The time evolution of initially localized wavepackets in the discrete Hatano-Nelson lattice displays a rich dynamical structure shaped by the interplay between dispersion and nonreciprocity. Our analysis reveals a characteristic evolution of the wave-packet center of mass, which undergoes an initial constant acceleration, subsequently decaying acceleration, and ultimately enters a regime of uniform motion, accompanied throughout by exponential amplification of the wave-packet amplitude. To capture this behavior, we develop a continuum approximation that incorporates higher-order dispersive and nonreciprocal effects and provides accurate analytical predictions across all relevant time scales. We then demonstrate the existence of a non-Hermiticity-induced jump—an abrupt spatial shift of the wave-packet center even in the absence of disorder—and derive its underlying analytical foundation. The analytical predictions are in excellent agreement with direct numerical simulations of the Hatano-Nelson chain. Our results elucidate the interplay between dispersion and nonreciprocity in generating unconventional transport phenomena and pave the way for controlling wave dynamics in nonreciprocal and non-Hermitian metamaterials.

Nitrogen-vacancy (NV) centers in diamond have precipitated profound advances in microwave detection, manifesting themselves both in spatial resolution and sensitivity. However, typical methods based on Rabi oscillations are subject to detunings due to thermal and magnetic fluctuations and/or gradients, which introduce systematic errors and render the measurements susceptible to environmental perturbations. Here, we propose and demonstrate a novel approach for determining both the magnitude and direction of microwaves, by exploiting the spectral line broadening effect in the optically detected magnetic resonance of NV centers. This method eliminates the requirement of aligning the MW frequency to the spin transitions and is therefore immune to variations and inhomogeneities of the magnetic field and temperature, providing an optimal tool for fast imaging applications. With this method, we achieved near-field microwave imaging of a microscale “$\mathrm{\Omega }$”-pattern antenna with a resolution of 800 nm. Using multiaxis NVs, a reconstruction of the vector microwave fields is obtained. Our results augment the applicability of diamond-based microwave near-field imaging in applications under complex scenarios, especially where large dynamic range, fast imaging, and highspatial resolution are demanded.

We demonstrate a triple-key optical encryption system that integrates orbital angular momentum (OAM) multiplexing with physical scattering and ultra-sparse sampling. At its core is an adaptive ResNeXt-SPD decoder that achieves 99.28% accuracy in decoding 24-bit OAM superposition states with only 64 pixels—a sampling point density of 0.13%. The system implements a cross-domain security architecture comprising three keys: a physical key (an unclonable scattering medium), a digital key (a sparse sampling pattern), and a computational key (trained network weights). We validate the sparse sampling performance in the full architecture, explore the sampling threshold under constrained networks, and investigate the criticality of each security key. Security analysis confirms that the absence or mismatch of any single key renders the system inoperative. Substituting the physical key drops accuracy to $\mathrm{approximately}50\%$. One pixel shift in the digital key reduces accuracy from 99.28% to $\mathrm{approximately}50\%$. Untrained model weights yield performance equivalent to random guessing. End-to-end image transmission under extreme sparsity maintains high reconstruction quality. This work advances OAM-based secure communication by achieving the lowest sampling-density and multilayer cryptographic protection simultaneously.

We demonstrate a robust, high-visibility nonlocal Franson interferometry for fiber-based quantum networks by copropagating a classical radio-over-fiber clock signal with energy-time entangled photon pairs in the same fiber. Utilizing cross-band allocation (O-band for classical, L-band for quantum signals), the spontaneous Raman scattering noise photons are effectively suppressed. At the same time, their environmental delay fluctuations remain highly correlated for common-mode noise cancellation, achieving a passive synchronization with picoseconds precision. Over 50 km of single-mode fiber, this copropagation enables nonlocal quantum interference with a visibility of $(88.35\pm 3.62)\%$, without relying on external dedicated timing infrastructure. This work provides a practical, scalable synchronization solution for metropolitan-scale entanglement-based quantum networks.

We propose and validate a framework for analog simulation of the Heisenberg spin model using a circuit-quantum-electrodynamics (circuit-QED) platform. To this end, we develop an $f$-deformed boson representation of the $SU(2)$ algebra, which includes the Holstein–Primakoff and Dyson–Maleev transformations as special cases. While this representation is generally non-Hermitian, for spin-$1/2$ systems, we introduce a procedure to circumvent this limitation, showing that the mapping yields the extended Bose-Hubbard (EBH) Hamiltonian. For the experimental realization of this EBH model, we design a scalable circuit-QED architecture based on an engineered Josephson junction array. Numerical simulations confirm that the microwave photon dynamics in this simulator accurately reproduces the original spin dynamics. Our work establishes an experimentally accessible method for investigating complex quantum spin dynamics in a highly controllable bosonic setting.

Nondestructive detection of single-electron motion is crucial for quantum information processing with electrons trapped in Paul traps. The standard approach in Penning traps is to detect the image current induced on the trap electrodes by the electron’s oscillatory motion. However, applying this approach in Paul traps for single electrons is currently hindered by motional frequency fluctuations arising from trap anharmonicities and instabilities in the rf trapping field. In this work, we propose a robust detection scheme exploiting the transient dynamics of parametric driving to overcome these limitations. Distinct from traditional steady-state approaches, our method focuses on the transient regime to break the temporal constraints imposed by steady-state assumptions, thereby enabling fast readout. We show that a controlled ramp of the parametric drive effectively locks the frequency of the electron motion in the transient regime, rendering the signal highly resilient to realistic experimental noise and inherent micromotion. This work paves the way for the experimental realization of nondestructive detection of single-electron motion in Paul traps.

Photons are ideal in many aspects for quantum technologies. However, the absence of direct photon-photon interaction and the problem of wave-packet distortion inherent in nonlinear media-based interactions have long posed a grand challenge in constructing two-qubit logic gates, which are indispensable for universal quantum information processing. Here we report on the theory and design to overcome the challenge, leading to a deterministic, passive, and near-unity-fidelity (exceeding 99%) controlled-$\pi$-phase gate for photonic qubits. The proposed gate comprises only a single two-level emitter and a few cavities and operates under the key concept of time-reversal-symmetric photon transport. It ensures a nonlinear $\pi$ phase shift and circumvents the long-standing difficulty of wave- packet distortion inherent in photonic phase gates using nonlinear media. We develop an analytical solution to reveal the dynamics of two-photon wave-packet transport and to obtain the optimal design. The proposed gate architecture is compatible with the platforms of integrated photonics.

Hopfions, associated with higher-dimensional topology through the Hopf fibration, exhibit exotic features like complex knots and improved stability compared to skyrmions, enhancing their appeal for innovative applications. In this paper, we study the nonlinear response of magnetic hopfion to microwave fields. We observe the emergence of higher-order harmonics of the driving microwave field as it interacts with the hopfion. By carefully selecting the driving frequency, the corresponding harmonic can efficiently excite the localized magnon state of a hopfion. Our results demonstrate the promising potential of hopfions in nonlinear magnonics.

Precise, real-time monitoring of magnetic field evolution is significant in applications including magnetic navigation and searches for physics beyond the standard model. One main field-monitoring technique, the spin-precession magnetometer (SPM), observes electron, nucleus, color center, or muon spins as they precess in response to their local magnetic field. Here, we study Bayesian signal-recovery methods for SPMs in the free-induction decay mode. In particular, we study tracking of field changes well within the coherence time of the spin system and thus well beyond the response bandwidth, as in [R. Jiménez-Martínez et al. Phys. Rev. Lett. 120, 040503 (2018)]. We derive the Bayesian Cramér-Rao bound that dictates the ultimate precision in estimating the Larmor frequency, which we show is attained by the computationally expensive prediction error method. Relative to this benchmark, we show that the extended Kalman filter (EKF) and cubature Kalman filter offer near-optimal tracking that is also computationally efficient, with the use of the latter giving better results only for a large spin number. Focusing thus on the EKF, we show that it is sufficient to accurately track fluctuating and unknown transient signals. Our methods can be easily adapted to other types of sensors undergoing nonlinear dissipative dynamics and experiencing intrinsic Gaussian-like stochastic noises.

A coupled-oscillator system displays enhanced sensitivity of its saturated steady-state (SS) oscillation frequency to small parameter perturbations near an exceptional-point degeneracy (EPD), a property that can be used to realize EPD-based sensors. Linear $\mathcal{P}\mathcal{T}$-symmetric systems, consisting of two coupled resonators, exhibit EPDs around which square-root sensitivity is observed. However, linear models are insufficient for realistic systems that rely on nonlinear, saturable-gain elements, particularly when $\mathcal{P}\mathcal{T}$-symmetry is broken. Thus, we study the SS of a general system of two coupled oscillators featuring EPDs and saturable nonlinear gain, using coupled-mode theory. We do this by synthesizing and extending prior SS analyses of the system’s stability and its square-root and cubic-root oscillation frequency sensitivity at a unique third-order SS-EPD. We add an SS analysis of saturated gain, energy, and oscillation-frequency sensitivity in the vicinity of the third-order SS-EPD, enabling characterization of the various SS regimes. We determine that the stable and bistable regions in parameter space directly depend on the saturated-gain values; that the dynamic range of high sensitivity around degenerate conditions is extended by increasing losses, consequently reducing the system’s stored energy; and that, to exploit the cubic-root-like sensitivity associated with the third-order SS-EPD, the suggested working regime is best confined to operation within the weakly coupled regime and not exactly at the third-order SS-EPD. Finally, we apply the model to two electronic circuits that exhibit cubic-root sensitivity, demonstrating the application and limitations of this analysis.

Scalable quantum computing in frequency-crowded nuclear spin registers promises long coherence times and native many-body logic. However, as system size increases, spectral crowding introduces two fundamentally competing challenges: coherent-control-induced spectral crosstalk and fragility to frequency fluctuations arising from charge and magnetic noise. Conventional pulse shaping optimized for crosstalk suppression is intrinsically incompatible with robustness against frequency fluctuations. In this work, we show that this incompatibility reflects a fundamental breakdown of single-qubit robust control principles in many-body entangling operations, manifested as a robustness inversion under single-tone ESR control: locally robust pulses disrupt intersubspace phase synchronization and degrade the robustness of many-body operations. We further uncover a Hilbert-space dilution effect, whereby $C$ Z gate robustness decays exponentially with system size, scaling as $1/2^M$. Leveraging these insights, we establish a phase-synchronized global multitone control paradigm that simultaneously suppresses frequency fluctuations and spectral crosstalk, in which square pulses—traditionally avoided due to spectral leakage—induce an intersubspace dynamical decoupling mechanism that converts unstructured crosstalk into effectively static, geometrically neutralized frequency noise. Full Hamiltonian simulations demonstrate programmable quantum logic units achieving the fidelities of many-body entangling operations approaching 99.99%, representing an order-of-magnitude improvement over conventional strategies, and establishing a scalable route toward fault-tolerant modular quantum computing.

Hong-Ou-Mandel (HOM) interference is a fundamental tool for assessing photon indistinguishability in quantum information processing. While the effect of chromatic dispersion on HOM interference has been widely studied, the interplay between dispersion and the finite detection window of realistic measurement devices remains underexplored. In this work, we demonstrate that the rectangular coincidence window inherent to modern time-tagging modules, which effectively acts as a temporal filter, breaks the standard dispersion cancellation condition and restores sensitivity to symmetric group-velocity dispersion. We derive an analytical model for type-II SPDC processes that predicts a modification of the HOM dip shape, specifically the emergence of characteristic oscillations and dip broadening. We experimentally validate this theoretical framework using a ppKTP source and transmission through optical fibers of lengths up to 29 km. The experimental data show excellent agreement with the model, confirming the presence of window-induced oscillations and allowing for the precise extraction of the fiber dispersion parameter. These findings underscore the significance of accounting for finite timing resolution in the design and characterization of dispersive quantum communication links.

Nitrogen-vacancy (NV) centers in diamond have been shown to be capable of detecting ac magnetic fields with high sensitivity, spectral resolution, and spatial resolution. However, most studies so far have focused on the regime of time-averaged or time-correlated measurements, while little attention has been paid to the single-shot regime. Here we show that the amplitude and phase of an ac field can be retrieved from a single pair of two consecutive measurements. We demonstrate this concept by measuring a 4 MHz ac field with a per-shot amplitude and phase sensitivity of $78\mathrm{nT}$ and $63\mathrm{mrad}$, respectively, at a temporal resolution of $320\mathrm{\mu }\mathrm{s}$. We also investigate the effects and quantify the errors resulting from probe frequency detunings, as well as operating in the strong field regime. Moreover, we showcase the ability of the measurement protocol to dynamically change the probe frequency in real time. This work advances the use of NV centers for real-time measurements of ac magnetic fields.

We study the propagation of charge carriers in planar graphene under the combined influence of a constant transversal magnetic field $B$ and an in-plane varying electric potential $\varphi (x)$. By suitably designing the potential landscape $\varphi (x)$, we may effectively steer charge carriers generated by photoexcitation, for example, in order to achieve an efficient charge separation. In comparison to previously considered scenarios for the magnetophotoelectric effect in graphene involving folded graphene or graphene edges, for example, this scheme offers advantages in terms of robustness, scalability, and control. Thus, our findings may pave the way for transport schemes (“graphene electronics”) or photoelectric/photovoltaic applications.

Exploring materials with unconventional spin transport properties and manipulating magnetic moments are core focuses in spintronics. Herein, we report the crystallographic orientation-dependent field-free switching of perpendicular magnetization in $\mathrm{STO}//{\mathrm{RuO}}_2(100)/[\mathrm{C}\mathrm{o}/\mathrm{Pt}{]}_2$ heterostructure, driven by spin splitting torque of ${\mathrm{RuO}}_2$. Unlike ${\mathrm{RuO}}_2(101)$-based systems, the $\mathrm{STO}//{\mathrm{RuO}}_2(100)/[\mathrm{C}\mathrm{o}/\mathrm{Pt}{]}_2$ eliminates confounding factors including crystal structural effects and perpendicular magnetic moment tilting, which allows us to attribute field-free switching exclusively to ${\mathrm{RuO}}_2$ antiferromagnetic order. When the Néel vector in $\mathrm{STO}//{\mathrm{RuO}}_2(100)$ deviates from the [001] easy axis and acquires an out-of-plane component, the anisotropic spin splitting effect generates out-of-plane spin polarization spin current, which provides damping-like torque to drive field-free switching at a critical current density of approximately $1.6\times {10}^7\text{A}/{\text{cm}}^2$. Complemented by temperature-dependent oscillating exchange bias that reverses sign at 90 K, our results unambiguously confirm the antiferromagnetic order of ${\mathrm{RuO}}_2$ in the heterostructure. This work offers evidence for spin splitting torque in ${\mathrm{RuO}}_2$-based heterostructures, deepens the understanding of altermagnetic spin transport, and paves the way for the development of field-free spintronic devices.

A major source of error in quantum error correction (QEC) arises from imperfect two-qubit gates, where leakage errors are notoriously difficult to correct within the QEC framework. The iswap gate’s inherently low-leakage nature makes it a compelling approach to address this challenge. However, its implementation in transmon qubits is hindered by parasitic $ZZ$ coupling induced by the required $XY$ interaction, posing a significant challenge for achieving high-fidelity control. In this work, we propose a Graph Surgery framework to theoretically analyze this problem and present a dual-microwave-drive scheme that dynamically cancels $ZZ$ interaction. To address residual transition errors, which we identified as the key bottleneck after $ZZ$ suppression, we further develop the Calibrated Derivative Error Nulling via Correlated Envelopes pulse-shaping protocol. Through this optimized approach, we demonstrate a 46-ns iswap gate with a fidelity of $(99.84\pm 0.06)\%$, suppressing intrinsic leakage to $(3.5\pm 2.6)\times {10}^{-5}$ and conditional phase error to $2.1\times {10}^{-6}$. The scheme features low dependency on specific hardware parameters and requires no auxiliary control architecture. Our results provide a flexible pathway to mitigate leakage challenges, establishing the iswap gate as a high-fidelity primitive for scalable QEC architectures.