High-frequency nanofluidics: an experimental study using nanomechanical resonators

Here we apply nanomechanical resonators to the study of oscillatory fluid dynamics. A high-resonance-frequency nanomechanical resonator generates a rapidly oscillating flow in a surrounding gaseous environment; the nature of the flow is studied through the flow-resonator interaction. Over the broad frequency and pressure range explored, we observe signs of a transition from Newtonian to non-Newtonian flow at omega tau approximately 1, where tau is a properly defined fluid relaxation time. The obtained experimental data appear to be in close quantitative agreement with a theory that predicts a purely elastic fluid response as omega tau --> infinity.     

Generating Squeezed States of Nanomechanical Resonator via a Flux Qubit in a Hybrid System

We propose a scheme for generating squeezed states based on a superconducting hybrid system.Our system consists of a nanomechanical resonator,a superconducting flux qubit,and a superconducting transmission line resonator.Using our proposal,one can easily generate the squeezed states of the nanomechanical resonator.In our scheme,the nonlinear interaction between the nanomechanical resonator and the superconducting transmission line resonator can be implemented by the flux qubit as 'nonlinear media' with a tunable Josephson energy.The realization of the nonlinearity does not need any operations on the flux qubit and just needs to adiabatically keep it at the ground state,which can greatly decrease the effect of the decoherence of the flux qubit on the squeezed efficiency.     

Quantum Entanglement Creating and Evolving in Two Charge Qubits Coupling to a Nanomechanical Resonator System

We investigate the coupling of two superconducting quantum interference devices (SQUIDs) via a metallic nanomechanical resonator (NAMR), and bring out the effective interaction between the two SQUIDs. By constructing the evolution operator, we also study the evolvement of entanglement in this composed system.     

金刚石氮空位色心耦合机械振子和腔场系统中方差压缩研究

研究了金刚石氮空位中心(NV色心)同时耦合腔场和机械振子系统中声子场的方差压缩动力学特性,分析了金刚石NV色心初态和NV色心与机械振子耦合强度对声子场方差压缩影响.结果发现:可以制备压缩时间长、压缩幅度大的声子场压缩态,其物理原因是机械振子具有最大相干性,并且通过调控NV色心初态以及磁场梯度可以实现对机械振子方差压缩非经典特性的操控,从而在理论上提供了一种调控声子场方差压缩的方式.     

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.     

Numerical simulation of gas bubble motion in a flow-through resonator

The problem of gas bubble motion in an acoustic resonator with a fluid flow is solved using numerical methods. It is shown that the distribution of the bubble concentration, which is nonuniform over the resonator length, is formed upon homogeneous introduction of bubbles. The problem on the bubble concentration distribution the along the resonator axis (with fluctuations of the bubble introduction period taken into account) is considered, and the fluctuation parameters are determined at which the periodic structure of the concentration distribution is preserved. The distribution of bubbles with different sizes over the resonator length is determined. It is shown that a resonator with a fluid flow accomplishes bubble selection by size (the average bubble concentration in the resonator increases with an increase in bubble size). The field in the resonator was calculated taking into account the effect of bubbles on sound velocity and damping.     

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.     

Bell States and Two-Qubit Logic Gate with Superconducting Charge Qubits Coupling to a Nanomechanical Resonator

We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling them to a nanomechanical resonator. We also show that it is possible to implement a two-qubit logic gate between the two charge qubits by choosing carefully the interaction time.     

Quantum control with Lyapunov function and bang–bang solution in the optomechanics system

We propose a quantum control scheme with the help of Lyapunov control function in the optomechanics system. The principle of the idea is to design suitable control fields to steer the Lyapunov control function to zero as t → ∞ while the quantum system is driven to the target state. Such an evolution makes no limit on the initial state and one needs not manipulate the laser pulses during the evolution. To prove the effectiveness of the scheme, we show two useful applications in the optomechanics system: one is the cooling of nanomechanical resonator and the other is the quantum fluctuation transfer between membranes. Numerical simulation demonstrates that the perfect and fast cooling of nanomechanical resonator and quantum fluctuation transfer between membranes can be rapidly achieved. Besides, some optimizations are made on the traditional Lyapunov control waveform and the optimized bang–bang control fields makes Lyapunov function V decrease faster. The optimized quantum control scheme can achieve the same goal with greater efficiency. Hence, we hope that this work may open a new avenue of the experimental realization of cooling mechanical oscillator, quantum fluctuations transfer between membranes and other quantum optomechanics tasks and become an alternative candidate for quantum manipulation of macroscopic mechanical devices in the near future.     

品质因子可调的石墨烯纳米机械振子

纳米机械振子尺寸小,质量轻,可以用来制作探测力、质量等微小物理量的超灵敏探测器.石墨烯拥有质量轻、密度低和杨氏模量高等特性,被认为是制作纳米机械振子的理想材料.石墨烯纳米机械振子因其具有的谐振频率高、品质因子高和谐振频率可调性高等优势,近年来得到了人们的广泛关注.作为表征纳米机械振子性能的一个重要指标,品质因子越高,意味着纳米机械振子耗散越低,纳米机械振子的灵敏度越高.本文通过微纳加工的工艺制备出一种谐振频率随栅压可调(调节的范围为73MHz~90MHz)的石墨烯纳米机械振子样品,研究其在极低温高真空环境下的品质因子与栅极电压之间的关系.实验表明通过栅压调节振子的内部应力,能够使石墨烯纳米机械振子品质因子从220提高到1000.我们的结果为二维材料纳米机械振子的耗散研究提供了一种新的研究思路.     

Frequency change by inter-walled length difference of double-wall carbon nanotube resonator

Ultrahigh frequency nanomechanical resonators based on double-walled carbon nanotubes with different wall lengths were investigated via classical molecular dynamics simulations. For a double-walled carbon nanotube resonator with a short outer wall, the free edge of the short outer wall plays an important role in the vibration of the long inner wall. For a double-walled carbon nanotube resonator with a short inner wall, the short inner wall can be considered as a flexible core, thus, the fundamental frequency is influenced by its length. By controlling the length of the inner or outer wall, various frequency devices can be realized by a single type of double-walled carbon nanotube with walls of equal length.     

Noise color and asymmetry in stochastic resonance with silicon nanomechanical resonators

Stochastic resonance with white noise has been well established as a potential signal amplification mechanism in nanomechanical two-state systems. While white noise represents the archetypal stimulus for stochastic resonance, typical operating environments for nanomechanical devices often contain different classes of noise, particularly colored noise with a 1/f spectrum. As a result, improved understanding of the effects of noise color will be helpful in maximizing device performance. Here we report measurements of stochastic resonance in a silicon nanomechanical resonator using 1/f noise and Ornstein-Uhlenbeck noise types. Power spectral densities and residence time distributions provide insight into asymmetry of the bistable amplitude states, and the data sets suggest that 1/f^α noise spectra with increasing noise color (i.e. α) may lead to increasing asymmetry in the system, reducing the achievable amplification. Furthermore, we explore the effects of correlation time τ on stochastic resonance with the use of exponentially correlated noise. We find monotonic suppression of the spectral amplification as the correlation time increases.     

Engineering quantum decoherence of charge qubit via a nanomechanical resonator

We propose a theoretical scheme to observe the loss of quantum coherence through the coupling of the superconducting charge qubit system to a nanomechanical resonator (NAMR), which has already been successfully fabricated in experiment and is convenient to manipulate. With a similar form to the usual cavity QED system, this qubit-NAMR composite system with engineered coupling exhibits the collapse and revival phenomenon in a progressive decoherence process. Corresponding to the two components of superposition of the two charge eigenstates, the state of the nanomechanical resonator evolves simultaneously towards two distinct quasi-classical states. Therefore the generalized which way detection by the NAMR induces the quantum decoherence of the charge qubit.Received: 21 May 2004, Published online: 9 September 2004PACS: 03.65.-w Quantum mechanics - 74.50. + r Tunneling phenomena; point contacts, weak links, Josephson effects - 03.67.Lx Quantum computation - 85.25.Dq Superconducting quantum interference devices (SQUIDs)     

Quantum Decoherence of Charge Qubit Coupled to Nonlinear Nanomechanical Resonator

When the nonlinearity of nanomechanical resonator is not negligible, the quantum decoherence of charge qubit is studied analytically. Using nonlinear Jaynes-Cummings model, one explores the possibility of being quantum data bus for nonlinear nanomechanical resonator, the nonlinearity destroys the dynamical quantum information-storage and maintains the revival of quantum coherence of charge qubit. With the calculation of decoherence factor, we demonstrate the influence of the nonlinearity of nanomechanical resonator on engineered decoherence of charge qubit.     

The 9th international symposium on fluid control, measurement and visualization (FLUCOME 2007)

This paper is the report on the Ninth International Symposium on Fluid Control, Measurement and Visualization. The symposium was scheduled on September 17–19, 2007 in Florida State University Center, Tallahassee Florida, U.S.A. Topics for FLUCOME 2007 included fluid processes across a wide range of scales in multiple disciplines: from micro-scale fluid flows in micro biomechanical devices, small-scale machine flows to large-scale civil and environmental fluid flows, and global scale geophysical and meteorological fluid flows.     

Mechanical systems in the quantum regime

Mechanical systems are ideal candidates for studying quantum behavior of macroscopic objects. To this end, a mechanical resonator has to be cooled to its ground state and its position has to be measured with great accuracy. Currently, various routes to reach these goals are being explored. In this review, we discuss different techniques for sensitive position detection and we give an overview of the cooling techniques that are being employed. The latter includes sideband cooling and active feedback cooling. The basic concepts that are important when measuring on mechanical systems with high accuracy and/or at very low temperatures, such as thermal and quantum noise, linear response theory, and backaction, are explained. From this, the quantum limit on linear position detection is obtained and the sensitivities that have been achieved in recent opto- and nanoelectromechanical experiments are compared to this limit. The mechanical resonators that are used in the experiments range from meter-sized gravitational wave detectors to nanomechanical systems that can only be read out using mesoscopic devices such as single-electron transistors or superconducting quantum interference devices. A special class of nanomechanical systems is bottom-up fabricated carbon-based devices, which have very high frequencies and yet a large zero-point motion, making them ideal for reaching the quantum regime. The mechanics of some of the different mechanical systems at the nanoscale is studied. We conclude this review with an outlook of how state-of-the-art mechanical resonators can be improved to study quantum mechanics.     

Generalized optical filters using a nonlinear micro ring resonator system

We present the interesting results of nonlinear behaviors of a soliton pulse within a nonlinear micro ring resonator system, where the optical filter characteristics in terms of frequency, wavelength and time can be functioned by using the chaotic filter within the micro ring resonator system. There are three forms of applications using the chaotic soliton behaviors and optical filter characteristics presented. Firstly, the simultaneous up-link and down-link frequency bands can be filtered and the required frequency bands obtained. Secondly, we propose the simple system of an extremely narrow light pulse generation over the spectrum range, where the required wavelengths can be filtered and obtained. Finally, a simple system of fast light generation by using a soliton pulse circulating in the integrated micro ring devices is proposed. Using such a system, an attosecond pulse and beyond can be easily filtered and obtained.     

Scalable Quantum Information Transfer between Individual Nitrogen-Vacancy Centers by a Hybrid Quantum Interface

We develop a design of a hybrid quantum interface for quantum information transfer(QIT),adopting a nanomechanical resonator as the intermedium,which is magnetically coupled with individual nitrogen-vacancy centers as the solid qubits,while capacitively coupled with a coplanar waveguide resonator as the quantum data bus.We describe the Hamiltonian of the model,and analytically demonstrate the QIT for both the resonant interaction and large detuning cases.The hybrid quantum interface aiiows for QIT between arbitrarily selected individual nitrogen-vacancy centers,and has advantages of the scalability and controllability.Our methods open an alternative perspective for implementing QIT,which is important during quantum storing or processing procedures in quantum computing.     

面向谐振式微光学陀螺应用的球形谐振腔DQ乘积优化

基于谐振式光学陀螺高灵敏度、低成本与微型化的发展需求, 为了实现高灵敏度的谐振式微光机电陀螺, 提出了以集成光学微谐振腔领域里高Q值、大直径谐振腔的制作为目标, 应用方向为谐振式光学陀螺的球形光学微谐振腔核心敏感单元. 在实验中以氢火焰作为热源采用熔融法制备球形光学微谐振腔. 通过调节氢气的流量控制氢火焰热源面积, 制备了不同直径(300-2200 μm)的球形谐振腔, 分析了球形谐振腔Q 值、DQ乘积、陀螺灵敏度与谐振腔直径D的对应关系及其原因, 获得了最优参数的面向谐振式光学陀螺的球形谐振腔敏感单元. D=1260 μm时, 球腔品质因数 Q=7.18×10⁷, 得到的最优陀螺灵敏度约为10°/h, 满足商业级应用的需求, 为芯片级、高精度、低成本的新型谐振式光学微腔陀螺的研究奠定了实验基础.     

Dynamical response of nanomechanical oscillators in immiscible viscous fluid for in vitro biomolecular recognition

Dynamical response of nanomechanical cantilever structures immersed in a viscous fluid is important to in vitro single-molecule force spectroscopy, biomolecular recognition of disease-specific proteins, and the study of microscopic protein dynamics. Here we study the stochastic response of biofunctionalized nanomechanical cantilever beams in a viscous fluid. Using the fluctuation-dissipation theorem we derive an exact expression for the spectral density of displacement and a linear approximation for resonance frequency shift. We find that in a viscous solution the frequency shift of the nanoscale cantilever is determined by surface stress generated by biomolecular interaction with negligible contributions from mass loading due to the biomolecules.