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.

This work investigates the modulation of x-rays by high-resolution zone plates (ZPs), challenging the limitations of traditional phasor-based theory when volume diffraction effects (VDE) dominate. Using the beam propagation method (BPM), we simulated the optical field dynamics and identified three key causes of efficiency degradation in traditional ZPs with rectangular profiles: amplitude-type modulation, focal spot displacement, and phase mismatch. Experimental validation using a 15 nm outermost-zone ZP fabricated via e-beam lithography and tested at Shanghai Synchrotron Radiation Facility (SSRF) confirms the superior accuracy of BPM over phasor-based theory. Furthermore, slant zone plates incorporating Bragg diffraction mitigate VDE-induced losses, achieving near-ideal phase modulation. Finally, a waveguide-based interpretation provides physical insight into VDE mechanisms, highlighting the potential of geometric innovations to overcome current limitations.

The thermal response of proximity Josephson junctions (JJs) is governed by the temperature ($T$)-dependent occupation of Andreev bound states (ABS), making them promising candidates for sensitive thermal detection. In this study, we systematically engineer ABS to enhance the thermal sensitivity of critical current ($I_{\mathrm{c}}$) of proximity JJs, quantified as $|d{I}_{\mathrm{c}}/dT|$ for the threshold readout scheme and $|d{I}_{\mathrm{c}}/dT·I_{\mathrm{c}}^{-1}|$ for the inductive readout scheme. Using a gate-tunable graphene-based JJ platform, we explore the impact of key parameters—including channel length, transparency, carrier density, and superconducting material—on the thermal response. Our results reveal that the proximity-induced superconducting gap plays a crucial role in optimizing thermal sensitivity. For the threshold scheme, we obtain a width-normalized sensitivity of $|d{J}_{\mathrm{c}}/dT|\approx 0.2\mathrm{\mu }\mathrm{A}{\mathrm{K}}^{-1}\mathrm{\mu }{\mathrm{m}}^{-1}$ at 0.1 K in an aluminum-based graphene JJ. Notably, we see a maximum $|d{I}_{\mathrm{c}}/dT·I_{\mathrm{c}}^{-1}|$ value of $0.6{\mathrm{K}}^{-1}$ at 50 mK with titanium-based graphene JJs. By demonstrating a systematic approach to engineering ABS in proximity JJs, this work establishes a versatile framework for optimizing thermal sensors and advancing the study of ABS-mediated transport.

Multimode superconducting circuits offer a promising platform for engineering robust systems for quantum computation. Previous studies indicate that single-mode devices cannot be engineered to simultaneously exhibit resilience against multiple decoherence sources due to conflicting requirements. In contrast, multimode systems offer increased flexibility and have proven capable of overcoming these fundamental limitations. Here, we present a multimode device optimized for quantum information processing. It features an anharmonicity of a third of the qubit frequency and reduced energy dispersion caused by charge and magnetic flux fluctuations. It exhibits improvements over the fundamental errors limiting transmon and fluxonium coherence and control, achieving ratios between the total coherence time and the gate time $T_2/t_{\mathrm{g}}$ one order of magnitude larger than transmon and two times larger than fluxonium for microwave charge drives, assuming equal dielectric and inductive loss quality factors and limited drive strength. Simulations further demonstrate the device’s robustness to circuit parameter deviations, a known limitation of many multimode devices.

Two-dimensional (2D) van der Waals (vdW) bilayers, with their intrinsic interlayer electric fields for enhanced carrier separation, provide a promising platform for efficient photocatalysis. However, the microscopic mechanisms linking these internal fields to higher photocatalytic activities remain elusive. Here, we construct ${\text{HfN}}_2$ bilayers with different stacking orders to explore how interlayer polarization governs carrier dynamics for higher photocatalytic water-splitting characteristics. First-principles calculations show that the AB stacking, which breaks interlayer symmetry, possesses a spontaneous polarization, leading to an intrinsic type-II band alignment and strongly suppressed electron-hole recombination. Thereby, AB stacking exhibits prolonged carrier lifetimes and enhanced solar-to-hydrogen conversion compared with the ${\text{AA}}^{\prime }$ stacking. Moreover, such spontaneous built-in fields can also generate stronger electron overpotentials, lowering hydrogen evolution reaction barriers and reducing external bias requirements during hydrogen evolution. Via interlayer sliding, the completely reversed interlayer polarization can exchange the oxidation and reduction planes, suggesting a viable route toward their switchable photocatalytic applications. Since the interlayer polarization originates purely from stacking asymmetry, these insights are broadly applicable to other 2D vdW bilayers. Therefore, our findings offer a feasible pathway for the next design and optimal regulation of 2D high-efficient photocatalysts.

Understanding the lattice-dynamical and electronic transport mechanisms of thermoelectric materials is essential for identifying systems that combine intrinsically low lattice thermal conductivity with favorable charge-transport characteristics. We present a comprehensive first-principles investigation of the thermoelectric properties of Li-based chalcopyrite compounds ${\text{LiXTe}}_2(\mathrm{X}=\text{Al},\text{Ga},\text{In})$. By combining the Boltzmann transport equation with self-consistent phonon theory, including bubble-term corrections and both three-phonon and four-phonon scattering, we reveal the microscopic origin of their intrinsically ultralow lattice thermal conductivity. Te-dominated isolated optical soft modes in the low-to-mid-frequency region, together with strong higher-order anharmonicity, substantially enhance phonon scattering. In particular, the inclusion of four-phonon processes reduces the lattice thermal conductivity of ${\text{LiInTe}}_2$ by 45% (41%) along the $c$-axis ($a/b$-axis) at 300 K, demonstrating pronounced anharmonic behavior. Electronic transport is evaluated using the AMSET framework, explicitly incorporating key scattering mechanisms and spin-orbit coupling (SOC) effects. ${\text{LiGaTe}}_2$ exhibits a highly dispersive, multivalley-degenerate band structure that significantly decouples $S\text{–}\sigma \text{–}{\kappa }_e$, leading to outstanding performance with an $n$-type $ZT$ of 2.8 at 800 K (2.2 with SOC). The experimental synthesis of ${\text{LiXTe}}_2$ would confirm the structural stability and practical viability of this family. These results establish ${\text{LiXTe}}_2$ as a promising high-performance thermoelectric system and provide essential microscopic insights for tuning strongly anharmonic semiconductors.