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Scattering obscures information carried by wave by producing a speckle pattern, posing a common challenge across various fields, including microscopy and astronomy. Traditional methods for extracting information from speckles often rely on significant physical assumptions, complex devices, or intricate algorithms. Recently, machine learning has emerged as a scalable and widely adopted tool for interpreting speckle patterns. However, most current machine learning techniques depend heavily on supervised training with extensive labeled datasets, which is problematic when labels are unavailable. To address this, we propose a strategy based on unsupervised learning for speckle recognition and evaluation, enabling to capture high-level information, such as object classes, directly from speckles without labeled data. By deriving invariant features from speckles, this method allows for the classification of speckles and facilitates diverse applications in image sensing. We experimentally validated our strategy through two significant applications: a noninvasive glucose monitoring system capable of differentiating time-lapse glucose concentrations, and a high-throughput communication system utilizing multimode fibers in dynamic environments. The versatility of this method holds promise for a broad range of far-reaching applications, including biomedical diagnostics, quantum network decoupling, and remote sensing.

Topological physics provides novel insights for designing functional photonic devices, such as magnetic-free optical diodes, which are important in optical engineering and quantum information processing. Past efforts mostly focus on the topological edge modes in two-dimensional (2D) photonic Chern lattices, which, however, require delicate fabrication and temporal modulation. In particular, the 1D nonreciprocal edge mode needs to be embedded in a 2D lattice, contradicting with the compactness of integrated photonics. To address these challenges, we investigate the optical nonreciprocity of the 1D Su-Schrieffer-Heeger (SSH) superradiance lattices in room-temperature atoms. The probe fields propagating in two opposite directions perceive two different SSH topological phases, which have different absorption spectra due to the interplay between the Zak phase and the thermal motion of atoms, resulting in optical nonreciprocity. Our findings reveal the relationship between 1D topological matter and optical nonreciprocity, simplifying the design of topologically resilient nonreciprocal devices., Comment: 4 figures

As a typical application of photon momentum transfer, optical levitation systems are known for their ideal isolation from mechanical dissipation and thermal noise. These characters offer extraordinary potential for acceleration precision sensing and have attracted extensive attention in both fundamental and applied physics. Although considerable improvements of optical levitation accelerometers has been reported, the dynamic testing of the sensing performance remains a crucial challenge before the utilization in practical application scenarios. In this work, we present a dual-beam optical levitation accelerometer and demonstrate the test with dynamic inputs for the first time. An acceleration sensing sensitivity of $0.1\mu g$ and a measurement range of $ 1g$ are achieved. These advancements solidify the potential of optical levitation accelerometer for deployment in practical domains, including navigation, intelligent driving, and industrial automation, building a bridge between the laboratory systems and real-world applications., Comment: 17 pages, 6 figures

Multiple optically levitated particles in vacuum can exhibit electrostatic interactions, optical binding, and non-reciprocal light-induced dipole-dipole interactions, making them promising platforms for exploring mesoscopic entanglement and complex interactions. However, in optical trap arrays, individually controlling the position and polarization of each trap is challenging, limiting the precise tuning of interactions between adjacent particles. This constraint hinders the study of complex interaction systems. In this work, we introduce a third nanoparticle as a coupler to two initially non-interacting nanoparticles, achieving tunable dipole-dipole coupling mediated by the third one. We investigated the effect of the particles' phases and positions on the interaction strength and demonstrated its broad tunability. Our method allows for precise control of interactions between any pair of adjacent particles in multi-particle systems, facilitating the further use of levitated nanoparticle arrays in macroscopic quantum mechanics and sensing.

Quantum simulation offers an analog approach for exploring exotic quantum phenomena using controllable platforms, typically necessitating ultracold temperatures to maintain the quantum coherence. Superradiance lattices (SLs) have been harnessed to simulate coherent topological physics at room temperature, but the thermal motion of atoms remains a notable challenge in accurately measuring the physical quantities. To overcome this obstacle, we invent and validate a velocity scanning tomography technique to discern the responses of atoms with different velocities, allowing cold-atom spectroscopic resolution within room-temperature SLs. By comparing absorption spectra with and without atoms moving at specific velocities, we can derive the Wannier-Stark ladders of the SL across various effective static electric fields, their strengths being proportional to the atomic velocities. We extract the Zak phase of the SL by monitoring the ladder frequency shift as a function of the atomic velocity, effectively demonstrating the topological winding of the energy bands. Our research signifies the feasibility of room-temperature quantum simulation and facilitates their applications in quantum information processing., Comment: 6 pages, 4 figures

In optomechanical systems, the libration and rotation of nanoparticles offer profound insights for ultrasensitive torque measurement and macroscopic quantum superpositions. Achievements include transitioning libration to rotation up to 6 GHz and cooling libration to millikelvin temperatures. It is undoubted that the libration and rotation are respectively driven by restoring and constant optical torques. The transition mechanisms between these two states, however, demand further exploration. In this perspective, it is demonstrated in this manuscript that monitoring lateral-scattered light allows real-time observation of libration/rotation transitions and associated hysteresis as ellipticities of trapping laser fields vary. By calculating optical torques and solving the Langevin equation, transitions are linked to the balance between anisotropic-polarization-induced sinusoidal optical torques and constant ones, with absorption identified as the main contributor to constant torques. These findings enable direct weak torque sensing and precise nanoparticle control in rotational degrees, paving the way for studying quantum effects like nonadiabatic phase shifts and macroscopic quantum superpositions, thereby enriching quantum optomechanics research.

Low-frequency (LF) wireless communications play a crucial role in ensuring anti-interference, long-range, and efficient communication across various environments. However, in conventional LF communication systems, their antenna size is required to be inversely proportional to the wavelength, so that their mobility and flexibility are greatly limited. Here we introduce a novel prototype of LF receiving antennas based on optically levitated nanoparticles, which overcomes the size-frequency limitation to reduce the antenna size to the hundred-nanometer scale. These charged particles are extremely sensitive to external electric field as mechanical resonators, and their resonant frequencies are adjustable. The effectiveness of these antennas was experimentally demonstrated by using the frequency shift keying (2FSK) modulation scheme. The experimental results indicate a correlation between error rate and factors such as transmission rate, signal strength, and vacuum degree with a signal strength of approximately 0.1V/m and a bit error rate below 0.1%. This advancement in leveraging levitated particle mechanical resonators (LPMRs) as LF antennas marks a significant stride in long-distance communication technology.

Optically levitated nanomechanical resonators in vacuum perform ultrahigh sensitivity for mechanical quantities by overcoming the limitations of clamped resonators. However, the generally levitated silica nanoparticles (NPs) with low absorption and high transparence still face difficulties surviving in high vacuum with unclear reason. By monitoring the physicochemical properties like scattering, mass and density of amorphous silica NPs during pumping process. we propose that the loss of NPs may arises from the motional instability induced by laser heating lead releasing at low pressure. In this work, two types of NPs are heat treated from 100 to 1200 degree Celsius to release impurities before being loaded into an optical trap. The high vacuum levitation ratio for both NPs increase obviously after heat treatment. In particular, for NPs heated to 600 degree Celsius, the ratio strikingly improves from ~30% to 100% and ~0 to 85% for two types of NPs. The loss mechanism is further confirmed by their relatively stable physicochemical parameters during pumping process. This work paves a way for wide application of levitated nano-resonators and indicates that levitated vacuum optomechanical systems could be a promising tool for dynamics and in-situ studying of small particles like aerosols and dusts.

Optically levitated microspheres are an excellent candidate for force and acceleration sensing. Here, we propose an acceleration sensing protocol based on an optically levitated microsphere array (MSA). The system consists of an $N$-microsphere array levitated in a driven optical cavity via holographic optical tweezers. By positioning the microspheres suitably relative to the cavity, only one of the collective modes of the MSA is coupled to the cavity mode. The optomechanical interaction encodes the information of acceleration acting on the MSA onto the intracavity photons, which can then be detected directly at the output of the cavity. The optically levitated MSA forms an effective large mass-distributed particle, which not only circumvents the problem of levitating a large mass microsphere but also results in a significant improvement of sensitivity. Compared with the traditional single-microsphere measurement scheme, our method presents an improvement in sensitivity by a factor of $\sqrt{N}$.

We experimentally demonstrate a nano-scale stochastic Stirling heat engine operating in the underdamped regime. The setup involves an optically levitated silica particle that is subjected to a power-varying optical trap and periodically coupled to a cold/hot reservoir via switching on/off active feedback cooling. We conduct a systematic investigation of the engine's performance and find that both the output work and efficiency approach their theoretical limits under quasi-static conditions. Furthermore, we examine the dependence of the output work fluctuation on the cycle time and temperature difference between the hot and cold reservoirs. We observe that the distribution has a Gaussian profile in the quasi-static regime, whereas it becomes asymmetric and non-Gaussian as the cycle duration time decreases. This non-Gaussianity is qualitatively attributed to the strong correlation of the particle's position within a cycle in the non-equilibrium regime. Our experiments provide valuable insights into stochastic thermodynamics in the underdamped regime and open up new possibilities for the design of future nano-machines.

The escape phenomenon, mainly caused by thermal effects, is known as an obstacle to the further practical application of optical levitation system in vacuum. Irregular photophoresis induced by thermal effects can act as an amplifier of Brownian motion. Studies on this topic provide interpretation for particle escaping phenomenon during the pressure decreasing process, as well as valuable insights into the micro- and nanoscale thermal effects in optical trap in vacuum. In this paper, we derive and test a dynamic model for the motion of an optically levitated particle in a non-equilibrium state and demonstrate the escaping mechanism of heated particles. The result of theoretical investigations is consistent with experimental escape at 0.1mbar. This work reveals and provides a theoretical basis for the stable operation of laser levitated oscillator in high vacuum and pave the way for the practicability of ultra-sensitive sensing devices.

Nanomechanical resonator based on levitated particle exhibits unique advantages in the development of ultrasensitive electric field detector. We demonstrate a three-dimensional, high-sensitivity electric field measurement technology using the optically levitated nanoparticle with a known net charge. By changing the relative position between nanoparticle and parallel electrodes, the three-dimensional electric field distribution is scanned. The measured noise equivalent electric intensity with charge amount of 100 reaches the order of {\rm{1\mu V/cm/H}}{{\rm{z}}^{{\rm{1/2}}}} at 1.4 \times {10^{ - 7}}mbar. Linearity analysis near resonance frequency shows a measured linear range over 91dB limited only by the maximum output voltage of the driving equipment. This work may provide avenue for developing a high-sensitive electric field sensor based on optically levitated nano-resonator., Comment: 15 pages, 10 figures. arXiv admin note: text overlap with arXiv:2008.05871 by other authors

In recent years, levitated particles of optical traps in vacuum have shown enormous potential in precision sensor development and searching for new physics. The accuracy of the calibration relating the detected signal to absolute displacement of the trapped particle is a critical factor for absolute measurement performance. In this paper, we suggest and experimentally demonstrate a novel calibration method for optical tweezers based on free-falling particles in vacuum, where the gravitational acceleration is introduced as an absolute reference. Our work provides a calibration protocol with great certainty and traceability, which is significant in improving the accuracy of precision sensing based on optically levitated particles., Comment: 10 pages, 5 figures

Oscillators based on levitated particles are promising for the development of ultrasensitive force detectors. The theoretical performance of levitated nanomechanical sensors is usually characterized by the so-called thermal noise limit force detection sensitivity, which does not exhibit spectral specificity in practical measurements. To characterize the actual detection performance, we propose a method for the force detection sensitivity calibration of a levitated nanomechanical sensor based on the harmonic Coulomb force. Utilizing the measured transfer function, we obtained the force detection sensitivity spectrum from the position spectrum. Although the thermal noise limit force detection sensitivity of the system reached $\rm\left( {4.39 \pm 0.62} \right) \times {10^{ - 20}} N/H{z^{1/2}}$ at $\rm{2.4\times10^{-6} mbar}$ with feedback cooling, the measured sensitivity away from the resonance was of the order of $\rm10^{-17} N/Hz^{1/2}$ based on the existing detection noise level. The calibration method established in our study is applicable to the performance evaluation of any optical levitation system for high-sensitivity force measurements.

Optical phase contains key information for biomedical and astronomical imaging. However, it is often obscured by layers of heterogeneous and scattering media, which render optical phase imaging at different depths an utmost challenge. Limited by the memory effect, current methods for phase imaging in strong scattering media are inapplicable to retrieving phases at different depths. To address this challenge, we developed a speckle three-dimensional reconstruction network (STRN) to recognize phase objects behind scattering media, which circumvents the limitations of memory effect. From the single-shot, reference-free and scanning-free speckle pattern input, STRN distinguishes depth-resolving quantitative phase information with high fidelity. Our results promise broad applications in biomedical tomography and endoscopy.

The rapid loading and manipulation of microspheres in optical trap is important for its applications in optomechanics and precision force sensing. We investigate the microsphere behavior under coaction of a dual-beam fiber-optic trap and a pulse laser beam, which reveals a launched microsphere can be effectively captured in a spatial region. A suitable order of pulse duration for launch is derived according to the calculated detachment energy threshold of pulse laser. Furthermore, we illustrate the effect of structural parameters on the launching process, including the spot size of pulse laser, the vertical displacement of beam waist and the initial position of microsphere. Our result will be instructive in the optimal design of the pulse-laser-assisted optical tweezers for controllable loading mechanism of optical trap.