The Toffoli gate is an important universal quantum gate, and will alongside the Clifford gates be available in future fault-tolerant quantum computing hardware. Many quantum algorithms rely on performing arbitrarily small single-qubit rotations for their function, and these rotations may also be used to construct any unitary from a limited (but universal) gate set. How to carry out such rotations is then of significant interest. In this work, we evaluate the performance of a recently proposed single-qubit rotation algorithm using the Clifford plus Toffoli gate set by implementation of a one-shot version on both a real and a simulated quantum computer. We test the algorithm under various simulated noise levels using a per-qubit depolarizing error noise model and examine how the probabilities and process fidelities are affected. We then conduct live runs and find that the results reasonably match the simulated results. We also attempt to model the hardware noise by combining a number of noise models, matching the results to results of the live runs to approximate the hardware noise. Our results suggest that the algorithm will perform well for up to $1\mathrm{\%}$ noise under the noise models we chose. We further posit the use of our algorithm as a benchmark for quantum processing units, given that it has a low complexity that is easy to fine-tune in small steps. We provide details for how to do this.

Quantum sensors offer exceptional sensitivity to nanoscale magnetic field fluctuations, where nonstationary effects—such as spin diffusion—and non-Markovian dynamics arising from coupling to few environmental degrees of freedom play critical roles. Because fully reconstructing the microscopic structure of realistic spin baths is often infeasible, a practical challenge is to identify the dynamical features that are actually encoded in the sensor’s decoherence signal. Here we demonstrate how quantum sensors can operationally characterize the statistical nature of environmental noise, distinguishing between stationary and nonstationary behaviors, as well as Markovian and non-Markovian dynamics. Using nitrogen-vacancy centers in diamond as a platform, we develop a physical noise model that captures the essential dynamical features of realistic environments relevant to sensor observables—independently of the microscopic bath details— and provides analytical predictions for Ramsey decay across different regimes. These predictions are experimentally validated through controlled noise injection with tunable correlation properties. Our results showcase the capability of quantum sensors to isolate and identify key dynamical properties of complex environments, without requiring full microscopic bath reconstruction. This work clarifies the operational signatures of nonstationarity and non-Markovian behavior at the nanoscale and lays the foundation for strategies that mitigate decoherence while exploiting environmental dynamics for enhanced quantum sensing.

We propose a practical hybrid decoding scheme for the parity-encoding architecture. This architecture was first introduced by N. Sourlas [Phys. Rev. Lett. 94, 070601 (2005)] as a computational technique for tackling hard optimization problems, especially those modeled by spin systems such as the Ising model and spin glasses, and reinvented by W. Lechner, P. Hauke, and P. Zoller [Sci. Adv. 1, e1500838 (2015)] to develop quantum annealing devices. We study the specific model, called the SLHZ model, aiming to achieve a near-term quantum annealing device implemented solely through geometrically local spin interactions. Taking account of the close connection between the SLHZ model and a classical low-density parity-check (LDPC) code, two approaches can be chosen for the decoding: (1) finding the ground state of a spin Hamiltonian derived from the SLHZ model, which can be achieved via stochastic decoders such as a quantum annealer or a classical Monte Carlo sampler; or (2) using deterministic decoding techniques for the classical LDPC code, such as belief propagation and a bit-flip decoder. The proposed hybrid approach combines the two approaches by applying bit-flip decoding to the readout of the stochastic decoder based on the SLHZ model. We present simulations demonstrating that this approach can reveal the latent potential of the SLHZ model, realizing the soft-annealing concept proposed by Sourlas.

Mobile gamma-ray spectrometry (MGRS) systems are essential for localizing, identifying, and quantifying gamma-ray sources in complex environments. Full-spectrum template matching offers the highest accuracy and sensitivity for these tasks but is limited by the computational cost of generating the required spectral templates. Here, we present a generalized full-spectrum modeling framework for MGRS systems in scattering media, enabling near-real-time template generation through dynamic, anisotropic instrument response functions. Benchmarked against high-fidelity brute-force Monte Carlo simulations, our method yields a computational speedup by a factor of $\mathcal{O}({10}^7)$, while achieving comparable accuracy with median spectral deviations below 6%. The methodology presented is platform-agnostic and applicable across marine, terrestrial, and airborne domains, unlocking new capabilities for MGRS in a variety of applications, such as environmental monitoring, geophysical exploration, nuclear safeguards, and radiological emergency response.

Semiconductor quantum dot (QD) devices have become central to advancements in spin-based quantum computing. However, the increasing complexity of modern QD devices makes calibration and control—particularly at elevated temperatures—a bottleneck to progress, highlighting the need for robust and scalable autonomous solutions. A major hurdle arises from trapped charges within the oxide layers, which induce random offset voltage shifts on gate electrodes, with a standard deviation of approximately 83 mV of variation within state-of-the-art present-day devices. Efficient characterization and tuning of large arrays of QD qubits depend on choices of automated protocols. Here we introduce a physically intuitive framework for a bootstrapping, autonomous testing, and initialization system (BATIS) designed to streamline QD device evaluation and calibration. BATIS navigates high-dimensional gate voltage spaces, automating essential steps such as leakage testing, formation of all current channels, and gate characterization in the presence of trapped charges. For forming the current channels, BATIS follows a nonstandard approach that requires a single set of measurements regardless of the number of channels. Demonstrated at 1.3 K on a quadruple QD $\mathrm{Si}/{\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}$ device, BATIS eliminates the need for deep cryogenic environments during initial device diagnostics, significantly increasing scalability and reducing setup times. By requiring only minimal prior knowledge of the device architecture, BATIS represents a platform-agnostic solution, adaptable to various QD systems, which bridges a critical gap in QD autotuning.

Optical fiber bundles enable diffraction-free transmission of two-dimensional optical field distributions between the bundle input and output ends, which is highly beneficial in many applications in remote sensing and imaging. The spatial resolution of fiber bundles is mostly limited by the mode field diameter of an individual fiber. When using common low-refractive-index fibers, the resolution is typically limited by the wavelength of light ($\sim \lambda$), while using high-refractive-index fibers allows pushing it into a subwavelength range ($\simeq 0.3\lambda$–$0.5\lambda$), as was recently reported for sapphire fiber bundles in the terahertz (THz) range. Despite advanced resolution, such bundles require complicated image readout aided by depixelization techniques based on computational imaging. The analytical models of image formation in such systems are largely absent, which hampers the development of such bundles, as well as efficient processing of collected images. In this paper, we develop a semi-analytical model based on the methods of Fourier optics and sampling theorem to answer the fundamental questions related to image quality and resolution of such bundle-based imaging systems within the modulation transfer function (MTF) formalism. Thus, the developed model is then applied to analyze the THz image formation by the tapered sapphire fiber bundles. The inferred MTFs agree with the experiments. We believe that our findings should be instrumental for designing and applications of optical fiber bundles.

Self-heating is a critical problem for $\mathrm{Ga}\mathrm{N}$-based devices in high-power and high-frequency applications. Heat dissipation in the latest $\mathrm{Ga}\mathrm{N}$-on-diamond technology lies in increasing the interfacial thermal conductance (ITC) of the $\mathrm{Ga}\mathrm{N}$/diamond interface. In this work, we systematically investigated the effect of interplay between morphology and thickness of a $\mathrm{Si}\mathrm{N}$ interlayer on the ITC of the $\mathrm{Ga}\mathrm{N}$/diamond interface through molecular dynamics simulations. It is found that as the thickness of the interlayer increases, for amorphous $\mathrm{Si}\mathrm{N}$, the ITC ($G_{\mathrm{amo}}$) decreases monotonically. However, for a crystalline-$\mathrm{Si}\mathrm{N}$ interlayer, the ITC ($G_{\mathrm{cry}}$) shows a nonmonotonic behavior, firstly decreasing, then experiencing an abnormal increase, and finally decreasing again. The ratio of $G_{\mathrm{cry}}$ to $G_{\mathrm{amo}}$ reaches 3.23 as the $\mathrm{Si}\mathrm{N}$ thickness increases to 10 nm. Our calculated results show good agreement with reported experimental values from different research teams. Since amorphous and crystalline structures represent two extreme morphologies, our calculated results can be considered as the high and low limits for the ITC of the $\mathrm{Ga}\mathrm{N}$/diamond interface with a $\mathrm{Si}\mathrm{N}$ interlayer. Further spectral analysis and lattice dynamics calculations reveal that the effect of the morphology and the thickness of the $\mathrm{Si}\mathrm{N}$ interlayer on the ITC is governed by the interplay among different mechanisms of phonon-disorder scattering, thermalization by inelastic scattering, and the phonon bridge effect. The findings here provide guidance for optimizing interlayers in facilitating thermal transport of $\mathrm{Ga}\mathrm{N}$-on-diamond devices.

Random number generators are an integral part of any cryptographic system. The security of the cryptographic system depends on the quality of the random number generators. In this work, we demonstrate a high-entropy (more than $0.95$ bits/bit) photon number source using a femtosecond pulsed laser that uses chirped-pulse amplification as a mechanism. The randomness arising from inherent thermal fluctuations is comprehensively analyzed. We further propose and analyze a randomness conditioning algorithm, the Borel Selector, which in real time produces an output that is an ($ϵ,m$)-limiting Borel sequence. The physical entropy source, as well as the conditioning algorithm, has been benchmarked against state-of-the-art methods, and demonstrated improved statistics and increased efficiencies. The proposed entropy source and extractor is, to our knowledge, the first of its kind, and is a promising candidate for application in entropy-as-a-service and postquantum cryptography architectures.

We investigate the robustness of bound states in the continuum (BICs) in a bilayer dielectric rod array against geometric and material perturbations. Our analysis focuses on both symmetry-protected and Fabry-Pérot BICs (FP BICs), examining their transformation into quasi-BICs under three structural modifications: (i) in-plane displacement of one layer, which breaks the ${\mathrm{C}}_2$ symmetry of the system; (ii) introduction of material losses that break time-reversal symmetry; and (iii) variation in the interlayer distance, which preserves structural symmetry. In particular, we demonstrate that material losses inevitably induce radiation in Fabry-Pérot BICs via second-order perturbation processes, converting them into quasi-BICs, while symmetry-protected BICs remain nonradiative. We further show that, despite the inherent instability of BICs under symmetry-breaking effects, their resilience can be significantly enhanced through proper design. Both Fabry-Pérot and symmetry-protected BICs exhibit exponentially weak sensitivity to ${\mathrm{C}}_2$-breaking perturbations as the interlayer distance increases. Finally, we show that additional FP BICs emerge under oblique incidence, originating from the interference of two high-$Q$ quasi-BICs near the symmetry-protected ones. Our findings pave the way for the development of BIC-based photonic devices with improved robustness against fabrication imperfections, environmental variations, and material losses.

Two-dimensional magnetic materials are promising candidates for next-generation spintronic devices because their magnetic order can be tuned by external factors, such as strain. In this work, we study $\mathrm{Fe}{X}_4$ ($X=\mathrm{N},\mathrm{P}$) in monolayer and bilayer forms through density-functional-theory calculations combined with Monte Carlo simulations and present a comprehensive picture of their structural, electronic, and magnetic behavior under biaxial strain. With respect to the monolayer configurations, the ${\mathrm{Fe}\mathrm{N}}_4$ structure exhibits a planar geometry and semiconducting properties, whereas the ${\mathrm{Fe}\mathrm{P}}_4$ structure adopts a buckled morphology and demonstrates metallic behavior. Both ML-${\mathrm{Fe}\mathrm{N}}_4$ and ML-${\mathrm{Fe}\mathrm{P}}_4$ are characterized by dynamic and thermal stability. In contrast, other pnictogen-containing monolayers, including ${\mathrm{Fe}\mathrm{As}}_4$, ${\mathrm{Fe}\mathrm{Sb}}_4$, and ${\mathrm{Fe}\mathrm{Bi}}_4$, display structural instability. Under applied biaxial strain, the electronic character of ML-${\mathrm{Fe}\mathrm{P}}_4$ changes from metallic to semiconducting, while ML-${\mathrm{Fe}\mathrm{N}}_4$ maintain their semiconducting nature. In the bilayer counterparts, interlayer interactions enhance magnetic moments and alter overall stability compared with those in the monolayers. Monte Carlo simulations reveal strain-driven magnetic phase transitions together with significant variations in transition temperatures. The Curie temperature reaches about 980 K in the ferromagnetic regime of ${\mathrm{Fe}\mathrm{N}}_4$ and around 300 K in the unstrained ferromagnetic state of ${\mathrm{Fe}\mathrm{P}}_4$. BL-${\mathrm{Fe}\mathrm{N}}_4$ remains antiferromagnetic under strain but switches between different antiferromagnetic configurations with transition temperatures in the several-hundred-kelvin range, while BL-${\mathrm{Fe}\mathrm{P}}_4$ exhibits a strain-induced ferromagnetic phase with a transition temperature close to 133 K. These findings demonstrate the potential of $\mathrm{Fe}$-based two-dimensional systems for strain-controlled and thermally robust low-power spintronic applications.

Acoustic metamaterials open compelling avenues for ultrathin low-frequency sound absorbers, yet their reliance on localized resonances renders a fundamental trade-off between deep-subwavelength thickness and attainable bandwidth. Therefore, achieving broadband absorption necessitates the spectral overlap of numerous resonant modes, inevitably resulting in intricate architectures that impede their practical applications. Moreover, sound absorbers under a rigid backing, constrained by the acoustic analogue of the Rozanov bound, remain inherently bulky when operating at extremely low frequencies. In this study, we put forward a paradigm to implement an ultrabroadband acoustically soft boundary via hybridizing an opening boundary with underdamped resonators. By coupling a thin layer of porous material to this hybridized soft boundary, we demonstrate an ultrabroadband absorber that achieves an average absorption of 92.5% in simulations and 91.4% in experiments across the 20- to 3000-Hz frequency range. The demonstrated absorber features an ultracompact profile, measuring a thickness of just 2.8 cm, and a simple configuration, consisting of only three resonant meta-atoms. We further apply the proposed absorber as an anechoic termination or a perfectly matched layer within a standard test system for measuring acoustic scattering coefficients, offering a more efficient and compact alternative than traditional apparatus composed of a 30-cm-thick sponge. This work offers a promising pathway toward compact ultrabroadband sound absorbers for practical applications.

Layered van der Waals (vdW) ferromagnetic materials, such as ${\mathrm{Cr}}_X{\mathrm{Te}}_Y$ have attracted enormous attention for their exciting electronic and magnetic properties. In this context, this study reports on the manifestations on the Berry curvature effect induced by systematically altering the structural quality and the thickness of the ${\mathrm{Cr}\mathrm{Te}}_2$ (CT) thin films. Of note, these CT films are deposited using dc-magnetron sputtering—a scalable and industrially robust technique, which, to the best of our knowledge, has not been employed previously for ${\mathrm{Cr}\mathrm{Te}}_2$ growth. This distinguishes the film-growth approach adopted in the present work for depositing the CT films from the widely reported molecular beam epitaxy (MBE) and chemical vapor deposition (CVD) routes, which are relatively far less suited for large-scale integration. Two different series of CT films having thickness in 20–60 nm range were deposited on $\mathrm{Si}(100)$ substrates at two different optimized growth temperature of 350 °C and 400 °C, which yielded relatively less crystalline (LC) and highly crystalline (HC) CT films, respectively. Although the Curie temperature ($T_C$) of the LC- and HC-CT films is found to be significantly dependent on their crystalline state, i.e., 140 and 220 K, respectively, a robust perpendicular anisotropy is observed in both the series of CT films (at thickness as high as 20–60 nm), with a high coercivity of 15 and 8 kOe for HC-CT and LC-CT films at 2 K, respectively. Remarkably, the sign of the AHE signal undergoes a change on cooling below 100 K only for the HC-CT films, which is caused by the temperature-dependent change in the Berry curvature. Furthermore, below $T_C$, the longitudinal resistivity of the HC-CT films is predominantly contributed by the electron-magnon scattering contribution as evidenced by its $T^2$ dependence, in sharp contrast to the semiconducting behavior exhibited by the LC-CT films. The sputtered HC-CT films possess superior two-dimentional ferromagnetic characteristics, which are comparable to the films grown via chemical vapor deposition and molecular beam epitaxy techniques.

Atomic force microscopy (AFM) is a versatile nanoscale imaging technique. Since its force detection accuracy and spatiotemporal resolution are fundamentally limited by the minimum detectable force (MDF) arising from system noise, a deep understanding of MDF is essential for both instrumentation and applications. In particular, elucidating the imaging conditions that minimize the MDF is crucial for observing fragile supramolecular complexes. However, the theoretical MDF of amplitude-modulation (AM) AFM has received little attention, and its formulations remain inconsistent. Specifically, although we recently clarified the strong dependence of force sensitivity on the cantilever’s driving frequency, the optimal excitation frequency from the MDF perspective remains unknown. Here, we present an exact solution for the MDF of AM-AFM that accounts for excitation-frequency-dependent noise and force conversion. Our results show that MDF is strongly governed by the driving frequency and the cantilever Q-factor. In the repulsive regime, driving above the resonance peak frequency causes a sharp MDF increase, exceeding that of other dynamic modes by over an order of magnitude, whereas lower-side-slope excitation yields only ∼1.41–1.73 times larger MDF; similar behavior is observed in the attractive regime. These findings resolve a long-standing inconsistency in the MDF of AM-AFM and demonstrate that slope excitation, rather than resonance excitation, enables the detection of several-fold weaker forces, leading to more accurate force estimation and visualization of previously unobservable fragile molecules.

Quantum error-correcting codes (QECCs) require high encoding rates in addition to high thresholds unless a sufficiently large number of physical qubits are available. Many-hypercube (MHC) codes, defined as concatenations of the $[[6,4,2]]$ quantum error-detecting code, have been proposed as high-performance and high-encoding-rate QECCs. However, concatenated codes have the disadvantage that the syndrome weight grows exponentially with respect to the concatenation level. To address this issue, here we propose subsystem quantum codes based on MHC codes. In particular, we study the smallest subsystem MHC codes, namely, subsystem codes derived from concatenated $[[4,2,2]]$ error-detecting codes. The resulting codes have a constant syndrome-measurement weight of 4, while keeping high encoding rates. We build block-MAP and neural-network decoders and show that they demonstrate superior performance to the bounded-distance decoder.

Path identity offers a powerful way for generating and detecting quantum states, particularly in quantum imaging and metrology with undetected photons. However, previous manipulations of first-order coherence in path identity systems have been restricted to dynamic phases. Here we extend the phase control into the geometric phase, arising from cyclic evolution in a photon’s state space, and further introduce rotational Doppler shifts as its dynamic counterpart. For second-order coherence, photon indistinguishability between two undetected photons plays a critical role, traditionally adjusted via the relative time delay. Here, we demonstrate the adjustment of photon indistinguishability via orbital angular momentum (OAM) mode conversion in an undetected photon. As the OAM mode changes, we observe distinct peaks and dips in the second-order coherence curve. Our experimental results are in good agreement with theoretical predictions. These results expand the toolbox for quantum coherence manipulation in path identity systems and may enable broader applications, such as enhanced quantum sensing, imaging, and high-dimensional entanglement, with undetected photons.