The ability to reliably inscribe information on single photons is a crucial requirement for quantum applications such as quantum communication and measurement-based photonic quantum computation. Experimental implementations generally employ phase modulators in single-pass or Mach-Zehnder-interferometer configurations to encode information on photonic qubits. However, these approaches are intrinsically sensitive to environmental influences, which limits the achievable quantum error rates in practice, posing a major bottleneck in the transition of quantum applications with deterministic sources from the laboratory to the field. Inspired by the adaptation of Sagnac interferometer encoders for laser-based applications, we report a demonstration of a polarization encoder for single-photon qubits based on a free-space Sagnac interferometer. The device showcases inherent phase stability and overcomes previous error-rate limitations: Telecom-wavelength photons emitted by a quantum dot are modulated at a rate of 152 MHz and with a quantum bit error rate of $0.69\pm 0.02\%$, marking the lowest value reported to date for MHz-rate information encoding on single photons by a factor of $>3$. This combination of low error rate, high modulation speed, stability, and operation with telecom-wavelength sub-Poissonian photons is an essential requirement for bringing quantum applications based on deterministic photon sources from the laboratory to the field and a significant step toward unlocking the full potential of a future quantum Internet.

High-rate remote entanglement between photon and matter-based qubits is essential for distributed quantum information processing. A key technique to increase the modest entangling rates of existing long-distance quantum networking approaches is multiplexing. Here, we demonstrate a temporally multiplexed ion-photon interface via rapid transport of a chain of nine calcium ions across $74\mathrm{\mu }\mathrm{m}$ within $86\mathrm{\mu }\mathrm{s}$. The nonclassical nature of the multiplexed photons is verified by measuring the second-order correlation function with an average value of $g^{(2)}(0)=0.060(13)$. This indicates low crosstalk of about 1% between the multiplexed modes, which can be reduced further once coupling of the photons to a single-mode fiber is incorporated. In addition, we characterize the motional degree-of-freedom of the ion crystal after transport and find that it is coherently excited to ${\overline{n}}_{\alpha }\approx 110$ for the center-of-mass mode. Our proof-of-principle implementation paves the way for large-scale quantum networking with trapped ions, but highlights some challenges that must be overcome.

Nonlinear phenomena play a crucial role across diverse physical systems, providing key insights into complex interactions and emergent collective behaviors. Nonlinear dynamics has been studied around phase transitions, which benefits from the reduced threshold of the intrinsic dynamical instability. Here, we report the experimental observation of magnon mode hopping near the second-order phase transition in yttrium iron garnet film. It is found that a cusplike soft mode exhibits mode hopping under strong driving. The experimental observations are numerically understood from the sharp decrease of the magnetization precession amplitude. The mode hopping is attributed to driving-induced dynamical instability near the phase transition. Our findings could pave the way for investigating nonlinear magnetization dynamics near the phase transition.

Satellite-based quantum key distribution (QKD) offers a promising approach toward the realization of global-scale quantum communication networks. However, current systems are restricted to nighttime operation, as intense daytime background noise drastically degrades the signal-to-noise ratio. While single-mode fiber coupling effectively suppresses background noise, maintaining high coupling efficiency and stability amidst strong atmospheric turbulence remains a significant challenge. In this study, we propose a deep-learning-based adaptive-optics method for turbulence correction, which is experimentally validated over 1.4- and 7-km free-space channels and compared with wave-front-sensor-based systems. The proposed method achieves substantial improvements in the Strehl ratio under strong turbulence conditions. Furthermore, we numerically evaluate the performance of a free-space quantum key distribution system incorporating our deep-learning-based method, which achieved higher key rates and longer propagation distances. By directly estimating phase information from a defocused image, this approach provides an efficient and cost-effective solution for strong turbulence correction, paving the way for practical daytime QKD.

The birefringence mode-locked fiber laser-based dual-comb sources have strong potential in the fast spectroscopy, ranging and imaging, due to its large repetition rate difference, configuration compactness, and common-mode noise suppression. However, the intrinsic effects of the mutual dynamics between the dual-polarization solitons (DPSs) output from the dual-comb source on the coherence and common-mode noise still have attracted few attentions. In this work, the polarization mode competition dynamics and the statistical correlation of the intensity jitter between the DPSs are studied, and the short-time common-mode noise of the dual-comb source is revealed. The noise floor of relative timing jitter is as low as $0.01\mathrm{fs}/{\mathrm{Hz}}^{1/2}$, and the integrated jitter from 200 kHz to 96 MHz reaches only 71 fs. The mutual dynamics shows that asynchronous sampling between DPSs can obtain effective time-domain interferometry signals. Eventually, the acoustical vibration signal carried by the sub-fs level relative timing jitter can be measured by calculating the phase of the interference pattern on the shot-to-shot spectrum with an update frame of up to the kHz level. This work provides a comprehensive understanding of the DPSs mutual dynamics and opens the avenue for its application in the time-resolved spectroscopy-based precise measurements.

This work proposes a nonlocal terahertz metasurface that suppresses the gain degradation intrinsic to local-metasurface-aided leaky-wave antennas by maintaining a stable scattering response as the angle at which the guided mode impinges on the metasurface varies with the scanning frequency. This angular insensitivity is realized by engineering the spatial dispersion (i.e., nonlocality) provided by four surface susceptibilities: tangential electric and magnetic, normal magnetic, and magnetoelectric coupling susceptibilities. We analyze the theoretical degrees of freedom available for angular-response control on the basis of these four susceptibilities within a reciprocal, lossless, dipolar framework in an asymmetric environment. On the basis of this analysis, an optimization-based synthesis method is applied to obtain the required susceptibilities, which yield a close approximation of the desired angle-independent scattering behavior. Additionally, an iterative truncation method is introduced to bridge the gap between abstract susceptibility design and physically realizable structures. Full-wave simulations demonstrate a beam-scanning range of nearly 50° across the 1.9–2.6 THz band, representing an approximately 2.6-fold expansion in continuous, well-formed scanning coverage compared with a local-metasurface counterpart designed under otherwise identical conditions.

We report the electrical detection of the spin resonance with temporal resolution in a two-dimensional electron system. Spin resonance was excited by pulses of subterahertz radiation characterized by relatively short rise and fall times on the order of 10 ns and was observed as a resonant peak in the high-frequency conductivity of the two-dimensional channel. The suggested approach is inherently broadband and enables the investigation of spin dynamics in two-dimensional electron systems across a wide range of magnetic fields and temperatures. The proposed technique was employed to measure spin relaxation in a Si/SiGe quantum well.

Background: The formation and spatial distribution of $\mu$-hotspots in high-energy photon radiotherapy are important factors influencing radiation-induced DNA damage. These hotspots can enhance the local linear energy transfer (LET) component, affecting therapeutic outcomes. Purpose: This study aims to investigate the characteristics of $\mu$-hotspots using measurements of the inclusive $\alpha$-particle spectrum from the ${}^{12}\mathrm{C}(\gamma ,3\alpha )$ breakup reaction, induced by 14.8 MeV bremsstrahlung photons, and to correlate these features with radiobiological effects, such as DNA double-strand breaks (DSBs) and micronuclei formation. Results: Geant4 simulations incorporating TALYS-based differential cross sections and angular distributions calculated via distorted wave Born approximation (DWBA), fitted with experimental measurement, reveal that $\mu$-hotspots have a characteristic root-mean-square diameter of approximately $12\mathrm{\mu }\mathrm{m}$ and a mean spatial separation of $120.73\pm 0.0075\mathrm{\mu }\mathrm{m}$ within a $1{\mathrm{cm}}^3$ volume, assuming uniform distribution. The enhancement in DSBs induced by $\mu$-hotspots shows a strong linear correlation with micronuclei formation, indicating a potential mechanistic link. Conclusion: The microscale clustering effect of $\mu$-hotspots significantly increases the high-LET component of the radiation field, with critical implications for radiobiological effectiveness and therapeutic outcomes in photon-based cancer treatments.

We demonstrate a practical and sensitive low-field approach to magnetic resonance imaging (MRI) of $\mathrm{\mu }\mathrm{L}$-scale samples using an optically pumped magnetometer (OPM). Using a simple setup where a commercial OPM is placed directly adjacent to a sample, without intermediary signal-pickup coils, we perform one- and two-dimensional imaging with a $>1\mathrm{cm}$ field of view and sub-mm Fourier-limited resolution at $10\mathrm{\mu }\mathrm{T}$, near Earth’s field. This enables (i) high-throughput, low-field MRI of fluidic and tissue samples, and (ii) a quantitative benchmark of the sensitive volume surrounding the OPM.

Quantum architecture search (QAS) has shown significant potential for automating quantum circuit design in variational quantum algorithms (VQAs). However, the application of current QAS methods to large-scale circuits remains challenging due to the high computational complexity of evaluating numerous circuit architectures. While performance predictors are a promising solution, they are conventionally trained with objectives such as mean squared error, which create a fundamental objective mismatch by failing to prioritize the discovery of the most elite, high-performing architectures. In this work, we resolve this objective mismatch by introducing a new training paradigm that directly optimizes a top-tier-focused ranking loss. To capture the causal information flow of quantum gates, we design a circuit-native Transformer equipped with reachability-based unitary-flow attention and depth-aware positional encoding. Furthermore, we implement a pretraining strategy based on circuit learnability, a metric that unifies expressibility and trainability, to extract functionally aware representations from unlabeled data, thereby significantly improving sample efficiency. Extensive results on multiple VQA benchmarks demonstrate that our approach consistently outperforms existing QAS frameworks in both ranking quality and the performance of the discovered circuits. Ablation studies confirm that the synergy of the differentiable top-tier-focused loss, the circuit-native Transformer, and learnability-based pretraining is essential for superior performance. Beyond energy-based benchmarks, we further validate the searched circuits under a device-calibrated noise model based on the IBM Kingston quantum computer and on a noisy 2D transverse-field Ising model benchmark. The results show that our method can identify compact circuits with fewer two-qubit gates while preserving physically meaningful properties, including fidelity, connected spin correlations, and magnetization.

We introduce excited local quantum annealing (ExcLQA), a classical, physics-inspired algorithm that extends local quantum annealing (LQA) to identify excited states of classical Ising Hamiltonians. LQA simulates quantum annealing while constraining the quantum state to remain in a product state and uses a gradient-based approach to find approximate solutions to large-scale quadratic unconstrained binary optimization problems. ExcLQA extends this framework by adding a penalty term in the cost function to target excited states, with a single hyperparameter that can be tuned via binary search to set the desired penalization level. We benchmark ExcLQA on fully connected Ising models with random interactions and on the shortest vector problem (SVP). The latter is a fundamental lattice problem underlying the security of many postquantum cryptographic schemes, and its solution can be mapped to the first excited state of an Ising Hamiltonian. For the fully connected Ising models, we show that, on the tested instances, ExcLQA outperforms both a matrix-product-state-based method and simulated annealing. Notably, even when only a lower bound on the ground-state energy is provided, rather than the exact ground-state information required by these competing methods, ExcLQA still achieves superior performance. For the SVP, ExcLQA finds exact solutions for instances up to rank 46 and outperforms the Metropolis-Hastings algorithm in terms of solved ratio, number of shots, and approximation factor on the tested instances.

We develop a theory for two quasiparticle-induced decoherence mechanisms of a driven superconducting qubit. In the first mechanism, an existing quasiparticle (QP) tunnels across the qubit’s Josephson junction while simultaneously absorbing a qubit excitation and one (or several) photons from the drive. In the second mechanism, a qubit transition occurs during the nonlinear absorption process converting multiple drive quanta into a pair of new QPs. Both mechanisms can remain significant in gap-engineered qubits whose coherence is insensitive to QPs without the drive. Our theory establishes a fundamental limitation on fidelity of the microwave qubit operations—such as readout and gates—stemming from QPs.

Isolators are commonly found in the amplification chain of microwave setups to shield sensitive devices such as superconducting qubits from noise and back-scattered signals. Conventional ferrite-based isolators are bulky, lossy, and rely on strong magnetic fields, which pose challenges for their co-integration in large-scale superconducting devices. Although several magnetless approaches based on parametric modulation have been explored to overcome these limitations, none has yet experimentally demonstrated wideband isolation on a par with ferrite devices. Here, we propose a compact modulation-based isolator that achieves large isolation bandwidth using a dispersion-engineered transmission line. The engineered line forms an effective two-mode system that enables broadband isolation by supporting adiabatic mode conversion over a wide instantaneous bandwidth. Numerical simulations show that this architecture can provide more than 20-dB isolation across 4–8 GHz, matching the performance of ferrite-based isolators. Moreover, we propose an on-chip superconducting device implementation that shows promise against parameter variations and enables a scalable path for co-integration with future large-scale superconducting systems.

Optical imaging plays an instrumental role in understanding the behavior of trapped neutral atoms. In this work, we describe a deep learning-based online image completion protocol that reduces interference fringes in optical absorption signals for a dual-species atomic system. Regardless of the distinct nature of the task for two different atomic species, ${}^6\mathrm{Li}$ and ${}^{23}\mathrm{Na}$, the method displays a robust solution for suppressing fringes. To incorporate this into daily operations, a transfer learning scheme is required that incrementally updates the previously learned parameters. We outline an online image completion method that efficiently adapts to drifting experimental conditions. Our method can be easily integrated into lab settings, where transfer learning can accelerate image analysis.

Control of the polarization of microwave fields is a key experimental capability for a number of atomic physics platforms. However, producing high-fidelity microwaves requires a well-controlled microwave environment, where reflections that distort the polarization must be avoided or well characterized, a constraint that often conflicts with other experimental design considerations. Here, we demonstrate a microwave control system capable of producing high-fidelity microwave polarizations in a Rydberg-ensemble experiment. We use three sets of in-vacuum dc electrodes, repurposed as microwave antennas, to produce imperfect and initially unknown polarizations. Each source is driven with independent phase and amplitude control to generate the desired microwave fields. We probe the fields produced at the position of the atoms using Rydberg-electromagnetically induced transparency spectroscopy of the microwave-induced avoided crossings. We produce ${\sigma }_{-}$, $\pi$, and ${\sigma }_{+}$ polarized microwaves with $>99\%$ fidelity and generate their combinations. We extend our purification techniques to frequencies away from Rydberg resonances by utilizing an auxiliary microwave field, generating two-photon microwave resonances. The techniques developed here will facilitate the engineering of dipolar interactions in atomic and molecular physics experiments.

We propose methods to mitigate single- and two-qubit control errors due to residual exchange coupling in systems of exchange-coupled resonant singlet-triplet qubits. Commensurate driving, where the pulse length is an integer multiple of the drive period, can mitigate errors from residual intraqubit exchange, including effects from counter-rotating terms and off-axis rotations, as well as leakage errors during two-qubit operations. Residual interqubit exchange creates crosstalk errors that reduce single-qubit control fidelities. We show that using a single-spin coupler between two resonant singlet-triplet qubits can reduce this crosstalk error by an order of magnitude. Assuming perfect coupler state preparation and realistic charge and hyperfine noise, we predict that coupler-assisted two-qubit gate errors can be below $3\times {10}^{-3}$ for gate times as short as $66\mathrm{ns}$, even in the presence of residual exchange levels exceeding several hundred kHz. Our results suggest the potential of utilizing coupler-based architectures for large-scale fault-tolerant spin qubit processors based on resonant singlet-triplet qubits.

Longitudinal coupling offers a compelling pathway for quantum nondemolition (QND) readout, but pulse design is constrained by hardware limitations, such as the maximum coupling strength and the intracavity photon number required to remain in the linear regime. Here, we formulate the pulse-design task as a low-dimensional constrained optimization problem. Building on inverse engineering (IE) within the shortcuts to adiabaticity (STA) framework, we parameterize the auxiliary control variable with a smooth B-spline basis and reconstruct the physical control from it. The analytical STA pulse provides the initialization for this constrained search. At a fixed short readout time, the optimized pulse yields an approximately 50% improvement in $\mathrm{SNR}$ over the STA baseline. Comparisons across multiple optimizers show that the IE-guided formulation consistently yields high-performance solutions, while the optimized pulse remains smooth, hardware compatible, and governed by an interpretable “saturate-and-hold” mechanism.

Solid-state batteries hold immense promise to deliver both high energy density and enhanced safety for advanced energy storage applications. However, low ionic conductivity and high interfacial resistance remain key challenges in the overall performance of practical sodium-ion devices. Therefore, herein, we fabricate and investigate freestanding composite polymer electrolytes (CPEs) comprising ${\mathrm{Na}}_3{\mathrm{Zr}}_2{\mathrm{Si}}_2{\mathrm{PO}}_{12}$ (NZSP) nanopowder, poly(vinylidene fluoride-co-hexafluoropropylene), polypropylene carbonates (PVDF-HFP/PPC), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), or ionic liquids or succinonitrile (SCN). The effects of ionic liquids [N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PMPFSI), N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PMPTFSI), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI)] and SCN on the crystal and vibrational structure, chemical environments and morphology are systematically examined. Furthermore, all the plasticized membranes exhibit suppressed irregular Na growth in symmetric cells, indicating stable and reversible Na stripping/plating over 300 h at $0.01\mathrm{mA}{\mathrm{cm}}^{-2}$, having lower overpotential than the NZSP membrane. Notably, the CPEs are electrochemically stable up to 5.0 V and EMIFSI-based CPE demonstrates a good transference number (0.75). Intriguingly, we find that the EMIFSI-based CPE outperforms the other electrolytes in terms of specific capacity, enabling the ${\mathrm{Na}}_3{\mathrm{V}}_2({\mathrm{PO}}_4{)}_2{\mathrm{F}}_3/\mathrm{C}$ cathode to deliver about $94\mathrm{mAh}{\mathrm{g}}^{-1}$ at 0.1 C and $22\mathrm{mAh}{\mathrm{g}}^{-1}$ at 2 C while maintaining stable cycling for up to 150 cycles at 0.5 C. This study proposes an innovative strategy for solid-state batteries to realize safer and more efficient energy storage systems.

High-precision free floating of test masses (TMs) is critical for TianQin, a space-based gravitational wave mission, as TMs serve as inertial references for laser interferometric measurements of spacetime perturbations induced by gravitational waves. A key challenge during TM release lies in electrostatic interactions between the TM and plungers of its grabbing positioning and release mechanism (GPRM)—exacerbated by nonideal conditions like plunger oscillation, asymmetric retraction, variable TM-plunger potential difference, and TM translation or rotation—which may degrade reference quality. To address this, a high-precision numerical model based on the finite-element method (FEM) is developed to investigate TM-plunger electrostatic coupling, with parameterized simulations via extreme-value and single-factor analyses to quantify electrostatic forces and torques on the TM and establish response models. Key results show electrostatic effects dominate along the $z$ axis due to GPRM geometric asymmetry, with the $z$-plunger more influential; plunger oscillation with maximum $2.6\mathrm{\mu }\mathrm{m}$ in the $x$ axis and $5\mathrm{\mu }\mathrm{m}$ in the $y$ axis does not exceed force thresholds, and retraction beyond $160\mathrm{\mu }\mathrm{m}$ renders plungers negligible; TM $x$-axis displacement beyond $4.76\mathrm{\mu }\mathrm{m}$ violates $z$-axis force requirements, while rotations up to 0.2 mrad about the $x$ and $y$ axes and 3 mrad about the $z$ axis stay acceptable. Under typical nonideal scenarios, TM electrostatic forces remain within TianQin’s limits, verifying the locking and release mechanism’s reliability and providing a FEM framework to support future noncontact attitude control in space-based gravitational wave detectors.