Implementation of quantum logic gates with linear optical elements plays a prominent role in quantum computing due to their relatively easy manipulation and realization. We present efficient schemes to implement controlled-not (cnot) gates and controlled-swap (Fredkin) gates by using solely linear optics. We encode the control qubits and target qudits in photonic polarization (two-level) and spatial degrees of freedom ($d$ level), respectively. On the basis of the hybrid encoding, cnot and Fredkin gates are constructed in a deterministic way without any borrowed ancillary photons or measurement-induced nonlinearities. Remarkably, the number of linear optics required to implement a cnot gate has been reduced to one polarizing beam splitter, while only $d$ polarizing beam splitters are necessary to implement a generalized Fredkin gate. The optical depths of all schemes are reduced to 1 and and are dimension independent. Besides, the fidelity of our three-qubit Fredkin gate is higher than 99.7% under realistic conditions, which is higher than in previous schemes.

The two-dimensional layered material-based multifunctional transistors are expected to be core devices in the post-Moore era. However, the relationship between layer thickness and device performance remains unclear. Here, we design the layer $\mathrm{In}\mathrm{Se}$ transistors integrating switching and photodetection functions, exhibiting the fast-switching time and high responsivity when choosing the layer numbers of 2 and 3. Additionally, the maximum photoresponsivity and external quantum efficiency reach up to 0.29 A/W and 136.4% at the wavelength of 310 nm, respectively. The layer-number changing also induces 2 orders of magnitude improvement in and delay time. The dependence between layer number and device performance can provide a basis for designing multifunctional devices.

Experiments have shown that the light-emission efficiency of indium gallium nitride [$(\mathrm{In},\mathrm{Ga})\mathrm{N}$] light-emitting diodes improves with increasing indium concentration. It is widely thought that compositional fluctuations due to indium incorporation suppress diffusion of carriers to nonradiative centers, thus leading to defect-insensitive emission. However, recent experiments have challenged this hypothesis by revealing unexpectedly long diffusion lengths at room temperature. Here, we demonstrate an alternative mechanism involving the correlated reduction in radiative and nonradiative recombination rates that explains the increase in light-emission efficiency of $(\mathrm{In},\mathrm{Ga})\mathrm{N}$ with increasing indium concentration, without invoking the suppression of carrier diffusion. Our analysis challenges the notion that carrier localization gives rise to defect tolerance in $(\mathrm{In},\mathrm{Ga})\mathrm{N}$.

Two-dimensional transition-metal dihalides possess immense potential for applications in low-dimensional nanodevices because of their exceptional thermal and chemical stabilities, unique mechanical and electronic properties, and ultrahigh carrier mobility. In this study, an extensive structural search utilizing first-principles total-energy calculations combined with the particle-swarm optimization algorithm is conducted on bulk ${\mathrm{Zr}\mathrm{I}}_2$ to explore various structures and assess the feasibility of obtaining monolayer phases through mechanical exfoliation. Four stable phases of bulk ${\mathrm{Zr}\mathrm{I}}_2$, namely the α(α′)-phase, hex-phase, and tet-phase, along with their corresponding monolayers, are successfully obtained. All bulk and monolayer phases exhibit dynamic and mechanical stability. The mechanical, electronic transport, and photoelectric properties of the ${\mathrm{Zr}\mathrm{I}}_2$ monolayers are systematically investigated, and conceptual nanodevices based on ml-α- and ml-hex-${\mathrm{Zr}\mathrm{I}}_2$ monolayers are constructed. These nanodevices show remarkable transport characteristics, including excellent rectifying effects, low threshold voltages, high current densities, outstanding field-effect behaviors, and sensitive photoelectric responses. Moreover, p-n junction diodes constructed using ml-α-${\mathrm{Zr}\mathrm{I}}_2$ demonstrate a remarkable negative differential conductance effect. These findings illuminate the multifunctional nature of ${\mathrm{Zr}\mathrm{I}}_2$ monolayers and highlight their potential applications in nanoelectronic devices.

Three-dimensional nodal-line semimetals (NLSMs) are of remarkable importance for both enriching topological physics and wave management. However, NLSMs realized in acoustic systems are twofold band degenerate and are called Weyl NLSMs. Here, we report on the experimental observation of Dirac NLSMs with fourfold degeneracy in sonic crystals. We reveal that the topological properties of the Dirac NLSMs are entirely different than those of the conventional Weyl NLSMs. The Berry phase related to the Dirac nodal line (DNL) is $2\pi$, which results in surface responses of the Dirac NLSMs in two radically different situations: a torus surface state occupying the entire surface Brillouin zone (SBZ) and one without any surface state in the SBZ. We further reveal that topological surface arcs caused by the DNL can change from open to closed contours. The findings of Dirac NLSMs and their unique surface response may bring about exciting frontiers for the flexible manipulation of acoustic surface waves.

We establish fundamental bounds on subwavelength resolution for the radar ranging problem, “superradar.” Information-theoretical metrics are applied to probe the resolution limits for the case of both direct electric field measurement and photon-counting measurements. To establish fundamental limits, we begin with the simplest case of range resolution of two point targets from a metrology perspective. These information-based metrics establish fundamental bounds on both the minimal discrimination distance of two targets and the precision on the separation of two subwavelength resolved targets. For the minimal separation distance, both the direct field method and photon counting method show that the discriminability vanishes quadratically as the target separation goes to zero, and is proportional to the variance of the second derivative of the electromagnetic field profile. Nevertheless, robust subwavelength estimation is possible. Several different band-limited function classes are introduced to optimize discrimination. We discuss the application of maximum likelihood estimation to improve the range precision with optimal performance. The general theory of multiparameter estimation is analyzed, and a simple example of estimating both the separation and relative strength of the two point reflectors is presented.

Complementary metal oxide semiconductor (CMOS) devices require both n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs), but achieving both types that meet the requirements of the International Technology Roadmap for Semiconductors (ITRS) at ultrashort gate lengths is a challenge. Recently synthesized two-dimensional crystal ${\mathrm{WSi}}_2{\mathrm{N}}_4$ exhibits high theoretical hole and electron carrier mobilities. In this study, we investigate the performance limits of double-gated (DG) monolayer (ML) ${\mathrm{WSi}}_2{\mathrm{N}}_4$ MOSFETs with sub-5-nm gate lengths using first-principles density-functional theory and the nonequilibrium Green's function method. Our results show that both the n-type and p-type DG ML ${\mathrm{WSi}}_2{\mathrm{N}}_4$ MOSFETs can meet the requirements of ITRS 2013 for high-performance (HP) applications at the 2028 technology node, even when the gate length is scaled to 3 nm. For low-power applications, the scaling limits for the gate lengths of the n-type and p-type DG ML ${\mathrm{WSi}}_2{\mathrm{N}}_4$ MOSFETs are 4 and 5 nm, respectively. Importantly, the on-state currents of the n-type and p-type HP DG ML ${\mathrm{WSi}}_2{\mathrm{N}}_4$ MOSFETs are highly symmetric, highlighting the potential of ML ${\mathrm{WSi}}_2{\mathrm{N}}_4$ as a promising material for building next-generation CMOS devices, especially for HP applications.

In the last decade, conductive domain walls (CDWs) in single crystals of the uniaxial model ferroelectric lithium niobate (${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$; LNO) have been shown to reach resistances more than 10 orders of magnitude lower than the resistance of the surrounding bulk, with charge carriers being firmly confined to sheets with a width of a few nanometers. LNO is thus currently witnessing increased attention because of its potential in the design of room-temperature nanoelectronic circuits and devices based on such CDWs. In this context, the reliable determination of the fundamental transport parameters of LNO CDWs, in particular the 2D charge carrier density $n_{2\mathrm{D}}$ and the Hall mobility ${\mu }_H$ of the majority carriers, is of great interest. In this contribution, we present and apply a robust and easy-to-prepare Hall-effect measurement setup by adapting the standard four-probe van der Pauw method to contact a single, hexagonally shaped domain wall that fully penetrates the 200-$\text{μ}\mathrm{m}$-thick LNO bulk single crystal. We then determine $n_{2\mathrm{D}}$ and ${\mu }_H$ for a set of external magnetic fields $B$ and prove the expected cosinelike angular dependence of the Hall voltage. Lastly, we present photoinduced-Hall-effect measurements of one and the same DW, by determining the impact of super-band-gap illumination on $n_{2\mathrm{D}}$.

Topological corner states are exotic topological boundary states bounded to zero-dimensional geometry even when the dimension of bulk systems is larger than one. So far, all previous realizations of higher-order topological insulators (HOTI) phases are hallmarked by ${\mathbb{Z}}_2$ topological invariants and therefore have only one corner state at each corner. Here, we report an experimental demonstration of $\mathbb{Z}$-class HOTI phases in electrical circuits, characterized by multipole chiral numbers $N$, hosting large-number corner modes at each corner. By measuring the impedance spectra and distributions, we clearly observe that the multipole corner modes in $\mathbb{Z}$-class HOTI phases feature scalable mode areas. Moreover, we find that the local density of states (LDOS) at each corner is maximally distributed at $N$ corner unit cells, differing conspicuously from the ${\mathbb{Z}}_2$-class case, where the LDOS only dominates over one corner unit cell, allowing us to probe the topological number $N$ and reveal the corresponding fractional corner charges. Our results extend the observation of HOTIs from the ${\mathbb{Z}}_2$ class to the $\mathbb{Z}$ class and the coexistence of spatially overlapping large numbers of corner modes that may enable exotic topological devices that require high-degeneracy boundary states.

We point out a critical flaw in the analysis of quantum key distribution protocols that employ the two-way error-correction protocol Cascade. Specifically, this flaw stems from an incomplete consideration of all two-way communication that occurs during the Cascade protocol. We present a straightforward and elegant alternative approach that addresses this flaw and produces valid key rates. We exemplify our new approach by comparing its key rates with those generated using older, incorrect approaches, for qubit BB84 and decoy-state BB84 protocols. We show that, in many practically relevant situations, our rectified approach produces the same key rate as older, incorrect approaches. However, in other scenarios, our approach produces valid key rates that are lower, highlighting the importance of properly accounting for all two-way communication during Cascade.

We demonstrate the capability of laboratory-based x-ray microscopes, using intensity-modulation masks, to access the submicron length scale in the dark-field contrast channel while maintaining micron resolution in the resolved (refraction and attenuation) channels. The dark-field contrast channel reveals the presence of ensembles of samples’ features below the system resolution. Resolved refraction and attenuation channels provide multimodal high-resolution imaging down to the micron scale. We investigate the regimes of modulated and unmodulated dark field as well as refraction, quantifying their dependence on the relationship between feature size in the imaged object and aperture size in the intensity-modulation mask. We propose an analytical model to link the measured signal with the sample’s microscopic properties. Finally, we demonstrate the relevance of the microscopic dark-field contrast channel in applications from both the life and physical sciences, providing proof-of-concept results for imaging collagen bundles in cartilage and dendritic growth in lithium batteries.

The thorium fuel cycle is emerging as an attractive alternative to conventional nuclear fuel cycles, as it does not require the enrichment of uranium for long-term sustainability. The operating principle of this fuel cycle is the irradiation of ${}^{232}\mathrm{Th}$ to produce ${}^{233}\mathrm{U}$, which is fissile and sustains the fission chain reaction. ${}^{233}\mathrm{U}$ poses unique challenges for nuclear safeguards, as it is associated with a uniquely extreme $\gamma$-ray environment from ${}^{232}\mathrm{U}$ contamination, which limits the feasibility of the $\gamma$-ray-based assay, as well as more conservative accountability requirements than for ${}^{235}\mathrm{U}$ set by the International Atomic Energy Agency. Consequently, instrumentation used for safeguarding ${}^{235}\mathrm{U}$ in traditional fuel cycles may be inapplicable. It is essential that the nondestructive signatures of ${}^{233}\mathrm{U}$ be characterized so that nuclear safeguards can be applied to thorium fuel-cycle facilities as they come online. In this work, a set of ${}^{233}{\mathrm{U}}_3{\mathrm{O}}_8$ plates, containing $984{\mathrm{g}}^{233}\mathrm{U}$, was measured at the National Criticality Experiments Research Center. A high-pressure ${}^4\mathrm{He}$ gaseous scintillation detector, which is insensitive to $\gamma$ rays, was used to perform a passive fast neutron spectral signature measurement of ${}^{233}{\mathrm{U}}_3{\mathrm{O}}_8$, and was used in conjunction with a pulsed deuterium-tritium neutron generator to demonstrate the differential die-away signature of this material. Furthermore, an array of ${}^3\mathrm{He}$ detectors was used in conjunction with the same neutron generator to measure the delayed neutron time profile of ${}^{233}\mathrm{U}$, which is unique to this nuclide. These measurements provide a benchmark for future nondestructive assay instrumentation development, and demonstrate a set of key neutron signatures to be leveraged for nuclear safeguards in the thorium fuel cycle.

Enhancing the capabilities of superconducting quantum hardware, requires higher gate fidelities and lower crosstalk, particularly in larger-scale devices, in which qubits are coupled to multiple neighbors. Progress towards both of these objectives would highly benefit from the ability to fully control all interactions between pairs of qubits. Here we propose an alternative coupler model that allows dispersively detuned transmon qubits to be fully decoupled from each other, i.e., $ZZ$ crosstalk is completely suppressed while maintaining a maximal localization of the qubits’ computational basis states. We further reason that, for a dispersively detuned transmon system, this can only be the case if the anharmonicity of the coupler is positive at the idling point. A simulation of a 40-$\mathrm{ns}$ CZ gate for a lumped-element model suggests that achievable process infidelity can be pushed below the limit imposed by state-of-the-art coherence times of transmon qubits. On the other hand, idle gates between qubits are no longer limited by parasitic interactions. We show that our scheme can be applied to large integrated qubit grids, where it allows a pair of qubits to be fully isolated, that undergoes a gate operation, from the rest of the chip while simultaneously pushing the fidelity of gates to the limit set by the coherence time of the individual qubits.

The synthetic gauge field, projectively enriching the algebraic structure of spatial symmetries, has become a hotspot in topological physics recently. The intrinsic orbital degrees of freedom, playing a fundamental role in solid-state materials and offering an alternative platform, have not yet been studied extensively in classical wave systems, such as acoustic systems. Here we propose orbital-dependent gauge fields by utilizing the intrinsic degenerate p orbitals in a square lattice of coupled acoustic cavities. To realize the orbital-related synthetic gauge fields, an acoustic disk-shaped resonator hosting degenerate p orbitals is designed, where the signs of transverse and longitudinal hoppings can be simultaneously tailored on demand by tuning the geometries of coupling waveguides in the dimer units. We then show two different types of orbital-dependent topological insulators resting with the orbital-dependent gauge fields via the tight-binding method and full-wave simulation. Moreover, an orbital-dependent semimetal phase is revealed in the square lattice with a varied dimerization pattern. Our findings reveal the existence of abundant physical phenomena as the cavity orbitals and gauge fields meet with the topology, initializing the framework for orbital-related topological physics and opening up opportunities for potential multifunctional acoustic applications, such as sound sensing and trapping.