Spatial mapping of thermal properties is critical for unveiling the structure-property relation of materials, heterogeneous interfaces, and devices. These property images can also serve as datasets for training artificial intelligence models for material discoveries and optimization. Here, we introduce a high-throughput thermal-property imaging method called compressive-sensing frequency-domain thermoreflectance (CS-FDTR), which can robustly profile thermal-property distributions with micrometer resolutions while requiring only a random subset of pixels to be experimentally measured. The high-resolution thermal-property image is reconstructed from the raw down-sampled data through ${\mathcal{L}}_1$-regularized minimization. The high-throughput imaging capability of CS-FDTR is validated using the following cases: (a) the thermal conductance of a patterned heterogeneous interface, (b) the thermal conductivity variations of an annealed pyrolytic graphite sample, and (c) the sharp change in thermal conductivity across a vertical aluminum/graphite interface. With less than half of the pixels being experimentally sampled, the thermal-property images measured using CS-FDTR show good agreement with the ground truth (point-by-point scanning), with a relative deviation below 15%. This work opens the possibility of high-throughput thermal-property imaging without sacrificing the data quality, which is critical for materials discovery and screening.

The ability to execute a large number of quantum gates in parallel is a fundamental requirement for quantum error correction, allowing an error threshold to exist under the finite coherence time of physical qubits. Recently, two-dimensional ion crystals have been demonstrated as a plausible approach to scale up the qubit number in a trapped ion quantum computer. However, although the long-range Coulomb interaction between the ions enables their strong connectivity, it also complicates the design of parallel gates and leads to intrinsic crosstalk errors. Here we examine the effects of crosstalk errors on a rotated surface code. We show that, instead of the distance-3 code considered in previous works, a distance-5 code is necessary to correct the two-qubit crosstalk error. We numerically calculate the logical error rates and coherence times under various crosstalk errors, gate infidelities, and coherence times of the physical qubits, and we optimize the parallelism level according to the competition between different error sources. We show that a break-even point can be reached under realistic parameters. We further analyze the spatial dependence of the crosstalk, and discuss the scaling of the logical error rate versus the code distance for the long-term goal of a logical error rate below ${10}^{-10}$.

Reservoir computation is a recurrent framework for learning and predicting time-series data, that benefits from extremely simple training and interpretability, often as the dynamics of a physical system. In this paper, we will study the impact of noise on the learning capabilities of analog reservoir computers. Recent work on reservoir computation has shown that the information processing capacity (IPC) is a useful metric for quantifying the degradation of the performance due to noise. We further this analysis and demonstrate that this degradation of the IPC limits the possible features that can be meaningfully constructed in an analog reservoir computing setting. We borrow a result from quantum complexity theory that relates the circuit model of computation to a continuous-time model, and demonstrate an exponential reduction in the accessible volume of reservoir configurations. We conclude by relating this degradation in the IPC to the fat-shattering dimension of a family of functions describing the reservoir dynamics, which allows us to express our result in terms of a classification task. We conclude that any physical, analog reservoir computer that is exposed to noise can only be used to perform a polynomial amount of learning, despite the exponentially large latent space, even with an exponential amount of postprocessing.

We use spectral-hole burning to investigate spin dynamics within the electronic Zeeman sublevels of the ground state, ${}^4{I}_{15/2}$, of the erbium (${\mathrm{Er}}^{3+}$) ions in erbium-doped fibers (EDFs). Conducted at ultralow temperatures and under varying magnetic fields, our study reveals distinct changes in spin-relaxation dynamics across different conditions. We identified three decay components at approximately $7$ mK, with one achieving spin lifetimes of over 9 h under optimal conditions, while two components were observed at higher temperatures. The fairly stable relative weights of the decay components across conditions suggest distinct ion populations contributing to the observed relaxation dynamics. While earlier studies struggled to account for all decay components at higher temperatures, our approach successfully models spin dynamics across all observed decay components, using a consistent set of underlying mechanisms—spin flip-flop interactions, direct coupling to two-level systems, and Raman-type processes—and distinguishing the decay components by the strengths with which these mechanisms contribute. These results suggest EDFs’ potential as a promising candidate for quantum memory applications, with further room for optimization.

Negative capacitance is an alternative hysteretic electric-field-induced behavior of the magnitude and sign of a solid-state ferroelectric polarization, fixed in direction along a particular crystallographic axis, as it is forced between Landau-like polarization-free energy minima. Here we show that negative capacitance can also appear in the recently discovered fluid ferroelectric nematic liquid crystal (FNLC) cells, in this case as a result of electric-field-induced reorientation of the polarization. In the FNLC case, the elements being charged are interfacial LC and electrode capacitors, one side of which receives only free charge and the other side of which receives only polarization charge, the latter occurring only if the FNLC polarization rotates appropriately. In response to applied voltage transients, viscosity retards polarization orientation, leading to apparent negative capacitance. The properties that make LCs useful in display applications (ambient temperature, low voltage, facile processibility, vetting as an industrial and consumer technology) make FNLCs attractive for applications where negative capacitance is desirable in flexible organic electrochemical transistor devices.

Achieving compact on-chip pulsed lasers with attractive performance metrics and compatibility with the silicon photonics platform is an important, yet elusive, goal in contemporary nanophotonics. Here the fundamental question of whether two-dimensional (2D) materials can be used as both gain and saturable absorption media to enable compact integrated passively $Q$-switched nanophotonic lasers is posed and addressed by examining a broad range of 2D material families. The study is conducted by developing a temporal coupled-mode theory framework involving semiclassical rate equations that is capable of rigorously handling gain and saturable absorption by 2D materials, allowing us to perform stability and bifurcation analysis covering broad parameter spaces. The range of pulse-train metrics (repetition rate, pulse width, and peak power) that can be obtained via different 2D materials is thoroughly assessed. Our work illustrates that nanophotonic cavities enhanced with 2D materials can enable passive $Q$-switching with repetition rates ranging up to 50 GHz, short pulse duration down to a few picoseconds, and peak power exceeding several milliwatts. Such attractive metrics, along with the ultrathin nature of 2D materials and the ability to electrically tune their properties, demonstrate the potential of the proposed platform for compact and flexible integrated laser sources.

We investigate nonreciprocal scattering within the modes of a microwave frequency comb. Adjusting the pump frequencies, amplitudes, and phases of a Josephson parametric oscillator, we control constructive interference for the $m⟶\ell$ scattering processes, while concurrently achieving destructive interference for the inverse process $\ell ⟶m$. We outline the methodology for realizing nonreciprocity in the context of two-mode isolation and a three-mode circulation, which we extend to multiple modes. We find good agreement between the experiments and a linearized theoretical model. Nonreciprocal scattering expands the toolset for parametric control, with the potential to engineer alternative quantum correlations.

Floquet engineering has recently been recognized as an important tool for manipulating the coherent magnon-photon interaction in cavity electromagnonics systems at microwave frequencies. In spite of the novel hybrid magnonic functionalities that have been demonstrated, the effect of the Floquet drive has been relatively weak due to the limited driving efficiency, limiting its broader application. This work shows that, both experimentally and theoretically, the Floquet drive in our cavity electromagnonic device can be drastically enhanced by utilizing $LC$ resonances, giving rise to drastically boosted interaction between hybrid modes with fundamentally different spectral characteristics compared with previous demonstrations. In addition, the Floquet drives can also be obtained from gigahertz signals on such a system, allowing the demonstration of more advanced signal operations. Our resonance-enhanced Floquet cavity electromagnonics points to a promising direction to fully unleash the potential of Floquet hybrid magnonics.

A monotonic stable error signal is essential for the Pound-Drever-Hall (PDH) laser-frequency stabilized system. However, several factors affect the line shape of the error signal even in steady states and the frequency-locked state. Among them, the coherence between the higher-order Gaussian modes and the fundamental modes of the resonate cavity will induce the asymmetry of the PDH error-signal line shape, as well as the zero-crossing-point bias. The effect of the spatial-mode coherence on the error signal is independent of the experimental frequency-scanning process and can still affect the PDH-locking status by changing the locking point of the PDH system. In this paper, we revise the theoretical expression of the PDH error signal according to the theory of coherence between the higher-order modes and the fundamental mode and give the analytical equation of the asymmetry of the PDH error signal. The validation of this theory has been provided by both numerical simulation and experiment.

A common method of controlling the chemical potential in topological insulators is applying a gate electrode. Simultaneously applying high source-drain bias currents in such devices can lead to parasitic effects due to the presence of a gate electrode, not intrinsic to the topological insulator. We derive that these parasitic effects lead to a gradient in the Hall effect along the current lead of a Hall bar. Consequently, nonreciprocal effects in both longitudinal and Hall voltages appear upon reversing the bias. These effects scale similarly to the magnetochiral anisotropy, requiring detailed analysis to make a distinction. Experimentally we show that nonreciprocal effects can appear in materials where magnetochiral anisotropy is not expected while a top gate is present. Without the gate electrode, this nonreciprocal effect is found to be absent. These results show the significance of considering and, if possible, excluding gate electrode-induced effects when searching for nonreciprocal resistance intrinsic to a material.

Fiber-based long-haul quantum communication would greatly benefit from a robust and deterministically integrated source of quantum states. Here, we report the design, fabrication, and optical characterization of $\mathrm{In}\mathrm{As}$/$\mathrm{In}\mathrm{P}$ quantum dots in the $\mathrm{In}\mathrm{P}$ H1 point-defect 2D photonic crystal cavity, integrated with a standard single-mode fiber employing microtransfer printing. The device is placed in a compact cryocooler maintaining a cryogenic temperature of 15 K, and it exhibits a low multiphoton contribution to emission, with $g^{(2)}(0)=0.14(14)$ in the all-fiber-based optical link between two laboratory nodes. In this way, we demonstrate a plug-and-play all-fiber single-photon source operating in the third telecom window, where standard telecommunication fiber networks can be used as a low-loss medium.

Optical modulators are essential building blocks for high-capacity optical communication and massively parallel computing. Among all types of optical modulators, traveling-wave Mach-Zehnder modulators (TW-MZMs) featuring high speed and efficiency are widely used, and have been developed on a variety of integrated material platforms. Existing methods to design and simulate TW-MZMs so far strongly rely on specific material properties, and thus inevitably involve complicated electrical-circuit models. As a result, these methods diverge significantly. In addition, they become increasingly inefficient and inaccurate for TW-MZMs with extended length and rising modulation speed, posing formidable challenges for millimeter-wave and terahertz operation. Here, we present an innovative perspective to understand and analyze high-speed TW-MZMs. Our perspective leverages nonlinear optics and complex band structures of periodic rf electrodes, and is thus entirely electromagnetic-wave-based. Under this perspective, we showcase the design, optoelectronic simulation, and experimental validation of high-speed TW-MZMs based on $\mathrm{Si}$ and ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$, and further demonstrate unambiguous advantages in simplicity, accuracy, and efficiency over conventional methods. Our approach can essentially be applied to almost any integrated material platform, including those based on semiconductors and electroabsorption materials. With high-frequency electrode designs and optoelectronic co-simulation, our approach facilitates the synergy and convergence of electronics and photonics, and offers a viable route to construct future high-speed millimeter-wave and terahertz photonics and quantum systems.

A sink enables subwavelength focusing by absorbing the converging wave at the focal point, preventing the creation of a diverging wave. We demonstrate in this paper that plasmas can behave as a microwave sink. This requires coupling the converging wave to localized surface-plasmon resonances, enabling perfect coherent absorption. We introduce a finite-difference time-domain body-of-revolution model, which couples Maxwell’s equations with a fluid description of the plasma. Our results indicate that the plasma can indeed act as a microwave sink for both continuous and broadband converging waves. The plasma parameters required to achieve this behavior are achievable experimentally, with plasma ignition taking place inside a cylindrical tube. The obtained field intensification and subwavelength focusing may provide a means to enhance nonlinear plasma ignition in plasmas sources.

Paramount for performances of quantum network applications are the structure and quality of distributed entanglement. Here we propose a scalable and efficient approach to reveal the topological information of unknown quantum networks, and quantify entanglement simultaneously. The scheme exploits entropic uncertainty, an operationally meaningful measure of correlation, by performing only two local measurements on each qubit. Moreover, when measurement outcomes in each node are collectively evaluated, integrating uncertainty and mutual information enables a direct count of the number of bipartite sources between any two nodes. This surpasses what is possible via applying either approach solely. Moreover, quantum error-mitigation techniques, including probabilistic error cancellation (PEC) and virtual distillation (VD), which have been widely applied to suppress biases in single expectation value, are further incorporated to mitigate errors in entropic quantities. We find that PEC successfully removes deviations in correlation estimations. Meanwhile, VD extends the depolarizing noise strength that allows for valid bipartite entanglement certification from 8.8% to 26.4%, thus substantially enhancing robustness against bias-inducing noise in practical situations. The proposal is applicable to a broad variety of platforms and helps to spur future studies toward harnessing the advantages of quantum networks.

Information reconciliation plays a crucial role in continuous-variable quantum key distribution (CVQKD), directly affecting the secret key rate and the maximum secure transmission distance. As the demand for CVQKD in both long-distance and numerous-user access network scenarios increases, high-performance error-correction codes tailored for low-SNR environments become essential for efficient reconciliation. However, traditional approaches face challenges such as complex construction and high system overhead, which hinder further development. To address these issues, we propose an error-correction scheme for CVQKD based on low-density parity-check (LDPC)-Hadamard codes, which incorporates multidimensional reconciliation and greatly simplifies the construction of low-rate codes, enabling efficient error correction at a code rate on the order of 0.001 without requiring multiple interactions. Results show that the LDPC-Hadamard-based reconciliation protocol achieves a code rate as low as 0.001 with a reconciliation efficiency of 95.98% at a signal-to-noise ratio of $-28.40$ dB, pushing the error-correction code rate formally into the thousandths regime while maintaining code lengths in the megabit range. The proposed method provides a practical technological foundation for point-to-point long-distance QKD and large-scale downstream CVQKD networks that support numerous users.

Advanced target production methods and characterization strategies can help unlock the application potential of laser-driven particle sources based on solid targets. Such compact multiradiation sources show great potential both in fundamental physics studies and application-oriented scenarios like nuclear medicine and materials science, but observation of their expected properties is often impeded by setup limitations like lack of control and uncertainties of target parameters. Here, we report on laser-driven proton acceleration and neutron generation at the high-intensity VEGA-3 laser, using targets fabricated with physical vapor deposition (PVD) techniques and characterized with advanced procedures. Magnetron sputtering enables the production of solid foils with reduced thickness variability, while pulsed-laser deposition allows for the production of low-density layers to enhance laser absorption. Accurate target characterization is achieved with scanning electron microscopy and energy dispersive x-ray spectroscopy. A calibrated magnetic spectrometer and a DIAMON detector are employed to monitor protons and neutrons. Our PVD single-layer targets show a reduced thickness uncertainty with respect to commercial ones and, since solid target thickness affects hadron acceleration and generation, they guaranteed an improvement in the achievable maximum particle energy. Moreover, optimizing laser-target coupling by adding a low-density layer on top of PVD-produced solid foils with PLD allowed us to get a further improvement in particle energy. Our work, focusing on the effect of target-related variables on laser-driven hadron sources, highlights the relevance of target manufacturing and characterization for the future applications of laser-driven sources.

We investigate the dynamic properties of elastic lattices defined by tessellations of a hyperbolic strip domain. These strip lattices are generated using a conformal map of tessellations of a hyperbolic disk. The resulting hyperbolically distributed lattice sites are coupled by Euclidean edges, leading to a natural grading of coupling strengths along the strip width. Their vibrational modes are organized into three distinct classes: boundary localized, interior localized, and global. This mode classification is governed by a computed localization index quantifying the spatial localization of each mode along the strip’s width. We show that, like hyperbolic lattices in the disk, hyperbolic lattices in the strip exhibit a dynamic spectrum populated by a majority of localized modes. This finding is supported by numerical studies of the dynamics of a strip lattice of structural beams. Computation of the integrated density of states for the boundary, interior, and global modes reveals the predominance of localized modes, and the local density of states allows for the identification of spectral bands dominated by particular mode classes. This analysis informs time-domain simulations of the lattice response to dynamic forcing by bandlimited inputs dominated by each mode class. The results illustrate distinctive wave-propagation behavior when the excited frequency band is dominated by boundary-localized, interior-localized, or global modes. We confirm these observations via vibrometry experiments in the frequency and time domains. In the frequency domain, the measured response confirms that the spectral neighborhoods of each excitation are indeed populated by the mode class predicted by numerical investigations. We further show that the time-averaged responses are consistent with simulations. Through this work, elastic hyperbolic strips emerge as a previously unexplored class of lattices with characteristic beam-like, truss-core architectures and as-yet unseen site arrangements. The considered configuration shows promising capabilities to confine and guide elastic waves along varying spatial regions depending on the frequency content of the excitation.