Gate-tunable bolometer based on strongly coupled graphene mechanical resonators.

Bolometers based on graphene have demonstrated outstanding performance with high sensitivity and short response time. In situ adjustment of bolometers is very important in various applications, but it is still difficult to implement in many systems. Here we propose a gate-tunable bolometer based on two strongly coupled graphene nanomechanical resonators. Both resonators are exposed to the same light field, and we can measure the properties of one bolometer by directly tracking the resonance frequency shifts, and indirectly measure the other bolometer through mechanical coupling. We find that the sensitivity and the response bandwidth of both bolometers can be independently adjusted by tuning the corresponding gate voltages. Moreover, the properties of the indirectly measured bolometer show a dependence on the coupling between the two resonators, with other parameters being fixed. Our method has the potential to optimize the design of large-scale bolometer arrays, and open new horizons in infrared/terahertz astronomy and communication systems.

Phonon lasing with an atomic thin membrane resonator at room temperature.

Graphene has been considered as one of the best materials to implement mechanical resonators due to their excellent properties such as low mass, high quality factors and tunable resonant frequencies. Here we report the observation of phonon lasing induced by the photonthermal pressure in a few-layer graphene resonator at room temperature, where the graphene resonator and the silicon substrate form an optical cavity. A marked threshold in the oscillation amplitude and a narrowing linewidth of the vibration mode are observed, which confirms a phonon lasing process in the graphene resonator. Our findings will stimulate the studies on phononic phenomena, help to establish new functional devices based on graphene mechanical resonators, and might find potential applications in classical and quantum sensing fields, as well as in information processing.

Flexible degenerate cavity with ellipsoidal mirrors.

Here we present a design of a traveling-wave optical cavity containing four identical ellipsoidal mirrors arranged in a square. The cavity proves to support more than 21 Laguerre-Gaussian modes simultaneously. There is a polarization splitting in the cavity that can be used for polarization filtering with a high isolation level.

Experimentally Robust Self-testing for Bipartite and Tripartite Entangled States.

Self-testing is a method with which a classical user can certify the state and measurements of quantum systems in a device-independent way. In particular, self-testing of entangled states is of great importance in quantum information processing. An understandable example is that the maximal violation of the Clauser-Horne-Shimony-Holt inequality necessarily implies that the bipartite system shares a singlet. One essential question in self-testing is that, when one observes a nonmaximum violation, how far is the tested state from the target state (which maximally violates a certain Bell inequality)? The answer to this question describes the robustness of the used self-testing criterion, which is highly important in a practical sense. Recently, J. Kaniewski derived two analytic self-testing bounds for bipartite and tripartite systems. In this Letter, we experimentally investigate these two bounds with high-quality two-qubit and three-qubit entanglement sources. The results show that these bounds are valid for various entangled states that we prepared. Thereby, a proof-of-concept demonstration of robust self-testing is achieved, which improves on the previous results significantly.

Degenerate cavity supporting more than 31 Laguerre-Gaussian modes.

Photons propagating in Laguerre-Gaussian modes have characteristic orbital angular momenta, which are fundamental optical degrees of freedom. The orbital angular momentum of light has potential application in high-capacity optical communication and even in quantum information processing. In this work, we experimentally construct a ring cavity with four lenses and four mirrors that is completely degenerate for Laguerre-Gaussian modes. By measuring the transmitted peaks and patterns of different modes, the ring cavity is shown to support more than 31 Laguerre-Gaussian modes. The constructed degenerate cavity opens a new way for using the unlimited resource of available angular momentum states simultaneously.

Experimental Demonstration of Higher Precision Weak-Value-Based Metrology Using Power Recycling.

The weak-value-based metrology is very promising and has attracted a lot of attention in recent years because of its remarkable ability in signal amplification. However, it is suggested that the upper limit of the precision of this metrology cannot exceed that of classical metrology because of the low sample size caused by the probe loss during postselection. Nevertheless, a recent proposal shows that this probe loss can be reduced by the power-recycling technique, and thus enhance the precision of weak-value-based metrology. Here we experimentally realize the power-recycled interferometric weak-value-based beam-deflection measurement and obtain the amplitude of the detected signal and white noise by discrete Fourier transform. Our results show that the detected signal can be strengthened by power recycling, and the power-recycled weak-value-based signal-to-noise ratio can surpass the upper limit of the classical scheme, corresponding to the shot-noise limit. This work sheds light on higher precision metrology and explores the real advantage of the weak-value-based metrology over classical metrology.

Tuning the nonlinearity of graphene mechanical resonators by Joule heating.

As an inherent property of the device itself, nonlinearity in micro-/nano- electromechanical resonators is difficult to eliminate, and it has shown a wide range of applications in basic research, sensing and other fields. While many application scenarios require tunability of the nonlinearity, inherent nonlinearity of a mechanical resonator is difficult to be changed. Here, we report the experimental observation of a Joule heating induced tuning effect on the nonlinearity of graphene mechanical resonators. We fabricated multiple graphene mechanical resonators and detected their resonant properties by an optical interference method. The mechanical vibration of the resonators will enter from the linear to the nonlinear intervals if we enhance the external driving power to a certain value. We found that at a fixed drive power, the nonlinearity of a mechanical resonator can be tuned by applying a dc bias current on the resonator itself. The tuning mechanism could be explained by the nonlinear amplitude-frequency dependence theory. Our results may provide a research platform for the study of mechanical nonlinearity by using atomic-thin layer materials.

Nanoscale depth control of implanted shallow silicon vacancies in silicon carbide.

Color centers in silicon carbide have recently attracted broad interest as high bright single photon sources and defect spins with long coherence time at room temperature. There have been several methods to generate silicon vacancy defects with excellent spin properties in silicon carbide, such as electron irradiation and ion implantation. However, little is known about the depth distribution and nanoscale depth control of the shallow defects. Here, a method is presented to precisely control the depths of the ion implantation induced shallow silicon vacancy defects in silicon carbide by using reactive ion etching with little surface damage. After optimizing the major etching parameters, a slow and stable etching rate of about 5.5 ± 0.5 nm min-1 can be obtained. By successive nanoscale plasma etching, the shallow defects are brought close to the surface step by step. The photoluminescence spectrum and optically detected magnetic resonance spectra are measured, which confirm that there were no plasma-induced optical and spin property changes of the defects. By tracing the mean counts of the remaining defects after each etching process, the depth distribution of the defects can be obtained for various implantation conditions. Moreover, the spin coherence time T2* of the generated VSi defects is detected at different etch depths, which greatly decreases when the depth is less than 25 nm. The method of nanoscale depth control of silicon vacancies would pave the way for investigating the surface spin properties and the applications in nanoscale sensing and quantum photonics.