dc voltage–biased Josephson junctions have recently been used in superconducting circuits for Hamiltonian engineering, demonstrating microwave amplification, single-photon sources, and entangled photon generation. Compared with more conventional approaches based on parametric pumps, this solution typically enables larger interaction strengths. In the context of quantum information, a two-to-one photon interaction can stabilize cat qubits, where bit-flip errors are exponentially suppressed, promising significant resource savings for quantum error correction. This work investigates how the dc bias approach to Hamiltonian engineering can benefit cat qubits. We find a simple circuit design that is predicted to showcase a two-to-one photon exchange rate larger than that of the parametric pump–based implementation while dynamically averaging typically resonant parasitic terms such as Kerr terms and cross-Kerr-terms. In addition to addressing qubit stabilization, we propose using injection locking with a cat qubit–adapted frequency filter to prevent long-term drifts of the cat qubit angle associated with dc voltage noise. The whole scheme is simulated without rotating-wave approximations, highlighting the amplitude of related oscillatory effects in cat-qubit-stabilization schemes. This study lays the groundwork for the experimental realization of such a circuit.

The realization of multiqubit entangling gates is essential for efficient, scalable, and fault-tolerant quantum information processing, reducing algorithmic complexity and circuit depth. We demonstrate a native three-qubit entangling gate implemented by simultaneously driving all qubits at a common frequency, exploiting engineered interactions to realize multicontrol operations in a single coherent step. By optimizing the conditional dynamics originating from drive-induced nonlocal contamination, desired interaction channels are selectively enhanced while spurious terms are suppressed, ensuring robust performance within the computational subspace. This gate enables key applications, including deterministic GHZ-state generation, Toffoli-class logic with a shortest gate duration of 90 ns and a highest fidelity of 99.72%, and a controlled-$ZZ$ gate tailored for fast surface-code quantum error correction. Simulations based on realistic IBM device parameters indicate that the gate maintains high fidelity and resilience under increasing excitation numbers and larger Hilbert-space dimensions. Our results establish a foundation for co-designing circuit architectures and control strategies that harness native multiqubit interactions as fundamental building blocks for next-generation superconducting quantum processors, thereby enabling improved gate performance with more flexible tuning of circuit parameters.

The fast dynamics of square lattice artificial spin ice made of circular magnetic tunnel junctions are investigated through magnetoresistance measurements on individual 60-nm devices. The common fixed layer leads to easy- and hard-axis behavior: devices that telegraph between parallel and antiparallel states, alternating with devices where the free-layer moment rotates. Preferred canting angles are observed and can be related to predictions based on the magnetostatic fields from near neighbors. Two timescales are observed, one corresponding to single nanomagnet fluctuations and the other to mesoscale rearrangements. Devices in canted states are part of nodes with nonzero net magnetic charge, known as emergent magnetic monopoles. While monopole-containing states are abundant, these excitations are often long-lived and their lifetime depends on the stability of the mesoscale flux closure patterns.

The Taiji mission, a pioneering Chinese space-borne gravitational wave observatory, requires ultraprecise calibration of its gravitational reference sensors (GRSs) to achieve its targeted sensitivity of $3\times {10}^{-15}\mathrm{m}{\mathrm{s}}^{-2}{\mathrm{Hz}}^{-1/2}$. Maintenance of this precision is challenged by time-varying scale factor drifts and dynamic center-of-mass (c.m.) offsets between the test masses (TMs) and spacecraft, driven by such factors as propellant consumption, thermal effects, and aging electronics. We develop an advanced in-orbit calibration framework that simultaneously estimates the GRS scale factors and c.m. offsets between TMs and spacecraft through a combination of spacecraft maneuvers and a Kalman filter. By applying periodic torque signals to induce controlled spacecraft angular accelerations, we leverage star tracker and GRS readouts to disentangle coupled disturbances and achieve dual-parameter calibration with remarkable precision, with scale factor errors below 0.2% and c.m. offset residuals within $100\text{μ}\mathrm{m}$, satisfying the Taiji-2 calibration requirements. This method is robust across different satellite configurations. The results not only ensure the feasibility of Taiji-2’s scientific objectives but also establish a scalable calibration paradigm for future missions, such as Taiji-3, where submicrometer c.m. stability and ultralow noise gravitational reference will be essential.

Quantitatively characterizing intra-meta-atom coupling is essential for understanding and controlling optical chirality in metasurfaces, yet it remains largely qualitative. Here, we propose a robust route to determine coupling strength based on a phase-transition optical activity phenomenon in chiral metasurfaces. By integrating the Born-Kuhn coupled-oscillator model with full-wave simulations, we reveal a sharp threshold behavior in polarization rotation, governed by a threshold coupling constant. This threshold enables precise extraction of the intra-meta-atom coupling strength, establishing a quantitative link between geometry and optical chirality. Multipolar analysis further allows determination of the damping coefficient, leading to accurate evaluation of the coupling parameter. This framework transforms the qualitative description of chiral interactions into a quantitative metric, offering physical insight and practical guidance for designing metasurfaces with enhanced optical activity toward applications in chiral sensing, enantiomer discrimination, and quantum photonics.

Electromagnetically induced transparency has become a significant method for manipulating the propagation of electromagnetic waves. However, due to its resonant nature, it typically suffers from a narrow bandwidth and limited tunability. Here, we employ a pump-induced magnon mode (PIM) to manipulate microwave scattering, thereby observing an electromagnetic transparency phenomenon with a tunable bandwidth induced by the magnon drag effect. We find that, when changing the microwave frequency, the PIM’s frequency follows the microwave and exhibits a drag effect, resulting in spectral distortion of the microwave scattering parameters. Specifically, the transmission coefficient of the microwave increases while its reflection coefficient decreases, leading to a transparency window in the frequency spectrum. The rate and bandwidth of this transparent window are tunable by the microwave power. It manifests as follows: the higher the microwave power, the larger the transparency bandwidth and the higher the transparency rate. These findings point out the direction of optimizing the electromagnetic transparency based on the PIM dynamics and may advance the development of magnonic devices for microwave engineering and information processing.

We present a probabilistic quantum algorithm for preparing mixed states which, in expectation, are proportional to the solutions of Lyapunov equations—linear matrix equations ubiquitous in the analysis of classical and quantum dynamical systems. Building on previous results by Zhang et al., arXiv:2304.04526, at each step the algorithm can (i) return the current state, (ii) apply a trace nonincreasing completely positive map, or (iii) restart. We introduce a deterministic stopping rule, which leads to an efficient algorithm with a bounded expected number of calls to oracles representing the two input matrices of the Lyapunov equations. We also consider preparing a mixed state that approximates the normalized inverse of a positive definite matrix $A$. In its most general form, the algorithm generates mixed states, which approximate matrix-valued weighted sums and integrals. It can be shown that block encodings and states yield two incomparable computational resources even when they represent the same piece of data. While block encodings of functions have received much attention in the literature, our work takes a step toward the less explored problem of encoding functions into mixed states.

Quantum linear system (QLS) algorithms offer the potential to solve large-scale linear systems exponentially faster than classical methods. However, applying QLS algorithms to real-world problems remains challenging due to issues such as state preparation, data loading, and efficient information extraction. In this work, we study the feasibility of applying QLS algorithms to solve discretized three-dimensional (3D) heterogeneous Poisson equations, with specific examples relating to groundwater flow through geologic fracture networks. We explicitly construct a block encoding for the 3D heterogeneous Poisson matrix by leveraging the sparse local structure of the discretized operator. While classical solvers benefit from preconditioning, we show that block encoding the system matrix and preconditioner separately does not improve the effective condition number that dominates the QLS run-time. This differs from classical approaches where the preconditioner and the system matrix can often be implemented independently. Nevertheless, due to the structure of the problem in three dimensions, the quantum algorithm achieves a run-time of $O(N^{2/3}\text{polylog }N\cdot \log (1/ϵ))$, outperforming the best classical methods (with run times of $O(N\log N\cdot \log (1/ϵ))$) and offering exponential memory savings. These results highlight both the promise and limitations of QLS algorithms for practical scientific computing, and point to effective condition-number reduction as a key barrier in achieving quantum advantages.

We describe a general quantum receiver protocol that maps laser-light-modulated classical communications signals into quantum processors for decoding with quantum logic gates. The quantum gates enable joint quantum measurements over a code word to achieve the quantum limit of communication capacity. Our receiver design requires qubit resources that only logarithmically increase with the size of the code word and accommodates practically relevant coherent-state modulation containing multiple photons per pulse. Focusing on classical-quantum polar codes, we outline the necessary quality of quantum operations and code-word lengths to demonstrate a quantum-processing-enhanced communication rate surpassing that of any known classical optical receiver-decoder pair. Specifically, we show that a small quantum receiver of four qubits with operational errors of approximately $0.2\mathrm{\%}$ can already provide a 5% gain in the communication rate in the weak-signal limit. Additionally, we outline a possible hardware implementation of the receiver where efficient spin-photon interfaces such as cavity-coupled diamond color centers or atomic qubits are used to input the received photonic signal to a small-scale quantum processor for decoding. Our results outline a promising route for potential quantum advantage in classical communication with near-term, small-scale quantum computers.

We report a compact single-cell source of a continuous cold-atom beam with three-dimensional (3D) cooling. By integrating an off-axis moving optical molasses (OM) with a two-dimensional magneto-optical trap, we achieve simultaneous 3D cooling within a $50\mathrm{mm}$ interaction region. The source delivers a continuous flux up to $4.9(5)\times {10}^9\mathrm{atoms}/\mathrm{s}$, with a transverse temperature of $94(5)\text{μ}\mathrm{K}$, a longitudinal temperature as low as $231(65)\text{μ}\mathrm{K}$, and a tunable mean velocity between 5 and $20\mathrm{m}/\mathrm{s}$. Custom in-vacuum mirrors integrate the reflective geometry for the off-axis OM beams with a $0.8\mathrm{mm}$ output aperture, ensuring stable alignment while suppressing stray light and fluorescence leakage. Ultralow light shift and decoherence are verified via continuous Raman-Ramsey interferometry, yielding a light shift of $-0.51(4)\mathrm{Hz}$ and a typical fringe contrast of $90.85(30)\mathrm{\%}$ at a Raman separation of $100\mathrm{mm}$ (interrogation time of $8.70\mathrm{ms}$). This compact continuous cold-atom beam source constitutes a practical building block for atomic-beam clocks and interferometers, enabling reduced aliasing noise together with improved sensitivity and accuracy for field applications.

We study the effects of magnetic anisotropy and crystalline axes in surface acoustic waves (SAWs) driven magnetic resonances of $\mathrm{Ni}/{\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ hybrid devices. SAW absorption from the interaction with magnons in $\mathrm{Ni}$ displays a strong anisotropic dependence on the direction of the applied in-plane magnetic field. Magnetic anisotropy is further investigated by magneto-optical Kerr effect measurements to show both uniaxial and biaxial anisotropy components in $\mathrm{Ni}$ films on ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$. By introducing a dipolar interaction term in addition to the anisotropies, we successfully explain the anisotropic SAW absorption in our devices. These findings show the significance of substrate-induced anisotropy and long-range dipolar effects in magnon-phonon hybrid devices and indicate future directions for optimizing these spin-acoustic devices through comprehensive anisotropy engineering.

Efficiently harnessing solar radiation pressure holds great promise for solar sailing, potentially revolutionizing deep space exploration with fast, low-cost, sunlight-propelled probes. However, conventional solar sails reflect light specularly, with radiation pressure forces normal to the sail surface. Here, we explore metasurface reflect arrays that allow for efficiently imparting in-plane radiation pressure forces under ambient sunlight. We show that segmented tapered patch nanoantenna metasurfaces are well suited for ultrawideband, polarization-insensitive anomalous reflection of sunlight. Theoretical studies show >60% anomalous reflection over a 400-nm band across a larger part of the solar spectrum. The calculated efficiency for generating in-plane radiation pressure force is approximately 50%. As one example scenario, we discuss solar sail spin control with such anomalous metasurfaces. Beyond space exploration, we envision that anomalous reflection of ambient sunlight will find use in solar concentration and energy harvesting, spectrum splitting, or even display technologies.

Implementing electromagnetic scattering suppression with angular stability and broad bandwidth for typical targets is highly demanded for stealth applications. Recent research into metagratings has enabled artificially engineered interfaces capable of wave diffraction manipulation, particularly for large-angle incidence. However, current metagratings designed for extreme wave front transformation mainly focus on scattering enhancement, and do not yet fully exploit the potential of spectrum-controlled scattering suppression, despite its significance in radar systems. Here, a simple scheme of a wideband metagrating diffuser is reported, which allows dual-polarized radar cross-section reduction at large-angle incidence through diffraction manipulation incorporating detour phase cancellation. Notably, the detour-phase response of the scatterer is facilely modulated by simply in-plane translation of the metallic strips. As exemplary demonstrations, metagrating right-angled dihedral corner structure is proposed and experimentally demonstrated, intended for low backscattering of typical targets, such as aircraft and vessels, with practical applications in stealth technique and electromagnetic compatibility. The proposed strategy can also be readily explored in other frequency bands and extended to polarization-multiplexed beam generation and angle-locked holographic image, including but not limited to scattering suppression, revealing rich possibilities for versatile diffraction engineering.

The coherence properties of optical emitters in crystals are crucial for quantum technologies and optical frequency metrology. Cooling to subkelvin temperatures can markedly enhance coherence, making it useful to identify the parameters governing emitter and host crystal behavior in this regime. We investigate a Czochralski-grown europium-doped yttrium orthosilicate crystal, reporting measurements of its heat capacity and optical coherence. Heat capacity not only informs thermal noise limits in metrology schemes but can also reveal two-level systems (TLS) arising from crystal imperfections via a linear-in-temperature term. Below 1 K, where phonon contributions are suppressed, TLS can drive decoherence, leading to a linear broadening of the homogeneous linewidth. From our data, we place an upper bound on the TLS contribution. This, together with constant optical linewidths between 300 mK and 2 K measured via photon-echo lifetimes, is consistent with minimal TLS effects in our sample. A low level of TLS is particularly useful for the performance of optical quantum devices based on doped crystals, since their presence could otherwise limit further improvements in coherence at subkelvin temperatures.

We measure the total-energy distribution of thermally emitted electrons from tungsten, lanthanum hexaboride, and yttrium oxide. The latter exhibits a surprisingly narrow distribution, with a full width at half maximum of approximately $200–400\mathrm{meV}$ across a broad temperature range. We detail our simulation-experiment approach to account for the response of the energy analyzer and energy-broadening mechanisms, establishing the validity of the acquired spectra. We also present electronic-structure calculations using density functional theory that reveal narrow, localized states arising from oxygen vacancies and yttrium self-interstitials, which may be responsible for the observed electron energy distributions. This work helps strengthen the link between thermal electron emission and the properties of the electron-emitting material.

Thermodynamics in quantum circuits aims to find improved functionalities of thermal machines, highlight fundamental phenomena peculiar to quantum nature in thermodynamics, and point out limitations in quantum information processing due to the coupling of the system to its environment. An important aspect in achieving some of these goals is the regime of strong coupling, which has remained until now a domain of theoretical works only. Our aim is to demonstrate strong coupling features in heat transport using a superconducting flux qubit, which is capable of reaching strong- to deep-ultrastrong-coupling regimes, as shown in previous studies. Here, we show experimental evidence of strong coupling by observing a hybridized state of the qubit with two cavities coupled to it, leading to a triplet-like thermal transport via this combined system around the minimum energy of the qubit at power levels of tens of femtowatts, exceeding by an order of magnitude those in earlier experiments. We also demonstrate a nearly 100% on-off switching ratio of heat current mediated by photons by applying magnetic flux to the qubit. Our experiment opens a way towards testing debated questions in strong-coupling thermodynamics, such as what heat is in this regime. We also present a theoretical model that aligns with our experimental findings and explains the mechanism behind heat transport in our device. Furthermore, our experiment opens possibilities for quantum thermodynamics, aiming to realize true quantum heat engines and refrigerators with enhanced power and efficiency, by leveraging ultrastrong coupling between the system and its environment in future experiments.

We present a two-step deconvolution algorithm for recovering the density of states (DOS) of the sample from scanning tunneling spectroscopy measurements without requiring prior knowledge of the tip state. The method first uses the DOS and the dI/dV spectrum of a known feature to characterize the product of the DOS of a tip and the tunneling probability. With this product and the dI/dV spectrum measured on the sample with the same tip, the DOS of the sample can be further derived. Applied to both simulated and experimental data on engineered quantum corrals, as well as the adatoms placed inside them, the algorithm exhibits robust reproducibility under various tip conditions and uncovers subtle modulations of adatom resonance states related to quantum confinement and inversion effects. By extracting a high-fidelity DOS, the method offers a powerful approach for investigating artificial nanostructures and the related quantum phenomena.

Proximity coupling of bilayer graphene (BLG) to transition metal dichalcogenides (TMDs) offers a promising route to engineer gate-tunable spin-orbit coupling (SOC) while preserving BLG’s exceptional electronic properties. This tunability arises from the layer-asymmetric electronic structure of gapped BLG, where SOC acts predominantly on the layer in contact with the TMD. Here, we present a high-quality $\mathrm{BLG}/{\mathrm{WSe}}_2$ device with a proximity-induced SOC gap and excellent electrostatic control. Operating in a quasiballistic regime, our double-gated heterostructure allows a gate-defined $p$-$n$-$p$ cavity to be formed and clear weak antilocalization (WAL) features to be shown consistent with Rashba-type SOC. At lower hole densities, a transition to a pronounced weak-localization (WL) feature is observed, signaling transport through a single spin-split valence band. These findings–in agreement with calculations–provide direct spectroscopic evidence of a proximity-induced spin-split band in BLG and underscore the potential of BLG/TMD heterostructures for spintronics and spin-based quantum technologies.