Generating EPR-type entanglement of degenerate optomechanical parametric oscillators

Einstein–Podolski–Rosen (EPR) entanglement states are achievable by combining two single-mode position and momentum squeezed states at a 50:50 beam splitter (BS). To generate the EPR mechanical entanglement, we consider the system consisted of two parametric optomechanical resonators, where two mechanical oscillators are linearly coupled. The linear coupling forms the symmetric and antisymmetric combinations of two mechanical modes, parallel to a 50:50 BS mixing. In the weak optomechanical coupling regime and via applying the opposite phases of parametric interactions, the symmetric and antisymmetric mechanical modes can be position and momentum squeezed, respectively. Therefore, two original mechanical modes are EPR entangled. Moreover, the mechanical thermal noise can decrease the entanglement. But with the parametric interaction enhanced optomechanical cooling, the influence of thermal noise on entanglement can be significantly suppressed, and the mechanical entanglement can be generated under a relatively high temperature. We also discuss the critical thermal occupation where the entanglement disappears, which is proportional to the optomechanical cooperativity parameter.     

Dynamic manipulation of nanomechanical resonators in the high-amplitude regime and non-volatile mechanical memory operation

The ability to control mechanical motion with optical forces has made it possible to cool mechanical resonators to their quantum ground states. The same techniques can also be used to amplify rather than reduce the mechanical motion of such systems. Here, we study nanomechanical resonators that are slightly buckled and therefore have two stable configurations, denoted 'buckled up' and 'buckled down', when they are at rest. The motion of these resonators can be described by a double-well potential with a large central energy barrier between the two stable configurations. We demonstrate the high-amplitude operation of a buckled resonator coupled to an optical cavity by using a highly efficient process to generate enough phonons in the resonator to overcome the energy barrier in the double-well potential. This allows us to observe the first evidence for nanomechanical slow-down and a zero-frequency singularity predicted by theorists. We also demonstrate a non-volatile mechanical memory element in which bits are written and reset by using optomechanical backaction to direct the relaxation of a resonator in the high-amplitude regime to a specific stable configuration.     

State transfer and entanglement of two mechanical oscillators in coupled cavity optomechanical system

We investigate coupled two-cavity optomechanical systems to show their potential usages by revealing the physical processes. Under two conditions, we deduce the correspondingly effective Hamiltonian with beam splitter type and nondegenerate parametric-down conversion type, respectively. Including the whole interactions, we show that the state transfer and the stationary entanglement between the two mechanical resonators can be achieved.     

Silicon-on-insulator based nanoresonators for mechanical mixing at radio frequencies

Nanomechanical resonators now allow operating frequencies approaching the range of several 100 MHz. Thus, nanomechanical devices become interesting for applications in signal processing. The main advantage of these devices is their high robustness against thermal and electrical shocks. Therefore, they can be used as very sensitive detectors or frequency selective components in communication electronics. Driving the resonators into nonlinear response increases the sensitivities further. Most importantly, such resonators can be used for a novel kind of mechanical mixing. Here, the mechanical oscillations of tiny bridges and oscillators can be used to realize such novel devices for high-frequency signal processing. We present measurements on mechanical mixing in a nanomechanical resonator operated at 100 MHz.     

The synchronization and entanglement of optomechanical systems

We investigate synchronization and entanglement in two coupled cavity optomechanical systems. The classical synchronization, quantum synchronization and entanglement of the two cavity fields and the two mechanical oscillators are analysed, respectively. Our results show that the two cavity resonators are synchronization without entanglement, while the two mechanical oscillators are entangled with quantum-phase synchronization. We conclude that the quantum synchronization and entanglement have no affirmatory relationship although they are both signature of correlation.     

Internal dielectric transduction: optimal position and frequency scaling

We propose the optimal design for "internal dielectric transduction" of longitudinal bulk mode resonators. This transduction increases in efficiency as the dielectric thickness approaches half the acoustic wavelength. With dielectric films at positions of maximum strain (minimum displacement) in the resonator, 60 GHz resonators are proposed with 50 Omega motional impedance.     

Mimicking a hybrid-optomechanical system using an intrinsic quadratic coupling in conventional optomechanical system

We consider an optical and mechanical mode interacting through both linear and quadratic dispersive couplings in a general cavity-optomechanical set-up. The parity and strength of an intrinsic quadratic optomechanical coupling (QOC) provides an opportunity to control the optomechanical (OM) interaction. We quantify this interaction by studying normal-mode splitting (NMS) as a function of the QOC's strength. The proposed scheme exhibits NMS features equivalent to a hybrid-OM system containing either an optical parametric amplifier or a Kerr medium. Such a system in reality could offer an alternative platform for devising state-of-art quantum devices with requiring no extra degrees-of-freedom as in hybrid-OM systems.     

Macroscopic tuning of nanomechanics: substrate bending for reversible control of frequency and quality factor of nanostring resonators

We have employed a chip-bending method to exert continuous and reversible control over the tensile stress in doubly clamped nanomechanical beam resonators. Tensile stress is shown to increase the quality factor of both silicon nitride and single-crystal silicon resonators, implying that added tension can be used as a general, material-independent route to increased quality factor. With this direct stretching technique, we demonstrate beam resonators with unprecedented tunability of both frequency and quality factor. Devices can be tuned back and forth between a high and low stress state, with frequency tunability as large as several hundred percent demonstrated. Over this wide range of frequency, quality factor is also tuned by as much as several hundred percent, providing insights into the loss mechanisms in these materials and this class of nanoresonator. Devices with frequencies in the 1-100 MHz range are studied, with quality factor as high as 390,000 achieved at room temperature, for a silicon nitride device with cross-sectional dimensions below 1 microm, operating in a high stress state. This direct stretching technique may prove useful for the identification of loss mechanisms that contribute to the energy balance in nanomechanical resonators, allowing for the development of new designs that would display higher quality factors. Such devices would have the ability to resolve smaller addendum masses and thus allow more sensitive detection and offer the potential for providing access to previously inaccessible dissipation regimes at low temperatures. This technique provides the ability to dramatically tune both frequency and quality factor, enabling future mechanical resonators to be used as variable frequency references as well as variable band-pass filters in signal-processing applications.     

Digital and FM Demodulation of a Doubly Clamped Single‐Walled Carbon‐Nanotube Oscillator: Towards a Nanotube Cell Phone

Electromechanical resonators are a key element in radio‐frequency telecommunication devices and thus new resonator concepts from nanotechnology can readily find important industrial opportunities. Here, the successful experimental realization of AM, FM, and digital demodulation with suspended single‐walled carbon‐nanotube resonators in a field‐effect transistor configuration is reported. The crucial role played by the electromechanical resonance in demodulation is clearly demonstrated. The FM technique is shown to lead to the suppression of unwanted background signals and the reduction of noise for a better detection of the mechanical motion of nanotubes. The digital data‐transfer rate of standard cell‐phone technology is within the reach of these devices.     

Optically driven resonance of nanoscale flexural oscillators in liquid

We demonstrate the operation of radio frequency nanoscale flexural resonators in air and liquid. Doubly clamped string, as well as singly clamped cantilever resonators, with nanoscale cross-sectional dimensions and resonant frequencies as high as 145 MHz are driven in air as well as liquid with an amplitude modulated laser. We show that this laser drive technique can impart sufficient energy to a nanoscale resonator to overcome the strong viscous damping present in these media, resulting in a mechanical resonance that can be measured by optical interference techniques. Resonance in air, isopropyl alcohol, acetone, water, and phosphate-buffered saline is demonstrated for devices having cross-sectional dimensions close to 100 nm. For operation in air, quality factors as high as 400 at 145 MHz are demonstrated. In liquid, quality factors ranging from 3 to 10 and frequencies ranging from 20 to 100 MHz are observed. These devices, and an all-optical actuation and detection system, may provide insight into the physics of the interaction of nanoscale mechanical structures with their environments, greatly extending the viscosity range over which such small flexural resonant devices can be operated.     

Ultra-sensitive NEMS-based cantilevers for sensing, scanned probe and very high-frequency applications

Scanning probe microscopies (SPM) and cantilever-based sensors generally use low-frequency mechanical devices of microscale dimensions or larger. Almost universally, off-chip methods are used to sense displacement in these devices, but this approach is not suitable for nanoscale devices. Nanoscale mechanical sensors offer a greatly enhanced performance that is unattainable with microscale devices. Here we describe the fabrication and operation of self-sensing nanocantilevers with fundamental mechanical resonances up to very high frequencies (VHF). These devices use integrated electronic displacement transducers based on piezoresistive thin metal films, permitting straightforward and optimal nanodevice readout. This non-optical transduction enables applications requiring previously inaccessible sensitivity and bandwidth, such as fast SPM and VHF force sensing. Detection of 127 MHz cantilever vibrations is demonstrated with a thermomechanical-noise-limited displacement sensitivity of 39 fm Hz(-1/2). Our smallest devices, with dimensions approaching the mean free path at atmospheric pressure, maintain high resonance quality factors in ambient conditions. This enables chemisorption measurements in air at room temperature, with unprecedented mass resolution less than 1 attogram (10(-18) g).     

A Suspended Silicon Single-Hole Transistor as an Extremely Scaled Gigahertz Nanoelectromechanical Beam Resonator

Suspended single-hole transistors (SHTs) can also serve as nanoelectromechanical resonators, providing an ideal platform for investigating interactions between mechanical vibrations and charge carriers. Demonstrating such a device in silicon (Si) is of particular interest, due to the strong piezoresistive effect of Si and potential applications in Si-based quantum computation. Here, a suspended Si SHT also acting as a nanoelectromechanical beam resonator is demonstrated. The resonant frequency and zero-point motion of the device are ≈3 GHz and 0.2 pm, respectively, reaching the best level among similar devices demonstrated with Si-containing materials. The mechanical vibration is transduced to electrical readout by the SHT. The signal transduction mechanism is dominated by the piezoresistive effect. A giant apparent effective piezoresistive gauge factor with strong correlation to single-hole tunneling is extracted in this device. The results show the great potential of the device in interfacing charge carriers with mechanical vibrations, as well as investigating potential quantum behavior of the vibration phonon mode.     

pH-dependent adsorption of Au nanoparticles on chemically modified Si3N4 MEMS devices

Microelectromechanical systems (MEMS) are devices that represent the integration of mechanical and electrical components in the micrometer regime. Self-assembled monolayers (SAMs) can be used to functionalise the surface of MEMS resonators in order to fabricate chemically specific mass sensing devices. The work carried out in this article uses atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS) data to investigate the pH-dependent adsorption of citrate-passivated Au nanoparticles to amino-terminated Si₃N₄ surfaces. AFM, XPS and mass adsorption experiments, using ‘flap’ type resonators, show that the maximum adsorption of nanoparticles takes place at pH = 5. The mass adsorption data, obtained using amino functionalised ‘flap’ type MEMS resonators, shows maximum adsorption of the Au nanoparticles at pH = 5 which is in agreement with the AFM and XPS data, which demonstrates the potential of such a device as a pH responsive nanoparticle detector.     

Motion transduction in nanoelectromechanical systems (NEMS) arrays using near-field optomechanical coupling

Development of efficient and sensitive motion transducers for arrays of nanoelectromechanical systems (NEMS) is important for fundamental research as well as for technological applications. Here, we report a single-wire nanomechanical transducer interface, which relies upon near-field optomechanical interactions. This multiplexed transducer interface comes in the form of a single-mode fiber taper on a fiber-optic cable. When the fiber taper is positioned sufficiently close to the NEMS array such that it can attain evanescent optical coupling with the array, individual NEMS resonances can be actuated using optical dipole forces. In addition, sensitive detection of nanomechanical motion can be realized when the evanescent waves confined around the taper are scattered by the motion. We have measured resonances from an array of 63 NEMS resonators with a displacement sensitivity of 2-8 pm·Hz(-1/2) at a detection power of ~100 μW (incident on the entire array).     

Characterization of MEMS Devices for the Study of?Superfluid Helium Films

Measurements on the mechanical properties of MEMS resonators were performed to characterize such devices at room temperature and low temperatures. Using state-of-the-art silicon integrated circuit technology, we have designed, fabricated, and manufactured resonators consisting of a pair of parallel plates with a well-defined gap whose size can be controlled with a high accuracy down to the sub-micron range. A full study of resonance properties at various pressures was performed at room temperature. We will discuss the details of design, fabrication, and operation. These studies open up a window of opportunities to look for novel phenomena in quantum fluids such as in superfluid ³He films.     

Soft lithographic fabrication of high Q polymer microcavity arrays

As new synthetic, low-loss polymers are developed, polymer optical cavities are experiencing a revolution, in both fabrication design and functionality. Recently, a fabrication technique was developed that enabled planar arrays of polymeric resonators to achieve cavity Q factors greater than 1 million. In the present letter, this molding technique is expanded to fabricate resonators from polymers that have either thermal or UV curing mechanisms. The quality factors and broad band spectrum of these devices are determined at 680, 1300, and 1550 nm. These resonant cavities demonstrate quality factors which are competitive with photonic crystals and microdisk resonators.     

Optical and mechanical anisotropies of aligned electrospun nanofibers reinforced transparent PMMA nanocomposites

This study aims to assess the nanofiber directionality effects on optomechanical properties of a widely used transparent thermoplastic poly(methyl methacrylate) (PMMA). Aligned fiber-hybrid mats consisted of nylon-6 (PA-6) nanofibers and PMMA microfibers are prepared using a self-blending co-electrospinning method, followed by hot press molding to fabricate into transparent nanocomposites. Effects of nanofiber orientation degree in two orthogonal directions and loading fraction on the optomechanical behavior of the nanocomposites are examined. Optical transmittance differences parallel and perpendicular to the nanofibers’ orientation are found to vary in a range of 3.9–5.4% at 589 nm, and strong mechanical anisotropy is observed with the 1% PA-6/PMMA nanocomposites. A maximal of 3% PA-6 nanofiber loading maintains the nanocomposite high transmittance (>75%) with improved strength and toughness along the nanofiber axis. This study reveals evident anisotropic optomechanical properties of transparent nanocomposites, and highlights the great designability of transparent nanocomposites by using aligned nanofibers as the designing elements.     

Field Deployable Microwave Filters Made from Superconductive Thick Films

Radio frequency (RF) resonators are made by depositing thick films of YBa₂Cu₃O_7– onto three-dimensional substrates. The superconducting resonators are then coupled together to form high performance RF filters. The topologies and frequency responses of some of these devices are briefly discussed prior to beginning a more detailed discussion aimed at addressing some of the common misconceptions of high temperature superconductive (HTS) thick film devices, namely the nonlinearity and the size. The intermodulation distortion (IMD) is shown to be below the noise floor in most practical applications, and a mathematical model that uses the empirical surface impedance data to predict the behavior of the IMD is described.     

Enhanced stress durability of nano resonators with scandium doped electrodes

To explore mechanical stress durability of thin aluminum–scandium (AlSc) films, 0.86 GHz nano resonators with AlSc electrodes have been manufactured. Four different samples have been prepared altering the Sc content in the alloy between 0.0% and 2.5%. A final lift-off step accomplished manufacture procedure of the devices. The resonators have been operated with heavy load to determine power durability. The resonators with AlSc electrodes show increased power durability compared to conventional Al metallized devices. Texture and grain structure of all films have been investigated by means of electron backscatter diffraction (EBSD) and atomic force microscopy (AFM). Material fatigue of electrodes has been visualized by scanning electron microscopy (SEM). The refined grain structure of these alloys can explain the enhanced mechanical stress durability of AlSc electrodes.     

Squeezing of the mechanical motion and beating 3 dB limit using dispersive optomechanical interactions

We study an optomechanical system consisting of an optical cavity and movable mirror coupled through dispersive linear optomechanical coupling (LOC) and quadratic optomechanical coupling (QOC). We work in the resolved side band limit with a high quality factor mechanical oscillator in a strong coupling regime. We show that the presence of QOC in the conventional optomechanical system (with LOC alone) modifies the mechanical oscillator’s frequency and reduces the back-action effects on mechanical oscillator. As a result of this the fluctuations in mechanical oscillator can be suppressed below standard quantum limit thereby squeeze the mechanical motion of resonator. We also show that either of the quadratures can be squeezed depending on the sign of the QOC. With detailed numerical calculations and analytical approximation we show that in such systems, the 3 dB limit can be beaten.