Normal mode splitting in hybrid BEC-optomechanical system

We consider an opto-mechanical cavity system consisting of Bose-Einstein condensate (BEC), trapped inside the optical cavity and driven by single mode laser field. The intracavity field acts as nonlinear spring which couples the condensate mode with moving end mirror of the cavity. We study the occurrence of normal mode splitting in the position spectra of the mechanical oscillator and condensate mode as a consequence of hybridization of the fluctuations of intracavity field, mechanical mode and condensate mode. We also discuss the modification in the dynamics of the mechanical oscillator due to frequency of the collective oscillations of cold atoms and the back action of the atoms on the mechanical mirror. Moreover, we investigate the normal mode splitting in the transmission spectrum of cavity field.     

A passive means for cancellation of structurally radiated tones

The concept of cancellation of constant-frequency sound radiated from a vibrating surface by means of an attached mechanical oscillator is discussed. It is observed that the mass of a mechanical oscillator whose spring is attached to the vibrating surface will vibrate at comparatively large amplitudes and out of phase with that surface, provided that the surface vibrates at a frequency that is slightly higher than the oscillator's natural frequency. From this observation it is concluded that an oscillator's mass with a relatively small surface area can produce a volume velocity that is equal and opposite to that of the vibrating surface, resulting in cancellation of the sound radiated from the surface. Practical considerations in the design of such an oscillator are discussed, and the canceling performance from oscillators consisting of edge-supported circular disks is analyzed. An experimental canceling oscillator consisting of an edge-supported disk is described, and measurements made with this disk attached to a piston are shown to be in good agreement with analytical predictions. A tonal noise reduction exceeding 20 dB was demonstrated experimentally.     

Calculation of the propagator for a time-dependent damped,forced harmonic oscillator using the Schwinger action principle

A calculation of the quantum mechanical propagator for a general time-dependent one-dimensional damped, forced harmonic oscillator based on a direct application of the Schwinger action principle is presented. Contact with an earlier general method of calculation is made and in particular two previously found results are recovered from our general expression. The apparent dependence of one of them upon some unphysical parameters is clarified. The method presented here can be applied to any system described by a quadratic Hamiltonian and is an immediate extension of the calculation for the propagator of a simple harmonic oscillator with constant frequency.     

Federbush mode decomposition of ϕ42

The procedure for computing the kernel for the quantum mechanical harmonic oscillator by path integrals using Fourier series to diagonalize the action (originally proposed by Feynman and Hibbs), can be shown to be inconsistent; it leads to a kernel which converges to 0. A rigorous computation starting directly from the Trotter formula is demonstrated. This leads to the correct kernel and throws light upon the convergence mentioned.     

Modification on static responses of a nano-oscillator by quadratic optomechanical couplings

A quadratic coupling enabled parametric oscillation in an optomechanical system is used to modify the nonlinear static responses of a mechanical oscillator with a normal linear coupling.The mean value study showed that the modification of the static response on a mechanical oscillator is extremely sensitive and useful,which can readily enhance or suppress the nonlinear displacement response from a bistability case to singlet or triplet well case,freely bifurcating the equilibrium position from one to two or three.The static equilibria structure and the stability regions for mean-value controls on nano-oscillator were analyzed under the possible modification parameters.     

A periodically forced piecewise linear oscillator

A single-degree of freedom non-linear oscillator is considered. The non-linearity is in the restoring force and is piecewise linear with a single change in slope. Such oscillators provide models for mechanical systems in which components make intermittent contact. A limiting case in which one slope approaches infinity, an impact oscillator, is also considered. Harmonic, subharmonic, and chaotic motions are found to exist and the bifurcations leading to them are analyzed.     

Extending Newton's law from nonlocal-in-time kinetic energy

We study a new equation of motion derived from a context of classical Newtonian mechanics by replacing the kinetic energy with a form of nonlocal-in-time kinetic energy. It leads to a hypothetical extension of Newton's second law of motion. In a first stage the obtainable solution form is studied by considering an unknown value for the nonlocality time extent. This is done in relation to higher-order Euler-Lagrange equations and a Hamiltonian framework. In a second stage the free particle case and harmonic oscillator case are studied and compared with quantum mechanical results. For a free particle it is shown that the solution form is a superposition of the classical straight line motion and a Fourier series. We discuss the link with quanta interpretations made in Pais-Uhlenbeck oscillators. The discrete nature emerges from the continuous time setting through application of the least action principle. The harmonic oscillator case leads to energy levels that approximately correspond to the quantum harmonic oscillator levels. The solution to the extended Newton equation also admits a quantization of the nonlocality time extent, which is determined by the classical oscillator frequency. The extended equation suggests a new possible way for understanding the relationship between classical and quantum mechanics.     

Improving optomechanical gyroscopes by coherent quantum noise cancellation processing

Coherent quantum noise cancellation(CQNC) method is used to beat standard quantum limit(SQL) for improving the performance of quantum optomechanical gyroscopes. The protocol for realizing CQNC is achieved by constructing an effective negative mass mechanical oscillator, which is simulated by an ancillary cavity. This oscillator shows an antiresponse relative to that of a real mechanical oscillator. Thus, the optomechanical back-action noise is counteracted or restrained, and we could increase our signal by increasing the coupling strength without increasing the noise.     

Effect of magnetic field on the dislocation structure and mechanical properties of alkali halide crystals deformed by ultrasound

The dislocation structure and mechanical properties of LiF and NaCl crystals under joint action of magnetic field and ultrasound in the range of longitudinal strain amplitudes corresponding to dislocation multiplication have been investigated. Ultrasonic deformation was implemented in a piezoelectric oscillator at a frequency of 80 kHz. It is established that the presence of a magnetic field facilitates cross slip; initiates displacement of block boundaries; and leads to the formation of labyrinth structures (characteristic of high-temperature loading), which strengthen the crystal.     

Sapphire test-masses for measuring the standard quantum limit and achieving quantum non-demolition

 In this paper we show that the available technology is sufficient to measure the Standard Quantum Limit (SQL) of a low loss acoustic oscillator, with a readout based on a microwave parametric transducer. The experiment makes use of the low electrical and acoustical losses in monocrystalline sapphire and new low-noise microwave technology. The crystal acts as an electrical vibration sensor and an acoustic oscillator in one monolithic structure. We analyze two new types of such structures: (1) The sapphire bar dielectric transducer and (2) the slotted sapphire dielectric transducer. We show that with a 40–60 dB double-cavity phase-noise suppression system the SQL may be measured using the sapphire bar. For the slotted structure, the phase noise requirements are less stringent because of its smaller resonant frequency and mass. We show that the SQL of this structure may be measured with a standard parametric readout. The principle of operation is demonstrated by some simple room-temperature experiments with all results verified using finite-element analysis. Given that we can expect to measure the SQL with one of these schemes, we analyze the properties of a microwave displacement measurement system based upon a high-Q parametric transducer and a double-frequency oscillator. Such a readout system represents a practical implementation of a black action evasion (BAE) displacement sensor allowing the discrimination between the quadratures of the mechanical oscillator. We determine the set of conditions which allows the enhanced sensitivity with respect to the desired quadrature and suppressed sensitivity to the unwanted quadrature. We find that tuning of the BAE system at the particular quadrature of interest can be performed by varying the phase relationship between the microwave carriers available from the double-frequency oscillator. We establish the importance of having the frequency and the phase-control servos to maintain the optimal tuning of the micro-wave BAE readout system, as both the mechanical oscillator and the double-frequency pump oscillator are always subject to various sources of environmental interference. Received: 28 March 1996/Revised version: 12 June 1996     

Enhancement of feasibility of macroscopic quantum superposition state with the quantum Rabi-Stark model

We propose an efficient scheme to generate a macroscopical quantum superposition state with a cavity optomechanical system, which is composed of a quantum Rabi-Stark model coupling to a mechanical oscillator. In a low-energy subspace of the Rabi-Stark model, the dressed states and then the effective Hamiltonian of the system are given. Due to the coupling of the mechanical oscillator and the atom-cavity system, if the initial state of the atom-cavity system is one of the dressed states, the mechanical oscillator will evolve into a corresponding coherent state. Thus, if the initial state of the atom-cavity system is a superposition of two dressed states, a coherent state superposition of the mechanical oscillator can be generated. The quantum coherence and their distinguishable properties of the two coherent states are exhibited by Wigner distribution. We show that the Stark term can enhance significantly the feasibility and quantum coherence of the generated macroscopic quantum superposition state of the oscillator.     

磁绝缘线振荡器阴极烧蚀与电压波形的关系研究

通过粒子模拟和实验研究相结合的方法,研究了磁绝缘线振荡器的阴极烧蚀与输入电压波形的关系,找到了造成阴极烧蚀的根本原因,给出了电子束回轰阴极的清晰图像,并通过对低阻抗加速器平台输出电压波形的调整,抑制了反向电压,解决了器件的阴极烧蚀问题.研究结果表明:在正向电压作用下已经发射出来的电子束在超过一定幅度的反向电压作用下发生反向运动并回轰阴极,产生反向电流并造成器件阴极的烧蚀,因此注入电压下降沿之后的反向电压是引起磁绝缘线振荡器的阴极烧蚀的最根本因素.     

强耦合光机械腔中的简正模式分裂和冷却

研究由辐射压力与驱动Fabry-Perot光学腔相耦合而产生的腔光机械动力学行为. 通过量子朗之万方程具体研究了机械振子的涨落光谱、机械阻尼与共振频移和基态冷却. 随着输入激光功率的增加,振子的涨落光谱呈现简正模式分裂的现象,并且数值模拟结果和实验结果相符合. 同时推导了有效机械阻尼和共振频移. 红移边带导致了机械模的冷却,蓝移边带引起了机械模的放大. 此外,引入一种近似机制来研究振子的基态冷却,并且考虑在解析边带机制下简正模式分裂对机械振子冷却的影响. 最后,数值讨论了初始浴温度、输入激光功率和机械品质因数这三个因素对机械振子冷却的影响. 关键词： 腔光机械 辐射压力 简正模式分裂 冷却     

Electrooptical oscillator using an integrated cutoff modulator

An integrated optical cutoff modulator is fed back electrically. In this way an electrooptical oscillator is built applicable as optical clock generator or electrical switchable oscillator for optical communication systems. Its center frequency is 380 MHz with a stability of 6 × 10^-5. The mode structure of the oscillator is investigated.     

线性振子过阻尼特性分析

分析了线性振子的过阻尼特性,指出处于过阻尼状态的线性振子在特定初始条件下能越过平衡位置一次,在另一特定初始条件下,振子将能最快地回到平衡位置。     

Properties of a distributed feedback dye laser with integrated amplifier

Several properties of a compact laser light source built up by a distributed feedback dye laser (DFDL) and an amplifier realized with only one dye solution cuvette are discussed. It is shown that in this arrangement the region of single pulse generation with respect to the pump energy applied to the DFDL is extended in comparison with a pure DFDL oscillator set-up. This effect is mainly caused by the radiation coupled back from the amplifier into the DFDL oscillator. The results of numerical simulations are discussed and compared with some experimental facts published in a previous paper.     

基于MgO:APLN的多光参量振荡器实验研究及其逆转换过程演化分析

对基于MgO:APLN的多光参量振荡器进行了实验研究. 通过优化MgO:APLN极化结构及参量光耦合输出透过率, 在200 kHz高重复频率1064 nm激光抽运下, 通过单极化晶体实现了1.57 μm, 3.84 μm跨周期参量光输出, 平均功率分别达到2.4 W和1.31 W, 对应光-光转换效率为11.54%和6.25%. 同时针对多光参量振荡过程的逆转换现象, 通过耦合波方程对其进行了数值演化, 并引入“逆转换能量传导区”概念, 指出逆转换能量传导区的存在促使弱增益光学参量振荡器的参量光得到二次增强, 所得结论与实验结果相符合.     

Radiation pressure cooling of a micromechanical oscillator using dynamical backaction

Cooling of a 58 MHz micromechanical resonator from room temperature to 11 K is demonstrated using cavity enhanced radiation pressure. Detuned pumping of an optical resonance allows enhancement of the blueshifted motional sideband (caused by the oscillator's Brownian motion) with respect to the redshifted sideband leading to cooling of the mechanical oscillator mode. The reported cooling mechanism is a manifestation of the effect of radiation pressure induced dynamical backaction. These results constitute an important step towards achieving ground state cooling of a mechanical oscillator.