Quantum networks hold promise for key distribution, private and distributed computing, and quantum sensing, among other applications. The scale of such networks for ground users is currently limited by one’s ability to distribute entanglement between distant locations. This can in principle be carried out by transmitting entangled photons through optical fibers or satellites. The former is limited by fiber-optic attenuation, while the latter is limited by atmospheric extinction and diffraction. Here, we propose a hybrid network and protocol that outperform both ground- and satellite-based designs and lead to high-fidelity entanglement at a continental or even global scale.

This paper assesses the numerical accuracy of the Harrow-Hassidim-Lloyd (HHL) algorithm in solving a finite-difference approximation of the Poisson equation, with the Thomas algorithm used as a comparative benchmark. In the one-dimensional setting with homogeneous boundary conditions, the HHL algorithm exhibits numerical accuracy comparable to the Thomas algorithm; however, the HHL algorithm exhibits increased sensitivity to variations in input parameters for simulations with nonhomogeneous boundary conditions. While the current implementation of the HHL algorithm is limited to solving the one-dimensional Poisson equation, we propose a hybrid framework to extend the applicability of the HHL algorithm to solving the two-dimensional Poisson equation. Our results show that although both algorithms perform similarly for small systems of $8\times 8$ mesh nodes, the HHL algorithm shows increased input-parameter sensitivity for systems of $16\times 16$ mesh nodes, indicating that further development is needed to scale the hybrid approach effectively.

In this work, we study the tomography of the spatial structure of light. We develop a simple technique that allows one to perform tomography over the space of fixed-order modes. The technique is based on two spatially resolved intensity measurements, the second of which is performed after the light field has undergone an astigmatic transformation implemented by a tilted lens. We demonstrate that this method is informationally complete within the considered subspaces, and this is experimentally verified in both the intense and photocount regimes. We also study the effect of obstructions on our ability to reconstruct the states. The work presented is expected to help the development of characterization techniques in the field of structured light and in its application to both classical and quantum information protocols.

We show that the current density-voltage characteristics, external quantum efficiency roll-off, and transient photoluminescence for various stacks of experimentally well-characterized thermally activated delayed-fluorescence-based white organic light-emitting diodes (OLEDs) can be successfully reproduced by three-dimensional kinetic Monte Carlo simulations using a single set of material parameters. Optimized electronic and excitonic device parameters are simultaneously extracted for complex multilayer OLED stacks with blended emissive layers and various device designs. A quantitative view of the complex interplay between the electronic energy-level structure, the exciton energies, and the charge-transport and excitonic process rates is presented, leading to a systematic understanding of the high efficiency of the devices studied. Based on the obtained physical insights, conceptually original device designs with improved efficiency are proposed.

Intraoperative measurements using magnetic sensors are a valuable technique in cancer surgery for finding magnetic tracers. Here we present a fiber-coupled nitrogen-vacancy center magnetometer capable of detecting iron oxide suspension (MagTrace™ from Endomagnetics Ltd.) used in breast cancer surgeries. Detection of an iron mass as low as 0.56 mg has been demonstrated, 100 times less than that of a recommended dose at a maximum distance of 5.8 mm. Detection of an iron concentration as low as 2.8 mg/ml has also been demonstrated, 20 times less than a recommended dose. The maximum working distance from the sensor can be as large as 14.6 mm for higher concentrations. The sensor head has a maximum diameter of 10 mm which would allow it to be used for endoscopy, laparoscopy, and intraoperative surgery.

High-dimensional entanglement, in the form of transverse spatial correlation between a pair of photons generated via spontaneous parametric down-conversion, is not only a valuable resource in many academic and real-life applications, but also provides access to several intriguing quantum phenomena. One such nonintuitive phenomenon is phase entanglement, in which the biphoton state is correlated in the complex phase of its wavefunction. This state, which emerges during the propagation of the biphoton wavefunction, exhibits no position correlation, yet retains full entanglement. In this work, we experimentally explore this state in two distinct ways. The first is by tracking the vanishing spatial photon number correlation over propagation distances lying in $[0,\mathrm{\infty })$, folded into a finite range using single-lens imaging. These observations show excellent agreement with our theoretical predictions based on the double Gaussian approximation of the biphoton state. The second approach involves performing a two-photon interference experiment using a double slit and this state, which reveals the correlated phase front. We show, both theoretically and experimentally, that the observed two-photon interference structure is markedly different from that produced by position-correlated photons, as confirmed by computing the joint probability distribution of photons and related metrics. Such interference using phase-entangled light has implications that open avenues for advanced experiments and applications in the field of spatial entanglement.

Experimentally fabricated semiconducting ${\mathrm{Cu}}_2\mathrm{Se}$ monolayers with a high electron mobility of approximately ${10}^3{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ and exceptional environmental stability are promising for next-generation electronic device applications, such as field-effect transistors (FETs). However, the challenge of achieving Ohmic contacts with electrode metals persists. This study systematically investigates the interfacial properties of monolayer ${\mathrm{Cu}}_2\mathrm{Se}$-based transistors with various common metals ($\mathrm{Ti}$, $\mathrm{Mo}$, $\mathrm{Cr}$, $\mathrm{W}$, $\mathrm{Sb}$, $\mathrm{Cu}$, $\mathrm{Co}$, and $\mathrm{Ni}$) as electrodes, leveraging first-principles calculations and quantum transport simulations. Our findings reveal that metal-induced gap states enable ${\mathrm{Cu}}_2\mathrm{Se}$ to form Ohmic contacts with all metal electrodes except $\mathrm{Sb}$ in the vertical direction. Furthermore, the absence of a tunneling barrier results in high carrier injection efficiency in the ${\mathrm{Cu}}_2\mathrm{Se}/\mathrm{Ti}$, /$\mathrm{Mo}$, /$\mathrm{Cr}$, and /$\mathrm{W}$ interfaces. The strong Fermi level pinning effects confine the Schottky barrier of ${\mathrm{Cu}}_2\mathrm{Se}/$metal lateral contacts to a small value. Notably, ${\mathrm{Cu}}_2\mathrm{Se}/\mathrm{Mo}$ and ${\mathrm{Cu}}_2\mathrm{Se}/\mathrm{Cu}$ FETs demonstrate ideal Ohmic contacts in both vertical and lateral directions, with $\mathrm{Mo}$ electrodes exhibiting the highest contact quality in ${\mathrm{Cu}}_2\mathrm{Se}$-based FETs. The transfer behaviors of the ${\mathrm{Cu}}_2\mathrm{Se}/\mathrm{Mo}$ FETs nearly satisfy the standards in the International Technology Roadmap for Semiconductors for high-performance devices, aligning with the predicted quality of the electrode contacts. This work provides valuable theoretical guidance for the design of high-performance FETs utilizing ${\mathrm{Cu}}_2\mathrm{Se}$.

Josephson traveling-wave parametric amplifiers (JTWPAs) are promising platforms for realizing broadband quantum-limited amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching of the signal, idler, and pump waves are satisfied—this is rendered particularly challenging in the presence of nonlinear effects, such as self- and cross-phase modulation, which scale with the intensity of propagating signals. In this work, we present a simple JTWPA based on “left-handed” (negative-index) nonlinear Josephson metamaterial, which has phase matching native to its design, precluding the need for any complicated circuit or dispersion engineering. The resultant efficiency of the four-wave-mixing process can implement gains in excess of 20 dB over few-gigahertz bandwidths with much shorter lines than previous implementations. Furthermore, the intrinsic phase matching considerably simplifies the JTWPA design and operation compared to the previous implementations based on “right-handed” (positive-index) Josephson metamaterials, making the proposed architecture particularly appealing for integration with large superconducting architectures. The left-handed Josephson transmission line introduced here constitutes an alternative modality in distributed Josephson circuits, and forms a crucial piece of the unified framework that can be used to inform the optimal design and operation of broadband microwave amplifiers.

Precise patterning of suspended inhomogeneities at the microscale has proven to be crucial for applications spanning a multitude of domains. The use of ultrasonic waves for microscale manipulation has emerged as a promising tool owing to its noninvasive and label-free nature. Alterations in acoustic-field configuration, a prerequisite to controlled pattern formation, have, however, mostly been achieved using arrays of piezoelectric sources, increasing the complexity of device operation. Here, we report tunable patterning of microparticles in a microfluidic cavity, driven by a single piezoelectric source. Our method exploits asymmetry incorporated in device design to generate diverse, frequency-dependent, acoustic potential landscapes. Remarkably, we show distinct microparticle aggregate patterns over a range of frequencies and capture underlying acoustic-field configurations by decoding nontrivial fluid-structure interactions. The hitherto unexplored design-incorporated asymmetries for reconfigurable aggregate patterning lays the groundwork for potential applications in microrobotics, microscale propulsion, and tissue engineering.

All-optical magnetization switching driven by femtosecond lasers offers a promising solution for data storage. To address power consumption, optical enhancement methods based on the two-temperature model can reduce energy requirements for magnetization reversal. To achieve this, we design a phase-matched optical resonant cavity formed between photonic crystals and multilayer ferrimagnetic films. This cavity with band filtering properties enables dual detection through transmission and reflection, similar to the all-optical switching films, facilitating high-density storage device integration. Finite element simulations are employed to adjust key photonic crystal parameters, ensuring theoretically optimal location of the pump laser. Experimental results demonstrate that over 87% of the 800-nm-pump laser is absorbed. A twofold pump laser fluence reductions for magnetization reversal are validated through static magneto-optical Kerr effect microscopy and time-resolved magneto-optical Kerr effect measurements. Our results provide substantial advances toward low-energy consumption and high-density compatibility characteristics for the next-generation ultrafast magneto-optical storage devices.

With his formal analysis in 1951, the physicist Pyotr Kapitza demonstrated that an inverted pendulum with an externally vibrating base can be stable in its upper position, thus overcoming the force of gravity. Kapitza’s work is an example that an originally unstable system can become stable after a minor perturbation of its properties or initial conditions is applied. Inspired by his ideas, we show how non-Foster circuits can be stabilized with the application of external electrical vibration, i.e., time modulations. Non-Foster circuits are highly appreciated in the engineering community, since their bandwidth characteristics are not limited by passive-circuit bounds. Unfortunately, non-Foster circuits are usually unstable and they must be stabilized prior to operation. Here, we focus on the study of non-Foster $L(t)C$ circuits with time-varying inductors and time-invariant negative capacitors. We find an intrinsic connection between Kapitza’s inverted pendulum and non-Foster $L(t)C$ resonators. Moreover, we show how positive time-varying modulations of $L(t)>0$ can overcome and stabilize non-Foster negative capacitances $C<0$. These findings open up an alternative manner of stabilizing electric circuits with the use of time modulations, and lay the groundwork for application of what we coin vibrational electromagnetics in more complex media.

We investigate the ultrafast photoelectric effect at sharp tungsten needles and find a considerable energy offset between thermally emitted and photoemitted electrons. Neither changes in temperature nor tuning the work function by the Schottky effect strongly affect the free-space energy of the photoelectrons. We explain these discoveries by a direct optical excitation within the band structure of tungsten, followed by scatter-free transport to the surface and emission into free space. Experiments at different photon energies support that the material and not the photon energy determines the primary properties of the electron beam.

Efficiently simulating large circuits is crucial to the development of superconducting nanowire-based electronics. However, current simulation tools for this technology are not adapted to the scaling of circuit size and complexity. We focus on the multilayered heater-nanocryotron (hTron), a promising superconducting nanowire-based switch used in applications such as superconducting nanowire single-photon detector readout. Previously, the hTron was modeled using traditional finite-element methods, which fall short in simulating systems at a larger scale. An empirical-based method would be better adapted to this task, enhancing both simulation speed and agreement with experimental data. In this work, we perform switching current and activation delay measurements on 17 hTron devices. We then develop a method for extracting physical fitting parameters used to characterize the devices. We build a SPICE behavioral model that reproduces the static and transient device behavior using these parameters, and validate it by comparing its performance to a model developed in prior work, showing an improvement in simulation time by several orders of magnitude. Our model provides circuit designers with a tool to help understand the hTron’s behavior during all design stages, thus enabling broader use of the hTron across various new areas of application.

Reservoir computing is an effective method for predicting chaotic systems by the use of a high-dimensional dynamic reservoir with fixed internal weights, while the learning phase is kept linear, which simplifies training and reduces computational complexity compared with fully trained recurrent neural networks. Quantum reservoir computing uses the exponential growth of Hilbert spaces in quantum systems, allowing greater information processing, memory capacity, and computational power. We present a hybrid neuromorphic quantum-classical approach that implements memory through classical postprocessing of quantum measurements, thus avoiding the need for multiple coherent input injections (as in the original proposal). We tested our model on two physical platforms—a fully connected Ising model and a Rydberg-atom array—and evaluated it on various benchmark tasks, including the chaotic Mackey-Glass time series prediction, where it demonstrates significantly enhanced predictive capabilities and achieves a substantially longer prediction time, outperforming previously reported approaches.

Magnetic systems possess the unique capability to access multiple magnonic bands within a single device by tuning the spin-wave dispersion relationship. In this work, we demonstrate that distinct nonlinear magnonic processes—including three-magnon scattering, four-magnon scattering, and high-harmonic generation—can be selectively activated and controlled within a single microconduit by engineering the magnon spectrum through an externally applied bias magnetic field. Four-magnon scattering and both resonant and nonresonant excitations are observed across all bias fields, whereas three-magnon scattering only occurs at low bias fields (<40 mT) within the same structure. Notably, the efficiency of harmonic generation exhibits a significant decline as the bias field increases. Additionally, a systematic width-dependent analysis reveals that increasing the conduit width suppresses both three- and four-magnon scattering and reduces harmonic generation efficiency. Spatially resolved imaging of spin-wave dynamics is performed using microfocused Brillouin light-scattering microscopy, and the experimental results are interpreted with the support of analytical modeling. These comprehensive findings establish a platform for tuning nonlinear magnonic responses in confined geometries and offer insights that are critical to developing magnon-based information processing technologies.

The inverted-coplanar, or bottom-gate bottom-contact (BGBC), architecture is well-suited for practical organic thin-film transistors (OTFTs). However, its performance is often limited by inefficient carrier injection at the semiconductor/electrode/dielectric ternary interface. Here, we demonstrate that interfacial carrier accumulation plays a crucial role in enabling efficient injection at these ternary interfaces. We fabricate prototypical single-crystal BGBC OTFTs using alkylated organic semiconductors and systematically tune the source/drain electrode work functions via self-assembled monolayer modifications. A substantial decrease in current is observed as the electrode work function decreases, even in sharp-switching OTFTs with nearly trap-free transport interfaces, achieved using CYTOP as the gate dielectric. Contact resistance for low-work-function electrodes is found to be several orders of magnitude higher than that for high-work-function electrodes, confirming that the current reduction originates from injection inefficiency. Moreover, current decreases drastically when a gate dielectric with a higher trap density is used, indicating that carrier traps at the ternary interface further hinder carrier injection. These results highlight the necessity of maintaining sufficient carrier accumulation while minimizing trapping at the ternary interface to achieve efficient carrier injection in BGBC OTFTs.

The development of working cryogenic memories is very important for the scalability and feasibility of quantum computing. In this context, $\mathrm{Fe}\mathrm{Co}\mathrm{B}$/$\mathrm{Mg}\mathrm{O}$-based spin-transfer-torque magnetic random-access memories emerge as promising candidates to address this challenge. At low temperatures, the reduction in thermal noise allows for a lower energy barrier while retaining sufficient memory performance. Since the effective anisotropy of the system is directly proportional to the energy barrier, understanding how it varies with material parameters and temperature is crucial. In this work, we present an experimental method for extrapolating the thin-film magnetic properties measured at room temperature to the electrical properties of nanofabricated devices at various targeted temperatures. We employ magneto-optical Kerr-effect (MOKE) magnetometry to calculate the effective anisotropy energy density across the entire 100-mm wafer surface at room temperature. This method is entirely adapted to probe wafers of various sizes, and it is found to be faster and equivalent to conventional methods, such as vibrating sample magnetometry and superconducting quantum interference device (SQUID) magnetometry. The temperature evolution of magnetic anisotropy is further investigated using SQUID magnetometry from 300 to 10 K. Finally, the critical switching voltage from 300 to 40 K is measured for various nanofabricated devices with different $\mathrm{Fe}\mathrm{Co}\mathrm{B}$ storage-layer thicknesses. A model correlating the switching voltage of these devices with the effective anisotropy at the thin-film level is used to explain their temperature and thickness dependencies. These results confirm the validity of the MOKE method presented in this work and its potential in selecting devices across the wafer to function at a given operational target temperature.