Pyroelectric energy converters are functional capacitors that use a pyroelectric material as the dielectric layer. By utilizing a first-order phase transformation of the material, a pyroelectric device can generate an adequate amount of electricity from small temperature fluctuations. However, most pyroelectric capacitors leak during energy conversion. In this paper, we analyze the thermodynamics of pyroelectric energy conversion with consideration of electric leakage. Our thermodynamic model is verified by experiments using three phase-transforming ferroelectric materials with different pyroelectric properties and leakage behaviors. We demonstrate that the impact of leakage on electric generation is prominent, and sometimes may be confused with the actual power generation by pyroelectricity. We discover a material candidate, $(\mathrm{Ba},\mathrm{Ca})(\mathrm{Ti},\mathrm{Zr},\mathrm{Ce}){\mathrm{O}}_3$, that exhibits a large pyroelectric current and an extremely low leakage current. A pyroelectric converter made of this material generates a pyroelectric current density of $1.95\mu \mathrm{A}/{\mathrm{cm}}^2$ and a pyroelectric work density of $0.2\mathrm{J}/{\mathrm{cm}}^3$ even after 1389 thermodynamic-conversion cycles.

X-ray ptychotomography in the near-field regime is a promising technique for high-resolution, quantitative, and nondestructive investigations in materials science, paleontology, and biomedicine. X-ray near-field ptychography has been previously demonstrated in projection and tomography mode, but the quantitativeness of the reconstructed data has never been discussed in detail. Here, we use measurements of a sample made of aluminum and nickel microparticles to evaluate the quantitativeness of the volumetric mass-density data. Moreover, we propose an algorithm (VortRem) for the removal of phase vortexes, a type of artifact that frequently occurs in holographic methods. VortRem and the results presented here may be fundamental for extending the applicability of this emerging technique to quantitative three-dimensional characterization studies of light as well as dense samples down to the nanoscale.

Harnessing the spontaneous emission of incoherent quantum emitters is one of the hallmarks of nano-optics. Yet, an enduring challenge remains—making them emit vector beams, which are complex forms of light associated with fruitful developments in fluorescence imaging, optical trapping, and high-speed telecommunications. Vector beams are characterized by spatially varying polarization states whose construction requires coherence properties that are typically possessed by lasers—but not by photons produced by spontaneous emission. Here, we show a route to weave the spontaneous emission of an ensemble of colloidal quantum dots into vector beams. To this end, we use holographic nanostructures that impart the necessary spatial coherence, polarization, and topological properties to the light originating from the emitters. We focus our demonstration on vector vortex beams, which are chiral vector beams carrying nonzero orbital angular momentum, and argue that our approach can be extended to other forms of vectorial light.

Non-Hermitian skin effect (NHSE) has led to interesting physics and sophisticated applications beyond the conventional framework. However, NHSE studies have been limited to an individual dimension due to the difficulty of constructing nonreciprocal coupling in higher-dimensional systems. With the concept of synthetic dimension, we realize two-dimensional (2D) NHSE in a synthetic photonic lattice. The synthetic photonic lattice is composed of a spatial dimension and a synthetic frequency dimension, which is constructed by introducing gain and loss and dynamically modulating the complex refractive index in a one-dimensional ring-resonator array. In the synthetic 2D NHSE system, we can manipulate the spatial position and frequency mode of the light in real time, thus enabling programmable light propagation and frequency conversion. Specifically, the incident light can be localized in the spatial dimension and the frequency dimension simultaneously, leading to second-order corner modes in the synthetic 2D NHSE lattice. Besides, the 2D NHSE system exhibits an excellent robustness for the disorder and point defect in the lattice. This work generalizes the non-Hermitian skin effect in synthetic dimension to control the light in different dimensions, which shows great promise for potential applications in on-chip light manipulation, frequency synthesis, and information processing.

Pulse-shape discrimination (PSD) is usually achieved using the different fast and slow decay components of inorganic scintillators, such as ${\mathrm{Ba}\mathrm{F}}_2$, $\mathrm{Cs}\mathrm{I}$:Tl, etc. However, ${\mathrm{La}\mathrm{Br}}_3$:$\mathrm{Ce}$ is considered to not possess different components at room temperature, but has been proved to have the capability of discriminating γ and α events using fast digitizers. In this paper, ionization-density-dependent transport and rate equations are used to quantitatively model the competing processes in a particle track. With one parameter set, the model reproduces the nonproportionality response of electrons or α particles, and explains the measured α and γ pulse-shape difference well. In particular, the nonlinear quenching of excited dopant ions, ${\mathrm{Ce}}^{3+}$, is confirmed herein to mainly contribute observable ionization α and γ pulse-shape differences. Further study of the luminescence quenching can also help to better understand the fundamental physics of nonlinear quenching and thus improve the crystal engineering. Moreover, based on the mechanism of dopant quenching, the ionization-density-dependent pulse-shape differences in other fast single-decay-component inorganic scintillators, such as lutetium yttrium oxyorthosilicate, ${\mathrm{Lu}}_{2(1\text{−}\mathrm{x})}{\mathrm{Y}}_{2\mathrm{x}}{\mathrm{Si}\mathrm{O}}_5:\mathrm{Ce}$ (LYSO) and ${\mathrm{Ce}\mathrm{Br}}_3$, are also predicted and verified with experiments.

Multiparty quantum communication provides delightful applications, including quantum cryptographic communication and quantum secret sharing. Quantum communication based on the Greenberg-Horne-Zeilinger (GHZ) state measurement provides a practical way to implement multiparty quantum communication. With the standard spatially localized GHZ state measurement, however, information can be imbalanced among the communication parties that can cause significant problems in some applications of multiparty cryptographic communication, e.g., secret sharing. Here, we propose an equitable multiparty quantum communication where information balance among the communication parties is achieved without a trusted third party. Our scheme is based on the GHZ state measurement that is not spatially localized but implemented in a way that all the distant communication parties symmetrically participate. We also verify the feasibility of our scheme by presenting the proof-of-principle experimental demonstration of informationally balanced three-party quantum communication using weak coherent pulses.

The parameters governing the thermoelectric efficiency of a material, Seebeck coefficient, electrical, and thermal conductivities, are correlated and their reciprocal interdependence typically prevents a simultaneous optimization. Here, we present the case of disordered cubic kesterite ${\mathrm{Cu}}_2{\mathrm{ZnSnS}}_4$, a phase stabilized by structural disorder at low temperature. With respect to the ordered form, the introduction of disorder improves the three thermoelectric parameters at the same time. The origin of this peculiar behavior lies in the localization of some $\mathrm{Sn}$ lone pair electrons, leading to “rattling” $\mathrm{Sn}$ ions. On one hand, these rattlers remarkably suppress thermal conductivity, dissipating lattice energy via optical phonons located below 1.5 THz; on the other, they form electron-deficient $\mathrm{Sn}$—$\mathrm{S}$ bonds leading to a p-type dopinglike effect and highly localized acceptor levels, simultaneously enhancing electrical conductivity and the Seebeck coefficient. This phenomenon leads to a 3 times reduced thermal conductivity and doubling of both electrical conductivity and the Seebeck coefficient, resulting in a more than 20 times increase in figure of merit, although still moderate in absolute terms.

We report the realization of coupling-independent, robust wireless sensing of fully passive resistive sensors. $\mathcal{P}\mathcal{T}$-symmetric operation obviates sweeping, permitting real-time, single-point sensing. Self-oscillation is achieved through a fast-settling nonlinearity whose voltage amplitude is proportional to the sensor’s resistance. These advances markedly simplify the reader. A dual time-scale theoretical framework generalizes system analysis to arbitrary operating conditions and a correction strategy reduces errors due to detuning from $\mathcal{P}\mathcal{T}$-symmetric conditions by an order of magnitude.

This paper reports on the experimental diagnostics of an entanglement-swapping protocol by means of collective entanglement witness. Our approach is suitable to detect disturbances occurring in the preparation of quantum states, quantum-communication channels, and imperfect Bell-state projections. More specifically, we demonstrate that our method can distinguish disturbances such as depolarization, phase damping, amplitude damping, and imperfect Bell-state measurement by observing four probabilities and estimating collective entanglement witness. Since entanglement swapping is a key procedure for quantum repeaters, quantum relays, device-independent quantum communications, and entanglement-assisted error correction, this can aid in faster and practical resolutions of quality of transmission related problems as our approach requires fewer measurements than other means of diagnostics.

Due to the single-photon interference at a third untrusted party, the twin-field quantum key distribution (TF-QKD) protocol and its variants can beat the well-known rate-loss bound without quantum repeaters and related experiments have recently been implemented. In general, quantum states in these schemes should be randomly switched between the code mode and the test mode. To adopt the standard decoy-state method, the phases of coherent-state sources in the test mode are assumed to be continuously randomized. However, such a crucial assumption cannot be satisfied well in experimental implementations. In this paper, to bridge the gap between theory and practice, we propose a TF-QKD variant with discrete-phase-randomized sources both in the code mode and the test mode and prove its security against collective attacks. Our simulation results indicate that, with only a small number of discrete phases, the performance of discrete-phase-randomized sources can overcome the rate-loss bound and approach that of continuous-phase-randomized sources.

We demonstrate inline holography with a soft-x-ray vortex beam having an orbital angular momentum. A hologram is recorded as an interference pattern between a Bragg-diffracted wave from a fork grating and a divergent wave generated by a Fresnel zone plate. The images obtained exhibit fork-shaped interference fringes, which confirm the formation of a vortex beam. By analyzing the interference images, we successfully obtain a spiral phase distribution with a topological charge $\ell =\pm 1$. The results demonstrate that the inline-holography technique may be an effective probe for the characterization of topological defects in magnetic textures.

We present a magneto-optical study of the carrier dynamics in compressively strained ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$ films with $\mathrm{Sn}$ content up to 10% epitaxially grown on $\mathrm{Ge}$ on $\mathrm{Si}$(001) virtual substrates. We leverage the Hanle effect under steady-state excitation to study the spin-dependent optical transitions in the presence of an external magnetic field. This allows us to obtain direct access to the dynamics of the optically induced carrier population. Our approach reveals that at cryogenic temperatures the effective lifetime of the photogenerated carriers in coherent ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$ is on the subnanosecond timescale. Supported by a model estimate of the radiative lifetime, our measurements indicate that carrier recombination is dominated by nonradiative processes. Our results thus provide central information to improve the fundamental understanding of carrier kinetics in this advanced direct-band-gap group-IV-material system. Such knowledge can be a stepping stone in the quest for the implementation of ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$-based functional devices.

Here we demonstrate an atomic magnetometer that has a bandwidth of more than 100 kHz and a sensitivity of $180\mathrm{fT/}\surd \mathrm{Hz}$ at a Fourier frequency of 8 Hz, and $0.7\mathrm{nT/}\surd \mathrm{Hz}$ at 100 kHz. These sensitivity measurements are achieved at geophysically useful magnetic field magnitudes (approximately $50\mu \mathrm{T}$ inside a three-layer $\mu$-metal shield) and are limited by the photon shot noise for frequencies above 8 Hz. This device is based on a nonlinear magneto-optical rotation sensor that is operated with an active feedback to the pump modulation frequency. We present a theoretical description of the response functions of the components in the magnetometer. We show that the range of operation of atomic magnetometers can thus be expanded beyond the conventional high-sensitivity, low-bandwidth domain, to provide a high-linearity, high-bandwidth, and high-sensitivity sensor.

Beam collimation in high-energy colliders is customarily carried out by means of massive amorphous absorbers surrounding the circulating beam. Several studies were performed in the last decades to establish an innovative collimation technique that relies on particle deflection by means of channeling between crystalline planes of a bent crystal. We report the operational use of crystal collimation in the Large Hadron Collider that was achieved during a special high-${\beta }^{\ast }$ physics run with low-intensity beams, representing a milestone for both accelerator and high-energy physics that could pave the way for new synergies in the near future. The deployment of this scheme was steered and motivated by machine-simulation studies, which were then confirmed experimentally using data provided by the experiments thanks to a sensitivity not accessible with the ring instrumentation. The evidence of beam-related experimental background reduction, improved data quality, and faster halo removal with respect to amorphous collimators is obtained using bent crystals as the primary collimation stage. A detailed description of preparatory studies and operational performance is reported, together with a comparison between experimental results and theoretical expectations.

The thermal stability in nanostructured magnetic systems is an important issue for applications in information storage. From a theoretical and simulation perspective, an accurate prediction of thermally activated transitions is a challenging problem because desired retention times are of the order of 10 years, while the characteristic timescale for precessional magnetization dynamics is of the order of nanoseconds. Here, we present a theoretical study of the thermal stability of magnetic elements in the form of perpendicularly magnetized ferromagnetic disks using the forward flux sampling method, which is useful for simulating rare events. We demonstrate how rates of thermally activated switching between the two uniformly magnetized “up” and “down” states, which occurs through domain-wall nucleation and propagation, vary with the interfacial Dzyaloshinskii-Moriya interaction, which affects the energy barrier separating these states. Moreover, we find that the average lifetimes differ by several orders of magnitude from estimates based on the commonly assumed value of 1 GHz for the attempt frequency.

We propose a detector of microwave photons that can distinguish the vacuum state, one-photon state, and the states with two or more photons. Its operation is based on the two-photon transition in a biased Josephson junction and detection occurs when it switches from a superconducting to a normal state. We model the detector theoretically. The detector performs with more than 90% success probability in several microseconds. The working frequency can be set at the design stage in the range from about 1 to 20 GHz.

Effects of a microwave voltage on magnetization precession are analyzed based on a macrospin model. The microwave voltage induces the oscillating anisotropy field through the voltage-controlled magnetic anisotropy (VCMA) effect, and then stimulates the magnetization. The large-angle precession is maintained if the magnetization synchronizes with the microwave voltage. The effective equations of motion of the magnetization with an oscillating anisotropy field are derived, and the mechanism of the synchronization is clarified by analyzing the derived equations of motion. The conditions of the angular frequency detuning and the amplitude of the oscillating anisotropy field for synchronization are obtained. The results are useful for development of VCMA-based energy-efficient spintronic devices using magnetization precession such as a VCMA-based magnetoresistive random-access memory and a nanoscale microwave magnetic field generator.

Quantum-wire intermediate-band solar cells (QW IBSCs) are good candidates for breaking the Shockley-Queisser limit; however, there are a few studies of them. In this paper, we derive the fundamental limiting efficiency (FLE), the theoretical upper limit of the power-conversion efficiency, for QW IBSCs by calculation of the intrinsic loss. To achieve this, based on a photon-electron detailed-balance principle, the intrinsic loss components (ILCs) are modeled in the QW IBSCs by our considering photon absorption and emission for two transverse directions of confined carriers and for a longitudinal direction of free carriers in the QWs. Furthermore, the ILCs and FLE are investigated in an experimental reported structure of an ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}/\mathrm{Ga}\mathrm{As}$ QW IBSC. For this purpose, the two-dimensional Schrödinger equation and the Bloch approximation are used to obtain the placement and width of the intermediate band, respectively. Besides, the effect of changing the indium content, the diagonal length, and the period of QWs, which is a way to engineer the placement and width of the intermediate band and consequently the ILCs and FLE, on the FLE of ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}/\mathrm{Ga}\mathrm{As}$ QW IBSCs is examined.