Scalable quantum networks rely on optical links between long-lived qubits to distribute entanglement. Tin-vacancy (${\text{SnV}}^{-}$) centers in diamond combine long spin coherence at liquid-helium temperatures with highly coherent, spin-dependent optical transitions, making them promising network qubits. Connecting independent centers, however, requires indistinguishable photons: solid-state inhomogeneity creates frequency mismatch, while inversion symmetry suppresses the first-order electrical response. Here, we establish optical connectivity between two remote ${\text{SnV}}^{-}$ centers in separate cryogenic nodes. Using local electrodes, we tune the optical transition by up to 4 GHz via the Stark effect while maintaining optical coherence. Bringing the two transitions into resonance yields remote Hong-Ou-Mandel interference with a measured zero-delay visibility of $80(6)\%$ without postprocessing. The same electrodes provide dynamic spectral control, producing resolved Floquet sidebands at drive frequencies up to $1.5\mathrm{GHz}$. These results establish a locally reconfigurable optical interface for connecting remote ${\text{SnV}}^{-}$ quantum-network nodes.

High $1/f$ noise in Cryogenic CMOS (CryoCMOS) devices is a critical parameter to keep under control in the design of complex circuits for low-temperature applications. Current models predict the $1/f$ noise to scale linearly with temperature, and gate oxide defects are expected to freeze out at cryogenic temperatures. Nevertheless, it has been repeatedly observed that $1/f$ noise deviates from the predicted behavior and that gate oxide defects are still active around 4.2 K, producing random telegraph noise. In this paper, we probe single-gate oxide defects in 2500 nMOS devices down to 5 K in order to investigate the origin of $1/f$ noise in CryoCMOS devices. From our results, it is clear that the number of defects active at cryogenic temperatures resulting in random telegraph noise is larger than at 300 K. Threshold voltage shifts due to charged defects are shown to be exponentially distributed, with different modalities across temperatures and biases: from monomodal at 300 K to trimodal below 100 K. Distributions’ shapes are interpreted in the framework of percolation theory. By fitting these distributions, it is shown that more than 80% of the detected defects belong to the bulk oxide. Afterward, starting from the raw data in the time domain, we reconstruct the low-frequency noise spectra, highlighting the contributions of defects belonging to different branches and, therefore, to different oxide layers. This analysis shows that, although interface traps and large defects associated with the third mode are the main sources of $1/f$ noise at 5 K, bulk oxide defects still contribute significantly to low-frequency noise at cryogenic temperatures. Finally, we show that defect time constants and step heights are uncorrelated, proving that the elastic tunneling model for charge trapping is not accurate.

We investigate the coherence properties of parity-protected $\cos (2\phi )$ qubits based on interference between two Josephson elements in a superconducting loop. We show that qubit implementations of a $\cos (2\phi )$ potential using a single loop, such as those employing semiconducting junctions, rhombus circuits, Flowermon, and KITE structures, can be described by the same Hamiltonian as two multiharmonic Josephson junctions in a SQUID geometry. We find that despite the parity protection arising from the suppression of single Cooper-pair tunneling, there exists a fundamental trade-off between charge and flux-noise dephasing channels. Using numerical simulations, we examine how relaxation and dephasing rates depend on external flux and circuit parameters, and we identify the best compromise for maximum coherence. With currently existing circuit parameters, the qubit lifetime $T_1$ can exceed milliseconds, while the dephasing time $T_{\phi }$ remains limited to only a few microseconds due to either flux or charge noise. Our findings establish practical limits on the coherence of this class of qubits and raise questions about the long-term potential of this approach.

Under strong drives, which are becoming necessary for fast high-fidelity operations, transmons can undergo drive-induced state transitions. These transitions can involve dressed states of the driven transmon, which are chaotic. Whenever the computational manifold containing the transmon ground and excited states couples to such states, enhanced offset-charge sensitivity and destructive effects in readout can appear. We show here that these detrimental effects can further propagate to other degrees of freedom, for example to neighboring qubits in a multiqubit system. Specifically, we show that a coherently driven transmon can act as a source of incoherent noise to another circuit element coupled to it. By using a full quantum model and a semiclassical analysis, we perform the noise spectroscopy of the driven transmon by considering its coupling to a two-level system (TLS), and we show that, in a certain limit, the interaction with the driven transmon can be modeled as a stochastic diffusive process driving the TLS.

Broadband achromatic acoustic focusing remains challenging because most metalenses provide only single frequency phase compensation and lack the approximately constant group delay that is required to suppress focal drift. Here, we show that achromatic focusing can be achieved when the unwrapped transmitted phase of each unit cell in the metalens varies linearly with frequency. Based on this criterion, we design a compact acoustic metalens with deep subwavelength side-branch cavity units. An analytical model is developed to describe the broadband transmission characteristics of the proposed units and to enable predictable linear phase control. Within the investigated parameter space, all unit cells exhibit inherently linear phase responses with tunable phase slopes and frequency-dependent transmission amplitudes. Leveraging these blocks, we realize achromatic focusing by mapping the required phase profile at each frequency onto the corresponding unit cells. Finite element simulations demonstrate a nearly stationary focal length over the frequency range from 3 to 8 kHz. Experimental measurements reproduce the main broadband focusing tendency, although larger deviations are observed at low frequency. These results support the proposed design criterion for broadband achromatic acoustic focusing. The adaptability of the analytical framework is further demonstrated through the design of a second metalens with a different focal length.

Mirror symmetry of transmission is generally considered an inherent property of reciprocal systems. Metagratings, governed by the acoustic diffraction laws in a periodic lattice, have brought vitality to classical wave physics and its manipulation. However, even using the diffraction ability of waves, it remains a challenge to break the mirror symmetry of wave transmission through a single passive metagrating, while simultaneously controlling the wavefront in acoustics. Here, we propose a widely applicable description of acoustic wave diffraction in metagratings by incorporating the coupling between transmitted and reflected waves. Through deliberate design of the transmission and reflection phase gradients, we construct a monolayer passive phase-gradient metagrating that offers advantages of structural integrity and ease of fabrication. This design enables the breaking of mirror symmetry in both acoustic plane wave transmission and reflection within a reciprocal system. We further demonstrate its applicability across a broad range of incident angles, facilitating versatile wavefront manipulation. Our work provides a pathway to advance acoustic communication and isolation, and the underlying principle can be extended to other classical wave systems.

We investigate the post-threshold emission characteristics of supersymmetric (SUSY) semiconductor laser arrays beyond the linear regime. In contrast to previous studies based primarily on linear analyses or simplified nonlinear descriptions, we employ a realistic class-B semiconductor laser model incorporating the full field-carrier rate equations. Using two representative SUSY laser configurations, we examine the stability of steady-state operation and the emergence of in-phase synchronization in the nonlinear regime. Our results show that the inclusion of a SUSY partner can significantly reshape the steady-state stability landscape and, in certain parameter regimes, promote single-mode operation in the fundamental in-phase supermode. However, we demonstrate that linear suppression of higher-order supermodes does not generically ensure robust single-mode emission once gain saturation, modal competition, and amplitude-phase coupling are taken into account. These findings establish that the operational performance of SUSY laser arrays cannot be inferred from linear spectral arguments alone. Instead, the interplay among coupling strength, dissipation, pump level, and carrier dynamics fundamentally restructures the nonlinear stability diagram. Our work underscores the necessity of comprehensive nonlinear modeling for the design and optimization of SUSY-based laser arrays aimed at achieving stable coherent emission. Beyond laser physics, our results may offer broader guidance for tailoring and engineering synchronization characteristics in other platforms, including mechanical and electronic systems.

Spin logic devices provide a promising route toward ultralow-power and nonvolatile information processing. In this work, we demonstrate field-free spin-orbit torque-induced asymmetric magnetization switching in in-plane anisotropy (IMA) and perpendicular magnetic anisotropy heterostructures, characterized by different critical switching currents under opposite current polarities. Combined experiments and macrospin simulations reveal that the asymmetric switching originates from an in-plane effective field $H_y$, which breaks the ${\mathcal{M}}_{yz}$ mirror symmetry of the system. By controlling the magnetization direction of the IMA layer, both the switching polarity and bias direction can be tuned. Building on four distinct types of asymmetric switching behaviors, we realize a reconfigurable spin logic operation within a single Hall-bar device. These results clarify the physical origin of asymmetric magnetization switching and demonstrate an approach for realizing reconfigurable spin logic devices.

Planar superconducting resonators are essential components in quantum circuits and highly sensitive sensors. However, their performance is often compromised by magnetic flux penetration, as the interaction of flux quanta and the induced radio-frequency (rf) currents in the superconducting thin film leads to significant energy dissipation. At low operating temperatures, this issue is aggravated as thermomagnetic instabilities can trigger the sudden propagation of magnetic flux avalanches. An important open question is whether the rf excitation itself stimulates the nucleation and propagation of magnetic flux avalanches in the superconducting thin film. The literature remains inconclusive on this point, partly due to the lack of compelling evidence for this phenomenon. In this work, we address this issue by unprecedented direct visualization of magnetic flux penetration through Faraday rotation imaging under simultaneous rf excitation. We demonstrate that the avalanche activity exhibits a weak dependence on the rf intensity for rf excitations within the linear Campbell regime. However, magnetic flux bursts clearly influence the rf transmission properties of the device. Furthermore, it is possible to unambiguously associate a particular avalanche event with a jump in resonance frequency. This enables us to identify the loci of most deleterious events and understand the distinct origins of upward and downward frequency shifts. These observations are supported by electromagnetic simulations in which local changes of the kinetic inductance mimic flux avalanches and confirm the invasive character of the magneto-optical imaging (MOI) technique. The insights gained from this study aim to contribute to the broader understanding of the magnetic resilience of superconducting resonators, with the goal of improving their efficiency and stability.

Discrete-modulation continuous-variable quantum key distribution (DM-CVQKD) has attracted considerable interest due to its compatibility with coherent optical communication systems and low hardware complexity. In DM-CVQKD protocols, postselection is widely employed as an effective technique to enhance protocol performance. However, conventional postselection schemes rely on fixed-shape regions in phase space, which fail to adapt to variations in the bit error rate (BER) distribution. In this work, we introduce a BER contour postselection (BER-PS) method, in which postselection regions are constructed according to the BER distribution, such that samples are selected based on their associated error probability. Under the trusted detector noise model, we perform a numerical security analysis of the BER-PS method in the asymptotic regime. Simulation results demonstrate that the BER-PS method consistently outperforms conventional fixed-shape postselection schemes in terms of achievable secret key rates. We perform experimental verification to confirm the feasibility of the BER-PS method. The results demonstrate that our scheme yields effective performance gains in both theoretical analysis and experimental measurements.

Precision sensing and imaging of weak static magnetic fields are crucial for a variety of emerging nanoscale applications. While nitrogen-vacancy (NV) centers in diamond provide exceptional ac magnetic field sensitivity with nanoscale spatial resolution, their sensitivity to static (dc) magnetic fields is fundamentally limited by the short dephasing time ($T_2^{*}$) due to spin-spin interactions. In this work, we present a hybrid sensing approach that integrates a soft ferromagnetic microwire with a single near-surface NV center to amplify its response to external static magnetic fields. This hybrid configuration achieves a dc magnetic field sensitivity of $63\mathrm{nT}/\sqrt{\mathrm{Hz}}$ for a single NV center—about 500 times greater than conventional inhomogeneous broadening- or $T_2^{*}$-limited magnetometry, with potential for further enhancement. The compact and highly sensitive nature of this sensor opens new opportunities for quantum sensing applications involving the detection of static or slowly varying magnetic fields across diverse scientific and technological domains.

Nondegenerate two-photon absorption (ND-TPA) detection has emerged as a highly promising approach for room-temperature mid-infrared (MIR) imaging by exploiting the nonlinear interaction between infrared photons and pump radiation in wideband gap semiconductors. However, scaling ND-TPA imagers toward wide-field operation remains challenging because the nonlinear interaction strength rapidly decreases with enlarged sensing area, thereby degrading detection sensitivity. Here, we demonstrate a wide-field MIR single-pixel ND-TPA imaging system, in which two-photon optical encoding is implemented in a direct-band gap GaAs photomultiplier tube with large photosensitive area and high internal gain. By combining spatial multiplexing with single-element integrated detection, the proposed scheme effectively enhances the collection and accumulation of weak nonlinear signals under a pump irradiance significantly lower than previous requirements. Moreover, the system achieves a spatial resolution of $44\mathrm{\mu }\mathrm{m}$ over a 4-mm field of view, corresponding to a record-high space-bandwidth product of $6.5\times {10}^3$ among existing TPA-based MIR imagers. This work establishes a scalable pathway toward wide-field and high-sensitivity MIR computational imaging, with promising applications in industrial inspection, remote sensing, and weak-target detection.

Active control of chiroptical responses in metasurfaces is critical for advancing photonic spin-selective technologies. Here, we propose and experimentally demonstrate a multifunctional chiral metasurface based on the phase-change material of vanadium dioxide (${\mathrm{VO}}_2$) that offers triple-state switching in circular dichroism. Dual channels of external electric voltages were adopted to independently drive the phase transition of two respective ${\mathrm{VO}}_2$ islands in a planar metasurface unit, where the selective control on the left-handed chiral, right-handed chiral, and achiral responses was experimentally achieved. Our method enables discrete switching between positive, zero, and negative chirality, as well as continuous circular dichroism strength tuning, surpassing the conventional single chiral state modulation. Such a dual-channel control method offers an easy pathway toward dynamic spin photonics and adaptive chiral optical components.

Unlike the conventional non-Hermitian skin effect (NHSE) that localizes bulk wave functions to the boundary, the hybrid skin-topological effect (HSE) arises from the interplay between topological edge states and the non-Hermitian skin effect, resulting in the further localization of edge state wave functions at the corners of the sample. While the HSE has been observed in passive platforms, these experimental investigations have generally been constrained by inherent material dissipation, often restricting observations to comparison or indirect reconstructions. In such systems, rapid energy dissipation made it difficult to determine whether localization originated from non-Hermitian physical mechanisms or simple energy loss, posing a significant challenge for the direct observation of the non-Hermitian skin states. Here, we introduce the complex-frequency excitation technique into a two-dimensional acoustic coupled-ring network to overcome the loss limits, successfully enabling the direct observation of the spin-dependent transient HSE. Our experiments clearly visualize the dynamic evolution of edge states with distinct pseudospins as they accumulate at opposite corners over time. This work not only establishes a pathway for detecting non-Hermitian eigenstates in lossy systems but also provides a versatile platform for the development of pseudospin-controlled topological acoustic devices.

Variational quantum algorithms offer a promising route to combinatorial optimization, but their applicability is limited by the challenge of encoding large-scale problems within restricted qubit resources. In this work, we introduce a qubit-efficient variational framework based on Pauli correlation encoding (PCE) and apply it to electric power demand portfolio optimization. Binary variables are represented through expectation values of Pauli correlation operators, which encode multibody correlations of the quantum state and provide a continuous relaxation enabling compact representations with few qubits. We further propose a two-stage hybrid formulation, in which a time-averaged problem provides initialization for a time-resolved optimization. Numerical simulations demonstrate near-optimal performance across problem sizes ranging from $m=18$ to $\mathrm{10,296}$, with normalized cost gaps on the order of ${10}^{-4}$ relative to solutions with certified optimality. We show that the performance is governed by the interplay between continuous relaxation and discretization: the effective resolution of the correlator representation determines how reliably improvements in the continuous loss translate into better discrete solutions, with larger systems exhibiting more consistent behavior. Finally, we demonstrate robustness on a trapped-ion quantum processor, where high-quality solutions are obtained despite noise and finite sampling. These results establish PCE as a physically motivated and qubit-efficient framework for large-scale combinatorial optimization.