Noise suppression for micromechanical resonator via intrinsic dynamic feedback

We study a dynamic mechanism to passively suppress the thermal noise of a micromechanical resonator through an intrinsic self-feedback that is genuinely non-Markovian. We use two coupled resonators, one as the target resonator and the other as an ancillary resonator, to illustrate the mechanism and its noise reduction effect. The intrinsic feedback is realized through the dynamics of coupling between the two resonators: the motions of the target resonator and the ancillary resonator mutually influence each other in a cyclic fashion. Specifically, the states that the target resonator has attained earlier will affect the state it attains later due to the presence of the ancillary resonator. We show that the feedback mechanism will bring forth the effect of noise suppression in the spectrum of displacement, but not in the spectrum of momentum.     

Noise suppression for micromechanical resonator via intrinsic dynamic feedback

We study a dynamic mechanism to passively suppress the thermal noise of a micromechanical resonator through an intrinsic self-feedback that is genuinely non-Markovian. We use two coupled resonators, one as the target resonator and the other as an ancillary resonator, to illustrate the mechanism and its noise reduction effect. The intrinsic feedback is realized through the dynamics of coupling between the two resonators: the motions of the target resonator and the ancillary resonator mutually inthence each other in a cyclic fashion. Specifically, the states that the target resonator has attained earlier will affect the state it attains later due to the presence of the ancillary resonator. We show that the feedback mechanism will bring forth the effect of noise suppression in the spectrum of displacement, but not in the spectrum of momentum.      

Decoherence suppression by cavity optomechanical cooling

We consider a cavity optomechanical cooling configuration consisting of a mechanical resonator (denoted as resonator b) and an electromagnetic resonator (denoted as resonator a), which are coupled in such a way that the effective resonance frequency of resonator a depends linearly on the displacement of resonator b. We study whether back-reaction effects in such a configuration can be efficiently employed for suppression of decoherence. To that end, we consider the case where the mechanical resonator is prepared in a superposition of two coherent states and evaluate the rate of decoherence. We find that no significant suppression of decoherence is achievable when resonator a is assumed to have a linear response. On the other hand, when resonator a exhibits Kerr nonlinearity and/or nonlinear damping the decoherence rate can be made much smaller than the equilibrium value provided that the parameters that characterize these nonlinearities can be tuned close to some specified optimum values.     

连续波锁模掺钕磷酸盐玻璃激光器光学谐振腔的分析

由于Nd:磷酸盐玻璃的热导率和破坏阀值都比较低,故连续波锈模钕磷酸盐玻璃激光器要求其谐振腔有特殊的设计.本文在谐振腔长度固定的限制下,分析了三元件式谐振腔的特性,并且讨论了连续波主动锁模Nd:磷酸盐玻璃激光器光学谐振腔的设计.我们讨论了在不同参量范围下谐振腔的稳定性范围和特性,并且阐明了有关的最佳参数的范围.给出了谐振腔最佳运转区参数的解析表达式.实验结果与理论预测符合得很好.这个解析式对设计三元件或多元件的任何端面泵浦和锁模谐振腔是很有用的.     

Characteristics of double-plasmonic-racetrack resonator to increase quality factor

We have numerically evaluated wavelength characteristics at telecommunication wavelengths by means of a doubleplasmonic-racetrack resonator using the finite-difference time domain method. We investigated the effect of the space between the two plasmonic racetracks of the resonator on the quality factor. The quality factor of the proposed structure is 57 when the space between two racetracks is 600 nm. The quality factor of a double-plasmonic-racetrack resonator of a dielectric-filled trench is 1.5 times greater than that of a single-plasmonic-racetrack resonator of an air-filled trench. The phase mismatch of the trench channel plasmon polaritons contributes to the quality factor of the double-plasmonicracetrack resonator.     

Experimental demonstration of plasmonic racetrack resonators with a trench structure

We fabricated and investigated a plasmonic racetrack resonator with a trench structure. Trench channel plasmon polaritons excited by end-fire coupling at a wavelength of 633 nm are observed in the fabricated racetrack resonator. The racetrack resonator also worked as a plasmonic racetrack resonator. The experimental and simulation results of the electric field distributions are in good agreement.     

Inertial attached neck length of Helmholtz resonators

We studied the inertial attached neck length (end correction) of different Helmholtz resonator configurations based on numerical calculations by the finite element method. First, we determined the eigenfrequency of the resonator, then on its basis, we calculated the attached neck length of the resonator. We analyzed the dependence of the attached neck length on the geometric parameters of the Helmholtz resonator. Using numerical calculations, we approximated the obtained dependences as analytic expressions.     

A subwavelength MIM waveguide resonator with an outer portion smooth bend structure

We systematically investigate bends in metal–insulator–metal (MIM) subwavelength plasmonic waveguides resonator, realized in a two-dimensional (2D) plasmon polariton metal using a finite-difference time-domain (FDTD) method with perfectly matched layers (PMLs) boundary conditions. We apply the outer portion of the bend structure in resonator which can lead to remarkably good bending transmission characteristics. We discuss the existence conditions of different modes which affect the device performance, and analyze coupling efficiency of the outer portion of the bend structure resonator in detail. Meanwhile, we find that the first dip of the outer portion smooth bend resonator nearly linear shifts toward longer wavelengths with the increase of the effective waveguiding length. In addition, add/drop directional couplers are realizable using the present resonator structure.     

High-sensitivity optical monitoring of a micromechanical resonator with a quantum-limited optomechanical sensor

We experimentally demonstrate the high-sensitivity optical monitoring of a micromechanical resonator and its cooling by active control. Coating a low-loss mirror upon the resonator, we have built an optomechanical sensor based on a very high-finesse cavity (30 000). We have measured the thermal noise of the resonator with a quantum-limited sensitivity at the 10(-19) m/sqrt[Hz] level, and cooled the resonator down to 5 K by a cold-damping technique. Applications of our setup range from quantum optics experiments to the experimental demonstration of the quantum ground state of a macroscopic mechanical resonator.     

Quantum dynamics of a mechanical resonator driven by a cavity

We explore the quantum dynamics of a mechanical resonator whose position is coupled to the frequency of an optical (or microwave) cavity mode. When the cavity is driven at a frequency above resonance the mechanical resonator can gain energy and for sufficiently strong coupling this results in limit-cycle oscillations. Using a truncated Wigner function approach, which captures the zero-point fluctuations in the system, we develop an approximate analytic treatment of the resonator dynamics in the limit-cycle regime. We find that the limit-cycle oscillations produced by the cavity are associated with rather low levels of energy fluctuations in the resonator. Compared to a resonator at the same temperature which is driven by a pure harmonic drive to a given average energy, the cavity-driven oscillations can have much lower energy fluctuations. Furthermore, at sufficiently low temperatures, the cavity can drive the resonator into a non-classical state which is number-squeezed.     

激光谐振腔自动稳定调节的一种方法

本文讨论了激光谐振腔的稳定调节系统.对失调的激光谐振腔的输出光斑进行图象处理,检测出光斑的内外圆环的边缘,然后用曲线拟合的方法得到内外圆环的几何中心坐标,计算出光斑的能量偏移和位置偏移.运用几何光学和衍射光学的有关知识,推导出激光谐振腔镜的倾斜角和光斑偏移量的关系,利用这个关系来实时调节谐振腔,使谐振腔准直.我们做了大量的实验证明这种方法是切实可行的.     

Cooling of a nanomechanical resonator in presence of a single diatomic molecule

We propose a theoretical scheme for coupling a nanomechanical resonator to a single diatomic molecule via microwave cavity mode of a driven LC$LC$ resonator. We describe the diatomic molecule by a Morse potential and find the corresponding equations of motion of the hybrid system by using Fokker–Planck formalism. Analytical expressions for the effective frequency and the effective damping of the nanomechanical resonator are obtained. We analyze the ground state cooling of the nanomechanical resonator in presence of the diatomic molecule. The results confirm that presence of the molecule improves the cooling process of the mechanical resonator. Finally, the effect of molecule’s parameters on the cooling mechanism is studied.     

Nonlinear coupling of nanomechanical resonators to josephson quantum circuits

We propose a technique to couple the position operator of a nanomechanical resonator to a SQUID device by modulating its magnetic flux bias. By tuning the magnetic field properly, either linear or quadratic couplings can be realized, with a discretely adjustable coupling strength. This provides a way to realize coherent nonlinear effects in a nanomechanical resonator by coupling it to a Josephson quantum circuit. As an example, we show how squeezing of the nanomechanical resonator state can be realized with this technique. We also propose a simple method to measure the uncertainty in the position of the nanomechanical resonator without quantum state tomography.     

Slotted Photonic Crystal Microring Resonators

We propose using a slotted photonic crystal nanobeam to construct a microring resonator. The transmission characteristics of the slotted photonic crystal nanobeam and the microring resonator are demonstrated by two-dimensional finite-difference time-domain simulation, and the mechanism of these characteristics is analyzed considering the introduction of the slot. The refractive index sensitivity of the slotted photonic crystal microring resonator is evaluated to be larger than those of a slot waveguide microring resonator and a nonslotted photonic crystal microring resonator.     

Self-Focusing and Channeling of Wave Beams in a Nonuniform Magnetic Field under Conditions of Ionization Nonlinearity

We study experimentally the effect of ionization self-channeling of waves at the whistler frequencies in a nonuniform magnetic field. It is shown that the formed plasma nonuniformity localizes the radiation from a short high-frequency source inside a discharge channel stretched along an external magnetic field. We found a possibility to control the parameters of the formed plasma-wave channel as well as the dispersion characteristics and structure of wave fields in wide limits by varying the magnetic field in a specified spatial region. We propose a method for the formation of a plasma resonator and test this method in the laboratory experiment. The spatial plasma and field distributions in this resonator are similar to those along a geomagnetic field tube of the magnetospheric resonator. We reveal the plasma instability in such a resonator in the vicinity of the frequency of electron bounce oscillations between magnetic mirrors.     

Ringdown spectroscopy of stimulated Raman scattering in a whispering gallery mode resonator

We report experimental observations of power-dependent, nonexponential decay of light stored in whispering gallery modes caused by stimulated Raman scattering in the resonator host material. Specifically, we show that the instantaneous decay rate of whispering gallery modes of a calcium fluoride resonator increases as the amount of light stored in the resonator decreases.     

Bright side of the Coulomb blockade

We explore the photonic (bright) side of the dynamical Coulomb blockade (DCB) by measuring the radiation emitted by a dc voltage-biased Josephson junction embedded in a microwave resonator. In this regime Cooper pair tunneling is inelastic and associated with the transfer of an energy 2eV into the resonator modes. We have measured simultaneously the Cooper pair current and the photon emission rate at the resonance frequency of the resonator. Our results show two regimes, in which each tunneling Cooper pair emits either one or two photons into the resonator. The spectral properties of the emitted radiation are accounted for by an extension to DCB theory.     

An investigation of quantum-chaotic signals generation using a fiber ring resonator and an add/drop multiplexer

We successfully generate the double security using a fiber ring resonator incorporating an add/drop device, whereas the quantum-chaotic encoding of light in a single fiber ring resonator is constructed. In the experiment, the nonlinear Kerr effects in the fiber ring resonator induced the chaotic wave form within the fiber ring resonator, which could be used to scramble or encode into the original signals. The laser input power used was 15 mW, with a fiber ring radius of 50 cm. We found that the double security can be formed, where the randomly polarized photons could be controlled by using the polarization controller and observed.     

High-quality-factor Bragg onion resonators with omnidirectional reflector cladding

We propose to approximate a spherically symmetric Bragg resonator in an onionlike geometry. We develop a transfer-matrix theory for calculation of the quality factors and analyze the effect of the onion stem on cavity Q factors. We find that it is possible to achieve significant inhibition of spontaneous emission in an onion resonator with omnidirectional cladding layers.