quadrature component of the anti-Stokes mode.     

Multimode stimulated Raman scattering with squeezed light

Stimulated Raman scattering of a multimode pump light on an one-mode phonon system is examined. The pump light is expected to be strong, so that it can be treated classically. The phonon mode and scattered Stokes and anti-Stokes modes are described quantally. The phonon is prepared in a coherent state and the scattered modes are prepared in displaced and squeezed states at the input.The author would like to thank Dr. J. Peina for fruitful discussions, and Dr. A. Luk for comments on the results.     

基于压缩光的量子精密测量

对任何物理量的测量都有一定的噪声, 经典测量所能达到的最小噪声一般称为散粒噪声, 对应着测量的标准量子极限. 利用压缩光可以突破标准量子极限, 从而提高测量精度. 本文介绍了压缩态光场用于突破标准量子极限的基本原理, 以及压缩态光场在相位测量、光学横向小位移及倾斜测量、磁场测量以及时钟同步等精密测量领域的应用和最新进展.     

Softening of phonon modes in C60 crystals induced by laser irradiation: Thermal effects

Reversible softening of the intramolecular A _g(2) pentagonal pinch (PP) mode of a C₆₀ single crystal in the face centered cubic phase has been studied as a function of laser power density by means of Raman scattering. The average temperature rise in the laser excitation spot has been determined using the Stokes to anti-Stokes integrated peak intensity ratio for the H _g(1) phonon mode. Softening of the PP-mode was found to be due to heating of the sample resulting from laser irradiation, in good quantitative agreement with experimental results obtained for uniformly heated samples. These findings are in excellent agreement with results obtained by numerical calculations of the local temperature distribution and average temperature in the laser spot based on calculated integrated intensities of the Stokes and anti-Stokes bands of the PP-mode. These calculations were based on experimental data for the temperature dependence of phonon frequency and width, absorbance, and thermal conductivity in solid C₆₀. Zh. éksp. Teor. Fiz. 114, 1785–1794 (November 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor     

Direct measurement of the lifetime of optical phonons in single-walled carbon nanotubes

Time-resolved anti-Stokes Raman spectroscopy has been applied to probe the dynamics of optical phonons created in single-walled carbon nanotubes by femtosecond laser excitation. From measurement of the decay of the anti-Stokes Raman signal in semiconducting nanotubes of (6,5) chiral index, a room-temperature lifetime for G-mode phonons of 1.1+/-0.2 ps has been determined. This lifetime, which reflects the anharmonic coupling of the G-mode phonons to lower-frequency phonons, is important in assessing the role of nonequilibrium phonon populations in high-field transport phenomena.     

CdSe/ZnS纳晶中相干电声耦合效应的二维电子光谱研究

Coherent exciton-phonon coupling in CdSe/ZnS nanocrystals have been investigated by temperature-dependent two-dimensional electronic spectroscopy (2DES) measurements. Benefiting from the ability of 2DES to dissect assembles in nanocrystal films, we have clearly identified experimental evidences of coherent coupling between exciton and phonon in CdSe/ZnS nanocrystals. In time domain, 2DES signals of excitonic transitions beat at a frequency resonant to a longitudinal optical phonon mode; in energy domain, phonon side bands are distinct at both Stokes and anti-Stokes sides. When temperature increases, phonon-induced exciton dephasing is observed with dramatic broadening of homogeneous linewidth. The results suggest exciton-phonon coupling is essential in elucidating the quantum dynamics of excitonic transitions in semiconductor nanocrystals.     

All-ultraviolet time-resolved coherent anti-Stokes Raman scattering

We report all-UV coherent anti-Stokes Raman scattering (CARS) in calcite with 250-280 nm pump, Stokes, probe, and anti-Stokes light. UV CARS efficiency is approximately 7x higher than for comparable scattering in the visible, 480-540 nm. Time-resolved UV CARS reveals lengthening of the dephasing time of 1086 cm(-1) CO3(2-) internal vibrations from 4 to 7 ps with increasing vibrational excitation, consistent with a phonon depletion model.     

Manifestation of outgoing resonance in stokes and anti-stokes spectra of ZnTe and ZnMgTe quantum wires

The spectra of resonant light scattering by ZnTe quantum wires have been measured at excitation energies of 2.18–2.72 eV. The quantum wires have been grown on Si(100) and GaAs(100) substrates by molecular beam epitaxy. The effect of outgoing resonance with the electron transition energy E ₀ on the intensity of phonon lines of the Stokes spectrum and on the intensity ratio of the Stokes and anti-Stokes spectral lines has been studied. The energy E ₀ has been determined in ZnTe and ZnMgTe quantum wires from the edge luminescence spectra.     

Phonon squeezing in a superconducting molecular transistor

Josephson transport through a single molecule or carbon nanotube is considered in the presence of a local vibrational mode coupled to the electronic charge. The ground-state solution is obtained exactly in the limit of a large superconducting gap and is extended by variational analysis. The Josephson current induces squeezing of the phonon mode, which is controlled by the superconducting phase difference and by the junction asymmetry. Optical probes of nonclassical phonon states are briefly discussed.     

第Ⅰ类两态叠加多模叠加态光场的N次方X压缩

利用多模辐射场广义非线性等幂次高次差压缩的一般理论,对第Ⅰ类两态叠加多模叠加态光场的等幂次N次方X压缩特性进行了详细研究,发现了其存在等幂次N次方X压缩效应的条件,还发现第Ⅰ、第Ⅱ两类两态叠加多模叠加态光场之间存在相似压缩和压缩简并现象,从而再次证明第Ⅰ类两态叠加多模叠加态光场是一种典型的多模非经典光场.     

在单模光纤中放大的反斯托克斯拉曼背向自发散射的温度效应

在单模光纤中,输入的激光功率大于阈值时．出现放大的反斯托克斯拉曼背向自发散射现象。实验发现：放大的反斯托克斯拉曼背向自发散射具有温度效应．与反斯托克斯拉曼背向自发散射一样,放大的拉曼散射光的光子通量受到光纤温度的调制。反斯托克斯拉曼背向白发散射的放大效应抑制了单模光纤中的相干噪声,改善了系统的信噪比。实验还发现．放大的反斯托克斯扎曼背向自发散射空域曲线上放大的端点位置随激发功率的增高前移并具有一定的规律性。放大的反斯托克斯拉曼背向自发散射的温度效应作为一种新的测温原理,已应用于远程30km分布光纤温度传感器系统。     

多模辐射场的广义非线性不等阶高阶压缩的一般理论

本文建立了多模辐射场的广义非线性不等阶高阶压缩的一般理论。首次提出了多模辐射场中各模压缩阶数不相等的N_j次方Y压缩、N_j次方H压缩以及N_j次方X压缩的一般性定义,并对N_j-Y最小测不准态、N_j-Y压缩最小测不准态、N_j-H最小测不准态、N_j-H压缩最小测不准态以及N_j-X最小测不准态和N_j-X压缩最小测不准态等进行了详细讨论。指出,Zhang等人在国际上提出的有关单模辐射场的振幅N次方压缩的定义、Mark Hilery在国际上提出的有关双模辐射场的“双模和压缩”与“双模差压缩”的定义以及由笔者新近提出的有关多模辐射场的N次方Y压缩、N次方H压缩和N次方X压缩等的定义,仅仅只是本文所提出的N_j次方Y压缩、N_j次方H压缩以及N_j次方X压缩等的一般性定义在各种不同条件下的特例.     

Parametric oscillation with the cavity mode driven by coherent light and coupled to a squeezed vacuum reservoir

We seek to investigate, employing stochastic differential equations, the squeezing and statistical properties of the cavity mode of a degenerate parametric oscillator driven by coherent light and coupled to a squeezed vacuum reservoir. Contrary to the case of the squeezed vacuum reservoir, it is found that the driving coherent light has no effect on the squeezing properties of the cavity mode. However, both the squeezed vacuum reservoir and the driving coherent light increase the mean photon number of the cavity mode.