Ultrasensitive and ultrastretchable electrically self-healing conductors.

Self-healing is a bioinspired strategy to repair damaged conductors under repetitive wear and tear, thereby largely extending the life span of electronic devices. The self-healing process often demands external triggering conditions as the practical challenges for the widespread applications. Here, a compliant conductor with electrically self-healing capability is introduced by combining ultrahigh sensitivity to minor damages and reliable recovery from ultrahigh tensile deformations. Conductive features are created in a scalable and low-cost fabrication process comprising a copper layer on top of liquid metal microcapsules. The efficient rupture of microcapsules is triggered by structural damages in the copper layer under stress conditions as a result of the strong interfacial interactions. The liquid metal is selectively filled into the damaged site for the instantaneous restoration of the metallic conductivity. The unique healing mechanism is responsive to various structural degradations including microcracks under bending conditions and severe fractures upon large stretching. The compliant conductor demonstrates high conductivity of ∼12,000 S/cm, ultrahigh stretchability of up to 1,200% strain, an ultralow threshold to activate the healing actions, instantaneous electrical recovery in microseconds, and exceptional electromechanical durability. Successful implementations in a light emitting diode (LED) matrix display and a multifunctional electronic patch demonstrate the practical suitability of the electrically self-healing conductor in flexible and stretchable electronics. The developments provide a promising approach to improving the self-healing capability of compliant conductors.

Silk-protein-based gradient hydrogels with multimode reprogrammable shape changes for biointegrated devices.

Biocompatible and morphable hydrogels capable of multimode reprogrammable, and adaptive shape changes are potentially useful for diverse biomedical applications. However, existing morphable systems often rely on complicated structural designs involving cumbersome and energy-intensive fabrication processes. Here, we report a simple electric-field-activated protein network migration strategy to reversibly program silk-protein hydrogels with controllable and reprogrammable complex shape transformations. The application of a low electric field enables the convergence of net negatively charged protein cross-linking networks toward the anode (isoelectric point plane) due to the pH gradient generated in the process, facilitating the formation of a gradient network structure and systems suitable for three-dimensional shape change. These tunable protein networks can be reprogrammed or permanently fixed by control of the polymorphic transitions. We show that these morphing hydrogels are capable of conformally interfacing with biological tissues by programming the shape changes and a bimorph structure consisting of aligned carbon nanotube multilayers and the silk hydrogels was assembled to illustrate utility as an implantable bioelectronic device for localized low-voltage electrical stimulation of the sciatic nerve in a rabbit.

Optically Readable, Physically Unclonable Subwavelength Pixel via Multicolor Quantum Dot Printing for Anticounterfeiting.

We present a secure and user-friendly ultraminiaturized anticounterfeiting labeling technique─the color-encoded physical unclonable nanotag. These nanotags consist of subwavelength spots formed by random combinations of multicolor quantum dots, which are fabricated using a cost-efficient printing method developed in this study. The nanotags support over 170,000 different colors and are inherently resistant to cloning. Moreover, their high brightness and color purity, owing to the quantum dots, ensure an ease of readability. Additionally, these nanotags can function as color-encrypted pixels, enabling the incorporation of labels (such as QR codes) into ultrasmall physically unclonable hidden tags with a resolution exceeding 100,000 DPI. The unique blend of compactness, flexibility, and security positions the color-encoded nanotag as a potent and versatile solution for next-generation anticounterfeiting applications.

Achromatic and Coma-Corrected Hybrid Meta-Optics for High-Performance Thermal Imaging.

Long-wave infrared (LWIR) imaging, or thermal imaging, is widely applied in night vision and security monitoring. However, the widespread use of LWIR imagers is impeded by their bulky size, considerable weight, and high cost. While flat meta-optics present a potential solution to these limitations, existing pure LWIR meta-optics face constraints such as severe chromatic or coma aberrations. Here, we introduce an approach utilizing large-scale hybrid meta-optics to address these challenges and demonstrate the achromatic, coma-corrected, and polarization-insensitive thermal imaging. The hybrid metalens doublet is composed of a metasurface corrector and a refractive lens, featuring a full field-of-view angle surpassing 20° within the 8-12 µm wavelength range. Employing this hybrid metalens doublet, we showcase high-performance thermal imaging capabilities both indoors and outdoors, effectively capturing ambient thermal radiation. The proposed hybrid metalens doublet holds considerable promise for advancing miniaturized, lightweight, and cost-effective LWIR optical imaging systems.

Polychromatic Dual-Mode Imaging with Structured Chiral Photonic Crystals.

Optical spatial differentiation is a typical operation of optical analog computing and can single out the edge to accelerate the subsequent image processing, but in some cases, overall information about the object needs to be presented synchronously. Here, we propose a multifunctional optical device based on structured chiral photonic crystals for the simultaneous realization of real-time dual-mode imaging. This optical differentiator is realized by self-organized large-birefringence cholesteric liquid crystals, which are photopatterned to encode with a special integrated geometric phase. Two highly spin-selective modes of second-order spatial differentiation and bright-field imaging are exhibited in the reflected and transmitted directions, respectively. Two-dimensional edges of both amplitude and phase objects have been efficiently enhanced in high contrast and the broadband spectrum. This work extends the ingenious building of hierarchical chiral nanostructures, enriches their applications in the emerging frontiers of optical computing, and boasts considerable potential in machine vision and microscopy.

Charge Generation Dynamics in Organic Photovoltaic Blends under One-Sun-Equivalent Illumination Detected by Highly Sensitive Terahertz Spectroscopy.

Organic photovoltaic (OPV) devices attain high performance with nonfullerene acceptors by utilizing the synergistic dual channels of charge generation that originate from excitations in both the donor and acceptor materials. However, the specific intermediate states that facilitate both channels are subject to debate. To address this issue, we employ time-resolved terahertz spectroscopy with improved sensitivity (ΔE/E < 10-6), enabling direct probing of charge generation dynamics in a prototypical PM6:Y6 bulk heterojunction system under one-sun-equivalent excitation density. Charge generation arising from donor excitations is characterized with a rise time of ∼9 ps, while that from acceptor excitations shows a rise time of ∼18 ps. Temperature-dependent measurements further reveal notably distinct activation energies for these two charge generation pathways. Additionally, the two channels of charge generation can be substantially manipulated by altering the ratio of bulk to interfaces. These findings strongly suggest the presence of two distinct intermediate states: interfacial and intramoiety excitations. These states are crucial in mediating the transfer of electrons and holes, driving charge generation within OPV devices.

Passive magnetic-free broadband optical isolator based on unidirectional self-induced transparency.

Achieving a broadband nonreciprocal device without gain and any external bias is very challenging and highly desirable for modern photonic technologies and quantum networks. Here we theoretically propose a passive and magnetic-free all-optical isolator for a femtosecond laser pulse by exploiting a new mechanism of unidirectional self-induced transparency, obtained with a nonlinear medium followed by a normal absorbing medium at one side. The transmission contrast between the forward and backward directions can reach 14.3 dB for a 2π - 5 fs laser pulse. The 20 dB bandwidth is about 56 nm, already comparable with a magneto-optical isolator. This work provides a new mechanism which may benefit non-magnetic isolation of ultrashort laser pulses.

Observation of quantum nonlocality in Greenberger-Horne-Zeilinger entanglement on a silicon chip.

Nonlocality is the defining feature of quantum entanglement. Entangled states with multiple particles are of crucial importance in fundamental tests of quantum physics as well as in many quantum information tasks. One of the archetypal multipartite quantum states, Greenberger-Horne-Zeilinger (GHZ) state, allows one to observe the striking conflict of quantum physics to local realism in the so-called all-versus-nothing way. This is profoundly different from Bell's theorem for two particles, which relies on statistical predictions. Here, we demonstrate an integrated photonic chip capable of generating and manipulating the four-photon GHZ state. We perform a complete characterization of the four-photon GHZ state using quantum state tomography and obtain a state fidelity of 0.729±0.006. We further use the all-versus-nothing test and the Mermin inequalities to witness the quantum nonlocality of GHZ entanglement. Our work paves the way to perform fundamental tests of quantum physics with complex integrated quantum devices.

Direct detection Φ-OTDR based on UWFBG array using linear-phase-modulated double-pulse.

We propose what we believe to be a novel direct detection phase-sensitive optical time-domain reflectometry (Φ-OTDR) based on ultra-weak fiber Bragg grating (UWFBG) array to achieve distributed vibration measurements with exceptional sensitivity and remarkable stability. Our system employs a pulse modulator to generate a double pulse and achieves linear phase modulation of one pulse by one cycle through a phase modulator. The phase change can be quantitatively demodulated using our proposed N-step phase-shifted demodulation algorithm. This method effectively mitigates the influence of phase noise of the laser and the pulse modulator, while also eliminating fluctuations in the half-voltage of the phase modulator. Compared with the existing phase modulation methods, our method avoids stringent requirements for the stability and precision of phase modulation. Moreover, we propose a phase-shifted approximation method, breaking the limitation of sensing length on the traditional differential approximation method and improving the accuracy significantly. The technique's effectiveness is experimentally demonstrated on a 1 km UWFBG array with a reflectivity of -40 dB to -45 dB and a spatial resolution of 10 m. Vibrations with different amplitudes are measured quantitatively with good linearity. The low-frequency self-noise is greatly suppressed and the overall self-noise is -54.3 dB rad2/Hz.

Quantum ghost imaging of a vector field.

Quantum ghost image technique utilizing position or momentum correlations between entangled photons can realize nonlocal reconstruction of the image of an object. In this work, based on polarization entanglement, we experimentally demonstrate quantum ghost imaging of vector images by using a geometric phase object. We also provide a corresponding theoretical analysis. Additionally, we offer a geometrical optics path explanation of ghost imaging for vector fields. The proposed strategy offers new insights into the fundamental development of ghost imaging and also holds great promise for developing complex structured ghost imaging techniques. Our work expanding the principle of ghost imaging to spatially varying vector beams will lead to interesting developments of this field.

Observation of Chiral Symmetry Breaking in Toroidal Vortices of Light.

In this Letter, we explore the intersection of chirality and recently discovered toroidal spatiotemporal optical vortices (STOVs). We introduce "photonic conchs" theoretically as a new type of toroidal-like state exhibiting geometrical chirality, and experimentally observe these wave packets with controllable topological charges. Unlike toroidal STOVs, photonic conchs exhibit unique chirality-related dynamical evolution in free space and possess an orbital angular momentum correlated with all the dimensions of space-time. This research deepens our understanding of toroidal light states and potentially advances various fields by unveiling similar wave phenomena in a broader scope of physics systems, including acoustics and electronics.

Generation of Perfect Electron Vortex Beam with a Customized Beam Size Independent of Orbital Angular Momentum.

The electron vortex beam (EVB)-carrying quantized orbital angular momentum (OAM) plays an essential role in a series of fundamental research. However, the radius of the transverse intensity profile of a doughnut-shaped EVB strongly depends on the topological charge of the OAM, impeding its wide applications in electron microscopy. Inspired by the perfect vortex in optics, herein, we demonstrate a perfect electron vortex beam (PEVB), which completely unlocks the constraint between the beam size and the beam's OAM. We design nanoscale holograms to generate PEVBs carrying different quanta of OAM but exhibiting almost the same beam size. Furthermore, we show that the beam size of the PEVB can be readily controlled by only modifying the design parameters of the hologram. The generation of PEVB with a customized beam size independent of the OAM can promote various in situ applications of free electrons carrying OAM in electron microscopy.

Smart Magnetic Optical Antenna for Automatic Nanoalignment and Photon Beaming from Prepatterned Single Quantum Dot Nanospot.

We present a unidirectional dielectric optical antenna, which can be chemically synthesized and controlled by magnetic fields. By applying magnetic fields, we successfully aligned an optical antenna on a prepatterned quantum dot nanospot with accuracy better than 40 nm. It confined the fluorescence emission into a 16-degree wide beam and enhanced the signal by 11.8 times. Moreover, the position of the antenna, and consequently the beam direction, can be controlled by simply adjusting the direction of the magnetic fields. Theoretical analyses show that this magnetic alignment technique is stable and accurate, providing a new strategy for building high-performance tunable nanophotonic devices.

Dielectric Metasurface for Synchronously Spiral Phase Contrast and Bright-Field Imaging.

Spiral phase contrast imaging and bright-field imaging are two widely used modes in microscopy, providing distinct morphological information about objects. However, conventional microscopes are always unable to operate with these two modes at the same time and need additional optical elements to switch between them. Here, we present a microscopy setup that incorporates a dielectric metasurface capable of achieving spiral phase contrast imaging and bright-field imaging synchronously. The metasurface not only can focus the light for diffraction-limited imaging but also can perform a two-dimensional spatial differentiation operation by imparting an orbital angular momentum to the incident light field. This allows two spatially separated images to be simultaneously obtained, one containing high-frequency edge information and the other showing the entirety of the object. Combined with the advantages of planar architecture and ultrathin thickness of the metasurface, this approach is expected to provide support in the fields of microscopy, biomedicine, and materials science.

Ultrastretchable Electrically Self-Healing Conductors Based on Silver Nanowire/Liquid Metal Microcapsule Nanocomposites.

Stretchable conductive nanocomposites are essential for deformable electronic devices. These conductors currently face significant limitations, such as insufficient deformability, significant resistance changes upon stretching, and drifted properties during cyclic deformations. To tackle these challenges, we present an electrically self-healing and ultrastretchable conductor in the form of bilayer silver nanowire/liquid metal microcapsule nanocomposites. These nanocomposites utilize silver nanowires to establish their initial excellent conductivity. When the silver nanowire networks crack during stretching, the microcapsules are ruptured to release the encased liquid metal for recovering the electrical properties. This self-healing capability allows the nanocomposite to achieve ultrahigh stretchability for both uniaxial and biaxial strains, minor changes in resistance during stretching, and stable resistance after repetitive deformations. The conductors have been used to create skin-attachable electronic patches and stretchable light-emitting diode arrays with enhanced robustness. These developments provide a bioinspired strategy to enhance the performance and durability of conductive nanocomposites.

Dynamically Modulating the Dissymmetry Factor of Circularly Polarized Organic Ultralong Room-Temperature Phosphorescence from Soft Helical Superstructures.

Achieving circularly polarized organic ultralong room-temperature phosphorescence (CP-OURTP) with a high luminescent dissymmetry factor (glum ) is crucial for diverse optoelectronic applications. In particular, dynamically controlling the dissymmetry factor of CP-OURTP can profoundly advance these applications, but it is still unprecedented. This study introduces an effective strategy to achieve photoirradiation-driven chirality regulation in a bilayered structure film, which consists of a layer of soft helical superstructure incorporated with a light-driven molecular motor and a layer of room-temperature phosphorescent (RTP) polymer. The prepared bilayered film exhibits CP-OURTP with an emission lifetime of 805 ms and a glum value up to 1.38. Remarkably, the glum value of the resulting CP-OURTP film can be reversibly controlled between 0.6 and 1.38 over 20 cycles by light irradiation, representing the first example of dynamically controlling the glum in CP-OURTP.

Cholesteric Liquid Crystal Polymeric Coatings for Colorful Artificial Muscles and Motile Humidity Sensor Skin Integrated with Magnetic Composites.

Structural colorful cholesterics show impressive susceptibility to external stimulation, leading to applications in electro/mechano-chromic devices. However, out-of-plane actuation of structural colorful actuators based on cholesterics and the integration with other stimulation remains underdeveloped. Herein, colorful actuators and motile humidity sensors are developed using humidity-responsive cholesteric liquid crystal networks (CLCNs) and magnetic composites. The developed colorful actuator can exhibit synergistic out-of-plane shape morphing and color change in response to humidity, with CLCNs as colorful artificial muscles. Through the integration with magnetic control, the motile sensor can be navigated to open and confined spaces with the aid of friction to detect local relative humidity. The integration of multi-stimulation actuation of cholesteric magnetic actuators will expand the research frontier of structural colorful actuators and motile sensors for confined spaces.

Ultrastretchable MXene Microsupercapacitors.

Stretchable microsupercapacitors represent emerging miniaturized energy-storage devices for next-generation deformable electronics. Two-dimensional (2D) transition metal carbides (MXenes) are considered attractive electrode materials due to their metallic conductivity, hydrophilic surfaces, and excellent processability. Here, an ultrastretchable microsupercapacitor of interdigitated MXene microelectrodes with crumpled surface textures is created. The microsupercapacitor shows a series of attractive properties including a high specific capacitance of ≈185 mF cm-2 , ultrahigh stretchability up to 800% area strain, and ≈89.7% retention of the initial capacitance after 1000 stretch-relaxation cycles. In addition to static strains, the microsupercapacitor demonstrates robust mechanical properties to retain stable charging-discharging capability under dynamic stretching at different strain rates. A self-powering circuit system utilizes four microsupercapacitor packs to power a light-emitting diode (LED) array, which exhibits stable operations under large tensile strain and skin-attached wearable settings. The developments offer a generic design strategy to enhance the deformability of microsupercapacitors based on 2D nanomaterials.

Distributed dynamic strain measurement with a direct detection scheme by using a three-step-phase-shifted double pulse in a UWFBG array.

We demonstrate a stable homodyne phase demodulation method with a double pulse based on an ultra-weak fiber Bragg grating (UWFBG) array. The technique divides one of the probe pulses into three sections and introduces successive 2π/3 phase differences into each section. By using a simple direct detection scheme, it can achieve distributed and quantitative vibration measurement along the UWFBG array. Compared to the traditional homodyne demodulation technique, the proposed technique is more stable and easier to accomplish. Moreover, the reflected light from the UWFBGs can provide a signal that is modulated uniformly by the dynamic strain and multiple results for averaging, resulting in a higher signal-to-noise ratio (SNR). We experimentally demonstrate the technique's effectiveness by monitoring different vibrations. The SNR for measuring a generic 100 Hz, 0.08 rad vibration in a 3 km UWFBG array with a reflectivity of -40 to -45 dB is estimated to be ∼44.92 dB.

On-Chip Generation and Collectively Coherent Control of the Superposition of the Whole Family of Dicke States.

Integrated quantum photonics has recently emerged as a powerful platform for generating, manipulating, and detecting entangled photons. Multipartite entangled states lie at the heart of the quantum physics and are the key enabling resources for scalable quantum information processing. Dicke state is an important class of genuinely entangled state, which has been systematically studied in the light-matter interactions, quantum state engineering, and quantum metrology. Here, by using a silicon photonic chip, we report the generation and collectively coherent control of the entire family of four-photon Dicke states, i.e., with arbitrary excitations. We generate four entangled photons from two microresonators and coherently control them in a linear-optic quantum circuit, in which the nonlinear and linear processing are achieved in a chip-scale device. The generated photons are in telecom band, which lays the groundwork for large-scale photonic quantum technologies for multiparty networking and metrology.