Optomechanical coupling in a suspended MoS2 air-gap nanocavity for sensitive force detection

Quantum mechanics continues to intrigue us with bizarre predictions that seemingly run counter to our everyday classical intuition. Superposition, zero-point motion, entanglement, and inescapable bounds on measurement precision are just a few purely quantum mechanical effects that come to mind. The promise of observing such effects in mesoscale mechanical resonators some orders of magnitude larger than the systems these effects had once been confined to, has resulted in surging interest in the field of cavity electro- and optomechanics. In these systems, the strong interaction of light and matter allows radiation pressure forces to provide significant damping to the mechanical motion, and serves as a means to mitigate the quantum-destroying, decohering effects of the pervasive thermal bath. However, for this backaction cooling to reduce the phonon occupation of a mechanical mode below unity, the confluence of the device and experimental setup must conform to a very strict set of conditions characterized by high optical and mechanical cavity quality factors, low optical absorption, low drive noise, and sufficiently sensitive detection. In this work, we describe the first optomechanical device and all-optical experimental setup to simultaneously satisfy these conditions, realizing the quantum ground state cooling of a 3.7 GHz mechanical mode (with a final phonon occupation of 0.85 +/- 0.08) in a picogram and micron-scale patterned nanobeam structure from a bath temperature of approximately 20 K. In context, subunity occupation of a mechanical mode in a similar-sized object had previously only been achieved by electromechanical devices operating in millikelvin dilution refrigerator environments. We also discuss the numerical simulation efforts involved in designing and optimizing these novel, coupled optical and mechanical resonators, and the fabrication procedure to realize them in silicon microchips. We recognize that this cooling result represents only an initial step toward the complete optical control of mesoscale mechanical oscillators in the quantum regime. To this end, we summarize an experiment we performed to detect the quantum zero-point motion of a nanobeam via scattering sideband asymmetry. We further show work in improving the optomechanical coupling and quality factors of these devices, as well as devising more efficient coupling schemes to improve measurement sensitivity.

In optomechanical systems, co-localizing light and mechanical oscillations at the nanoscale can lead to strong interaction between photons and phonons. Such optomechanical coupling enables sensitive detection of nanoscale motion, as well as control of the motion through optical forces down to the quantum level [1]. In the vast majority of cases, the optomechanical coupling can be regarded as linear. In this work, we exploit subwavelength optical field confinement to realize record-high interaction strengths, such that thermal motion induces optical frequency fluctuations larger than the intrinsic optical linewidth. The system thereby operates in a new — fully nonlinear — regime, which pronouncedly impacts optical response, displacement measurement, and radiation pressure effects [2]. We explore those implications, and demonstrate that the strong nonlinearity could be used for novel ways to measure and control mechanical quantum states.

For a wide range of health applications, label-free sensing is essential, and microphotonics offers innovative technical solutions for pursuing important objectives. It has been shown that the strong light/matter coupling formed between a cavity and molecules through light excitation enhances biological and clinical applications by providing deep insights into molecular analysis. The multilayer cavity’s proposed architecture is meant to promote a robust interaction between light and matter. The top layer was made of silver Ag multishape features that, after being synthesized and characterized, were immobilized on the surface of a multilayer system. A layer of indium tin oxide (ITO) was flipped to produce two distinct layouts. An investigation of the mode behavior was conducted to describe the two layouts; experimental and numerical results point to a strong light/matter interaction by the ITO/SiO2/spacer/Ag design. For the characterization of light/matter coupling, a fluorophore was adsorbed on the surface; the anticrossing energy was then examined by integrating the experimental data with a three mechanical oscillator model. To show the system’s sensitivity, the analysis was carried out again using bovine serum albumin (BSA). The protein is water-soluble and exhibits an infrared absorption band (amide I), while also being active in the Raman region. In addition, it may consistently bind to Ag multishape features. The excellent sensitivity was demonstrated, enabling the use of image analysis to capture the surface-enhanced Raman scattering of BSA. In conclusion, the suggested sensing approach raises fresh possibilities for highly sensitive biomolecule detection method and encourages results when used as a fundamental sensing technique to investigate molecular patterns.

Flexible and stretchable tactile sensors are attracted in the fields of soft robotics, wearable electronics, and healthcare monitoring. The sensing performance of tactile sensors is commonly affected by external deformations like stretching, bending, and twisting, thus they may fail to function on deformable object surfaces. This paper presents a stretchable tactile sensor array using kirigami‐patterned structural design and soft hinges to reduce the influences of deformation. The kirigami pattern of sensor array is parametrically studied to achieve the required expansion patterns. Laser engraving is employed to modify the micropillars on the force‐sensitive rubber surface to increase the sensitivity. Characterization tests show that the sensor array has high sensitivity (≈1.49 × 10−1 kPa−1) for force sensing, and the stretching and bending deformation have almost negligible effects on sensing performance. Under 40% stretching or 180° bending conditions, the measured resistance changes (ΔR/R0) is ≈0.03 and 0.06, respectively. To demonstrate the capability of developed sensor array, it is mounted on an expandable balloon surface for force detection. The recorded signals changed less than 1.5% during expanding process while rapidly rose under applied force, which indicated that the sensor array has the potential to effectively function on complex and deforming surfaces.

The DNA double helix was first elucidated by J.D. Watson and F.H.C. Crick over a half century ago. However, no one could actually "see" the well-known structure ever. Among all real-space observation methods, only atomic force microscopy (AFM) enables us to visualize the biologically active structure of natural DNA in water. However, conventional AFM measurements often caused the structural deformation of DNA because of the strong interaction forces acting on DNA. Moreover, large contact area between the AFM probe and DNA hindered us from imaging sub-molecular-scale features smaller than helical periodicity of DNA. Here, we show the direct observation of native plasmid DNA in water using an ultra-low-noise AFM with the highly sensitive force detection method (frequency modulation AFM: FM-AFM). Our micrographs of DNA vividly exhibited not only overall structure of the B-form double helix in water but also local structures which deviate from the crystallographic structures of DNA without any damage. Moreover, the interaction force area in the FM-AFM was small enough to clearly discern individual functional groups within DNA. The technique was also applied to explore the synthesized DNA nanostructures toward the current nanobiotechnology. This work will be essential for considering the structure-function relationship of biomolecular systems in vivo and for in situ analysis of DNA-based nanodevices.

We investigate the utility of nonclassical states of simple harmonic oscillators, particularly a superposition of coherent states, for sensitive force detection. We find that like squeezed states, a superposition of coherent states allows displacement measurements at the Heisenberg limit. Entangling many superpositions of coherent states offers a significant advantage over a single-mode superposition state with the same mean photon number.

Phase detection method with positive-feedback control using a quartz resonator based atomic force microscope in a liquid environment

Atomic force microscopy has evolved into an imaging method that yields fine structural details on live, biological samples like proteins, nucleotides, membranes and cells in their physiological environment and at ambient conditions. Due to its high lateral resolution and sensitive force detection capability, the exciting option of measuring inter- and intra-molecular forces of biomolecules on the single-molecule level has also become possible. The proof-of-principle stage of the pioneering experiments has already evolved into high-end analyses methods for exploring kinetic and structural details of interactions underlying protein folding and molecular recognition processes. Data obtained from force spectroscopy include physical parameters not measurable by other methods and opens new perspectives in exploring the regulation of the dynamics of biological processes. New instrumental developments allow to investigate the chemical composition of the sample. Together with improvements of the sensitivity and acquisition speed this has paved the way to exciting fields in nano-bioscience and nano-biotechnology.

Composition-Dependent Alterations in Thickness and Physical Properties of Lipid Bilayer FILM Revealed by Frequency Modulation Atomic Force Microscopy

Flexoelectric Effect in Pb(Zr0.53ti0.47)O3/Graphene Girder Structure for Highly Sensitive Force Detection

Triboelectric nanogenerators (TENGs) offer great opportunities to deploy advanced wearable electronics that integrate a power generator and smart sensor, which eliminates the associated cost and sustainability concerns. Here, an embodiment of such integrated platforms has been presented in a graphene oxide (GO) based single-electrode TENG (S-TENG). The as-designed multifunctional device could not only harvest tiny bits of mechanical energy from ambient movements with a high power density of 3.13 W·m-2 but also enable detecting dynamic force with an excellent sensitivity of about 388 μA·MPa-1. Because of the two-dimensional nanostructure and excellent surface properties, the GO-based S-TENG shows sensitive force detection and sound antimicrobial activity in comparison with conventional poly(tetrafluoroethylene) (PTFE) electrodes. This technology offers great applicability prospects in portable/wearable electronics, micro/nanoelectromechanical devices, and self-powered sensors.

Advances in cellular nanoscale force detection and manipulation

Normal-mode splitting (NMS) is an evident signature of strong coupling interactions for observing quantum phenomena, such as optomechanical squeezing and entanglement. In the previous literature, optical parametric amplifier (OPA) and coherent feedback are independently proposed to enhance the NMS. Here, we combine OPA and coherent feedback into a single optomechanical system to enhance the NMS. Controllable parameters, such as input optical power, OPA gain and phase, coherent feedback strength, are varied to observe NMS variations. In particular, we consider positive and negative feedback in terms of the amplitude reflectivity of the beam splitter for coherent feedback. The NMS appears mostly with the positive coherent feedback rather than the negative. Furthermore, the largest mode separation occurs at an OPA phase of approximately −π/4 rather than zero because the effective cavity detuning changes the effective intracavity round-trip phase, and therefore changes the OPA amplification/deamplification condition. The results indicate that the interplay between OPA and coherent feedback can enhance the NMS with more controllable parameter freedoms. This scheme provides a promising way to increase the optomechanical coupling strength, thereby having potential applications in the ground state cooling of a mechanical oscillator, the preparation of optomechanical quantum states, and the sensitive detection of a weak force.

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).

We propose and investigate an ultra-sensitive optical sensor system based on optomechanically induced nonlinear effects in high-Q optical resonators. In both dispersive and dissipative optomechanical systems, a positive feedback is formed between the optical resonance frequency and the mechanical displacement, which results in nonlinear transmission spectra different from a Lorentzian profile. Given the same resonator design, the optomechanical nonlinearity can increase the overall sensitivity by at least two orders of magnitude. Further improvement is possible by employing the phase sensitive detection. For the stable operation of the proposed sensor, we also analyze the requirement on the input power and the optomechanical coupling rate to overcome the thermal-optically induced frequency shift.