Superconducting circuits are a leading platform for scalable quantum computing, where parametric modulation is a widely used technique for implementing high-fidelity multiqubit operations. A critical challenge, however, is that this modulation can induce a dense landscape of parasitic couplings, leading to detrimental frequency collisions that constrain processor performance. In this work, we develop a comprehensive numerical framework, grounded in Floquet theory, to systematically analyze and mitigate these collisions. Our approach integrates this numerical analysis with newly derived analytical models for both qubit-modulated and coupler-modulated schemes, allowing us to characterize the major parasitic sideband interactions captured by the model and their distinct error budgets. This analysis forms the basis of a constraint-based optimization methodology designed to identify parameter configurations that satisfy the derived physical constraints, thereby avoiding detrimental parasitic interactions. We illustrate the utility of this framework with applications to analog quantum simulation and gate design. Our work provides a predictive tool for co-engineering device parameters and control protocols, enabling the systematic suppression of crosstalk and paving the way for large-scale, high-performance quantum processors.

Mechanically isolated defect centers in hexagonal boron nitride are promising coherent quantum emitters, yet spectral instabilities persist, and their spin-related nature remains unclear. Here we investigate a single mechanically isolated quantum emitter in $h\mathrm{BN}$ integrated onto a coplanar waveguide. The emitter exhibits exceptionally bright photoluminescence excitation signals with saturation count rates exceeding $10\mathrm{Mc}/\mathrm{s}$. High-resolution spectroscopy reveals two closely spaced zero-phonon-line transitions originating from the same defect complex. Time-resolved spectroscopy shows that these transitions exhibit markedly different spectral diffusion dynamics, consistent with distinct donor-acceptor-pair-like recombination pathways with different sensitivities to local electrostatic fluctuations. Off-resonant blue illumination redistributes emission between the two transitions and increases the emission duty cycle without significantly modifying the dominant spectral diffusion rates at low temperature, indicating repumping from long-lived shelving states. Magnetic-field-dependent photoluminescence, optically detected magnetic resonance, and pump-probe measurements reveal millisecond-scale relaxation dynamics and magnetic-field-dependent fluorescence contrast, demonstrating spin-dependent population dynamics in the metastable shelving state. These results clarify how charge-driven spectral fluctuations and spin-dependent shelving jointly shape the optical cycling dynamics.

Maintaining phase consistency under noisy conditions is a key issue in high-fidelity signal transmission. Traditional single-threshold phase detection methods rely on history-independent polarity discrimination, rendering them prone to waveform distortion. Non-Hermitian systems, although promising for sensitivity enhancement, remain susceptible to noise-induced eigenvalue fluctuations. Here, we theoretically propose and experimentally demonstrate a nonlinear non-Hermitian memory system (NNHMS) for noise-resilient phase detection based on a non-Foster circuit. The NNHMS embeds prior state information of signals into Hamiltonian switching, producing a memory region that confines signals to discrete states against external disturbances and thus ensuring reliable phase fidelity. By mapping the nonlinear memory effect to electronic dynamics, we experimentally observe a tunable Hamiltonian transition originating from loss engineering, enabling the NNHMS to adapt to different noise intensities. As a representative example, we apply the system to acoustic vortex phase detection, achieving a significant increase in signal similarity (approximately $76\%$) relative to traditional methods. Good agreement between experimental and numerical results verifies the effectiveness of our proposed NNHMS. The demonstrated nonlinear non-Hermitian memory effect opens a new route for noise-immune phase preservation in fields ranging from biomedical monitoring to industrial diagnostics.

Controlling correlated electron dynamics is a central challenge in ultrafast science, with implications for the development of coherent light sources and quantum information technologies. Traditional methods for manipulating strong-field ionization processes often rely on complex laser fields, limiting their practical utility. Here, we demonstrate that a common laser parameter—chirp—can serve as a robust and efficient optical switch to selectively control the pathway of nonsequential double ionization (NSDI) in argon atoms. Using a three-dimensional classical ensemble model, we show that chirped pulses can continuously tune the dominant mechanism between direct electron-impact ionization and recollision-excitation with subsequent ionization. Notably, at a laser intensity of $I_0=0.07\text{PW}/{\mathrm{cm}}^2$, tuning the chirp parameter to $|\xi |=3$ reduces the electron-impact contribution to less than 2.5%, demonstrating near-complete switching to the recollision-excitation-dominated NSDI regime. This chirp-induced pathway switching demonstrates the potential for application-specific control over strong-field processes, which may be relevant to the generation of high-Rydberg states and the optimization of attosecond extreme-ultraviolet pulses.

Magnetic flux (vortex) trapping remains a major obstacle to very large scale integration in superconducting electronics. Moats—etched regions in circuit layers placed in ground planes and around critical circuitry—offer a simple passive approach to sequester flux. Here, we systematically examine the effectiveness of moat arrays in superconducting niobium films as a function of geometry (size, shape, and density) and background magnetic field. By measuring the vortex expulsion field, we estimate the flux saturation number and flux trapping temperature for a range of geometries. We find that many moat designs effectively sequester flux in magnetically shielded environments ($<1\mathrm{\mu }\mathrm{T}$), with high-aspect-ratio rectangular “slit” moats providing the strongest mitigation at minimal area cost. However, our measurements show that moats alone do not eliminate flux trapping in nonideal films, as vortices can preferentially pin at material defects. These results provide design guidance for flux mitigation in superconducting integrated circuits and highlight the need for combined optimization of circuit geometries and materials.

Photoacoustic imaging (PAI) enables high optical contrast at ultrasonic imaging depths; however, real-time volumetric imaging remains challenging due to the complexity of two-dimensional arrays or the slow mechanical scanning of one-dimensional arrays. In this study, we propose a strategy for scan-free four-dimensional imaging that combines photoacoustic signals with ultrasonic timecoding (PAUTC). For targets possessing both optical absorption and acoustic impedance contrast, we utilize a 1D array to acquire volumetric images in a single data acquisition. By synchronizing pulsed optical excitation with orthogonal ultrasound emissions, elevational spatial information is encoded into temporal delays of scattered ultrasound and subsequently combined with the photoacoustic signals. This encoding strategy enables single-shot 3D reconstruction, without the need for 1D array scanning or complex 2D array detection. We theoretically demonstrate that the spatial resolution of the PAUTC method is mainly determined by the effective bandwidth of the 1D array and provide an analytic expression for the resolution. The performance of the PAUTC method is validated through simulations and experiments. PAUTC restores elevational clarity and achieves volumetric imaging of complex 3D structures with optical and acoustic impedance contrast properties, whereas conventional photoacoustic tomography fails due to the lack of elevational resolution missing in a 1D array. Phantom experiments validate the effectiveness of PAUTC in reconstructing complex 3D structures. Furthermore, real-time 4D imaging is demonstrated by quantitatively tracking a moving microbead at a frame rate of 10 Hz. With the efficient continuous volumetric imaging capability, PAUTC might hold promise for applications in hemodynamic monitoring, fluid dynamics characterization, tracking exogenous dual-contrast agents, guiding interventional metallic needles, and superresolution imaging.

Carbon nanotube (CNT) transistors have been experimentally demonstrated to reach performance comparable to and even surpassing that of silicon transistors. Further improvement requires addressing nonidealities arising from device fabrication that impact performance and reproducibility. One performance metric that determines energy efficiency is the subthreshold swing (SS), which is often observed to be 3–4 times larger than the ideal thermal limit. In this work, we present simulations indicating that a discrete number of variable-occupancy hole trapping sites can explain the large subthreshold swing. Our simulations indicate that while three-dimensional trap distributions influence the subthreshold swing, only the traps in close proximity to the nanotubes have a significant impact. The results suggest that a density of trapping sites on the order of $0.5\text{e}/{\mathrm{nm}}^2$ near the nanotubes is sufficient to significantly increase the subthreshold swing, requiring the removal or passivation of only a few sites per carbon nanotube.

Fusion measurements are a key primitive for linear-optical quantum computing and quantum networks. Type-I and type-II fusion gates are widely used to combine small entangled resource states into larger photonic states, but without ancillary resources their success probability is limited to $1/2$. Existing $3/4$-efficient type-I schemes rely on entangled Bell-pair ancillary states, whose preparation is itself probabilistic and resource-intensive. Here, we propose a boosted type-I fusion gate using only four ancillary single photons and standard linear-optical primitives. For multiqubit GHZ and graph states, the gate succeeds directly with probability $5/8$, while a distillation protocol converts partially entangled outcomes into additional successful events, raising the total success probability to $11/16$ after one stage and asymptotically to $3/4$. We quantify the practical advantage of this scheme by estimating the photonic resources required for generating representative large entangled photonic states and show that the proposed gate significantly reduces the required overhead compared with existing schemes. These results expand the set of resource-efficient linear-optical primitives and enable a substantial reduction in the resource requirements for scalable photonic quantum computing and quantum communication.

Understanding defects in atomically thin van der Waals (vdW) semiconductors is essential for advancing their use in next-generation optoelectronic and photovoltaic devices. Here, we apply a combination of various impedance spectroscopy techniques to two-dimensional (2D) vdW GaSe doped with silicon (Si) to reconstruct deep trap states across the full bandgap. Deep-level transient spectroscopy reveals three distinct deep states, 0.33, 0.68, and 0.24 eV, below the conduction band edge. Complementary deep-level optical spectroscopy and photocapacitance measurements identify two deep states at 1.4 and 1.8 eV below the conduction band edge and one at 2.0 eV above the valence band edge, with thermal admittance spectroscopy providing additional verification and further resolving two trap states at 0.16 eV above the valence band edge and at 0.26 eV below the conduction band edge. By comparing the experimentally extracted ionization energies with the predictions of density functional theory, our results attribute these trap states primarily to Si-related defects and metal vacancies. This work presents a comprehensive defect map of Si-doped GaSe, providing critical insights into carrier trapping mechanisms that are essential for optimizing the design of 2D material-based devices for industrial applications.

Ultraviolet light emitters based on the semiconductor alloy aluminum gallium nitride, (Al,Ga)N, have attracted significant interest in recent years due to their potential for optoelectronic devices. To guide the design of such devices with improved efficiencies, theoretical frameworks based on so-called $\mathbf{k}·\mathbf{p}$ methods have found widespread application in the literature. Given that $\mathbf{k}·\mathbf{p}$ models are empirical in nature, parameters such as effective masses or crystal-field splitting energies of (Al,Ga)N alloys have to be provided as input from first-principles calculations or experiment. Although these parameters are available for GaN and AlN, detailed information on their composition dependence is sparse. Here, we address this question and provide (Al,Ga)N band parameters for widely used multiband $\mathbf{k}·\mathbf{p}$ Hamiltonians. We start from density functional theory (DFT) to sample the electronic structure of (Al,Ga)N alloys over the full composition range. The $\mathbf{k}·\mathbf{p}$ band parameters are treated as free parameters to reproduce the DFT data. For GaN and AlN, the parameters extracted here agree well with literature values. When turning to the composition dependence of the $\mathbf{k}·\mathbf{p}$ parameters, our calculations show that most parameters deviate significantly from a linear interpolation of the GaN and AlN values, an approximation widely made in the literature. Moreover, to describe changes in the band parameters with Al content, composition-dependent bowing parameters have to be considered for an accurate description of the DFT data. Finally, our analysis also provides initial insight into consequences of the nonlinear composition dependence of the $\mathbf{k}·\mathbf{p}$ parameters for the electronic structure of (Al,Ga)N alloys. We find that, in particular, the band ordering is affected by the nonlinear evolution of the crystal-field splitting energy with composition, which is an important aspect for the light polarization characteristics of high Al content (Al,Ga)N alloys.

PulsePol is an elegantly designed pulse-sequence-based quantum control scheme that enables polarization transfer between electron and nuclear spins. However, previous analyses of PulsePol assumed very strong, close to ideal, instantaneous microwave pulses, which is rarely achievable as one goes to higher magnetic fields. We revisit the PulsePol scheme under finite-pulse constraints and show that its performance significantly degrades because of finite-pulse effects. Using bimodal Floquet theory, we identify the symmetry-breaking mechanism responsible for this deteriorating fidelity. By phase adjustment, we reestablish the proper symmetry of the interaction-frame spin Hamiltonian—leading to a sequence called Q-PulsePol, where ‘Q’ reflects the restored quadrature symmetry. Our results demonstrate robustness to finite-pulse effects and improved polarization transfer efficiency, establishing Q-PulsePol as a practical and reliable scheme for bulk hyperpolarization of nuclear spins in solid-state using a single-mode (zero-quantum or double-quantum) transfer. This work bridges idealized quantum control with realistic pulse engineering, establishing design rules for spin-based quantum-control protocols.

2D/3D heterostructures provide a powerful platform for uncovering how reduced dimensionality governs radiation response. While two-dimensional (2D) materials such as graphene, transition metal dichalcogenides, and MXenes have demonstrated notable structural resilience to radiation, fundamental differences in their radiation response compared with bulk three-dimensional (3D) crystals remain largely unverified. Here, we fabricate patterned $a$-${\mathrm{Al}}_2{\mathrm{O}}_3$/graphene/H-intercalated SiC(0001) heterostructures and expose them to fast neutrons (1–2 MeV) across fluences from $1.9\times {10}^{17}$ to $6.5\times {10}^{18}\mathrm{n}/{\mathrm{cm}}^2$. The results reveal a striking disparity: despite the 3D environment, graphene accumulates damage 69–273 times more slowly than SiC, with its resilience further enhanced at high fluences due to early saturation, soft limited to only 0.0064% at $1.3\times {10}^{19}\mathrm{n}/{\mathrm{cm}}^2$. This behavior is attributed to a two-channel defect accumulation model in 2D materials, involving interfacial evolution that dominates the early-stage response when the interface is chemically active, and direct lattice damage from atomic displacements, which persists but remains comparatively weak. These findings establish 2D lattices as fundamentally more radiation-resistant than 3D crystals and demonstrate that their advantages persist in realistic device architectures. Harnessing this resilience offers orders-of-magnitude improvements in structural stability for technologies operating under extreme irradiation, including fusion and fission reactors, particle accelerators, and aerospace systems.

Color-center spins in 4H-SiC offer a rare combination of wafer-scale materials maturity with long spin coherence and chip-level photonics, making them promising building blocks for scalable quantum technologies. In particular, the silicon vacancy hosts an $\mathrm{S}=3/2$ ground state, a native qudit that enables compact encodings and subspace-selective control but also introduces spectator transitions: short, detuned pulses can coherently drive nonaddressed level pairs and create crosstalk. Here we use broadband Ramsey interferometry to reveal and quantify such spectator-transition crosstalk. Experimentally, the Ramsey Fourier spectra display multiple lines beyond the addressed single-quantum transition. Analytically, we map each line to a pairwise energy difference between qudit levels of the rotating-frame Hamiltonian and assign its weight via compact amplitudes set by the prepared state and the microwave pulse parameters, predicting a deterministic six-branch structure. Numerical time-domain propagation with the experimental sampling reproduces the detuning map, and the measured peak positions coincide with the analytic branch lines without frequency fitting. Together these results provide a practical, spectator-aware framework for multilevel control in the silicon-vacancy qudit. The approach offers clear guidance to suppress crosstalk or, conversely, to exploit spectator lines, e.g., as additional constraints for in situ pulse calibration and for phase-sensitive quantum state and process estimation.

The concept of a microwave planar antenna for the excitation of dielectric paramagnetic media is proposed. The shape and size of the electrodes are designed for the generation of a uniform magnetic field parallel to the surfaces of a single- or multilayer dielectric, with a specific resonance frequency and bandwidth. One or both electrodes can be semireflective to allow the optical accessibility of the paramagnetic media and, possibly, to enhance the collection efficiency by beaming the optical emission of quantum emitters. This device is particularly useful in optically detected magnetic resonance due to the large bandwidth of the microwave excitation and favorable conditions for optical excitation and detection. Applications are devised especially in vector magnetometry and microwave spectral analysis because of the paramagnetic quantum properties of emitters such as the nitrogen-vacancy center in diamond.

A concept for microwave (MW) amplification and maser generation in compact planar waveguides embedding a thin layer of paramagnetic color centers is presented. The ground state of the color centers can be optically or electrically spin-polarized, while population inversion is attained by Zeeman shifting of one spin sublevel below the populated state. A signal traveling along the waveguide, if resonant with the spin transition, can be amplified, or a self-sustained MW oscillation can be generated. A general analysis of the conditions for amplification and self-oscillation is developed for nitrogen-vacancy-rich diamond films, together with practical examples of impedance matching and resonator design. The proposed architecture combines near-unity filling factors with relatively low electromagnetic quality factors, enabling operation in strongly coupled configurations and broad frequency tunability through the external magnetic field. The same formalism naturally extends to compact lumped-element resonators operating at a few gigahertz while preserving millimeter-scale dimensions. Compared with the present state of the art of diamond masers, the approach offers reduced size, simplified integration with external electronics, and relaxed requirements on cavity quality factor.

A coupled spintronic-oscillator array has been considered attractive for neuromorphic computing applications. Experimental reports have shown the nanoconstriction geometry to be a relatively easier-to-fabricate platform for implementing such spin oscillators, but most prior reports on training and inference algorithms for neuromorphic computing using spin oscillators have been mostly restricted to the nanopillar geometry. Also, those prior reports involve updating the natural frequency values of the oscillators and moving the synchronization regions onto the data clusters during the offline learning phase, which has associated challenges. In this context, we design and simulate a novel artificial neural network (ANN)—oscillator neural network (ONN)—algorithm wherein, in the offline learning phase, the weight parameters of the ANN are updated such that the data clusters are instead moved to the synchronization regions of spin Hall nanooscillators (SHNOs) in the nanoconstriction geometry, as obtained through micromagnetic simulations. We further simulate the on-chip inference part of the ANN-ONN algorithm, where the ANN is implemented on a crossbar array of domain-wall synapse devices, as simulated here through micromagnetics, and the ONN is implemented on nanoconstriction SHNOs. We show successful data classification for both binary and multiclass classification tasks to demonstrate the generalizability of our proposed scheme.

We propose a broadband Purcell-protection scheme based on a single shared filter integrated directly into the feedline, enabling simultaneous protection of multiple qubits in a compact architecture with minimal hardware overhead. The filter consists of two open-ended stubs connected by an in-line transmission line, forming a $\mathrm{\Pi }$ geometry, and operates via engineered passive microwave interference that suppresses the real part of the environmental admittance over a wide frequency window. Circuit simulations and finite-element modeling show that transmission is suppressed by several orders of magnitude within the target band (the qubits’ frequencies) while preserving the readout mode of the multiplexed architecture. For realistic device parameters, the proposed design yields Purcell-limited relaxation times exceeding 1 ms over a frequency span of approximately 1.5 GHz. Our results establish the $\mathrm{\Pi }$ filter as a compact and scalable solution for broadband impedance engineering in superconducting quantum circuits, compatible with standard dispersive readout protocols.