Characterizing quantum correlations in many-body systems is essential for understanding emergent phenomena in quantum materials. The correlation entropy serves as a key metric for assessing the complexity of a quantum many-body state in interacting electronic systems. However, its determination requires the measurement of all single-particle correlators across a macroscopic sample, which can be impractical. Machine learning methods have been shown to enable the correlation entropy to be learned from a reduced set of measurements, yet these methods assume that the targeted system is contained in the set of training Hamiltonians. Here we show that a transfer learning strategy enables correlation entropy learning from a reduced set of measurements in variants of Hamiltonians never considered in the training set. We demonstrate this transfer learning methodology in a wide variety of interacting models, including local and nonlocal attractive and repulsive many-body interactions, long-range hopping, doping, magnetic field, and spin-orbit coupling. Furthermore, we show that this transfer learning methodology enables the detection of phases in quantum many-body systems beyond those present in the training set. Our results demonstrate that correlation entropy learning can be performed experimentally without requiring training in the experimentally realized Hamiltonian.

We demonstrate quantitative measurement of the ferromagnetic resonance (FMR) precession cone angle of a microscale sample of vanadium tetracyanoethylene (V[TCNE]${}_{x\sim 2}$) using diamond spins. V[TCNE]${}_{x\sim 2}$ is a low-damping, low-magnetization ferrimagnet with potential for scalable spintronics applications. Our study is motivated by the persistent need for quantitative metrology to accurately characterize magnetic dynamics and relaxation. Recently, diamond spins have emerged as sensitive probes of static and dynamic magnetic signals. Unlike analog sensors that require additional calibration, diamond spins respond to magnetic fields via a frequency shift that can be compared with frequency standards. We use a spin-echo-based approach to measure the precession-induced change to the static stray dipolar field of a pair of V[TCNE]${}_{x\sim 2}$ disks under FMR excitation. Using these stray dipolar field measurements and micromagnetic simulations, we extract the precession cone angle. Additionally, we quantitatively measure the microwave field amplitude using the same diamond spins, thus forming a quantitative link between drive and response. We find that our V[TCNE]${}_{x\sim 2}$ sample can be driven to a cone angle of at least $6^{\circ }$ with a microwave field amplitude of only 0.53 G. This work highlights the power of diamond spins for local, quantitative magnetic characterization.

Chip-scale, electrically tunable, continuous-wave, coherent terahertz (THz) radiation sources are critical for emerging applications in sensing, imaging, spectroscopy, communications, space, and quantum technologies. Here, we demonstrate a robust source-on-a-chip THz emitter based on a layered high-temperature superconductor, engineered with an elliptical microcavity and capable of sustained coherent emission over an unprecedented operational lifetime exceeding 11 years. This compact THz source operates up to 60 K (with $T_{\mathrm{c}}$ ≈ 90 K), delivering stable radiation in the 0.7–0.8 THz range, with on-chip electrical tunability from 100 GHz to 1 THz. Coherence arises from the phase-locked oscillation of intrinsic Josephson junction arrays, resonantly coupled to transverse electromagnetic modes within the cavity, analogous to a laser cavity, yielding collective macroscopic oscillations. THz emission remains detectable across an approximately 0.5-m free-space open-air link at room temperature. We analyse the cavity-mode structure and extract THz photon generation rates up to approximately 503 photons ${\mathrm{fs}}^{-1}$ in cryogenic conditions and 50–260 photons ${\mathrm{ps}}^{-1}$ over the air. These results demonstrate, for the first time, sustained and electrically tunable coherent THz emission from superconductors over multiyear timescales, defining another class of robust, chip-integrated THz lasers with applications in scalable THz and quantum technologies.

Ultrasonic wave-front shaping is crucial for biomedical and industrial applications but remains severely constrained by longitudinal-transverse mixed-mode scattering at solid interfaces, resulting in substantial energy leakage and consequently poor transmission. Perfect refraction under these conditions remains unattainable even with conventional generalized Snell’s law approaches, due to the difficulty of fully addressing complex volumetric-shear coupling in solids. Here, we reveal that ideal power efficiency cannot be achieved without a novel material concept, the cross-modal Willis approach, and propose a rationally designed Willis-type metasurface that enables perfect wave steering in arbitrary directions while eliminating undesired parasitic modes. Our finding uncovers a critical yet previously overlooked mechanism: cross-modal anisotropy in Willis media, which fundamentally governs wave mode coupling behavior. We develop a systematic design methodology for Willis unit cells through intentional unbalancing of fully anisotropic effective masses, providing precise control over wave propagation characteristics. Experimental validation using ultrasonic measurements confirms successful implementation across mode-preserving and mode-converting refraction scenarios, demonstrating the versatility and robustness of our approach. This work not only extends the theoretical framework of Willis materials but also establishes paradigms for ideal controllability in ultrasound engineering applications.

Particles floating at an oil-water interface can aggregate via lateral capillary interactions to form granular rafts with unique mechanical properties. When destabilized—either spontaneously or through external forcing—these rafts can encapsulate oil within armored drops. Here, we investigate the forced destabilization of such rafts by indenting them with cylinders of varying size and at various speeds. We identify three distinct phases of destabilization: stable deformation, particle ejection, and oil encapsulation. The onset of particle ejection is explained by considering the cumulative weight of particles coating the indenter, with the particle ejection rate increasing with indentation depth. The encapsulation process consists of a dripping regime, where individual encapsulated oil drops grow and detach under gravity, and a jetting regime, where a continuous oil thread breaks into drops via capillary instability. In the dripping regime, drop size increases with the indenter size, and drop frequency increases with indentation depth. In contrast, the jetting regime produces smaller, more frequent drops with greater size variability due to the dynamic nature of the instability. After destabilization, a residual cap of particles remains adhered to the indenter whose size scales with an effective Bond number incorporating the total particle weight.

The photophoretic effect is considered a potential mechanism for generating lift and enabling long-duration flight in the mesosphere. The most prominent photophoretic effect occurs during the transition regime. However, developing a reliable model and accurately quantifying the photophoretic lift remains a significant challenge. In this study, we directly measure the photophoretic lift through conducting takeoff acceleration tests on polyester films coated with carbon nanotubes. By integrating experimental data with direct simulation Monte Carlo (DSMC) simulations to obtain the thermal accommodation coefficient, we develop an accurate semi-analytical model for predicting the photophoretic lift. The result shows an error of less than 10% compared with experimental measurements. Additionally, we use the model to analyze the effects of ambient pressure, surface thermal accommodation coefficient, and sample characteristic dimensions on the photophoretic lift. This study provides valuable insights into the photophoretic mechanism and has profound implications for the design of future photophoretic-based flight vehicles.

Piezoelectric microelectromechanical guided acoustic wave (GAW) sensors are widely used across a range of applications, from inertial sensing to environmental and chemical sensing. These devices typically rely on the resonance frequency of a Lamb mode as readout parameter, making them well suited for detecting parameters of interest (PoIs) that act over their entire vibrating structure. However, this approach is less effective for monitoring localized PoIs. To address this limitation, prior efforts have focused on miniaturizing GAW sensors. While this miniaturization strategy permits us to enhance responsivity to localized PoIs, it also causes a degradation of the limit of detection (LoD). In this paper, we present a GAW sensor for localized PoIs that overcomes the trade-off between responsivity and limit of detection by leveraging topological interface states (ISs). We demonstrate the effectiveness of our approach by sensing the infrared (IR) power emitted by a laser with a 5-$\text{μ}\mathrm{m}$-diameter beam size, focused on the interface at which the IS is transduced. Our results show that harnessing ISs yields significantly higher responsivity to IR power ($R=835\mathrm{Hz}/\text{μ}\mathrm{W}$) and a 2 orders of magnitude better limit of detection (${\mathrm{LoD}}_{\mathrm{tm}}=79\mathrm{fW}/\sqrt{\mathrm{Hz}}$) compared to conventional Lamb modes. Our findings pave the way for deploying GAW sensors in emerging applications that require monitoring localized parameters, such as proteomics, spintronics, mass spectroscopy, and more.

Wavefront shaping enables precise control of light propagation through multimode fibers (MMFs), facilitating diffraction-limited focusing for applications such as high-resolution single-fiber imaging and high-power fiber amplifiers. While the theoretical intensity enhancement at the focal point is dictated by the number of input degrees of freedom, practical constraints—such as phase-only modulation and experimental noise—impose significant limitations. Despite its importance, the upper bounds of enhancement under these constraints remain largely unexplored. In this work, we establish a theoretical framework to predict the fundamental limits of intensity enhancement with phase-only modulation in the presence of noise-induced phase errors, and we experimentally demonstrate wavefront shaping that approaches these limits. Our experimental results confirm an enhancement factor of 5000 in a large-core MMF, approaching the theoretical upper bound, enabled by noise-tolerant wavefront shaping. These findings provide key insights into the limits of phase-only control in MMFs, with profound implications for single-fiber imaging, optical communication, high-power broad-area fiber amplification, and beyond.

Nonlinear equations are generally challenging to solve. As analytical solutions typically do not exist, numerical methods have been developed to find their solutions. In this article, building upon the classical Newton method and the recent quantum singular value transformation framework, we give a quantum algorithm for solving a system of nonlinear algebraic equations, in which each equation is a homogeneous polynomial of an even degree. A detailed analysis is then carried out to reveal that our method achieves polylogarithmic time relative to the number of variables. Furthermore, the number of required qubits is logarithmic in the number of variables. In particular, we also show that our method can be generalized to deal with polynomials of various types. Some potential applications stem from various contexts, such as the Gross-Pitaevski equation, the Lotka-Volterra equations, and the intersection of algebraic varieties. Our work thus marks a significant step forward toward quantum advantage in nonlinear science, highlighting a promising avenue for future exploration.

Over recent decades, quantum key distribution (QKD) has arisen as a promising solution for secure communications; however, like all cryptographic protocols, implementations of QKD can open security vulnerabilities. Until now, the study of physical vulnerabilities in QKD setups has focused primarily on the optical channel. In classical cryptoanalysis, power and electromagnetic side-channel analysis are powerful techniques that can be used to access secret information about the encryption key in symmetric-key algorithms. Such attacks have rarely been used in QKD, since they require an eavesdropper to have access to Alice’s or Bob’s setup; however, security proofs of QKD protocols generally assume that these setups are secure, making it crucial to understand the security measures required to ensure this protection. In this work, we propose and implement a power side-channel analysis of a QKD system by exploiting the power consumption of the electronic driver controlling the electro-optical components of the QKD transmitter. QKD modules typically require very precise electronic drivers, such as field-programmable gate arrays (FPGAs). Here, we show that the FPGA’s power consumption can leak information about the QKD operation and consequently the transmitted key. Our results are consistent and show critical information leakage, having reached a maximum accuracy of 73.35% in predicting transmitted qubits at a 100-MHz repetition frequency. We also discuss possible countermeasures to prevent such an attack.

Coherence is a fundamental property of light. Recent years have witnessed a growing interest in coherence structuring, yielding a new type of partially coherent source with spatially tailored nonuniform correlations. However, the routine way of producing entangled photons via parametric down-conversion is to use a highly coherent laser source to pump nonlinear crystals. Here, we present a new strategy of exploiting such nonuniformly partially coherent sources to excite parametric down-conversion and thus endow the generated entanglement with a tailored and unusual spatial symmetry. To reveal the spatially varying degree of entanglement, we demonstrate the observation of an unusual Einstein-Podolsky-Rosen (EPR) correlation by transferring the circular structure of the coherence of the pump beam onto that of down-converted photons. For this, we observe both anomalous ghost diffraction and normal ghost images to examine the EPR-type inequalities and showcase the transition from nonentanglement to entanglement. Our work suggests that coherence structuring can offer a new dimension to generate and control quantum entanglement.

We present a theoretical investigation of epitaxial strain effects on the magnetic fluctuation properties of ${\mathrm{Mn}}_3\mathrm{Sn}$ noncollinear antiferromagnets. Employing density functional theory (DFT), we uncover significant strain-induced modifications to key magnetic parameters, including magnetic anisotropy and both bilinear and biquadratic exchange interactions. Our findings reveal that the biquadratic exchange, often neglected, plays a crucial role in defining the magnetic energy landscape and its response to strain. These microscopic changes directly impact the energy barriers governing magnetic switching, thereby influencing thermal stability and fluctuation rates. Using macrospin-based simulations based on DFT-derived parameters, we provide a quantitative analysis of the macroscopic magnetic fluctuations influenced by these microscopic interactions. These insights are particularly relevant for applications requiring precisely controlled magnetic behavior, such as hardware for probabilistic computing.

We observe blockade of microwave photons in a Tavis-Cummings system comprising a superconducting cavity and up to $N=3$ transmon qubits. The effect is characterized with photon-number-resolving spectroscopy using an additional dispersively coupled transmon “witness” qubit to directly probe the cavity’s photon-number distribution. We first observe polariton formation with splitting proportional to $\sqrt{N}$, confirming the Tavis-Cummings coupling, and subsequently obtain sub-Poissonian cavity photon statistics when the cavity is driven at polariton frequencies.

Here, we show that up-converting nanoparticles are able to function as stochastic non-Poissonian emitters suitable for superresolution optical fluctuation imaging. We uncover ranges of parameters where up-converting media with emitters such as rare-earth ions can exhibit nonexponential statistics of photon emission times. We also show that photon bunching can be induced by interactions between emitters. This effect can be used for a stochastic imaging modality in which only the contributions of interacting emitters to the cumulant image are enhanced. We also develop a method to use spatial cross-correlations of the registered field to enhance resolution.

The anomalous Nernst effect (ANE) generates electromotive forces transverse to temperature gradients and has attracted much attention for potential applications into alternative thermoelectric power generators. ANE efficiency is generally characterized by uniform temperature gradients in a steady state prepared by heaters. However, although focusing laser beams on a magnetic film can form much larger temperature gradients, the laser irradiation method has not been sufficiently considered for quantifying the ANE coefficient due to the difficulty in estimating the localized in-homogeneous temperature gradients. In this study, we present a quantitative study of ANE in $\mathrm{Ru}$(5 nm)/$\mathrm{Co}$($t_{\mathrm{Co}}$) ($t_{\mathrm{Co}}$= 3, 5, 7, 10, 20, 40, and 60 nm) bilayers on sapphire (0001) substrates by combining a laser irradiation approach with finite-element analysis of temperature gradients under laser excitation. We find that the estimated ANE coefficients are consistent with previously reported values and one independently characterized using a heater. Our results also reveal the advantages of the laser-irradiation method over the conventional method using heaters. Intensity-modulated laser beams can create ac temperature gradients as large as approximately ${10}^3$ K/mm at a frequency of tens of kilohertz in a micrometer-scale region.